Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)
The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)
The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.
Unsaturated hydrocarbons of the type Cn-H2n, indicated by the suffix -ene. (Grant & Hackh's Chemical Dictionary, 5th ed, p408)
Hydrocarbons with at least one triple bond in the linear portion, of the general formula Cn-H2n-2.
Enzymes of the isomerase class that catalyze reactions in which a group can be regarded as eliminated from one part of a molecule, leaving a double bond, while remaining covalently attached to the molecule. (From Enzyme Nomenclature, 1992) EC 5.5.
A chemical element having an atomic weight of 106.4, atomic number of 46, and the symbol Pd. It is a white, ductile metal resembling platinum, and following it in abundance and importance of applications. It is used in dentistry in the form of gold, silver, and copper alloys.
The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.
Phosphoric or pyrophosphoric acid esters of polyisoprenoids.
The study of the structure, preparation, properties, and reactions of carbon compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)
Acyclic branched or unbranched hydrocarbons having two carbon-carbon double bonds.
Peptides whose amino and carboxy ends are linked together with a peptide bond forming a circular chain. Some of them are ANTI-INFECTIVE AGENTS. Some of them are biosynthesized non-ribosomally (PEPTIDE BIOSYNTHESIS, NON-RIBOSOMAL).
Alicyclic hydrocarbons in which three or more of the carbon atoms in each molecule are united in a ring structure and each of the ring carbon atoms is joined to two hydrogen atoms or alkyl groups. The simplest members are cyclopropane (C3H6), cyclobutane (C4H8), cyclohexane (C6H12), and derivatives of these such as methylcyclohexane (C6H11CH3). (From Sax, et al., Hawley's Condensed Chemical Dictionary, 11th ed)
Any chemical species which accepts an electron-pair from a LEWIS BASE in a chemical bonding reaction.
Rhodium. A hard and rare metal of the platinum group, atomic number 45, atomic weight 102.905, symbol Rh. (Dorland, 28th ed)
A technology, in which sets of reactions for solution or solid-phase synthesis, is used to create molecular libraries for analysis of compounds on a large scale.
A class of enzymes that catalyze geometric or structural changes within a molecule to form a single product. The reactions do not involve a net change in the concentrations of compounds other than the substrate and the product.(from Dorland, 28th ed) EC 5.
Group of alkaloids containing a benzylpyrrole group (derived from TRYPTOPHAN)
A continuous circle of peptide bonds, typically of 2-3 dozen AMINO ACIDS, so there is no free N- or C-terminus. They are further characterized by six conserved CYSTEINE residues that form CYSTINE KNOT MOTIFS.
Ring compounds having atoms other than carbon in their nuclei. (Grant & Hackh's Chemical Dictionary, 5th ed)
The characteristic three-dimensional shape of a molecule.
A class of organic compounds containing four or more ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic.
The creation of an amine. It can be produced by the addition of an amino group to an organic compound or reduction of a nitro group.
Enzymes that catalyze the cleavage of a carbon-carbon bond by means other than hydrolysis or oxidation. This subclass contains the DECARBOXYLASES, the ALDEHYDE-LYASES, and the OXO-ACID-LYASES. EC 4.1.
Compounds with a 5-membered ring of four carbons and an oxygen. They are aromatic heterocycles. The reduced form is tetrahydrofuran.
A class of compounds composed of repeating 5-carbon units of HEMITERPENES.
Organic compounds that include a cyclic ether with three ring atoms in their structure. They are commonly used as precursors for POLYMERS such as EPOXY RESINS.
Large enzyme complexes composed of a number of component enzymes that are found in STREPTOMYCES which biosynthesize MACROLIDES and other polyketides.
Cyclic compounds with a ring size of approximately 1-4 dozen atoms.
The excision of in-frame internal protein sequences (INTEINS) of a precursor protein, coupled with ligation of the flanking sequences (EXTEINS). Protein splicing is an autocatalytic reaction and results in the production of two proteins from a single primary translation product: the intein and the mature protein.
A plant genus of the family RUBIACEAE. Some species are used as an ingredient in Chinese and African traditional medicines. Members contain kalata B1, a macrocyclic peptide.
The collective name for the boron hydrides, which are analogous to the alkanes and silanes. Numerous boranes are known. Some have high calorific values and are used in high-energy fuels. (From Grant & Hackh's Chemical Dictionary, 5th ed)
Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.
Techniques used to synthesize chemicals using molecular substrates that are bound to a solid surface. Typically a series of reactions are conducted on the bound substrate that results in either the covalent attachment of specific moieties or the modification of existing function groups. These techniques offer an advantage to those involving solution reactions in that the substrate compound does not have to be isolated and purified between the reaction steps.
A class of organic compounds containing two ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic.
A homologous group of cyclic GLUCANS consisting of alpha-1,4 bound glucose units obtained by the action of cyclodextrin glucanotransferase on starch or similar substrates. The enzyme is produced by certain species of Bacillus. Cyclodextrins form inclusion complexes with a wide variety of substances.
The internal fragments of precursor proteins (INternal proTEINS) that are autocatalytically removed by PROTEIN SPLICING. The flanking fragments (EXTEINS) are ligated forming mature proteins. The nucleic acid sequences coding for inteins are considered to be MOBILE GENETIC ELEMENTS. Inteins are composed of self-splicing domains and an endonuclease domain which plays a role in the spread of the intein's genomic sequence. Mini-inteins are composed of the self-splicing domains only.
Amino acid sequence in which two disulfide bonds (DISULFIDES) and their connecting backbone form a ring that is penetrated by a third disulfide bond. Members include CYCLOTIDES and agouti-related protein.
Spectroscopic method of measuring the magnetic moment of elementary particles such as atomic nuclei, protons or electrons. It is employed in clinical applications such as NMR Tomography (MAGNETIC RESONANCE IMAGING).
Natural compounds containing alternating carbonyl and methylene groups (beta-polyketones), bioenergenetically derived from repeated condensation of acetyl coenzyme A via malonyl coenzyme A, in a process similar to fatty acid synthesis.
Compounds with a core of 10 carbons generally formed via the mevalonate pathway from the combination of 3,3-dimethylallyl pyrophosphate and isopentenyl pyrophosphate. They are cyclized and oxidized in a variety of ways. Due to the low molecular weight many of them exist in the form of essential oils (OILS, VOLATILE).
A plant genus in the family PINACEAE, order Pinales, class Pinopsida, division Coniferophyta. Balm of Gilead is a common name more often referring to POPULUS and sometimes to COMMIPHORA.
Organic compounds containing a carbonyl group in the form -CHO.
Twenty-carbon compounds derived from MEVALONIC ACID or deoxyxylulose phosphate.
Naphthalene derivatives carrying one or more hydroxyl (-OH) groups at any ring position. They are often used in dyes and pigments, as antioxidants for rubber, fats, and oils, as insecticides, in pharmaceuticals, and in numerous other applications.
A plant genus of the family LOGANIACEAE (classified by some botanists as Strychnaceae).
A group of compounds consisting in part of two rings sharing one atom (usually a carbon) in common.
A genus of bacteria that form a nonfragmented aerial mycelium. Many species have been identified with some being pathogenic. This genus is responsible for producing a majority of the ANTI-BACTERIAL AGENTS of practical value.
Organic nitrogenous bases. Many alkaloids of medical importance occur in the animal and vegetable kingdoms, and some have been synthesized. (Grant & Hackh's Chemical Dictionary, 5th ed)
Synthetic organic reactions that use reactions between unsaturated molecules to form cyclical products.
Inorganic compounds that contain bromine as an integral part of the molecule.
Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.
The study of crystal structure using X-RAY DIFFRACTION techniques. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)
A highly toxic gas that has been used as a chemical warfare agent. It is an insidious poison as it is not irritating immediately, even when fatal concentrations are inhaled. (From The Merck Index, 11th ed, p7304)
1,4-alpha-D-Glucan-1,4-alpha-D-glucan 4-alpha-D-glucosyltransferase/dextrin 6 alpha-D-glucanohydrolase. An enzyme system having both 4-alpha-glucanotransferase (EC 2.4.1.25) and amylo-1,6-glucosidase (EC 3.2.1.33) activities. As a transferase it transfers a segment of a 1,4-alpha-D-glucan to a new 4-position in an acceptor, which may be glucose or another 1,4-alpha-D-glucan. As a glucosidase it catalyzes the endohydrolysis of 1,6-alpha-D-glucoside linkages at points of branching in chains of 1,4-linked alpha-D-glucose residues. Amylo-1,6-glucosidase activity is deficient in glycogen storage disease type III.
Esters formed between the aldehydic carbon of sugars and the terminal phosphate of guanosine diphosphate.
Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.

Do enzymes obey the Baldwin rules? A mechanistic imperative in enzymatic cyclization reactions. (1/1346)

It is commonly assumed that enzymes have evolved to abide by the same energetic and stereoelectronic principles that govern reactions in solution. The principles formulated for organic ring-closure reactions can be used to develop a hypothesis for analysis of enzyme-catalyzed cyclization reactions.  (+info)

Purification and characterization of 2-deoxy-scyllo-inosose synthase derived from Bacillus circulans. A crucial carbocyclization enzyme in the biosynthesis of 2-deoxystreptamine-containing aminoglycoside antibiotics. (2/1346)

The biosynthesis of 2-deoxystreptamine, the central aglycon of a major group of clinically important aminoglycoside antibiotics, commences with the initial carbocycle formation step from D-glucose-6-phosphate to 2-deoxy-scyllo-inosose. This crucial step is known to be catalyzed by 2-deoxy-scyllo-inosose synthase, which has not yet been characterized so far. Reported in this paper is the first purification of 2-deoxy-scyllo-inosose synthase from butirosin-producing Bacillus circulans SANK 72073 to electrophoretic homogeneity. The enzyme was isolated as a heterodimeric protein comprising from a 23 kDa- and a 42 kDa polypeptide chains. The Km of the enzyme for D-glucose-6-phosphate was estimated to be 9.0 x 10(-4) M and that for NAD+ 1.7 x 10(-4) M, kcat for D-glucose-6-phosphate being 7.3 x 10(-2) s(-1). The presence of Co2+ was essential for the enzyme activity, but Zn2+ was totally inhibitory. While the reaction mechanisms are quite similar, 2-deoxy-scyllo-inosose synthase appears to be distinct from dehydroquinate synthase in the shikimate pathway, with respect to the quaternary structure, metal ion requirement, and the kinetic parameters.  (+info)

Elucidating the mechanism of chain termination switching in the picromycin/methymycin polyketide synthase. (3/1346)

BACKGROUND: A single modular polyketide synthase (PKS) gene cluster is responsible for production of both the 14-membered macrolide antibiotic picromycin and the 12-membered macrolide antibiotic methymycin in Streptomyces venezuelae. Building on the success of the heterologous expression system engineered using the erythromycin PKS, we have constructed an analogous system for the picromycin/methymycin PKS. Through heterologous expression and construction of a hybrid PKS, we have examined the contributions that the PKS, its internal thioesterase domain (pikTE) and the Pik TEII thioesterase domain make in termination and cyclization of the two polyketide intermediates. RESULTS: The picromycin/methymycin PKS genes were functionally expressed in the heterologous host Streptomyces lividans, resulting in production of both narbonolide and 10-deoxymethynolide (the precursors of picromycin and methymycin, respectively). Co-expression with the Pik TEII thioesterase led to increased production levels, but did not change the ratio of the two compounds produced, leaving the function of this protein largely unknown. Fusion of the PKS thioesterase domain (pikTE) to 6-deoxyerythronolide B synthase (DEBS) resulted in formation of only 14-membered macrolactones. CONCLUSIONS: These experiments demonstrate that the PKS alone is capable of catalyzing the synthesis of both 14- and 12-membered macrolactones and favor a model by which different macrolactone rings result from a combination of the arrangement between the module 5 and module 6 subunits in the picromycin PKS complex and the selectivity of the pikTE domain.  (+info)

Heterologous expression, purification, reconstitution and kinetic analysis of an extended type II polyketide synthase. (4/1346)

BACKGROUND: Polyketide synthases (PKSs) are bacterial multienzyme systems that synthesize a broad range of natural products. The 'minimal' PKS consists of a ketosynthase, a chain length factor, an acyl carrier protein and a malonyl transferase. Auxiliary components (ketoreductases, aromatases and cyclases are involved in controlling the oxidation level and cyclization of the nascent polyketide chain. We describe the heterologous expression and reconstitution of several auxiliary PKS components including the actinorhodin ketoreductase (act KR), the griseusin aromatase/cyclase (gris ARO/CYC), and the tetracenomycin aromatase/cyclase (tcm ARO/CYC). RESULTS: The polyketide products of reconstituted act and tcm PKSs were identical to those identified in previous in vivo studies. Although stable protein-protein interactions were not detected between minimal and auxiliary PKS components, kinetic analysis revealed that the extended PKS comprised of the act minimal PKS, the act KR and the gris ARO/CYC had a higher turnover number than the act minimal PKS plus the act KR or the act minimal PKS alone. Adding the tcm ARO/CYC to the tcm minimal PKS also increased the overall rate. CONCLUSIONS: Until recently the principal strategy for functional analysis of PKS subunits was through heterologous expression of recombinant PKSs in Streptomyces. Our results corroborate the implicit assumption that the product isolated from whole-cell systems is the dominant product of the PKS. They also suggest that an intermediate is channeled between the various subunits, and pave the way for more detailed structural and mechanistic analysis of these multienzyme systems.  (+info)

Protein aging hypothesis of Alzheimer disease. (5/1346)

Alzheimer disease (AD), the most common form of aging-related neurodegenerative disorders, is associated with formation of fibrillar deposits of amyloid beta-protein (Abeta). While the direct involvement of Abeta in AD has been well documented, the relations between Abeta production, amyloid formation, and neurodegeneration remain unknown. We propose that AD is initiated by a protein aging-related structural transformation in soluble Abeta. We hypothesize that spontaneous chemical modification of aspartyl residues in Abeta to transient succinimide induces a non-native conformation in a fraction of soluble Abeta, rendering it amyloidogenic and neurotoxic. Conformationally altered Abeta is characterized by increased stability in solution and the presence of a non-native beta-turn that determines folding of Abeta in solution and the structure of Abeta subunits incorporated into amyloid fibrils. While the soluble 'non-native' Abeta is both the factor triggering the neurodegenerative cascade and the precursor of amyloid plaques, these two events result from interaction of Abeta with different sets of cellular components and need not coincide in space and time. Extensive literature data and experimental evidence are provided in support of this hypothesis.  (+info)

Site-directed mutagenesis of squalene-hopene cyclase: altered substrate specificity and product distribution. (6/1346)

BACKGROUND: Two regions of squalene-hopene cyclase (SHC) were examined to define roles for motifs posited to be responsible for initiation and termination of the enzyme-catalyzed polyolefinic cyclizations. Specifically, we first examined the triple mutant of the DDTAVV motif, a region deeply buried in the catalytic cavity and thought to be responsible for the initiation of squalene cyclization. Next, four mutants were prepared for Glu45, a residue close to the substrate entrance channel proposed to be involved in the termination of the cyclization of squalene. RESULTS: The DDTAVV motif in SHC was changed to DCTAEA, the corresponding conserved region of eukaryotic oxidosqualene cyclase (OSC), by the triple mutation of D377C/V380E/V381A; selected single mutants were also examined. The triple mutant showed no detectable cyclization of squalene, but effectively cyclized 2,3-oxidosqualene to give mono- and pentacyclic triterpene products. Of the Glu45 mutants, E45A and E45D showed reduced activity, E45Q showed slightly increased activity, and E45K was inactive. A normal yield of pentacyclic products was produced, but the ratio of hopene 2 to hopanol 3 was significantly changed in the less active mutants. CONCLUSIONS: Initiation and substrate selectivity may be determined by the interaction of the DDTAVV motif with the isopropylidene of squalene (for SHC) and of the DCTAEA motif with the epoxide of oxidosqualene (for OSC). This is the first report of a substrate switch determined by a central catalytic motif in a triterpenoid cyclase. At the termination of cyclization, the product ratio may be largely controlled by Glu45 at the entrance channel to the active site.  (+info)

Aureusidin synthase: a polyphenol oxidase homolog responsible for flower coloration. (7/1346)

Aurones are plant flavonoids that provide yellow color to the flowers of some popular ornamental plants, such as snapdragon and cosmos. In this study, we have identified an enzyme responsible for the synthesis of aurone from chalcones in the yellow snapdragon flower. The enzyme (aureusidin synthase) is a 39-kilodalton, copper-containing glycoprotein catalyzing the hydroxylation and/or oxidative cyclization of the precursor chalcones, 2',4',6',4-tetrahydroxychalcone and 2',4',6',3,4-pentahydroxychalcone. The complementary DNA encoding aureusidin synthase is expressed in the petals of aurone-containing varieties. DNA sequence analysis revealed that aureusidin synthase belongs to the plant polyphenol oxidase family, providing an unequivocal example of the function of the polyphenol oxidase homolog in plants, i.e., flower coloration.  (+info)

Intramolecular proton transfer in the cyclization of geranylgeranyl diphosphate to the taxadiene precursor of taxol catalyzed by recombinant taxadiene synthase. (8/1346)

BACKGROUND: The committed step in the biosynthesis of the anticancer drug taxol in yew (Taxus) species is the cyclization of geranylgeranyl diphosphate to taxa-4(5),11(12)-diene. The enzyme taxadiene synthase catalyzes this complex olefin cation cyclization cascade involving the formation of three rings and three stereogenic centers. RESULTS: Recombinant taxadiene synthase was incubated with specifically deuterated substrates, and the mechanism of cyclization was probed using MS and NMR analyses of the products to define the crucial hydrogen migration and terminating deprotonation steps. The electrophilic cyclization involves the ionization of the diphosphate with closure of the A-ring, followed by a unique intramolecular transfer of the C11 proton to the re-face of C7 to promote closure of the B/C-ring juncture, and cascade termination by proton elimination from the beta-face of C5. CONCLUSIONS: These findings provide insight into the molecular architecture of the first dedicated step of taxol biosynthesis that creates the taxane carbon skeleton, and they have broad implications for the general mechanistic capability of the large family of terpenoid cyclization enzymes.  (+info)

TY - JOUR. T1 - An arene-alkene photocycloaddition-radical cyclization cascade. T2 - The first synthesis of cis,cis,cis,trans-[5.5.5.5]-fenestranes. AU - Wender, Paul A.. AU - Dore, Timothy. AU - DeLong, Mitch A.. PY - 1996/10/21. Y1 - 1996/10/21. N2 - The first cis,cis,cis,trans-[5.5.5.5]-fenestranes have been synthesized in three steps using a novel arene-alkene photocycloaddition-radical cyclization cascade, which creates overall 5 new rings and 8 stereogenic centers. A lead tetraacetate mediated ring expansion of a 5,5-fused ring system, discovered in the course of exploring the chemistry of these new materials, is also described.. AB - The first cis,cis,cis,trans-[5.5.5.5]-fenestranes have been synthesized in three steps using a novel arene-alkene photocycloaddition-radical cyclization cascade, which creates overall 5 new rings and 8 stereogenic centers. A lead tetraacetate mediated ring expansion of a 5,5-fused ring system, discovered in the course of exploring the chemistry of these new ...
The Nazarov cyclization is a common synthetic tool in the synthesis of cyclopentenone rings. The reaction is characterized by a divinyl ketone starting reagent that undergoes a 4π-electron electrocyclization after addition of a Lewis/Brønsted acid; forming the cyclopentadienyl cation that undergoes cyclization. An extension of this methodology involves using a divinyl imine starting reagent. This cyclization is less favoured due to the electron donating ability of the nitrogen atom, causing the pentadienyl cation to be relatively stable and unwilling to undergo cyclization. To improve this cyclization, the imine is replaced with the electron withdrawing nitronate functionality. It is hypothesized that by doing so the addition of an acid will form the cyclopentadienyl cation that will readily undergo Nazarov cyclization. The synthesis of an aryl vinyl silyl nitronate was optimized and the compound was tested with a number of different acid catalysts to determine if the nitronate Nazarov ...
Effect of primary polymer chain rigidity on intramolecular cyclization and intramolecular crosslinking in free-radical crosslinking monomethacrylatedimethacrylate copolymerizations., The effluent analysis of several pyrrone and polyimide precursors during cyclization., Reduction and cyclization to form poly(benzimidazole amide imide) copolymers., Thermal degradation of polymers. Part XIX. The thermal cyclization and characterization of quinazolone pre-polymers, Cationic cyclization of cis-1 4-polybutadiene I. Synthesis and technological evaluation of the polymer, ThreeFourFive-Component Diastereoselective Cyclization of Fischer Carbene Complexes Lithium Enolates and Allylmagnesium Bromide., Evolution of aggregation structure of polyacrylonitrile fibers in the cyclization reaction., Epoxy resins based on aromatic glycidylamines. III. Kinetics of intramolecular cyclization of N N-bis(2-hydroxy-3-chloropropyl)aniline, Cyclization during polyesterification Isolation of an 18-member ring compound from
A proposed universal monoterpene synthases (cyclases) cyclization mechanism topologically requires an isomerization step of the substrate geranyl diphosphate (GPP) to the formation of the proposed universal intermediate linalyl diphosphate (LPP), which has never been directly observed. The study described here was designed to investigate the cyclization mechanism by studying a model enzyme, (4R)-(+)-limonene synthase ((+)-LS), a monoterpene cyclase that produces (+)-limonene by using substrate GPP. The study synthesized two novel difluorinated substrate analogues, 8,9-difluorogeranyl diphosphate (DFGPP) and 8,9-difluorolinalyl diphosphate (DFLPP), which were designed to retard the cyclization step in order to observe the intermediate at the enzyme active site. Both analogues are proved to be substrates for (+)-LS. Compared to GPP, which has a kcat value of 0.0905 +/- 0.0070 s-1, DFGPP has a reduced kcat value at 0.00144 +/- 0.00002 s-1, showing a 69-fold slower rate in the catalytic reaction. ...
TY - JOUR. T1 - Systematic investigations on fused π-system compounds of seven benzene rings prepared by photocyclization of diphenanthrylethenes. AU - Fujino, Shota. AU - Yamaji, Minoru. AU - Okamoto, Hideki. AU - Mutai, Toshiki. AU - Yoshikawa, Isao. AU - Houjou, Hirohiko. AU - Tani, Fumito. N1 - Publisher Copyright: © 2017 The Royal Society of Chemistry and Owner Societies.. PY - 2017. Y1 - 2017. N2 - We studied the photoproducts of 1-(n-phenanthryl)-2-(m-phenanthryl)ethenes (nEm; n, m = 1, 3 and 9) for understanding photocyclization patterns based on NMR spectroscopy. The crystal structures of the photoproducts were analyzed by X-ray crystallography, and the photophysical features of the photocyclized molecules were investigated based on emission and transient absorption measurements. Phenanthrene derivatives substituted at the 1- and 3-positions were prepared for synthesizing nEm by photocyclization of stilbene derivatives. We obtained four types of primary photoproducts ([email protected]) from the ...
The iodine-catalyzed Prins cyclization of homoallylic alcohols and aldehydes was investigated under metal-free conditions and without additives. Anhydrous conditions and inert atmosphere are not required. The reaction of 2-(3,4-dihydronaphthalen-1-yl)propan-1-ol and 21 aldehydes (aliphatic and aromatic) in CH2Cl2 in the presence of 5 mol % of iodine gave 1,4,5,6-tetrahydro-2H-benzo[f]isochromenes in 54%-86% yield. Under similar conditions, the Prins cyclization of six alcohols containing an endocyclic double bond (primary, secondary, or tertiary) led to dihydropyrans in 52%-91% yield. The acyclic homoallylic alcohols gave 4-iodo-tetrahydropyran in 29%-41% yield in the presence of 50 mol % of iodine. This type of substrate is the main limitation of the methodology. The relative configuration of the products was assigned by NMR and X-ray analysis. The mechanism and the ratio of the products are discussed, based on DFT calculations.
Title: Metal-mediated Heterocyclization: Synthesis of Heterocyclic Compounds Containing More Than One Heteroatom Through Carbon-Heteroatom Bond Forming Reactions. VOLUME: 14 ISSUE: 8. Author(s):K. C. Majumdar, B. Roy, P. Debnath and A. Taher. Affiliation:Department of Chemistry, University of Kalyani, Kalyani- 741 235, India.. Abstract: Heterocyclic compounds are versatile building blocks in organic synthesis. These are important part in various natural products and bioactive compounds. Several methodologies have been developed to synthesize these heterocyclic compounds. This review article covers an updated (published during 2005 to 2008) summary of transition-metal catalyzed approaches for the syntheses of commonring heterocycles containing more than one heteroatom via the selective formation of carbon-heteroatom bonds. The five-membered ring heterocycles with two nitrogen atoms include imidazoles, pyrazoles, indazoles, imidazoindolones etc. and heterocycles with one nitrogen and one oxygen ...
TY - JOUR. T1 - Ammonia synthons for the multicomponent assembly of complex γ-lactams. AU - Tan, Darlene Q.. AU - Martin, Kevin S.. AU - Fettinger, James C.. AU - Shaw, Jared T.. PY - 2011/4/26. Y1 - 2011/4/26. N2 - The synthesis of γ-lactams that are unsubstituted at the 1-position (nitrogen) as well as their subsequent N-functionalization is reported. A recently discovered four-component reaction (4CR) is employed with either an ammonia precursor or a protected form of ammonia that can be deprotected in a subsequent synthetic step. These methods represent the first multicomponent assembly of complex lactam structures that are unsubstituted at nitrogen. In addition, two methods for the introduction of nitrogen substituents that are not possible through the original 4CR are reported. X-ray crystallographic analysis of representative structures reveals conformational changes in the core structure that will enable future deployment of this chemistry in the design and synthesis of diverse ...
A highly efficient method for the construction of pyrrolidinyl spirooxindoles with 3-isothiocyanato oxindoles and chalcones via a Michael/cyclization cascade reaction has been developed by using bifunctional cinchona-derived squaramide organocatalysts. A series of complex pyrrolidinyl spirooxindoles could be
It seemed plausible that the biosynthesis of Bistellettadine A (9) was proceeding by intermolecular dimerization of the monomeric carboxylic acid corresponding to 7. Barry B. Snider of Brandeis University found (Org. Lett. 2010, 12, 828. ) that that intermolecular dimerization did proceed efficiently, but to give a 5:4 mixture of diastereomers. In contrast, the linked diester 7 cyclized with exclusive diastereocontrol. The product 8 was readily carried on to Bistellettadine A 9. This raises the possibility that a chiral template, attached either covalently or through salt formation, could be designed that would direct the absolute configuration of the cycloaddition.. ...
In this review James C. Collins and Keith James from the Scripps Research Institute critically analyse macrocyclization reactions published over the last three years. Based upon on this analysis, and first-hand experience of macrocyclization, Collins and James propose a macrocyclization efficiency index, Emac, as a means of determining the true efficiency of a macrocyclization reaction.. Emac takes into account both reaction yield and concentration, which Collins & James state addresses the key factors that determine the practicality of using a given reaction in a drug discovery context. In other words, the Emac for a reaction indicates the likelihood of being able to conduct the reaction on a sufficiently large scale whilst remaining resource efficient.. This index also allows comparison of a large number of literature macrocyclization reactions and identifies those which deliver the powerful combination of high yield and high practicality. Collins and James hope that those who are actively ...
The (3+2)-cycloaddition reaction involving oxyallyl cations has proven to be a versatile and efficient approach for the construction of five-membered carbo- and heterocycles, which are prevalent frameworks in natural products and pharmaceuticals. The following article will provide a brief summary of recent disclosures on this process featuring chemo-, regio- and diastereoselective oxyallyl cycloadditions with both electron-rich and electron-deficient 2π partners.
The unprecedented combination of a palladium(ii) complex with a chiral Bu-QUOX ligand and a chiral phosphoric acid enables the highly efficient asymmetric oxidative tandem cyclization of N-(2,2-disubstituted hex-5-en-1-yl)acrylamides, providing a straightforward method to access chiral 6,5-bicyclic aza-heter
List of : One-pot reductive cyclization to antitumor quinazoline precursorsOn resonance interactions in methyl 4-X-benzoates and the effect of 2,6-dimethyl substitution. 13C or 17O NMR chemical shifts as effective indicators of π-electron-density distribution?Open-chain and cyclic amidrazones forming persistent radicals. An electrochemical and quantum chemical studyOne-pot synthesis of stable phosphorus ylides using aldehyde phenylhydrazone derivativesOne-pot synthesis of 5-carboxanilide-dihydropyrimidinones using etidronic acid
A cobalt-rhodium heterobimetallic nanoparticle-catalyzed reductive cyclization of 2-(2-nitroaryl)acetonitriles to indoles proceeds without any additives under mild conditions. The catalytic can be reused more than ten times without loss of catalytic activity.. ...
SYNTHESIS OF FUSED PYRAZOLES VIA INTRAMOLECULAR CYCLIZATION OF APPROPRIATELY ortho -SUBSTITUTED NITROARENES AND NITROHETEROARENES
Home » Visible light photocatalysis of radical cation Diels-Alder cycloadditions: preparation of tris(2,2-bipyrazyl)ruthenium(II) bis(tetrakis(3,5-bis(trifluoromethyl)phenyl)borate ...
TY - JOUR. T1 - SilverCatalyzed Cascade Carboxylation and Cyclization of Trimethyl(2-methylenebut-3-yn-1-yl)silane Derivatives. AU - Sekine, Kohei. AU - Sadamitsu, Yuta. AU - Yamada, Tohru. PY - 2015/11/20. Y1 - 2015/11/20. N2 - C-C bond-forming carboxylation and cyclization of trimethyl(2-methylenebut-3-yn-1-yl)silane derivatives and carbon dioxide was developed. Silver catalysts and CsF promoted the reaction to afford the corresponding 2-furanone and 2-pyrone derivatives in good-to-high yields. The structure of the 2-furanone was confirmed by single-crystal X-ray crystallography, which revealed that the geometry of the exo-olefin was that of a Z-isomer. When an aromatic ring-substituted alkyne was used, 2-furanone derivatives were selectively obtained via 5-exo-dig cyclization, whereas the reaction of alkyl-substituted alkynes produced 2-pyrone derivatives with high selectivity.. AB - C-C bond-forming carboxylation and cyclization of trimethyl(2-methylenebut-3-yn-1-yl)silane derivatives and ...
Oxidative photoinduced electron transfer (PET) reactions have been performed with various silyl enol ethers and silyloxy-2H-chromones bearing an olefinic or silylacetylenic side chain, The reactions result in regioselective ring closure with the formation of bi- to tetracyclic ring systems with a well-defined ring juncture, e.g. perhydrophenanthrenones 13 or benzo-annellated xanthenones 24. Our investigations have focussed on the optimization of this cyclization method with regard to irradiation time and product yield. The irradiation times could be reduced by using the cosensitized PET method. Modifying the substrate at the silyl group led to enhanced yields. In addition, we found that solvent and pressure dependences are important tools, allowing control of the regiochemistry. Both the synthesis of 6-endo products by radical cationic reaction pathways, as well as 5-exo ring closure by radical intermediates was achieved. Mechanistic details, including findings from deuterium labelling ...
TY - JOUR. T1 - Enantioselective organo-SOMO cascade cycloadditions. T2 - A rapid approach to molecular complexity from simple aldehydes and olefins. AU - Jui, Nathan T.. AU - Lee, Esther C.Y.. AU - MacMillan, David W.C.. PY - 2010/7/28. Y1 - 2010/7/28. N2 - A highly selective, radical-mediated (4 + 2) coupling reaction of aldehydes and conjugated olefins has been achieved through asymmetric SOMO-catalysis. A radical-polar crossover mechanism is proposed wherein olefin addition to a transient enamine radical cation and oxidation of the resulting radical furnishes a cation which is vulnerable to nucleophilic addition. A range of aromatic aldehydes are shown to couple with styrenes and dienes to provide cyclic products with high chemical efficiency, regioselectivity, and stereoselectivity.. AB - A highly selective, radical-mediated (4 + 2) coupling reaction of aldehydes and conjugated olefins has been achieved through asymmetric SOMO-catalysis. A radical-polar crossover mechanism is proposed ...
ESI Induced Gas-Phase Nazarov Cyclization of (2E)-3-(2-Methoxyphenyl)-1-(thiophen-2-yl)-prop-2-en-1-one and its Oxygen Analogue ...
I. The acid catalyzed reactions of certain 1,5-epoxyolefins. The monoxides of a number of 1,5-dienes were prepared and treated with a variety of acidic reagents known to induce cyclization of the parent diolefins. In all cases the major reaction observed was the isomerization of the epoxide to a carbonyl function. No cyclic products were observed. These results are discussed in terms of the general requirements for cyclization.. II. The alkylative cyclization of 1,5-hexadiene The alkylation of 1,5 -hexadiene with t-butyl chloride in the presence of aluminum trichloride was studied. The major monomeric reaction products were cyclic, and both the t-butylcyclohexane and neopentylcyclopentane skeletons were identified among them. Formation of the latter ring system appeared to be slightly favored over formation of the six-membered ring. This preference is undoubtedly due to both steric and electronic factors.. III. The acid catalyzed cyclization of cis, cis- and trans, trans-2,6-octadiene. Both cis, ...
In organic chemistry, an electrocyclic reaction is a type of pericyclic rearrangement where the net result is one pi bond being converted into one sigma bond or vice versa. These reactions are usually categorized by the following criteria: Reactions can be either photochemical or thermal. Reactions can be either ring-opening or ring-closing (electrocyclization). Depending on the type of reaction (photochemical or thermal) and the number of pi electrons, the reaction can happen through either a conrotatory or disrotatory mechanism. The type of rotation determines whether the cis or trans isomer of the product will be formed. The Nazarov cyclization reaction is a named electrocyclic reaction converting divinylketones to cyclopentenones. A classic example is the thermal ring-opening reaction of 3,4-dimethylcyclobutene. The cis isomer exclusively yields cis,trans-2,4-hexadiene whereas the trans isomer gives the trans,trans diene: This reaction course can be explained in a simple analysis through the ...
A novel cascade reaction involving oxidative dearomatization/semipinacol rearrangement of indol-2-yl cyclobutanols is explored with N-sulfonyloxaziridine (Davis oxaziridines) as oxidant, generating various 2-spiroquaternary 3-oxindoles in modest to good yields. This method might be useful in the synthesis of indole-based alkaloids bearing 2-spiroquaternary carbon centers. PTS=p-toluenesulfonic acid monohydrate. ...
Significant advances in metal-catalyzed reactions, especially cyclizations, have dramatically improved the efficiency of organic synthesis over the last three decades. To date these transformations are widely used in the area of synthesis of both natural products and therapeutic agents. Science of Synthesis: Metal-Catalyzed Cyclization Reactions presents the most commonly used and significant metal-catalyzed reactions for modern organic synthesis. The basic principles, the current state of the art, scope, limitations, and mechanism of these reactions are also discussed. Typical examples of target synthesis are provided to help inspire further applications ...
Thieme eBooks, Significant advances in metal-catalyzed reactions, especially cyclizations, have dramatically improved the efficiency of organic synthesis over the last three decades. To date these transformations are widely used in the area of synthesis of both natural products and therapeutic agents. Science of Synthesis: Metal-Catalyzed Cyclization Reactions presents the most commonly used and s...
Synthesis of Novel Steroid-Peptoid Hybrid Macrocycles by Multiple Multicomponent Macrocyclizations Including Bifunctional Building Blocks MiBs. . Biblioteca virtual para leer y descargar libros, documentos, trabajos y tesis universitarias en PDF. Material universiario, documentación y tareas realizadas por universitarios en nuestra biblioteca. Para descargar gratis y para leer online.
Chen, H. [陳浩國]. (2009). Silver catalyzed enyne cyclization reactions. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_ ...
The importance of dynamics in simple reactions is made yet again in a recent study by Doubleday and Houk in 1,3-dipolar cycloadditions.1 They looked at the reaction of acetylene or ethylene with either nitrous oxide, diazonioazanide, or methanediazonium. The transition state for these 6 reactions all show a concerted reaction. The transition vector has three major components; (a) symmetric formation/cleavage of the two new σ bonds, (b) bending of the dipolar component, or (c) symmetric bending of the hydrogens of ethylene or acetylene.. Classical trajectories were traced from the transition state back to reactant and forward to product. In the approach of the two fragments, the dipole bend vibrates, but then after the TS, it needs to bend quickly to close the 5-member ring. This means that the bending mode effectively has to turn a corner in phase space, and without energy in this mode, the molecules will simple bounce off of each other. Analysis of the reactants indicates significant ...
Synlett, 2009, 1208-1218. Anodic electrochemistry is a powerful tool for generating radical cation intermediates and initiating new cyclization reactions. Like most electrochemical reactions, the transformations involve umpolungs. In this review, recent studies examining the intramolecular coupling of radical cations derived from enol ethers, vinyl sulfides, and ketene acetals with carbon, oxygen, and nitrogen trapping groups are discussed to highlight their synthetic potential.. ...
Steric effects are important in synthesis. Whilst steric hindrance is well known in hindering reactions, steric effects can also be employed to accelerate reactions, in particular cycloaddition reactions, and even to promote reactions that otherwise do not occur. A survey is included in previous work on steric effects in chemical reactions, principally cycloadditions. This includes a brief discussion on the importance of orientation and solvent effects on Diels-Alder cyclisations and ene reactions. The effect of substituents on the cyclisation of N-allyl furfurylamines has been studied. It was shown that bulky N-protecting groups enhance cyclisation, an effective buttress being the trityl (triphenylmethyl) group. The latter has the added advantage of being particularly easy to remove. A study of some ene reactions has also been carried out and steric acceleration of these processes has also been observed. A novel reaction involving an intermolecular cycloaddition followed by a sterically ...
The dissertation herein describes the first total synthesis of the complex Daphniphyllum alkaloid, (-)-calyciphylline N. This alkaloid was chosen as the target in our synthetic program due its unprecedented structure, the inherent challenges associated with its synthesis, and limited reports of synthetic studies towards members of this family of natural products. An initial unsuccessful approach is discussed, followed by a revised, ultimately successful approach. Highlights of the synthesis include a substrate controlled, intramolecular Diels-Alder reaction to build the bicyclo[2.2.2]octane core and set four contiguous stereocenters, a transannular enolate alkylation to secure ring D, a highly efficient Stille carbonylation/Nazarov cyclization sequence to construct ring E with concomitant activation of a hindered silyl group towards Fleming-Tamao oxidation, and an unprecedented, homogeneous hydrogenation of an exceptionally hindered diene ester to complete the eastern hemisphere, a structural motif that
Autor: Glas, Adrian et al.; Genre: Zeitschriftenartikel; Im Druck veröffentlicht: 2015-01; Keywords: cyclic peptides; hydrophobic cross-links; ring-closing metathesis; protein-protein interactions; Pseudomonas aeruginosa; Titel: Constraining Peptide Conformations with the Help of Ring-Closing Metathesis
TY - JOUR. T1 - Synthetic studies of cis-3a-aryloctahydroindole derivatives by copper- catalyzed cyclization of N-allyltrichloroacetamides. T2 - Facile construction of benzylic quaternary carbons by carbon-carbon bond-forming reactions. AU - Iwamatsu, Sho Ichi. AU - Matsubara, Kouki. AU - Nagashima, Hideo. PY - 1999/12/24. Y1 - 1999/12/24. N2 - Cyclization of N-(2-aryl-2-cyclohexen-1-yl)trichloroacetamides by a copper catalyst was investigated. It is crucially important for successful cyclization under mild conditions that alkoxycarbonyl groups are introduced to the nitrogen atom of the N-allyltrichloroacetamides as well as that CuCl- (bipyridine) is used as the catalyst. Three compounds, N-(2-phenyl-2- cyclohexen-1-yl)-, N-[2-(3,4-dimethoxyphenyl)-2-cyclohexen-l-yl]-, and N-[2- (3,4-methylenedioxyphenyl)-2-cyclohexen-1-yl]trichloroacetamides, where the Cbz or MeO2C- group was attached to the nitrogen atom, were instantly converted to the corresponding trichlorinated cis-3a-aryloctahydroindol-2- ...
This video was recorded at CHEM 125b: Freshman Organic Chemistry II. Cyclic conjugation that arises when p-orbitals touch one another can be as important for transition states as aromaticity is for stable molecules. It is the controlling factor in pericyclic reactions. Regiochemistry, stereochemistry, and kinetics show that two new sigma bonds are being formed simultaneously, if not symmetrically, in the 6-electron Diels-Alder cycloaddition. Although thermal dimerization of thymine residues in DNA is forbidden, photochemistry allows the 4-electron cycloaddition. Electrocyclic ring opening or closing chooses a conrotatory Möbius pathway, or a disrotatory Hückel pathway, according to the number of electron pairs involved and whether light is used in the process. Dewar benzene provides an example of a very unstable molecule that can be formed photochemically and then persists because of unfavorable orbital overlap in the transition state for ring opening ...
Extra info for Chemistry of Heterocyclic Compounds: The Purines, Supplement 1, Volume 54. Sample text. C. D. E. F. G. 2. 3. 4. 5. . . . . . . . . . 22 Cyclization with Formic Acid (H33) . . . . . . . . . . . . . . Cyclization with Dithioformic Acid (H38) . . . . . . . . . . . . Cyclization with Other Carboxylic Acids (H41) . . . . . . . . . . . Cyclization with Acid Anhydrides (H44) . . . . . . . . . . . . Cyclization with Acid Chlorides (H47) . . . . . . . . . . . . . Cyclization with Orthoesters and Diethoxymethyl Acetate (H50) . It is postulated that 63 arises from attack by a second molecule of thiourea on the 5-thioureidopyrimidine initially formed, displacing the 4-amino group; the product (64)then cyclizes with elimination of g ~ a n i d i n e . ~ ~ 59 60 61 0. Cyclizationwith Cyanates, lsocyanates and Derivatives (H61) Under reflux conditions methyl isocyanate and 4,5-diamino-l,2,3,6-tetrahydro-2-oxo-6-thioxopyrimidinein pyridine (3 h) give the corresponding 5-(N- * Removal of an ...
The enantiopure γ-amino alcohols 7 and 18 are prepared by using the diastereoselective michael addition of lithium N-benzyl ( R )-α-methylbenzylamide to α,β-unsaturated esters as a key step. The michael addition of 7 or 18 to an alkynone 8 followed by an intramolecular cyclization afford the cyclic enzmine 10 or 20. which are subjected to the diastereoselective hydrogenation, and the subsequent transformations provide 6-epi-alkaloid 223A and alkaloid 223A, respectively ...
Photochemical cleavage reactions have found a widespread used in biological applications that require the photorelease of biologically active molecules such as proteins, peptides, neurotransmitters, and nucleotide phosphates. This research focuses on the design of photoremovable protecting groups which can be utilized to release these biomolecules by photolysis. These biomolecules are attached to the photoremovable protecting group at the sites of functional groups that are present within these substrates. Such functional groups are carboxylates, phosphates, thiolates, or phenolates, which upon exposure to light, are released as anions of varying basicities. The photochemical reaction involved is an electrocyclic ring closure between aromatic groups that are bridged by a carboxamide linkage. The key intermediate produced by electrocyclization is thought to have zwitterionic character. This zwitterionic intermediate is believed to expel the leaving group as the anion. One of the aromatic groups attached
The research developed in this Doctoral Thesis comprises from the preparation of polyaromatic compounds to the synthesis of natural product derivatives, highlighting the proficiency of homogeneous gold catalysis for the construction of molecular diversity.. A novel approach for the synthesis of a new trindane-based crushed fullerene C60 was developed by a threefold palladium-catalyzed cross-coupling of four suitably functionalized C15 trindene fragments. The trindane C15 skeleton of the central motif was constructed through a triple gold(I)-catalyzed oxidative cyclization.. The scope of the intramolecular gold(I)-catalyzed formal [2+2+2] cycloaddition reaction was extended to O-protected homopropargylic and allylic oxo-1,5-enynes. Under the optimized reaction conditions, the cyclization of (Z)- and (E)- isomers takes place with moderate to excellent yield and increased selectivity in most of the cases, providing access to octahydro-1H-indenes skeletons.. The mastery of gold(I) complexes for the ...
Molecular complexity is one of the key reasons why fragment-based lead discovery should work. As described in 2001 by Mike Hann and colleagues at GlaxoSmithKline, the idea is that very small, simple molecules are likely to be able to bind to many different sites on many different proteins; think of the water molecule as being an extreme example of this. As molecules become larger and more complex, they are less likely to bind to any given site on a protein, though if they are complementary to a site the potency will be greater. Similarly, more complex molecules are more likely to have a single binding mode than smaller, less-decorated molecules, which could assume multiple orientations at a single site. These intuitive ideas were supported by a simple computational model that suggested that there is an optimum complexity where molecules would be simple enough that they would bind to several different targets (and thus be useful in a screening collection) while still being complex enough to bind ...
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TY - BOOK. T1 - Solid-Phase Iminium Cyclization Reactions for the Synthesis of Natural Product-Like Diketopiperazines. AU - Petersen, Rico. PY - 2012. Y1 - 2012. N2 - The development of methodology for the solid-phase synthesis of fused 2,5-diketopiperazines with an emphasis on structural and stereochemical control, has been accomplished through two different approaches. The first approach was based on a highly trans-stereoselective (82% d.e.) intramolecular N-acyliminium ion cyclization of N-terminal peptide glyoxylamides, assembling the complete molecular skeleton in a single step. The second approach aimed for the use of a cis-stereoselective intermolecular Pictet-Spengler cyclization to construct the first part of the ringsystem and a subsequent diketopiperazine formation to close the second ring. In the first approach, four different methods for accessing the glyoxylamide cyclization precursor were developed; oxidative cleavage of a serine, dihydroxylation/oxidative cleavage of an ...
TY - JOUR. T1 - Carbene and silicon routes as methods for the generation and dipolar cycloaddition reactions of methyl nitrile ylide. AU - Padwa, Albert. AU - Gasdaska, John R.. AU - Tomas, Miguel. AU - Turro, Nicholas J.. AU - Cha, Yuan. AU - Gould, Ian. PY - 1986. Y1 - 1986. N2 - Methyl nitrile ylide was generated by both a photochemical and desilylation route and has been characterized by UV spectroscopy and by its kinetic and cycloaddition behavior. The dipole is formed by the addition of singlet methylene to acetonitrile and shows a strong transient absorption at 280 nm which is quenched by the addition of standard dipolarophiles. The relative rates of formation of 1,3-dipolar adducts and the relative rates of quenching of the transient absorption are in excellent agreement. Generation of the dipole from a silylthioimidate followed by dipolar cycloaddition also gave rise to related cycloadducts. The ratio of cycloadducts obtained from an unsymmetrically substituted dipolarophile was found ...
Stereogenic-at-Mo monoalkoxide and monoaryloxide complexes promote enyne ring-closing metathesis (RCM) reactions, affording the corresponding endo products with high selectivity (typically ,98:,2 endo:exo). All catalysts can be prepared and used in situ. Five-, six-, and seven-membered rings are obtained through reactions with enyne substrates that bear all-carbon tethers as well as those that contain heteroatom substituents. The newly developed catalytic protocols complement the related exo-selective Ru-catalyzed processes. In cases where Ru-based complexes deliver exo and endo products nondiscriminately, such as when tetrasubstituted cyclic alkenes are generated, Mo-catalyzed reactions afford the endo product exclusively. The efficiency of synthesis of N- and O-containing endo diene heterocycles can be improved significantly through structural modification of Mo catalysts. The modularity of Mo-based monopyrrolides is thus exploited in the identification of the most effective catalyst variants. ...
TY - JOUR. T1 - Multicomponent reactions of phosphines, diynedioates, and aryl aldehydes generated furans appending reactive phosphorus ylides through cumulated trienoates as key intermediates. T2 - A phosphine α-addition-δ-evolvement of an anion pathway. AU - Deng, Jie Cheng. AU - Chuang, Shih-Ching. PY - 2014/11/7. Y1 - 2014/11/7. N2 - Multicomponent reactions of phosphines, diynedioates, and aryl aldehydes have been demonstrated, providing trisubstituted furans appending reactive phosphorus ylides, through cumulated trienoates as key intermediates. The proposed trienoate intermediates, 1,5-dipolar species formed via nucleophilic α-attack of phosphines toward diynedioates (α-addition-δ-evolvement of an anion, abbreviated αAδE), undergo addition to aryl aldehydes followed by 5-endo-dig cyclization, proton transfer, and resonance to give trisubstituted furans. Furthermore, the phosphorus ylides are oxidized to α-keto ester furans and utilized as Wittig reagents.. AB - Multicomponent ...
Title:Organocatalyzed Transient Dienamine-Mediated Diels-Alder Reactions between α,β-Unsaturated Ketones and Alkenes. VOLUME: 15 ISSUE: 5. Author(s):Iosune Arrastia, Ana Arrieta and Fernando P. Cossio*. Affiliation:Donostia International Physics Center, San Sebastian/Donostia, Donostia International Physics Center, San Sebastian/Donostia, Donostia International Physics Center, San Sebastian/Donostia. Keywords:Organocatalysis, diels-Alder reactions, cycloadditions, michael additions, pericyclic reactions, stepwise mechanisms.. Abstract:Organocatalyzed (4+2) cycloadditions (Diels-Alder reactions) are reviewed in this manuscript. Among the different catalytic alternatives, reactions involving α,β-unsaturated ketones and alkenes are considered. In these processes, substituted cyclohexanones are obtained via HOMO activation generated by amine organocatalysis that generate transient dienamine species. Both concerted and stepwise mechanisms are described. In most cases, excellent regio-, ...
An enantioselective total synthesis of zampanolide has been accomplished using a novel DDQ/Brønsted acid promoted cyclization as the key reaction. The synthesis features cross-metathesis to construct the trisubstituted olefin and a ring-closing metathesis to form the macrolactone. The final N-acyl aminal formation was stereoselectively accomplished by an organocatalytic reaction.
This Mouse Glutaminyl-peptide cyclotransferase-like protein (QPCTL) ELISA Kit employs a two-site sandwich ELISA to quantitate QPCTL.,QPCTL; FLJ20084; glutaminyl cyclase-like,QPCTL, also termed Iso-glutaminyl cyclase catalyzes the intramolecular cyclization of N-terminal glutamine residues into pyroglutamic acid with liberation of ammonia and the intramolecular cyclization of N-terminal glutamate residues into pyroglutamic acid with liberation of water. Glutaminyl cyclase (QPCT) catalyzes the intramolecular cyclization of N-terminal glutamine residues into pyroglutamic acid liberating ammonia. In contrast, the physiological function of the plant QC is less clear. In case of the enzyme from C. papaya, a role in the plant defence against pathogenic microorganisms was suggested. Putative QCs from other plants were identified by sequence comparisons. The physiological function of these enzymes, however, is still ambiguous.
Pascal begins with the assumption that terminal aryl substitution on the enediyne will both (a) inhibit the C1-C6 cyclization due to steric interactions and (b) the C1-C5 cyclization should be enhanced due to stabilization of the radical by the neighboring aryl group. He computed the activation energies of a series of analogues, some of which are listed in Table 1. The transition state structures are shown in Figure 1 for 1b and 1c. Phenyl substitution does accomplish both suggestions: the activation barrier for the Bergman cyclization increases by 4 kcal mol-1, while the barrier for the C1-C5 cyclization is lowered by nearly 6 kcal mol-1. Further substitution of the phenyl ring by either chloro or methyl groups brings the barriers into near degeneracy.. Table 1. RBLYP/6-31G(d) Activation energies (kcal mol-1) ...
TY - JOUR. T1 - Synthesis, spectroscopy, and applications of small nitrile oxides. AU - Pasinszki, Tibor. AU - Westwood, Nicholas P.C.. PY - 2011/6. Y1 - 2011/6. N2 - Small covalent nitrile oxides are important transient species in organic synthesis and widely used especially for dipolar cycloaddition reactions. Due to their instability, their isolation and characterization are challenging. This review focuses on the generation, spectroscopy, structural properties, and synthetic application of small nitrile oxides, XCNO, where the X substituent group is smaller than five atoms, viz. X= hydrogen, halogen, pseudohalogen, alkyl, vinyl, ethynyl, or nitro.. AB - Small covalent nitrile oxides are important transient species in organic synthesis and widely used especially for dipolar cycloaddition reactions. Due to their instability, their isolation and characterization are challenging. This review focuses on the generation, spectroscopy, structural properties, and synthetic application of small ...
Abstract: The mechanisms of cycloaddition reactions of singlet dibromocarbene and formaldehyde have been studied using density functional theory of quantum chemistry method at B3LYP/6-31G* level. The geometrical parameters, harmonic vibrational frequencies and energies of stationary points on the potential energy surface are calculated. The structures of the stationary points were optimized, and the intermediates and transition states were detected by the frequency analysis. The calculation results show that the reaction has four possible reaction pathways. According to the data of the activation energy, we predict that path c would be the major reactive channel of the cycloaddition reactions of singlet dibromocarbene with formaldehyde, which proceeds in three steps and the energy barrier for the key step is 13.7 kJ·mol-1. Key words: Density functional theory, Cycloaddition reaction, Transition states, Dibromocabene, B3LYP level ...
Diversity-oriented synthesis yields a new drug lead for treatment of chagas disease.: A phenotypic high-throughput screen using ∼100,000 compounds prepared usin
TY - JOUR. T1 - Trifluoromethanesulfonic acid-catalyzed tandem semi-pinacol rearrangement/alkyne-aldehyde metathesis reaction of arylpropagylsulfonamide- tethered 2,3-epoxycyclohexan-1-ols to spiropiperidines. AU - Lin, Ming Nan. AU - Wu, Shih Hui. AU - Yeh, Ming-Chang P.. PY - 2011/12/1. Y1 - 2011/12/1. N2 - A simple and efficient trifluoromethanesulfonic acid-catalyzed cycloisomerization of arylpropagylsulfonamide-tethered 2,3-epoxycyclohexan-1-ols is described. The cyclization proceeds via tandem semi-pinacol rearrangement/alkyne-aldehyde metathesis to afford spiropiperidines under mild reaction conditions.. AB - A simple and efficient trifluoromethanesulfonic acid-catalyzed cycloisomerization of arylpropagylsulfonamide-tethered 2,3-epoxycyclohexan-1-ols is described. The cyclization proceeds via tandem semi-pinacol rearrangement/alkyne-aldehyde metathesis to afford spiropiperidines under mild reaction conditions.. KW - alkyne/aldehyde metathesis. KW - semi-pinacol rearrangement. KW - ...
We developed an efficient, stereoselective synthetic method for the diketopiperazine moiety of neoechinulin A and its derivatives. The intramolecular cyclization at 80 ºC proceeded with minimal racemization of the stereogenic center at C-12 on neoechinulin A, even though the cyclization at 110 ºC caused partial racemization. In contrast with these results, the cyclization on diketopiperazine of 8,9-dihydroneoechinulin A derivatives did not cause epimerization of the stereogenic centers, even at 110 °C. We examined the structure-activity relationships for the cytoprotective activity against cytotoxicity induced by 3-morpholinosydnonimine (SIN-1) in nerve growth factor (NGF)-differentiated PC12 cells. The C-8/C-9 double bond, but not the stereogenic center derived from alanine, was found to play a key role in the cytoprotective activity.
TY - JOUR. T1 - Regioselective synthesis of thiophene fused sultam derivatives via iodocyclization approach and their application towards triazole linker. AU - Barange, Deepak Kumar. AU - Kavala, Veerababurao. AU - Kuo, Chun Wei. AU - Wang, Cheng Chuan. AU - Rajawinslin, R. R.. AU - Donala, Janreddy. AU - Yao, Ching Fa. PY - 2014/10/14. Y1 - 2014/10/14. N2 - An efficient regioselective synthesis of 4-iodo-2,3-disubstituted-2H-thieno[3,2-e][1,2]thiazine-1,1-dioxide derivatives via iodocyclization approach using iodine under mild reaction condition described herein. This coupling-iodocyclization strategy tolerated a variety of functional groups such as alkyl, cycloalkyl, phenyl producing the six-membered heterocyclic ring selectively. The resulting 4-iodo-2,3-disubstituted-2H-thieno[3,2-e][1,2]thiazine-1,1-dioxide was coupled with a variety of boronic acids (Suzuki coupling) and activated alkenes (Heck coupling). The iodo group was utilized for Sonogashira coupling followed by efficient ...
ADP-ribosyl cyclases catalyze the transformation of nicotinamide adenine dinucleotide (NAD+) into the calcium-mobilizing nucleotide second messenger cyclic adenosine diphosphoribose (cADP-ribose) by adenine N1-cyclization onto the C-1 position of NAD+. The invertebrate Aplysia californica ADP-ribosyl cyclase is unusual among this family of enzymes by acting exclusively as a cyclase, whereas the other members, such as CD38 and CD157, also act as NAD+ glycohydrolases, following a partitioning kinetic mechanism. To explore the intramolecular cyclization reaction, the novel nicotinamide 2-fluoroadenine dinucleotide (2-fluoro-NAD+) was designed as a sterically very close analogue to the natural substrate NAD+, with only an electronic perturbation at the critical N1 position of the adenine base designed to impede the cyclization reaction. 2-Fluoro-NAD+ was synthesized in high yield via Lewis acid catalyzed activation of the phosphoromorpholidate derivative of 2-fluoroadenosine 5-monophosphate and coupling
TY - JOUR. T1 - Hypervalent iodine in synthesis 93. A facile synthesis of 2-substituted imidazo[1,2-a]pyrimidines by cyclocondensation of alkynyl(phenyl)iodonium salts and 2-aminopyrimidine. AU - Zhi, Liu. AU - Chen, Zhen-Chu. AU - Zheng, Qinguo. PY - 2003/9. Y1 - 2003/9. N2 - Simple stirring of a mixture of the alkynyl(phenyl)iodonium salts 1 with 2-aminopyrimidine 2 in chloroform under reflux for two hours in the presence of K2CO3 gave, after workup, the 2-substituted imidazo[1,2-]pyrimidines 3 in moderate to good yields. A possible mechanism for the formation of 3 involves the intramolecular cyclization of the intermediate alkylidenecarbene 6.. AB - Simple stirring of a mixture of the alkynyl(phenyl)iodonium salts 1 with 2-aminopyrimidine 2 in chloroform under reflux for two hours in the presence of K2CO3 gave, after workup, the 2-substituted imidazo[1,2-]pyrimidines 3 in moderate to good yields. A possible mechanism for the formation of 3 involves the intramolecular cyclization of the ...
Oxidative cyclizations of a variety of heteroatom nucleophiles onto unactivated olefins are catalyzed by palladium(II) and pyridine in the presence of molecular oxygen as the sole stoichiometric oxidant in a nonpolar solvent (toluene). Reactivity studies of a number of N-ligated palladium complexes show that chelating ligands slow the reaction. Nearly identical conditions are applicable to five different types of nucleophiles: phenols, primary alcohols, carboxylic acids, a vinylogous acid, and amides. Electron-rich phenols are excellent substrates, and multiple olefin substitution patterns are tolerated. Primary alcohols undergo oxidative cyclization without significant oxidation to the aldehyde, a fact that illustrates the range of reactivity available from various Pd(II) salts under differing conditions. Alcohols can form both fused and spirocyclic ring systems, depending on the position of the olefin relative to the tethered alcohol; the same is true of the acid derivatives. The racemic ...
In an effort to make diverse molecular complexity from simple hydrocarbons, tricarbonyl(cyclohexadienyl)iron(+1) cation was prepared in two steps from 1, 3-cycloxehadiene. Reactivity of the symmetric iron cation with heteroatom nucleophiles and stabilized carbon nucleophiles was studied. Nucleophilic attack of potassium phthalimide at the dienyl terminus of the cation followed by oxidative decomplexation with Ce4+ provided the ligand N-(2,4-cyclohexadiene-1-yl)phthalimide. A series of stereochemically diverse polyhydroxyl aminocyclohexane aminocyclitols derivatives and a number of racemic and optically active hydroxy-and polyhydroxy 1,3-diaminocyclohexane derivatives have been synthesized from N-(2,4-cyclohexadiene-1-yl)phthalimide. The relative stereochemistries of the compounds ware assigned on the basis of the 1H NMR data as well as X-ray single crystal diffraction analysis. In a similar attempt tricabonyl(η5-6-styrylcyclohepta-2,4-diene-1-yl)iron(+1) cation was synthesized in three steps from 1,
TY - JOUR. T1 - Selective [3+2] Cycloadditions of β-Amino-α,β-unsaturated Pentacarbonylcarbenechromium Complexes to Alkynes-A New Approach to Functionally Substituted Cyclopentadienes. AU - Flynn, Bernard L.. AU - Funke, Frank J.. AU - Silveira, Claudio C.. AU - Meijere, Armin De. PY - 1995/10/1. Y1 - 1995/10/1. N2 - (3-Amino-1-ethoxyalkenylidene)pentacarbonylchromium complexes 2 react with alkynes in pyridine or acetonitrile to give highly substituted 5-amino-3-ethoxycyclopentadienes 3 as formal [3+2]-cycloadducts selectively in high yields rather than the usually favored [2+2+1]-cycloadducts, 5-methylene-2-cyclopenten-1-ones.. AB - (3-Amino-1-ethoxyalkenylidene)pentacarbonylchromium complexes 2 react with alkynes in pyridine or acetonitrile to give highly substituted 5-amino-3-ethoxycyclopentadienes 3 as formal [3+2]-cycloadducts selectively in high yields rather than the usually favored [2+2+1]-cycloadducts, 5-methylene-2-cyclopenten-1-ones.. KW - 1-Metalla-1,3,5-hexatrienes. KW - ...
Medvedev, et al. have examined the cyclization step in the formation of Spinosyn A, which is catalyzed by the putative Diels-Alderase enzyme SpnF.1 This work follows on the computational study done by Houk, Singleton and co-workers,2 which I have discussed in this post (Dynamics in a reaction where a [6+4] and [4+2] cycloadditons compete). In fact, I recommend that you read the previous post before continuing on with this one. In summary, Houk, et al. found that a single transition state connects reactant 1 to both 2 and 3. The experimental product with the enzyme SpnF is 3. In the absence of enzyme, Houk, et al. suggest that reactions will cross the bispericyclic transition state TS-BPC (TS1 in the previous post) leading primarily to 2, which then undergoes a Cope rearrangement to get to product 3. Some molecules will follow pathways that go directly to 3 ...
Conjugated dienes exist in two conformation called s-cis and s-trans. They interconvert freely in open-chain dienes, by single bond rotation, but may not be able to in some cyclic cases. For the Diels-Alder reaction to occur, the s-cis conformation needs to be present, so the two carbons of the alkene can connect to both of them simultaneously. The reaction occurs in a single step during which the pi electrons reorganize through a cyclic transition state, forming two new single bonds to the ends of the diene. It is one of the reactions among a larger class called cycloaddition, and cycloaddition falls into a broader class called pericyclic - reactions which involve no intermediate, only a cyclic reorganization of electrons. Good yields of Diels-Alder products are obtained when the dienophile (alkene) has electron-withdrawing groups, often carbonyl groups, ester groups or cyano groups. Maleic anhydride is often used as a dienophile. ...
Oxidosqualene cyclases are a group of enzymes that cyclize 2,3-oxidosqualene to any of over 80 triterpene skeletons. Sequence correlation suggests these enzymes share a common overall structure and subtle changes in active site residues are responsible for differences in the structure of the cyclization product. Further characterization of conserved residues has lead to a better understanding of the mechanisms through which regio- and stereo-selective cyclization occurs. This work has resulted in the cloning of three new oxidosqualene cyclases. By cloning triterpene synthases from far-diverged organisms, new sequence data has been added for correlation and has provided new information regarding evolution of the enzymes from a common ancestor. Arabidopsis thaliana lupeol synthase was cloned and the full-length cDNA expressed in yeast. Degenerate PCR primers designed from regions of highly conserved sequence were used to clone cycloartenol synthase and a presently uncharacterized triterpene ...
Polyesters have been used for many biomedical applications ranging from sutures to drug delivery vehicles. However, their bulk degradation results in an accumulation of acidic byproducts, which is detrimental to the human body. In order to circumvent this problem, as well as to impart new properties and functions to polymers for biomedical applications, poly(ester amide)s (PEAs) have been proposed as a different class of biodegradable polymers. However, up to date, there exists no way to stimulate the degradation of these polymers. The Gillies research group has previously incorporated self-immolative spacers into polymers and has been able to stimulate their degradation by adding the appropriate trigger. The objective of this thesis was to incorporate amino acids capable of 1,5-cyclization into the PEA backbone such that upon activation of the functional moiety, a 1,5-cyclization was induced, leading to degradation of the PEA backbone. PEAs containing L-2,4-diaminobutyric acid and DL-homocysteine were
A carbohydrate-based synthesis of both cis- and trans-fused bicylic ethers has been achieved by radical cyclization of epoxides using a transition-metal radical source. Thus, 6-exo radical cyclizations of the carbohydrate derivatives using [bis(cyclopentadienyl) titanium(III)]chloride (Cp2TiCl) as the radical source has resulted in corresponding cis- and trans-fused bicyclic ethers. While the trans-fused compound has allowed stereoselective radical cyclization, the cis-fused has ended up only in a mixture of isomers. The functionalities present in the bicyclic compounds are potential intermediates as multifunctional conformationally rigid scaffolds ...
Enantioselective approaches, where the stereocontrol of the cyclization is not governed by a stereocentre already in the cyclization precursor, have received much less attention than the diastereoselective, racemic or achiral version of the PS reaction. It was shown in 1996 that the PS reaction could be effected with superstoichiometric Lewis acid - in this case the cyclization of the (Z)-nitrone derived from Nb-hydroxytryptamine using diisopinocampheylchloroborane (Ipc2BCl) to give the corresponding tetrahydro-β-carboline products (Scheme Nakagawa 1998).(10.1016/0957-4166(96)00134-6 and 10.1021/jo980810h) The racemic cyclization could be effected with Bronsted acid and a number of achiral Lewis acids, but it was found that Ipc2BCl gave high yields and ee with reduced temperatures. Lowering the quantity of Ipc2BCl to 0.5 eq. caused a significant reduction of yield, while attempts to alter the Lewis acidity by substitution of the chloride (with e.g. fluoride or triflate) did not improve yield or ...
Enantioselective approaches, where the stereocontrol of the cyclization is not governed by a stereocentre already in the cyclization precursor, have received much less attention than the diastereoselective, racemic or achiral version of the PS reaction. It was shown in 1996 that the PS reaction could be effected with superstoichiometric Lewis acid - in this case the cyclization of the (Z)-nitrone derived from Nb-hydroxytryptamine using diisopinocampheylchloroborane (Ipc2BCl) to give the corresponding tetrahydro-β-carboline products (Scheme Nakagawa 1998).(10.1016/0957-4166(96)00134-6 and 10.1021/jo980810h and 10.3987/REV-98-SR1) The racemic cyclization could be effected with Bronsted acid and a number of achiral Lewis acids, but it was found that Ipc2BCl gave high yields and ee with reduced temperatures. Lowering the quantity of Ipc2BCl to 0.5 eq. caused a significant reduction of yield, while attempts to alter the Lewis acidity by substitution of the chloride (with e.g. fluoride or triflate) ...
TY - JOUR. T1 - Microwave-assisted deacylation of unactivated amides using ammonium-salt-accelerated transamidation. AU - Shimizu, Yuhei. AU - Morimoto, Hiroyuki. AU - Zhang, Ming. AU - Ohshima, Takashi. PY - 2012/8/20. Y1 - 2012/8/20. N2 - Easy does it! The chemoselective oxidative ?-C(sp3)H alkylation/cyclization reaction of N-benzyl carbamates using simple mono-, di-, and trisubstituted olefins provides functionalized N-heterocycles such as oxazinones (see picture). A TEMPO oxoammonium salt serves as the oxidant, making it possible to carry out the reaction at low temperatures. Neither a metal catalyst nor preactivation in the ?-position to the nitrogen group are needed.. AB - Easy does it! The chemoselective oxidative ?-C(sp3)H alkylation/cyclization reaction of N-benzyl carbamates using simple mono-, di-, and trisubstituted olefins provides functionalized N-heterocycles such as oxazinones (see picture). A TEMPO oxoammonium salt serves as the oxidant, making it possible to carry out the ...
Although the [2 + 2] cycloaddition of alkenes and ketenes to form cyclobutanones is one of the few general methods for the construction of four-membered rings, the intramolecular version of this reaction had been little explored when we started work in this area in the early 1980s.109 These reactions differ from most other pericyclic reactions in that the ketene is a reactive intermediate, which will either rapidly form a cyclobutanone or decompose. The yield is determined by the relative rate of these two processes. Alkenyloxyketenes were chosen for the initial exploratory work because the alkenyloxy carboxylic acids were easily prepared by alkylation of unsaturated alcohols with α-bromo carboxylic acids. The electronic effects of the alkyl substituents on the alkene control the regiochemistry of the cycloaddition and the yield depends on the balance between the nucleophilicity of the alkene and steric hindrance.83,90,109 Leading bond formation occurs between the electrophilic carbonyl carbon ...
Microwave-assisted organic synthesis in near-critical water (NCW) in the 270-300 °C temperature range has been investigated in a dedicated multimode microwave reactor utilizing heavy-walled quartz reaction vessels. Several different known transformations such as the hydrolysis of esters or amides, the hydration of alkynes, Diels-Alder cycloadditions, pinacol rearrangements, and the Fischer indole synthesis were successfully performed in microwave-generated NCW without the addition of an acid
Looking for Electrocyclic? Find out information about Electrocyclic. The interconversion of a linear π-system containing n π-electrons and a cyclic molecule containing π-electrons which is formed by joining the ends of the... Explanation of Electrocyclic
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A synthetic strategy was developed for the preparation of porphyrins containing between one and four stereogenic centers, such that their molecular weights vary only as a result of methyl groups which give the chiral forms. The low-dimensional nanoscale aggregates of these compounds Reveal the profound effects of this varying molecular chirality on their supramolecular structure and optical activity. The number of stereogenic centers influences significantly the self-assembly and chiral structure of the aggregates of porphyrin molecules described here. A scanning tunneling microscopy study of monolayers on graphite shows that the degree of structural chirality with respect to the surface increases almost linearly with the number of stereogenic centers, and only one handedness is formed in the monolayers, whereas the achiral compound forms a mixture of mirror-image domains at the surface. In solution, four hydrogen bonds induce the formation of an H-aggregate, and circular dichroism measurements ...
Fabio Aricò has started working in the field of Green Chemistry in 2005 after being awarded his Ph.D. at Reading University and post-doc position at UCLA, Los Angeles, CA. He is now associate professor of organic chemistry at Ca Foscari University, Venice, Italy. His research interest within Green Chemistry is to develop innovative reaction pathways focussing on chlorine-free synthetic approaches via dialkyl carbonate (DAC) chemistry. Fabio Aricò has exploited dialkyl carbonates chemistry in the phosgene-free synthesis of carbonates and carbamates with potential applications as monomers for polycarbonate/polyurethane. He also contributed to demonstrate that DACs are highly selective alkylating agents that can be used in substitution of alkyl halides and dimethyl sulphate for alkylation of numerous nitrogen and oxygen substrates. He has reported on the DAC-mediated cyclization reactions can be used as sacrificial molecules in cyclization reaction instead of halogenated compound. As a result, ...
Three synthetic methodologies are studied in details in this dissertation. For 1,5-hydride shift of alkenyl sulfoximine methodology, the reaction mechanism was studied using deuterium labeling. An uncommon 6-endo-trig 1,5-hydride shift process was discovered. The scope and limitation were studied using N-alkyl, N-allyl, and N-benzyl-substituted S-alkenyl sulfoximines. N-H-S-alkyl sulfoximines, four- and six-membered heterocyclic rings and a new class of chiral dienes were obtained. In [4+3] cycloaddition and ring opening chapter, we demonstrated an ene-like reaction using a symmetric oxyallylic cation can provide α-substituted cyclopentenones. Enantio pure products are potentially accessible by this method. [4+3] Cycloaddition of the symmetric oxyallylic cation with substituted furans, and the ring-opening process of the resulting 8-oxabicyclo[3.2.1]oct-6-en-3-one were also studied. The reaction conditions and scope were investigated. An acid-catalyzed mechanism was proposed for the ...
The thermal cyclisation of enediynes to benzene-1,4-diyl diradicals (Bergman cyclisation) is affected by geometrical and electronic conditions. While the effect of ring strain or conformational constrains on the cyclisation temperature has been investigated in detail, electronic contributions have been less studied. Often geometrical and electronic contributions cannot be clearly distinguished. In most cases metal ion chelation does involve both. In this review we have summarised clear-cut observations of electronic substituents effects on the thermal enediyne reactivity. The effects of substituents in the vinylic and terminal alkyne position, the influence of benzo-fusion and hetarene fusion, as well as the changes induced by heteroatoms in the enediyne skeleton, are within the scope of this review. With the exception of more complex heterocyclic hetarene-fused enediynes the experimental data of electronic substituent effects on the thermal Bergman cyclisation of enediynes follow theoretical ...
The Diels-Alder reaction is the reaction between a conjugated diene and an alkene (dienophile) to form unsaturated six-membered rings. Since the reaction involves the formation of a cyclic product via a cyclic transition state, it is also referred to as a cycloaddition. The Diels-Alder reaction is an electrocyclic reaction, which involves [4+2]‑cycloaddition of 4 π-electrons of the conjugated diene and 2 π-electrons of the dienophile (an alkene or alkyne). The reaction involves the formation of new σ-bonds, which are energetically more stable than the π-bonds. This reaction has great synthetic importance and was discovered by two German chemists, Otto Diels and Kurt Alder in 1928. They were awarded the Nobel Prize in 1950.1 ...
Sumanirole (PNU-95,666) is a highly selective D2 receptor full agonist, the first of its kind to be discovered. It was developed for the treatment of Parkinsons disease and restless leg syndrome. While it has never been approved for medical use it is a highly valuable tool compound for basic research to identify neurobiological mechanisms that are based on a dopamine D2-linked (vs. D1, D3, D4, and D5-linked) mechanism of action. In 2004, Pfizer announced the end of their clinical development program for sumanirole, citing recent studies that failed to sufficiently distinguish sumanirole from currently available therapies. Ropinirole Romero AG, et al. Synthesis of the selective D2 receptor agonist PNU-95666E from D-phenylalanine using a sequential oxidative cyclization strategy. Journal of Organic Chemistry. 1997; 62(19):6582. McCall RB, Lookingland KJ, Bédard PJ, Huff RM (September 2005). Sumanirole, a highly dopamine D2-selective receptor agonist: in vitro and in vivo pharmacological ...
A novel Ferrier-type carbocyclization is reported. It involves a carbohydrate-derived lactone acetal synthesized from methyl α-d-glucopyranoside, which upon treatment with excess vinylmagnesium bromide provides a highly substituted carbocyclic product as a single stereoisomer. The yield is greatly increased when N,N,N′,N′-tetramethylethylenediamine is added to the reaction mixture. Optimized reaction conditions have been applied to lactone acetals derived from other carbohydrates. Based on the obtained results, a possible reaction mechanism has been proposed. Furthermore, scalability of the reaction up to 15 g scale and derivatization of the carbocyclic product has been demonstrated, including the formation of a rare trans-bicyclo[4.3.0]nonene scaffold via a ring-closing metathesis. The structure of this and all carbocyclic products were confirmed by X-ray crystallographic analysis. ...
Cyclisation of Monosaccharides[edit]. A monosaccharide often switches from the acyclic (open-chain) form to a cyclic form, ... Cyclization creates a new stereogenic center at the carbonyl-bearing carbon. The −OH group that replaces the carbonyl's oxygen ...
For Bergman cyclization to occur, the epoxide must be removed. Myers-Saito cyclization is another triggering mechanism by which ... The diradicals generated by Bergman and Myers-Saito cyclization are highly reactive. The cyclization of the enediyne functional ... Bergman cyclization restructures the enediyne ring into two smaller rings. One electron from each of the enediyne triple bonds ... "Bergman Cyclization". www.organic-chemistry.org. Retrieved 2018-05-05. Smith AL, Nicolaou KC (May 1996). "The enediyne ...
"Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English. 8 (10): 727-733. doi:10.1002/anie. ...
Trost, B. M.; Greenspan, P. D.; Yang, B. V.; Saulnier, M. G. (1990). "An unusual oxidative cyclization. A synthesis and ...
Trost BM, Greenspan PD, Yang BV, Saulnier MG (November 1990). "An unusual oxidative cyclization. A synthesis and absolute ...
Denmark, S. E.; Jones, T. K. (1982-05-01). "Silicon-directed Nazarov cyclization". Journal of the American Chemical Society. ... From Polyene Cyclizations to Origin of Biomolecular Homochirality. ETH Zurich (Switzerland). Retrieved 2019-11-16. ... where his laboratory's early work focused on investigation of the Nazarov cyclization reaction and Claisen rearrangement. This ...
This causes cyclization and gives rise to (2S,4S)-4-hydroxy-2,3,4,5-tetrahydrodipicolinate. 4-hydroxy-tetrahydrodipicolinate ... this prevents spontaneous cyclization. The enzyme N-acetylglutamate synthase (glutamate N-acetyltransferase) is responsible for ...
The importance of cyclization effects". International Journal of Quantum Chemistry. doi:10.1002/qua.25489.. ...
The use of thiyl radicals as initiators of cyclization has been employed in the synthesis of a number of natural products, ... This section examines intramolecular thiol-ene cyclization reactions, which yields a mixture of 5-exo and 6-endo products in ... The conditions under which these cyclization reactions occur follow Baldwin's rules for ring closure. Given the reversibility ... Lynch, Dylan M.; Scanlan, Eoin M. (2020-07-07). "Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of ...
This cyclization is one of the most complex known enzyme functions and is highly selective. In the enzyme's active site, a ... Oxidosqualene cyclases (OSC) are enzymes involved in cyclization reactions of 2,3-oxidosqualene to form sterols or triterpenes ... Stork, Gilbert; Burgstahler, A. W. (1955-10-01). "The Stereochemistry of Polyene Cyclization". Journal of the American Chemical ...
B. E. Maryanoff; H.-C. Zhang; J. H. Cohen; I. J. Turchi; C. A. Maryanoff (2004). "Cyclizations of N-acyliminium ions". Chem. ... Larghi, E. L.; Kaufman, T. S. (2006). "The oxa-Pictet-Spengler Cyclization. Synthesis of Isochromanes and Related Pyran-Type ... Instead of catalyzing the Pictet-Spengler cyclization with strong acid, one can acylate the iminium ion forming the ...
Chamberlin, A. R.; Nguyen, H. D.; Chung, J. Y. L. (1984). "Cationic cyclization of ketene dithioacetals. A general synthesis of ...
Johnson, W.S.; Mathews, F.J. (1944). "Cyclization studies in the benzoquinoline series". J. Am. Chem. Soc. 66 (2): 210-215. doi ... Johnson, W.S.; Mathews, F.J. (1944). "Cyclization studies in the benzoquinoline series". J. Am. Chem. Soc. 66 (2): 210-215. doi ...
Youngs, Wiley J.; Djebli, Abdellah.; Tessier, Claire A. (1991-07-01). "Lithium-induced cyclization of tribenzo cyclotriynes". ...
At this point cyclization takes place. This is followed by protonation; the source of proton being the hydrogen which was ...
"Cyclization recombinase [Escherichia coli] - Protein - NCBI". Sternberg N, Hamilton D (August 1981). "Bacteriophage P1 site- ... The Cre protein (encoded by the locus originally named as "Causes recombination", with "Cyclization recombinase" being found in ...
Padwa, Albert; Kassir, Jamal M.; Xu, Simon L. (1 March 1997). "Cyclization Reactions of Rhodium Carbene Complexes. Effect of ...
5-Exo cyclization, which establishes a five-membered ring with an exocyclic alkene, is the most facile cyclization mode in ... 7) Endo cyclization is observed most often when small or large rings are involved. For instance, 5-endo cyclization is ... 12) The closest competing method to IMHR is radical cyclization. Radical cyclizations are often reductive, which can cause ... 6) 6-Exo cyclization is also common. The high stability of Heck reaction catalysts permits the synthesis of highly strained ...
... cyclization then affords the observed product (4). The amide function is then converted to the iminochloride with phosphorus ...
Another method is the Volhard-Erdmann cyclization. Thiophene is produced on a modest scale of around 2,000 metric tons per year ...
The radical intermediate can engage in secondary reactions such as cyclisation. With diaddition the 1,2-disulfide or the 1,1- ... "Sulfanyl radical mediated cyclization of aminyl radicals". Tetrahedron Letters. 39 (49): 9077. doi:10.1016/S0040-4039(98)01998- ...
This reaction is called Simonis chromone cyclization. The ketone in the ketoester is activated by P2O5 for reaction with the ...
Titanium(III)-induced cyclization of epoxy olefins". Journal of the American Chemical Society. 110 (25): 8561-8562. doi:10.1021 ... A regioselective epoxide opening and 5-exo dig radical cyclization to forge the core of ceratopicanol. Addition of a ... mediated radical cyclizations of epoxygermacrolides. Straightforward synthesis and absolute stereochemistry of (+)-3α- ... and tetrasubstituted olefins by tandem cyclization addition reactions featuring vinyl radicals". Angewandte Chemie ...
Aziridine occurs by the cyclization of chloroethylamine; piperazines are formed by cyclization of a two-ethylene unit compound ...
"Metal-Free Electrophilic Phosphination/Cyclization of Alkynes". Journal of the American Chemical Society. 139 (17): 6106-6109. ...
Titanium(III)-induced cyclization of epoxy olefins". J. Am. Chem. Soc. 110 (25): 8561-8562. doi:10.1021/ja00233a051. Kuester, ... Kablaoui, N. M.; Buchwald, S. L. (1998). "Development of a Method for the Reductive Cyclization of Enones by a Titanium ... A similar reaction is the reductive cyclization of enones to form the corresponding alcohol in a stereoselective manner. ...
Diesters possessing 10 or more carbons undergo cyclisation very easily. The cyclization of diesters by intramolecular acyloin ... In general, compared to other cyclization reactions that proceed under basic conditions like the Ziegler-Thorpe and Dieckmann ... Finley, K. T. (1964). "The Acyloin Condensation as a Cyclization Method". Chem. Rev. 64 (5): 573-589. doi:10.1021/cr60231a004. ... Thus, the reactive ends are not available for polymerisation, thereby decreasing competition for the cyclisation process. ...
Titanium(III)-induced cyclization of epoxy olefins". J. Am. Chem. Soc. 110 (25): 8561-8562. doi:10.1021/ja00233a051. Jungst, ...
Thiazol(in)es are the result of cyclization of Cys residues in the precursor peptide, while (methyl)oxazol(in)es are formed ... Plantazolicin is a LAP with extensive cyclization. Two sets of five heterocycles endow the natural product with structural ... Amatoxins and phallotoxins are 8- and 7-membered natural products, respectively, characterized by N-to-C cyclization in ...
"Enantioselective cyclizations and cyclization cascades of samarium ketyl radicals". Nature Chemistry. 9 (12): 1198-1204. ... Huang, Huan-Ming; McDouall, Joseph J. W.; Procter, David J. (2019). "SmI2-catalysed cyclization cascades by radical relay". ... pleuromutilin via SmII-mediated radical cyclization cascades of dialdehydes, prepared by a one-pot, copper catalyzed double ... Catalyzed Double Additions and Radical Cyclization Cascades in the Re‐Engineering of the Antibacterial Pleuromutilin". Chem. ...
Anionic Michael-type cyclization is an alternative to radical cyclization of activated olefins. Metal-catalyzed cyclization ... Radical cyclizations are much faster than analogous anionic cyclizations, and avoid β-elimination side reactions. ... 8) In comparison to cationic cyclizations, radical cyclizations avoid issues associated with Wagner-Meerwein rearrangements, do ... exo cyclization is favored over endo cyclization (macrocyclizations constitute the major exception to this rule). 5-hexenyl ...
The Pschorr cyclization is a name reaction in organic chemistry, which was named after its discoverer, the German chemist ... The Pschorr cyclization has a relatively good atom economy, since essentially only nitrogen is produced as a waste material. ... However, when considering the atom economy it has to be mentioned that the Pschorr cyclization has often only low yields. ... The following reaction scheme shows the Pschorr cyclization for the example of phenanthrene: In the course of the Pschorr ...
... utilized to prepare in situ a dipeptide precursor which then sequentially underwent an alkaline mediated keto-amide cyclization ... A one-pot multicomponent coupling/cyclization for natural product herbicide (±)-thaxtomin A J. P. Bourgault, A. R. Maddirala ... A one-pot multicomponent coupling/cyclization for natural product herbicide (±)-thaxtomin A† ... utilized to prepare in situ a dipeptide precursor which then sequentially underwent an alkaline mediated keto-amide cyclization ...
Gold-Catalyzed Cyclizations of cis-Enediynes: Insights into the Nature of Gold-Aryne Interactions. Title. Gold-Catalyzed ... Cyclizations of cis-Enediynes: Insights into the Nature of Gold-Aryne Interactions. ...
9. A Mannich-Cyclization Approach for the Asymmetric Synthesis of Saturated N-Heterocycles. A. Münch, B. Wendt, M. Christmann. ... 9. A Mannich-Cyclization Approach for the Asymmetric Synthesis of Saturated N-Heterocycles ... 9. A Mannich-Cyclization Approach for the Asymmetric Synthesis of Saturated N-Heterocycles ... Our approach utilizes an optimized Mannich reaction of functionalized aldehydes, followed by a novel dehydrative cyclization ...
Novel Aza-Prins Cyclization and [3+2] Dipolar Cycloaddition Toward N-Heterocyclic Molecules and Studies Toward the Total ... Liu, Xiaoxi, "Novel Aza-Prins Cyclization and [3+2] Dipolar Cycloaddition Toward N-Heterocyclic Molecules and Studies Toward ...
Synthesis of an isomer of lycoplanine a via cascade cyclization to construct the spiro-N,O-acetal moiety ... Synthesis of an isomer of lycoplanine a via cascade cyclization to construct the spiro-N,O-acetal moiety. Organic & ...
Unusual rearrangements and cyclizations involving polycyclic indolic systems. Alamdar Ashnagar, Patrick D. Bailey, Philip J. ... Unusual rearrangements and cyclizations involving polycyclic indolic systems. / Ashnagar, Alamdar; Bailey, Patrick D.; Cochrane ... Ashnagar, A., Bailey, P. D., Cochrane, P. J., Mills, T. J., & Price, R. A. (2007). Unusual rearrangements and cyclizations ... N2 - During the course of experiments to explore and develop cyclization reactions of indolic systems, a number of unusual ...
Lactams and Cyclization Reactions for Organic Chemistry. This is one of many videos provided by Clutch Prep to prepare you to ... Im just trying to give you an overview of different cyclizations that we might have missed to this point, so the first one is ... Now I want to discuss lactones, lactams and cyclization reactions.. It turns out that esters and amides can be made to form ... The way that you get these is through the cyclization of either hydroxycarboxylic acids. Here I have an example, a hydroxyl ...
keywords = "Electro-reduction, Fluorene, Mediator, Radical cyclization, Reductive cyclization",. author = "Koichi Mitsudo and ... Electro-reductive cyclization of aryl halides promoted by fluorene derivatives. Koichi Mitsudo, Yumiko Nakagawa, Jun Ichi ... Electro-reductive cyclization of aryl halides promoted by fluorene derivatives. Electrochimica Acta. 2012 Nov 1;82:444-449. ... Electro-reductive cyclization of aryl halides promoted by fluorene derivatives. In: Electrochimica Acta. 2012 ; Vol. 82. pp. ...
An efficient NaBArF4-catalyzed oxidative cascade cyclization of N-propargyl ynamides has been developed, where NaBArF4 is ... An efficient NaBArF4-catalyzed oxidative cascade cyclization of N-propargyl ynamides has been developed, where NaBArF4 is ... Silver(I)-catalyzed sequential hydroamination and Prins type cyclization for the synthesis of fused benzo--sultams ... Transition-metal-free oxidative cyclization of N-propargyl ynamides: stereospecific construction of linear polycyclic N- ...
Edukondalu, A, Vagh, SS, Lin, TH & Lin, W 2021, Construction of indeno[1,2-b]pyrrolesviachemoselectiveN-acylation/cyclization/ ... Construction of indeno[1,2-b]pyrrolesviachemoselectiveN-acylation/cyclization/Wittig reaction sequence. Chemical Communications ... Dive into the research topics of Construction of indeno[1,2-b]pyrrolesviachemoselectiveN-acylation/cyclization/Wittig reaction ... Construction of indeno[1,2-b]pyrrolesviachemoselectiveN-acylation/cyclization/Wittig reaction sequence. In: Chemical ...
Use of the Tandem Transposition/π-Cyclization of N -Acyliminium Species Anthony Pesquet 1 Adam Daïch 1 Luc van Hijfte Details. ... Use of the Tandem Transposition/π-Cyclization of N -Acyliminium Species. Journal of Organic Chemistry, American Chemical ...
One-pot synthesis of 3-allyl- and 3-benzyl-Δ3-cephems through a sequential reductive 1,2-elimination/addition/cyclization of 3 ... N2 - One-pot synthesis of 3-allyl- and 3-benzyl-Δ3-cephems through a sequential reductive 1,2-elimination/addition/cyclization ... AB - One-pot synthesis of 3-allyl- and 3-benzyl-Δ3-cephems through a sequential reductive 1,2-elimination/addition/cyclization ... Synthesis of 3-allyl- and 3-benzyl-Δ3-cephems through sequential reductive 1,2-elimination/addition/cyclization of 3,4- ...
Backbone cyclization of analgesic conotoxin GeXIVA facilitates direct folding of the ribbon isomer.. *Post by: tcs1aded ... Backbone cyclization of analgesic conotoxin GeXIVA facilitates direct folding of the ribbon isomer.. ... Backbone cyclization of analgesic conotoxin GeXIVA facilitates direct folding of the ribbon isomer. ...
Development of a strategy for the regio- and stereoselective oxidative cyclization of 3-(ω-nucleophile)- tethered indoles. In: ... The brominative cyclization of diastereomeric β-silyloxy tryptophan derivatives proceeded with divergent regiochemistry (C(2) ... N2 - The brominative cyclization of diastereomeric β-silyloxy tryptophan derivatives proceeded with divergent regiochemistry (C ... AB - The brominative cyclization of diastereomeric β-silyloxy tryptophan derivatives proceeded with divergent regiochemistry (C ...
... mediated Dieckmann cyclization of dicarboxylic acids with acid chlorides. ...
The cyclization products 6 exhibit interesting inhibition of RNase H and DNA-polymerase activity of reverse transcriptase (RT) ... N-Alkylation of the starting amino esters to 5 and 3 was followed by halogen/lithium exchange and double cyclization. ... Double cyclization of bis(α-hetarylmethyl)amino esters to optically active bridged N-heterocycles of HIV-inhibiting activity ... Double cyclization of bis(α-hetarylmethyl)amino esters to optically active bridged N-heterocycles of HIV-inhibiting activity ...
... catalyzed cascade cyclization of azide‐ynamides via α‐imino copper carbene intermediates is reported, w... ... Ynamide Cyclization for Generation of α‐Imino Copper Carbenes: Divergent and Enantioselective Access to Polycyclic N‐ ... 我室叶龙武教授在 ACIE 上发表论文:Copper‐Catalyzed Azide‐Ynamide Cyclization for Generation of α‐Imino Copper Carbenes: Divergent and ... ACIE] 我室叶龙武教授发表论文:Copper‐Catalyzed Azide‐Ynamide Cyclization for Generation of α‐Imino
... intramolecular cyclization of thiobenzanilides, and (iv) tandem cyclization of anilines/ nitroarenes- with elemental sulfur or ... 2-arylbenzothiazole - amyloid imaging agents - condensation - intramolecular cyclization - C-H functionalization *. References ...
A cyclization reaction between enamides and alkynes catalyzed by palladium(ii) acetate is described. In this method, the ... A cyclization reaction between enamides and alkynes catalyzed by palladium(II) acetate is described. In this method, the ...
repraesentin F - gold(I)-mediated cyclization - cyclization cascade - Still-Gennari olefination - Simmons-Smith ...
Lanosterol synthase, an essential enzyme that catalyzes the cyclization of squalene 2,3-epoxide, a step in ergosterol ...
5 Lewis Acid Mediated Nazarov Cyclization as a Versatile Method for C-Nor-D-homo-steroid Synthesis ...
A palladium-assisted C-C intramolecular cyclization of the coupling products gave thienocarbazoles and the dechlorinated ...
Synthesis of a Common Heterocyclic Core via a Novel Radical Cyclization / Allene Reduction Sequence ...
Dive into the research topics of Total Synthesis of a Dimeric Thymol Derivative Isolated from Arnica sachalinensis. Together they form a unique fingerprint. ...
The reaction proceeds in one-pot via a highly diastereoselective cyclisation of an a. ... The reaction proceeds in one-pot via a highly diastereoselective cyclisation of an amino gem-diiodide intermediate. ...
PubMed:Reprogramming the chemodiversity of terpenoid cyclization by remolding the active site contour of epi-isozizaene ...
Journal Article] Facile synthesis of indolizino[3,4,5-ab]isoindoles by an acid-induced cyclization of 1,2-di(1H-pyrrol-2-yl) ...
The second step is cyclization of the acquired pseudoionone in the presence of an acidic catalyst, which produces a mixture of ... The ratio of the acquired α- and β-isomers depends on the selection of catalyst, reaction temperature and cyclization time. ... The majority of works utilize alkaline hydroxides for the condensation and inorganic and organic acids for the cyclization. ...
Cyclization of amic acids deprotonated in amid group leads primarily to imides, while those protonated in carboxyl group yield ... The activation energy of cyclization is higher in the neutral form than in the ionic forms of all amic acids investigated. In ... 23]A. V. Yakimanskii, et al., Quantum chemical study of cyclization mechanism in polyamic acids, Polymer Science U.S.S.R., vol ... 12]J. A. Kreuz, et al., Studies of Termal Cyclization of Polyamic acids and Tertiary Amine Salts, Journal of Polymer Science ...
  • The Pschorr cyclization is a name reaction in organic chemistry, which was named after its discoverer, the German chemist Robert Pschorr (1868-1930). (wikipedia.org)
  • The following reaction scheme shows the Pschorr cyclization for the example of phenanthrene: In the course of the Pschorr cyclization, a diazotization of the starting compound occurs, so that an aryldiazonium salt is formed as intermediate. (wikipedia.org)
  • As a final step of the catalytic reaction, the dipeptidyl group undergoes intramolecular cyclization to generate the target cyclodipeptide product. (nature.com)
  • In this work, we investigated the cyclization reaction in the cyclodipeptide synthase AlbC using QM/MM methods and free energy simulations. (nature.com)
  • Results also show that the residues E182, N40, Y178 and H203 maintain the correct conformation of the dipeptide needed for the cyclization reaction. (nature.com)
  • Although initial studies led to unexpected reaction outcomes, we ultimately implemented a sequence of carbazolyne cyclization followed by Rh-catalysed fragmentation to install the seven-membered ring and vicinal quaternary stereocentres of the natural product. (nature.com)
  • C. wherein sufficient of said alkali metal carbonate is added to the reaction zone to maintain a pH between 0.1 and 4.0 in the reaction zone during the cyclization. (patentgenius.com)
  • 5. A process in accordance with claim 4 wherein sufficient of the sodium carbonate is added to the reaction zone to maintain the pH between 0.5 and 2.5 during the cyclization reaction. (patentgenius.com)
  • C., are especially advantageous in that both fast reaction rate and high cyclization yields are obtained compared to the use of cold temperaturesor temperatures even as high as 25.degree. (patentgenius.com)
  • The carbon skeleton of ecologically and pharmacologically important iridoid monoterpenes is formed in a reductive cyclization reaction unrelated to canonical terpene cyclization. (jic.ac.uk)
  • The key steps were microwave assisted Friedel-crafts acylation and diol cyclization carried out via an ultra sonication of Mitsunobu reaction using DEAD (diethylazodicarboxylate), TPP in THF for 1 h. (hindawi.com)
  • Chosen reaction conditions (70 °C, ratio aldehyde:isoprenol 0.9:1, catalyst amount 110 wt%, solvent toluene) were used in Prins cyclization of other aldehydes with the similar results. (springer.com)
  • Approaches to α-cyanopyrrolidines, -piperidines, and -azepanes, as well as their bi- and polycyclic analogues are surveyed, which are based on Strecker reaction - intramolecular nucleophilic cyclization. (enamine.net)
  • Special attention is paid to one-pot tandem Strecker reaction - S N 2-type nucleophilic cyclization (STRINC), or "cyanide-induced dynamic intramolecular cyclization", which is an efficient and convenient approach to various mono- and bicyclic α-amino nitriles and α-amino acids. (enamine.net)
  • The reaction of CLIPS Cyclization is extremely clean and fast. (creative-peptides.com)
  • Therefore, CLIPS Cyclization avoids the need for complex synthetic strategies and this makes the reaction highly versatile with a very wide scope. (creative-peptides.com)
  • The mechanistic rationale for the reaction suggests tandem cyclizations involving copper-catalyzed cycloaddition and 6-endo carbocyclization reactions. (biomedsearch.com)
  • A new method for the kinetic study of cyclization reaction using the chemical shrinkage was described. (springer.com)
  • The results indicate that the method is feasible and the order of cyclization reaction is relevant to stabilization temperature with an activation energy of 159.11 kJ/mol. (springer.com)
  • Reductive amination of 16-acetyl-15,16-epoxylabda-8(9),13,14-triene and subsequent reaction of the resulting amine with 2-methylprop-2-enoyl chloride give intramolecular cyclization products in high yield without isolation of intermediate furfurylacryloyl derivative. (springer.com)
  • In this research, SnCl2·2H2O is the efficient reducing agent for the in‐situ reduction and cyclization reaction of nitro‐compound. (deepdyve.com)
  • Another InBr3 catalyzed Prins reaction initiated polyene cyclization also has been developed, which allowed for the rapid synthesis of 3-oxaterpenoids. (ntu.edu.sg)
  • The reaction that started all the excitement is the C 1 -C 6 cyclization (the Bergman cyclization, Reaction 1). (comporgchem.com)
  • Meyers and Saito then proposed the alternative C 2 -C 7 cyclization (Reaction 2), and a variant on this, the Schmittel cyclization (Reaction 3) followed soon thereafter. (comporgchem.com)
  • Now, Pascal completes the theme with a report on the C 1 -C 5 cyclization (Reaction 4). (comporgchem.com)
  • However, when the reaction is done in the absence of 1,4-cyclohexadiene and at lower temperature (180 °C), the C 1 -C 5 cyclization is still observed and no Bergman cyclization is seen. (comporgchem.com)
  • It appears that C 1 -C 5 cyclization of enediynes is a viable reaction. (comporgchem.com)
  • An enantioselective cascade Mannich intramolecular ring cyclization-tautomerization reaction of malononitrile with 2-hydroxyl N-protected α-amido sulfone is described (see scheme), which provides a new route to the synthesis of the privileged scaffold 2-amino-4H-chromene in high yields (up to 94 %) and with good to high enantiomeric excesses (74-89 % ee). (nus.edu.sg)
  • A novel class of tricyclic tropane analogues has been synthesized by making use of radical cyclization technology in combination with the Stille coupling reaction. (elsevier.com)
  • Concentrating on alkyne and allene cyclisation and upon reaction mechanisms postulated on the basis of empirical and theoretical results, we have examined the coordination of gold fragments to triple bonds, the modification of gold(I) precatalysts to effect specific reaction pathways or enantioselectivity and the isolation of coordinated intermediates or model compounds thereof. (sun.ac.za)
  • hydroxyethyl)-1,4-dimethoxynaphthalene 1 to afford trans-3,4-dihydro-5,10-dimethoxy-1,3-dimethylnaphtho[2,3-c]pyran 2 is investigated by replacing each of the methoxy groups in the substrate by an ethyl substituent and subjecting these to cyclization reaction conditions identical to those originally reported. (edu.au)
  • Although PPA is the cyclizing acid used commercially , other acidic agents like benzoyl chloride in nitrobenzene and acid chlorides hke PCI5, POCI3, AICI, SiCh, or hydrofluoric acid have been used successfully in this cyclization reaction. (chempedia.info)
  • Reaction of 3-substituted dienamides produces beta-lactams via a 4-exo cyclization with termination of the reaction occurring via either halogen atom transfer, trapping with oxygen, elimination, or radical-radical coupling depending upon the diene. (warwick.ac.uk)
  • Kendall Houk and co-workers reported in JACS on a mechanistic investigation on a reaction discovered by Tius: the asymmetric Nazarov cyclization catalyzed by a thiourea-primary amine catalyst. (wordpress.com)
  • 10. Transition Metal Catalyzed Cyclization Reactions of Functionalized Alkenes, Alkynes, and Allenes (Nitin T. Patil and Yoshinori Yamamoto). (organic-chemistry.org)
  • Li G, Gu Y, Ding Y, Yong Z, Hanpeng W, Jianming G, Qiang Y, Liang SL (2004) Wells-Dawson type molybdovanadophosphoric heteropolyacids catalyzed Prins cyclization of alkenes with paraformaldehyde under mild conditions-a facile and efficient method to 1,3-dioxane derivatives. (springer.com)
  • Also included are cyclization reactions of alkenes, alkynes, and allenes, cycloisomerizations, and intramolecular C-N and C-O bond formation. (thieme.de)
  • Their [3+2] cyclization with alkenes and protonation by water-alcohols to yield iminium ions", JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2 , 1998, pp. 2735-2740. (uni-bielefeld.de)
  • In the final step, the target cyclodipeptide is obtained through intramolecular cyclization. (nature.com)
  • Chuang, T.-H. Hypervalent Iodine(III)-Induced Domino Oxidative Cyclization for the Synthesis of Cyclopenta[ b ]furans. (mdpi.com)
  • Primary alcohols undergo oxidative cyclization without significant oxidation to the aldehyde, a fact that illustrates the range of reactivity available from various Pd(II) salts under differing conditions. (caltech.edu)
  • The cyclization reactions lead to products having stereochemistry that is directly analogous to oxidative cyclization reactions utilizing ketene dithioiacetal radical cations and alcohol trapping groups. (wustl.edu)
  • There is compelling experimental and theoretical evidence for formation of nondirect sequence ions via cyclization/reopening chemistry in the CID spectra of the b tons when the His residue is near the C-terminus. (springer.com)
  • Paramita Das and Chhanda Mukhopadhyay, "Microwave Irradiation for Catalyst and Solvent Free Knoevenagel/Michael Addition/Cyclization/Aromatization Cascades", Current Microwave Chemistry (2014) 1: 98. (eurekaselect.com)
  • Wenkert, Ernest (1980) A formylation-cyclization method of synthesis of cycloalkenones from unsaturated ketones Journal of Organic Chemistry, 45 (6). (ias.ac.in)
  • The iodine-catalyzed Prins cyclization of homoallylic alcohols and aldehydes was investigated under metal-free conditions and without additives. (mdpi.com)
  • Under similar conditions, the Prins cyclization of six alcohols containing an endocyclic double bond (primary, secondary, or tertiary) led to dihydropyrans in 52%-91% yield. (mdpi.com)
  • Reddy KR, Rosa IML, Doriguetto AC, Bastos EL, Silva LF Jr (2013) Iodine-catalyzed prins cyclization of homoallylic alcohols and aldehydes. (springer.com)
  • Naphthopyrans and their C4 Alcohols by Cyclization of Substituted Naphthalenes using Potassium t-Butoxide in Dimethylformamide. (edu.au)
  • Enantioselective cyclization of enamide-ynes and application to the synthesis of the kopsifoline core. (biomedsearch.com)
  • We report the palladium-catalyzed enantioselective cyclization of 1,6-enamidynes to form spirocyclic ring systems. (biomedsearch.com)
  • Nickel-catalyzed additions of arylboronic acids to alkynes, followed by enantioselective cyclizations of the alkenylnickel species onto tethered ketones or enones, are reported. (nottingham.ac.uk)
  • The group publishes a novel approach to enantioselective polyene cyclizations via organo-SOMO catalysis. (princeton.edu)
  • The application of the 'direct amide cyclization' conditions to the linear delta-hydroxy diamide 11 is described (Scheme 3). (uzh.ch)
  • 25. Asymmetric Organocatalyzed Cyclization Reactions (Liu-Zhu Gong, Jun Jiang, Meng-Xia Xue, and Shi-Wei Luo). (organic-chemistry.org)
  • CLIPS (Chemical Linkage of Peptides onto Scaffolds) Cyclization is an integrated technology that combines chemical linkage of a linear peptide to a synthetic scaffold with conformational fixation of the peptide. (creative-peptides.com)
  • As a technology for peptide cyclization, the CLIPS TM (Chemically Linked Peptides on Scaffolds) has been applied successfully in identifying the epitope on human CD20 and reconstructing the conformational epitope on follicle stimulating hormone. (creative-peptides.com)
  • Rapid and quantitative cyclization of multiple peptide loops onto synthetic scaffolds for structural mimicry of protein surfaces. (creative-peptides.com)
  • The first approach was based on a highly trans-stereoselective (82% d.e.) intramolecular N-acyliminium ion cyclization of N-terminal peptide glyoxylamides, assembling the complete molecular skeleton in a single step. (dtu.dk)
  • The cyclization of the peptide around a metal core was shown to greatly increase the affinity of the peptide for its target. (umsystem.edu)
  • The primary problem with the cyclization of the peptide is the fact that two main products are produced. (umsystem.edu)
  • Backbone cyclization is a strategy that we developed to improve drug-like properties of linear peptide leads without jeopardizing the integrity of functionally relevant side-chains. (eurekaselect.com)
  • A highly efficient iron-catalyzed approach to polysubstituted pyrroles has been developed through the [4C+1N] cyclization of 4-acetylenic ketones with primary amines , leading to the synthesis of a variety of tetra- and fully-substituted pyrroles as well as fused pyrrole derivatives in good to excellent yields. (rsc.org)
  • Chapter 1 gives an introduction to tungsten catalysis and its application in the formation of heterocycles via cyclization of alkyne derivatives. (ntu.edu.sg)
  • In addition, pyrroles, pyridines and isoquinolines were also efficiently synthesized via cyclization of alkyne derivatives tethered to nitrogen nucleophiles under thermal conditions in the presence of tungsten catalysis. (ntu.edu.sg)
  • This article aims at reviewing the utilities of ene cyclization reactions for the synthesis of various ring sizes of oxygen, nitrogen and sulfur heterocycles. (rsc.org)
  • Alkynoic acids derived from salicylic acid and analogues undergo arylative cyclization with arenediazonium salts promoted by gold in the absence of external ligands. (rsc.org)
  • Breugst M, Grée R, Houk KN (2013) Synergistic effects between Lewis and Brønsted acids: application to the Prins cyclization. (springer.com)
  • Borkar P, Weghe P, Reddy BVS, Yadav JS, Grée R (2012) Unprecedented synergistic effects between weak Lewis and Brønsted acids in Prins cyclization. (springer.com)
  • The objective of this thesis was to incorporate amino acids capable of 1,5-cyclization into the PEA backbone such that upon activation of the functional moiety, a 1,5-cyclization was induced, leading to degradation of the PEA backbone. (uwo.ca)
  • Chapter 3 details the tungsten-catalyzed cyclization of α-alkynyl-β-keto acids, keto esters, and diketones to afford methylenelactones, furans, and methylenecyclopentanes via 5-exo-dig cyclization under photo conditions. (ntu.edu.sg)
  • Whereas other methods of cyclizing acids such as (1) to 4-ketotetrahydroquin-olines (2) had required protection of the secondary amino hydrogen by tosylation, Koo found that with PPA cyclization can be effected directly in one step. (chempedia.info)
  • It was not fully realized until my breakthrough using superacids ( vide infra ) that, to suppress the deprotonation of alkyl cations to olefins and the subsequent formation of complex mixtures by reactions of olefins with alkyl cations, such as alkylation, oligomerization, polymerization, and cyclization, acids much stronger than those known and used in the past were needed. (chempedia.info)
  • Gerasimov, V. A. / Cyclization of acetylenylpyrazolecarboxylic acids . (elsevier.com)
  • A long-standing proposal envisaged electron transfer from dimsyl anions (formed by deprotonation of the solvent DMSO) but this pathway shows an exceptionally high kinetic barrier, while direct 5-endo-trig cyclization of the alkoxides and amides is much more easily achievable. (strath.ac.uk)
  • Chapter 2 describes the tungsten-catalyzed cyclization of N-propargylic amides to afford the corresponding oxazolines or oxazines via 5-exo-dig or 6-endo-dig mode. (ntu.edu.sg)
  • Computational studies have been performed on potassium alkoxide-allenes, as well as potassium and lithium amido-allenes to probe the mechanism of their cyclizations to dihydrofurans and to 2,5-dihydropyrroles. (strath.ac.uk)
  • The energy profiles for 4-exo-trig cyclizations onto the allenes are also explored, and the preferred formation of the observed five-membered products is rationalized. (strath.ac.uk)
  • 13. Transition-Metal-Catalyzed Cycloisomerizations and Nucleophilic Cyclization of Enynes (Elena Herrero-Gomez and Antonio M. Echavarren). (organic-chemistry.org)
  • The primary peroxide adducts subsequently undergo intramolecular Diels-Alder (IMDA) cyclization, affording a number of diastereomeric tricyclic adducts that have characteristic carbonyl (13)C chemical shifts at ~198 ppm. (sigmaaldrich.com)
  • In contrast, cyclizations of deuterium-labeled carboxylic acid substrates undergo anti oxypalladation. (caltech.edu)
  • This cyclization is less favoured due to the electron donating ability of the nitrogen atom, causing the pentadienyl cation to be relatively stable and unwilling to undergo cyclization. (smu.ca)
  • It is hypothesized that by doing so the addition of an acid will form the cyclopentadienyl cation that will readily undergo Nazarov cyclization. (smu.ca)
  • This unified approach to (thio)chromenones is readily applicable to aryl- and alkylalkynes where the stereochemically well-defined β-chlorovinyl ketone intermediates undergo distinctively different cyclization pathways. (ndsl.kr)
  • Prins cyclization of isoprenol with benzaldehyde as a model aldehyde was performed using montmorillonite K10 as an acid catalyst. (springer.com)
  • Yheng K, Liu X, Qin S, Xie M, Lin M, Hu C, Feng X (2012) Completely OH-selective FeCl3-catalyzed Prins cyclization: highly stereoselective synthesis of 4-OH-tetrahydropyrans. (springer.com)
  • More GP, Rane M, Bhat SV (2012) Efficient Prins cyclization in environmentally benign method using ion exchange resin catalyst. (springer.com)
  • Yadav JS, Reddy BVS, Kumar NGGKS, Aravind S (2008) The 'aqueous' Prins cyclization: a diastereoselective synthesis of 4-hydroxytetrahydropyran derivatives. (springer.com)
  • Yadav JS, Reddy BVS, Chaya DN, Kumar NGGK, Naresh P, Jagadeesh B (2009) Heteropoly acid-catalyzed aza-Prins-cyclization: an expeditious synthesis of 4-hydroxypiperidines. (springer.com)
  • A new iron(III) halide-promoted aza-Prins cyclization between γ,δ-unsaturated tosylamines and aldehydes provides six-membered azacycles in good to excellent yields. (csic.es)
  • In addition, the alkyne aza-Prins cyclization between homopropargyl tosylamine and aldehydes gives 2-alkyl-4-halo-1-tosyl-1,2,5,6-tetrahydropyridines as the only cyclic products. (csic.es)
  • Conversion of Protein Active Regions into Peptidomimetic Therapeutic Leads Using Backbone Cyclization and Cycloscan - How to Do it Yourself! (eurekaselect.com)
  • Macrocyclic peptides are classified into three groups by cyclization style: sidechain-to-sidechain, head-to-sidechain, and head-to-tail (backbone) cycles are all found in natural products. (frontiersin.org)
  • Naturally occurring backbone macrocyclic peptides are generally matured from their linear counterparts by their specific cyclases, some of which have substrate promiscuity, and may be utilized for cyclization of other peptides. (frontiersin.org)
  • The cascade cyclization leads to an increase in molecular complexity to furnish naphtho[1,2-d]triazoles in satisfactory yields. (biomedsearch.com)
  • Three conditions must be met for an efficient radical cyclization to take place: A method must be available to generate a radical selectively on the substrate. (wikipedia.org)
  • An antibody has been induced that efficiently catalyzes a cationic cyclization in which an acyclic olefinic sulfonate ester substrate is converted almost exclusively (98 percent) to a cyclic alcohol. (sciencemag.org)
  • The thiol-to-amine cyclization reactions showed unexpectedly high yields for a wide substrate range, which obviated product purification and enabled the generation and screening of an 8988 macrocycle library with a comparatively small effort. (epfl.ch)
  • CLIPS Cyclization can be used for conformational fixation of free peptides in solution, while it also applies to solid-phase attached peptides in microarrays used for antibody-screening. (creative-peptides.com)
  • 5-hexenyl radicals are the most synthetically useful intermediates for radical cyclizations, because cyclization is extremely rapid and exo selective. (wikipedia.org)
  • 2) Cyclization reactions of vinyl, aryl, and acyl radicals are also known. (wikipedia.org)
  • Moreover, the ease of regio- and stereoselectivity of ene cyclization has led to the development of new types of heterocyclic compounds. (rsc.org)
  • Freeman, F. & Robarge, K. D. Stereoselectivity in electrophile-mediated intramolecular cyclizations of hept-2-enitols. (nature.com)
  • New catalysts for cationic cyclization may be of general use in the formation of carbon-carbon and carbon-heteroatom bonds leading to multi-ring molecules including steroids and heterocyclic compounds. (sciencemag.org)
  • The ene cyclization has evolved to become an indispensable tool for the synthesis of various ring size heterocyclic compounds. (rsc.org)
  • 15. Cyclization of Cyclopropane- or Cyclopropene-Containing Compounds (Junliang Zhang and Yuanjing Xiao). (organic-chemistry.org)
  • However, when considering the atom economy it has to be mentioned that the Pschorr cyclization has often only low yields. (wikipedia.org)
  • It is important to note that the Au(I)-catalyzed cyclization proceeds in high yields in a sterically congested environment. (beilstein-journals.org)
  • However, one might recognize that the low chemical yields encountered in some steps undermine the efficacy of the Au(I)-catalyzed cyclization approach. (beilstein-journals.org)
  • Oxidation and cyclization of casbene in the biosynthesis of Euphorbia factors from mature seeds of Euphorbia lathyris L. (pnas.org)
  • Here, we describe the discovery of a biosynthetic route in Euphorbia lathyris L. (caper spurge) in which regio-specific oxidation of casbene is followed by an unconventional cyclization to yield jolkinol C, a probable key intermediate in the biosynthesis of macrocyclic diterpenes, including ingenol mebutate. (pnas.org)
  • Although the cyclization of enol ether 5 can produce 5- exo and 6- endo products, we found that gold complexes 6 , having bulky phosphine ligands such as 2-bis( tert -butylphosphino)biphenyl, gave exclusively the 6- endo-dig cyclized products 7 ( Scheme 1 ). (beilstein-journals.org)
  • The second derivative of Fourier transform infrared and Gaussian fitting was used to analyze the tapes cyclization due to stabilization treatment through introducing I sd index. (deepdyve.com)
  • Pascal begins with the assumption that terminal aryl substitution on the enediyne will both (a) inhibit the C 1 -C 6 cyclization due to steric interactions and (b) the C 1 -C 5 cyclization should be enhanced due to stabilization of the radical by the neighboring aryl group. (comporgchem.com)
  • However, low concentrations of a radical scavenger establish thermodynamic control and provide access to 6-endo products-not via 6-endo cyclization, but by 5-exo cyclization followed by 3-exo closure and subsequent fragmentation (Dowd-Beckwith rearrangement). (wikipedia.org)
  • This indicates less active cyclization/reopening followed by fragmentation of common structures for b n ions containing His than for sequences of solely aliphatic residues. (springer.com)
  • Despite more energetically favorable cyclization barriers for the b 5 structures, the b 4 ions experimental data show more clear evidence of cyclization and sequence scrambling before fragmentation. (springer.com)
  • Bio-inspired acetal induced polyene cyclization : the development and applications. (ntu.edu.sg)
  • The development of a bio-inspired acetal induced intermolecular polyene cyclization is described. (ntu.edu.sg)
  • By exploiting the acetal induced intermolecular polyene cyclization, a highly efficient method to construct 8-oxabicyclo[3,2,1]octanes was discovered. (ntu.edu.sg)
  • The Nazarov cyclization is a common synthetic tool in the synthesis of cyclopentenone rings. (smu.ca)
  • The synthesis of an aryl vinyl silyl nitronate was optimized and the compound was tested with a number of different acid catalysts to determine if the nitronate Nazarov cyclization is possible. (smu.ca)
  • This entry was posted on October 1, 2015 at 6:04 am and is filed under Computational , DFT , Mechanistic , Named Reactions , Nazarov cyclization . (wordpress.com)
  • Tyrosine-lipid peroxide adducts from radical termination: para coupling and intramolecular Diels-Alder cyclization. (sigmaaldrich.com)
  • The reactions are categorized according to the nature of the internal electrophile participating in the cyclization step, i.e. carboxylic acid or its derivative, carbonyl compound, or alkylating agent. (enamine.net)
  • Radical cyclization reactions are organic chemical transformations that yield cyclic products through radical intermediates. (wikipedia.org)
  • Radical cyclization reactions produce mono- or polycyclic products through the action of radical intermediates. (wikipedia.org)
  • Cyclization of the homologous 6-heptenyl radical is still selective, but is much slower-as a result, competitive side reactions are an important problem when these intermediates are involved. (wikipedia.org)
  • In the past and recent years, many exciting reports have demonstrated the broad scope and synthetic utility of ene cyclization and the versatility of oxonium ion, iminium ion and thionium ion intermediates. (rsc.org)
  • Coupled with a late-stage radical cyclization to construct the [3.2.2]-bridged bicycle, these efforts have enabled the total synthesis of tubingensin B. The design and evolution of our succinct total synthesis underscores the utility of long-avoided aryne intermediates for the introduction of structural motifs that have conventionally been viewed as challenging. (nature.com)
  • The second approach aimed for the use of a cis-stereoselective intermolecular Pictet-Spengler cyclization to construct the first part of the ringsystem and a subsequent diketopiperazine formation to close the second ring. (dtu.dk)
  • The generality of the high-yielding, stereoselective cyclization of 2-allyl-3-(1? (edu.au)
  • Glycal Cyclization InBr3-Catalyzed Cyclization of Glycals with Aryl Amines** Jhillu S. Yadav,* Basi V. S. Reddy, Katta V. Rao, Kavuda Saritha Raj, Atlaluri R. Prasad, Singarapu Kiran Kumar, Ajit C. Kunwar, Panjula Jayaprakash, and Bulusu Jagannath Scheme 1. (docme.ru)
  • Thus, it is easy to work through 'Handbook auf Cyclization Reactions' and keep possible synthetic strategies in the back of the mind for later access when needed. (organic-chemistry.org)
  • A new synthetic approach to thieno[2,3-d]imidazoles is presented on the basis of the N′-(3-halothiophen-2-yl)amidine cyclization under copper-catalyzed cross-coupling. (enamine.net)
  • On the other hand, the other methods of cyclization use an amino acid's sidechain. (frontiersin.org)
  • Under conditions of kinetic control, 5-exo cyclization takes place preferentially. (wikipedia.org)
  • The ultimate and only reference source in this field, this handbook discusses the latest advances on the reactions leading to the formation of cyclic structures and includes chapters presenting the most synthetically attractive cyclization reactions. (organic-chemistry.org)
  • A novel route to cyclic imines based on 5-exo radical cyclization is explored. (diva-portal.org)
  • Description on the cyclization-prenylation sequence. (ebscohost.com)
  • Nitrogen-centered radical cyclizations onto silyl enol ethers were utilized for the syntheses of protected polyhydroxylated pyrrolidines 2-hydroxymethyl-3-hydroxypyrrolidine and 1,4-dideoxy-1,4-imino-L-ribitol. (ubc.ca)
  • To improve this cyclization, the imine is replaced with the electron withdrawing nitronate functionality. (smu.ca)
  • Side reactions are sometimes a problem, and cyclization is especially slow for small and large rings (although macrocyclizations, which resemble intermolecular radical reactions, are often high yielding). (wikipedia.org)
  • Reversible Bergman cyclization. (sciencephoto.com)
  • Atomic force microscopy (AFM) image of the starting point (a brominated aromatic compound) for a reversible Bergman cyclization. (sciencephoto.com)
  • Phenyl substitution does accomplish both suggestions: the activation barrier for the Bergman cyclization increases by 4 kcal mol -1 , while the barrier for the C 1 -C 5 cyclization is lowered by nearly 6 kcal mol -1 . (comporgchem.com)
  • With BLYP, the C 1 -C 5 cyclization is favored by a significant amount over the Bergman cyclization. (comporgchem.com)
  • It was found that mild aqueous conditions result in the cyclization of creatine ethyl ester to provide inactive creatinine as the exclusive product, and this transformation becomes nearly instantaneous as the pH approaches 7.4. (nih.gov)
  • This study demonstrates that mild non-enzymatic conditions are sufficient for the cyclization of creatine ethyl ester into creatinine, and together with previous results obtained under enzymatic conditions suggests that there are no physiological conditions that would result in the production of creatine. (nih.gov)
  • The second approach included two distinct routes involving an ethyl glyoxylate or a glyoxylic acid Pictet-Spengler cyclization. (dtu.dk)
  • forming the cyclopentadienyl cation that undergoes cyclization. (smu.ca)
  • Figure 5: Radical cyclization and first generation total synthesis of tubingensin B. (nature.com)
  • To realize the strategy shown in Figure 3 , cis -bicyclo[3.3.0]octane-3,7-dione ( 1 ) [44-50] was subjected to twofold Fischer indole cyclization to generate the diindole derivative 6 by using 1-methy-1-phenylhydrazine ( 5 ) under HCl/EtOH reflux conditions. (beilstein-journals.org)