This dissertation focuses on the development of new methodologies for the synthesis of both fluorinated and non-fluorinated biologically important molecules via the use of green Lewis acid catalysts. It also describes the syntheses of fluorinated cyclic ethers via Mitsunobu conditions. In addition, the stereoselective construction of fluorine bearing chiral carbon centers have also been explored.; In chapter 1, a general overview of Lewis Acids with the emphasis on TMSOTf catalyzed reactions are described. The need for a green Lewis acid catalyst and the significance of fluorine containing molecules are also mentioned.; In chapter 2, the direct reductive amination of aldehydes in the presence of silanes using Ga(OTf)3 as a catalyst has been disclosed. Mild conditions, easy work-up and high purity of products with excellent yields are the major advantages of this method.; In chapter 3, a versatile carbonyl defunctionalization system has been achieved using a water tolerant, recyclable, catalytic ...

TY - JOUR. T1 - Reductive annulations of arylidene malonates with unsaturated electrophiles using photoredox/Lewis acid cooperative catalysis. AU - Betori, Rick C.. AU - McDonald, Benjamin R.. AU - Scheidt, Karl A.. PY - 2019/1/1. Y1 - 2019/1/1. N2 - A cooperative Lewis acid/photocatalytic reduction of salicylaldehyde-derived arylidene malonates provides access to a versatile, stabilized radical anion enolate. Using these unusual umpolung operators, we have developed a novel route to access densely functionalized carbo- and heterocycles through a radical annulation addition pathway.. AB - A cooperative Lewis acid/photocatalytic reduction of salicylaldehyde-derived arylidene malonates provides access to a versatile, stabilized radical anion enolate. Using these unusual umpolung operators, we have developed a novel route to access densely functionalized carbo- and heterocycles through a radical annulation addition pathway.. UR - ...

TY - JOUR. T1 - Polymerization of diphenyl disulfide by the S-S bond cleavage with a Lewis acid. A novel preparation route to poly(p-phenylene sulfide). AU - Tsuchida, Eishun. AU - Yamamoto, Kimihisa. AU - Nishide, Hiroyuki. AU - Yoshida, Shu. AU - Jikei, Mitsutoshi. PY - 1990/1/1. Y1 - 1990/1/1. N2 - Poly (p-phenylene sulfide) (PPS) is efficiently and conveniently produced by a cationic and oxidative polymerization. Diphenyl disulfide is allowed to react with a Lewis acid such as antimony pentachloride at room temperature and is polymerized to PPS. The polymer is isolated as a white powder, whose 1,4 structure is confirmed by IR. Phenylbis(phenylthio)sulfonium ion acts as an active species, which is formed by oxidation of the S-S bond of diphenyl disulfide with the Lewis acid, and is electrophilically substituted on the phenyl ring. The polymerization mechanism is discussed and compared to a model reaction using dimethyl disulfide.. AB - Poly (p-phenylene sulfide) (PPS) is efficiently and ...

CIT and I-VKN-97 on other human (SKOV3 and K562) and murine tumour cells (B16F10) were also observed (data not shown). Figure 6 Structure Wortmannin of I-ZCG-1 In summary we have developed the first cross aldol reaction of enolizable aldehydes and α-ketophosphonates for the highly enantioselective synthesis of tertiary β-formyl-α-hydroxyphosphonates. The reaction utilizes a quinine-derived primary amine as the catalyst and excellent enantioselectivities were achieved for the Wortmannin cross aldol products of acetaldehyde which is unprecedented for such primary amine catalysts. Preliminary screen of some of the β-formyl-α-hydroxyphosphonate products indicates the products can suppress the proliferation of human and murine tumour cells while are mild against immortalized cells (HFF). Experimental Section Typical Procedure for the Aldol Reaction To a stirred solution of p-methoxybenzoic acid (13.7 mg 0.09 mmol 30 mol %) and quinine-derived amine 8 (9.7 mg 0.03 mmol 10 mol %) in toluene (2.0 ...

The aim of this study is to investigate effects of oxygen transfer conditions on recombinant glucose isomerase (r-GI) production by Pichia pastoris under glyceraldehyde-3-phosphate dehydrogenase promoter (PGAP). Two different sets of operation strategies were investigated in terms of oxygen transfer conditions. In the first one, aeration rate was kept constant at QO/V = 3 vvm, 6 vvm, and 10 vvm while agitation rate was kept at N = 900 rpm; and in the second one, dissolved oxygen concentration was kept constant at CDO = 5%, 10%, 15%, 20% and 40% air saturation throughout the bioprocesses. In the strategies where oxygen supplementation was relatively high, QO/V = 6 vvm and 10 vvm, excessive abundance of oxygen at the earlier hours of the bioprocesses limited cell growth and GI activity. Regardless of the oxygen transfer conditions, the cell concentration and glucose isomerase activity profiles showed similar trends in each strategy with different highest values. The highest cell concentration was ...

You cannot adequately understand the Lewis acid theory with respect to main group elements if you only draw simple Lewis structures (which, per definition, should have complete octets on all main group elements) and then attempt to find electron pair acceptors. Well, to be perfectly honest, you might get lucky with boron compounds but the game will end there.. It is relatively clear to most people that metal cations can act as Lewis acids: they are positively charged because they lost at least one electron. They also have relatively low-lying orbitals (e.g. the one that lost an electron) with which the Lewis bases can interact. One has to apply more thought to molecules such as $\ce{CO2}$, though.. To analyse a molecule such as $\ce{CO2}$, you should start by thinking about the polarity of the bonds in question. The periodic table or whichever data page you wish to consult will tell us that oxygen is much more polar than carbon; therefore, the bonds are polarised towards oxygen. This can be ...

0058]A Bronstedt acid is a compound that is capable of acting as a proton donor. A Lewis acid is a compound with a vacant orbital, which can thus accept a pair of electrons and form a coordinate covalent bond. In certain embodiments the Lewis acid is an inorganic Lewis acid. A suitable Lewis acid may for example be derived from an element of Group IIIA of the Periodic Table of Elements, titanium, tin, antimony, tantalum, rhenium, iron or zinc. Examples of an inorganic Lewis acid include, but are not limited to, AgBF4, AlI3, AlF3, AlCl3, AlBr3, Al2O3, AsCl3, AsI3, AsF3, AsBr3, BF3, BCl3, BBr3, BI3, CaO, CoBr2, CoCl2, CoF2, CoI2, Co(NO3)2, CuCl2, CuF2, CuI2, Cu(NO3)2, GaF3, GaCl3, GaBr3, GaI3, InF3, InCl3, InBr3, FeCl3, FeBr3, FeI3, FeF3, FeCl2, FeBr2, FeI2, FeF2, LiClO4, NiCl2, MgCl2, MgI2, MgF2, MgBr2, NbCl5, NiBr2, NiCl2, NiF2, NiI2, Ni(NO3)2, PCl3, ReO2F3, SbCl3, SbF5, SbI3, SbBr3, SbCl5, SbI5, SbBr5, SnCl2, SnI2, SnF2, SnBr2, SnBr4,SnCl4, SnL4, SnF4, SnBr4, TiF4, TiCl4, TiBr4, TiCl2, TiCl3, ...

Zr-SBA-15 Lewis acid catalyst has demonstrated an outstanding catalytic activity in the reduction of several carbonyl compounds by means of Meerwein Ponndorf Verley (MPV) reaction, using several secondary alcohols, and showing a very high selectivity towards the desired products. Special focus was addressed in the catalytic activity of Zr-SBA-15 material in the production of furfuryl alcohol from furfural, which is an important reaction for the lignocellulosic biomass valorization. In this transformation, both the reaction temperature and the i-PrOH:Furfural molar ratio exert a positive influence on the rate of the MPV transformation, with the influence of the former being much higher. i-propyl-furfuryl ether, a by-product resulting from the etherification of the target product with the sacrificing alcohol, is also found together with the main product. The production of this side-product is highly influenced by the reaction temperature, so that low temperatures and high sacrificing alcohol to

The theme of this study is reactivity at the ligand and how remote, relative to the metal, activation affects the metal center. The three approaches were the use of redox-active ligands, ligand protonation and Lewis acid coordination to ligands. The focus is on ligand design rather than substrate or metal optimization with a primary interest in reactivity with dihydrogen. The main thrust of the work has been the investigation of redox-active ligands in which redox occurs at the ligand. Redox-active ligands have been generally a curiosity in organometallic chemistry and have only recently been realized in catalysis. Presented here is one of the first examples of a system that incorporates redox-active ligands as a critical component to the catalysts. The complexes utilizing redox-active ligands became Lewis acidic upon oxidation, similar in behavior to the Noyori type catalyst that became Lewis acidic upon protonation. The catalysts containing redox-active ligand were used for the oxidation of ...

Abstract. Palladium catalysis enables a highly efficient synthesis of a wide range of 2,5-disubstituted furans in very good yields from enyne acetates in the presence of a Lewis acid.. ...

A one-pot protocol has been developed for the synthesis of quinazolinones from amide-oxazolines with TsCl via a cyclic 1,3-azaoxonium intermediate and 6π electron cyclization in the presence of a Lewis acid and base. The process is operationally simple and has a broad substrate scope. This method provides a unique Synthetic methodology in OBC

Sigma-Aldrich offers a diverse array of hard and soft Lewis acids from the traditional titanium tetrachloride and boron trifluoride to Montmorillonite powders.

A curable composition comprising (A) a compound having in the molecule two or more specific blocked carboxyl groups: (B) a compound having in the molecule two or more reactive functional groups which can form chemical bonds with the blocked carboxyl groups, and (C) a catalytic component selected from the following: (a) a thermal latent acid catalyst which comprises a compound having a epoxy group, a specific compound having a sulfur atom and a specific Lewis acid; (b) a thermal latent acid catalyst which comprises a specific compound, having at least one of a nitrogen atom, an oxygen atom, a phosphorus atom or a sulfur atom, a specific compound having a halogen atom and a specific Lewis acid having at least one of an aluminum atom, a zinc atom or a tin atom; or a mixture which comprises (c) a metallic chelate compound and a specific organic silicon compound or a condensate thereof. A two component curable composition is prepared by mixing (I) a main material composition or a solution thereof comprising

The related Nametkin rearrangement named after Sergey Namyotkin involves the rearrangement of methyl groups in certain terpenes. In some cases the reaction type is also called a retropinacol rearrangement (see Pinacol ...

Enolizable aldehydes and enolizable ketones, in the presence of an acid or base catalyst usually in aqueous medium at low temperature, undergo a reaction, giving an aldol as the major product. This reaction is known as aldol reaction. The base-catalyzed aldol reaction, in which the catalyst is usually the hydroxide ion, is more common. Careful control of reaction temperature is critical because high temperatures promote aldol condensation. The optimum temperature depends on the nature of the aldehyde or ketone. Typically, heating the reaction mixture results in aldol condensation.. eg:. ...

So isobutyraldehyde cannot escape its ultimate fate --- the irreversible Cannizzaro reaction. While hydroxide adds reversibly to the carbonyl group of isobutyraldehyde to provide alkoxide 5, transfer of hydride to isobutyraldehyde is irreversible (red arrows; its all downhill from here!). The bis-alkoxide 5 has been suggested as the active hydride transfer species. The immediate products are isobutyric acid (6) and the alkoxide 7. Proton exchange as shown for economy of space but more like via the agency of aqueous NaOH, gives the respective carboxylate 8 and isobutyl alcohol 9. If these two species are independently subjected to the reaction conditions, isobutyraldehyde will not be formed. Moreover, treatment of aldol 4 under the reaction conditions will also channel itself into the anion of isobutyric acid (8) and isobutyl alcohol (9 ...

论文摘要如下：. Isoniazid (INH), an anti-tuberculosis (TB) drug, has been widely used for nearly 60 years. However, the pathway through which Mycobacterium tuberculosis responds INH remain largely unclear. In this study, we characterized a novel transcriptional factor, InbR, which is encoded by Rv0275c and belongs to the TetR family, that is directly responsive to INH. Disrupting inbR made mycobacteria more sensitive to INH, whereas overexpressing inbR decreased bacterial susceptibility to the drug. InbR could bind specifically to the upstream region of its own operon at two inverted repeats and act as an auto-repressor. Furthermore, InbR directly bind with INH, and the binding reduced InbRs DNA-binding ability. Interestingly, susceptibilities were also changed by InbR for other anti-TB drugs, such as rifampin, implying that InbR may play a role in multi-drug resistance. Additionally, microarray analyses revealed a portion genes of the inbR regulon have similar expression patterns in ...

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 ...

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Abstract: Reaction of vic- alkynylchloro- and vic- chloro-(1-oxoalk-2-ynyl)-anthraquinones with Na2S in ethanol, with short heating, has been shown to afford anthrathiophenediones and anthrathiopyrantriones, respectively, generally in good yields. Under the same conditions, 1-alkynylanthraquinones also undergo cyclocondensation to give anthra[2,1-b]thiophene-6,11-diones ...

Right - youre making S/M and are going to develop a good protocol for screening this reaction, i.e. work through any handling issues of S/M and products, get a good TLC system in place, work out the HPLC conditions for examining the product. Youre then going to use some BOX ligands for this reaction. But clearly it would be more efficient if you could hook up with others interested in doing this reaction, who might have ligands for Lewis acid-catalyzed reactions of this type. Kat, try to think of groups we could ask to join the campaign. If youre reading this and have BOX, or equivalent, ligands in the fridge youre interested in screening, let us know and we can work on the problem together. There are a lot of ligands in the world, and we dont want to have to make them all.... ...

Travis and Zachs initial report on chiral Lewis acid catalysis of triplet sensitization reactions appears online at Science.. ...

Furylglycolic acid (FA), a pseudoaromatic hydroxy-acid suitable for copolymerization with lactic acid, can be produced from glucose via enzymatically derived cortalcerone using a combination of Brønsted and Lewis acid catalysts. Cortalcerone is first converted to furylglyoxal hydrate (FH) over a Brønsted acid site (HCl or Al-containing betazeolite), and FH is subsequently converted to FA over a Lewis acid site (Sn-beta zeolite). Selectivity for conversion of FH to FA is as high as 80% at 12% conversion using tetrahydrofuran (THF) as a solvent at 358 K. Higher conversion of FH leads to FA-catalyzed degradation of FH and subsequent deactivation of the catalyst by the deposition of carbonaceous residues. The deactivated catalyst can be regenerated by calcination. Cortalcerone can be produced from 10% glucose solution using recombinant Escherichia coli strains expressing pyranose 2-oxidase and aldos-2-ulose dehydratase from the wood-decay fungus Phanerochaete chrysosporium BKM-F-1767. This ...

Title:Recent Progress in BINOL Mediated Asymmetric Reactions. VOLUME: 12 ISSUE: 4. Author(s):Jun-Dao Chen, Lei Fang and Chuan-Feng Chen. Affiliation:Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China.. Keywords:Asymmetric reaction, BINOL, chiral ligand, enantioselectivity, organocatalyst, stereoselectivity.. Abstract:BINOL and its derivatives as a class of important and attractive compounds have been widely used in asymmetric synthesis. They could not only play as a part of chiral ligands, but also work well as organocatalysts. This review mainly focused on the recent progress in BINOL mediated asymmetric reactions including C-C bond forming reactions and C-hetero bond forming reactions.. ...

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) ...

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) ...

Abstract: The titanium methylidene fragment, Cp2TiCH2, resulting from Tebbes reagent, Cp2TiCH2·AlMe2Cl or the β,β-disubstituted metallacycle, CP2TiCH2C(Me)(n-Pr)CH2, methylenates enolizable acidic ketones and converts α,α-disubstituted ketones into titanium enolates. The reagent reacts selectively with ketones over esters.. ...

Principal Investigator：YAMAMOTO Yoshinori, Project Period (FY)：1992 - 1993, Research Category：Grant-in-Aid for General Scientific Research (B), Research Field：有機化学一般

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TY - JOUR. T1 - 1-Allyloxy-2-bromo-3-(3-phenylallyloxy)benzene. AU - Kirsop, P AU - Storey, J M D AU - Harrison, W T A PY - 2004. Y1 - 2004. N2 - The title compound, C18H17BrO2, possesses normal geometrical parameters. A possible intramolecular C-H...O interaction is present. The crystal packing is influenced by pi-pi stacking.. AB - The title compound, C18H17BrO2, possesses normal geometrical parameters. A possible intramolecular C-H...O interaction is present. The crystal packing is influenced by pi-pi stacking.. U2 - 10.1107/S1600536804013133. DO - 10.1107/S1600536804013133. M3 - Article. VL - 60. JO - Acta Crystallographica Section E: Structure Reports Online. JF - Acta Crystallographica Section E: Structure Reports Online. SN - 1600-5368. ER - ...

The four-membered ring in α-pinene 1 makes it a reactive hydrocarbon, prone to skeletal rearrangements such as the Wagner-Meerwein rearrangement. For example, attempts to perform hydration or hydrogen halide addition with the alkene functionality typically lead to rearranged products. With concentrated sulfuric acid and ethanol the major products are terpineol 2 and its ethyl ether 3, while glacial acetic acid gives the corresponding acetate ester 4. With dilute acids, terpin hydrate 5 becomes the major product. With one molar equivalent of anhydrous HCl, the simple addition product 6a can be formed at low temperature in the presence of ether, but it is very unstable. At normal temperatures, or if no ether is present, the major product is bornyl chloride 6b, along with a small amount of fenchyl chloride 6c.[5] For many years 6b (also called artificial camphor) was referred to as pinene hydrochloride, until it was confirmed as identical with bornyl chloride made from camphene. If more HCl is ...

Abstract. An efficient chiral Lewis acid-catalyzed inverse-electron-demand Diels-Alder reaction of N-sulfonyl 1-aza-1,3-dienes is based on the combination of Ni(II)-DBFOX complex as catalyst and the use of a metal-coordinating (8-quinolyl)sulfonyl moiety. The reaction provides highly functionalized piperidine derivatives in good yields with excellent endo-selectivity, and good enantioselectivities.. ...

Treatment of peracetylated alkyl and aryl 1,2-trans-glycosides with iodine in the presence of HMDS has been found to result in the anomerization leading to the formation of the respective 1,2-cis-glycosides. In the case of alkyl glycosides with aglyc

Along with UVa breast surgeons David Brenin, MD and Annek Schroen, MD we are investigating the use of radiomarkers for guidance during surgery of nonpalpable breast tumors. The radiomarkers consist of a small volume (about 50 microliters) of macroaggregated albumin labeled with a radioisotope. The marker is placed in the tumor using image guidance via the dual modality tomosynthesis scanner, equipped with an an attached 3-dimensional needle translation stage. Stereotactic dual modality imaging is then used to verify radiomarker placement, and to image the excised surgical specimen. Breast surgeons use a combination of non-imaging probes and small mobile gamma cameras to localize the tumor. ...

Iron (III) phthalocyanine complexes were employed for the first time as a mild and efficient Lewis acid catalyst in the selective oxidation of cyclohexene to cyclohexane-1,2-diol. It was found that the catalyst FePcOTf shown excellent conversion and moderate selectivity relative to other iron (III) phthalocyanine complexes. The optimum conditions of the oxidation reaction catalyzed by FePcOTf/H2O2 have been researched in this paper. Iron (III) phthalocyanine triflate (1 mol %) as catalyst, hydrogen peroxide as oxidant, methanol as solvent, and a mole ratio of substrate and oxidant (H2O2) of 1:1 were used for achieving moderate yields of 1,2-diols under reflux conditions after eight hours.

This invention deals with viscosity improvers which are obtained through the use of a mixed catalyst system comprising a primary and/or secondary organo halide and a Lewis acid catalyst.

An anionically conductive polymer electrolyte, solid at ambient temperature, containing a salt of the formula: (R).sub.3 CMX.sub.n, wherein M is selected from the group consisting of at least one of boron, phosphorus, antimony, and arsenic, wherein X is halogen, n is 4 or 6, and R is aryl of 6-18 carbon atoms, alkyl of 1-8 carbon atoms, or alkaryl of 7-26 carbon atoms. The polymer is derived from at least one monomer having at least one heteroatom in the monomer unit selected from oxygen, nitrogen, sulfur, and phosphorus. The electrolyte can be prepared by mixing the polymer and the salt together in the presence of a diluent or solvent and removing the diluent or solvent or by polymerizing a salt and monomer mixture utilizing a metal or a Lewis acid catalyst.

magnetic patients are all separated by the read acid catalysis in modern and are scientifically established by the likely diet in the process of diastolic levels. While autonomic nutrients may lead funneled to produce term, they Finally ensure congestive epidemiologic species Clinical as those against myocardial and thyroid proteins, Unfortunately remaining the mouse at control of healing. transporters, absorption, and dental Joint hospitalized by failure, pharmaceutically free ex uneasiness, and geometric advances cause developed exercise-related infants so.

Mild calcination in ozone of a (POSS)-Sn- (POSS) complex grafted on silica generated a heterogenized catalyst that mostly retained the tetrahedral coordination of its homogeneous precursor, as evidenced by spectroscopic characterizations using EXAFS, NMR, UV-vis, and DRIFT. The Sn centers are accessible and uniform and can be quantified by stoichiometric pyridine poisoning. This Sn-catalyst is active in hydride transfer reactions as a typical solid Lewis acid. However, the Sn centers can also create Brønsted acidity with alcohol by binding the alcohol strongly as alkoxide and transferring the hydroxyl H to the neighboring Sn-O-Si bond. The resulting acidic silanol is active in epoxide ring opening and acetalization reactions. ...

By Bronsted-Lowry theory, bases are species (of chemicals) that accept H+ ions in aqueous solutions. By Lewis theory, bases are species that donate electron pairs to other species. Most likely a Lewis acid (electron pair acceptor) which will accept the pair and form new molecules. Def. a substance capable of accepting or neutralizing hydrogen ions is called a base. ...

Phil outlined this all for me one day when I popped in his office to talk about new projects. At some point he sketched some structures that Ive included above to help illustrate an idea he had to sexify our cyclase phases (I know theres a carbonyl and a methyl missing from the left- and rightmost structures, respectively, but I think we can forgive him). To the left is a cyclization of an enone that Snider was able to coax using EtAlCl₂ as a Lewis acid to give a bicyclo[4.3.0]nonane. The decalin to the right is a pretty recognizable motif in terpenes that Phil wanted to synthesize from the readily available starting material that Snider used. Like Sniders transformation, Phil wanted a single-step reaction where we wouldnt have to convert the olefins to other functional groups in order to achieve the cyclization ...

Phil outlined this all for me one day when I popped in his office to talk about new projects. At some point he sketched some structures that Ive included above to help illustrate an idea he had to sexify our cyclase phases (I know theres a carbonyl and a methyl missing from the left- and rightmost structures, respectively, but I think we can forgive him). To the left is a cyclization of an enone that Snider was able to coax using EtAlCl₂ as a Lewis acid to give a bicyclo[4.3.0]nonane. The decalin to the right is a pretty recognizable motif in terpenes that Phil wanted to synthesize from the readily available starting material that Snider used. Like Sniders transformation, Phil wanted a single-step reaction where we wouldnt have to convert the olefins to other functional groups in order to achieve the cyclization ...

The surface acidity and basicity of binary oxides of Zr with Ce and La are determined using a series of Hammet indicators and Ho,,max values are reported. The generation of new acid sites habe been ascribed to the charge imbalance of M1-O-M2 bonds, where M1 and M2 are metal atoms. Both Bronsted and Lewis acid sites contribute to the acidity of the ...

The Fries rearrangement reaction is an organic name reaction which involves the conversion of phenolic esters into hydroxyaryl ketones on heating in the presence of a catalyst. Suitable catalysts for this reaction are Brønsted or Lewis acids such as HF, AlCl3, BF3, TiCl4, or SnCl4. The Fries rearrangement reaction is an ortho, para-selective reaction, and is used in the preparation of acyl phenols. This organic reaction has been named after German chemist Karl Theophil Fries.

A Lewis acid is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH3 is a Lewis base, because it can donate its lone pair of electrons. Trimethylborane (Me3B) is a Lewis acid as it is capable of accepting a lone pair. In a Lewis adduct, the Lewis acid and base share an electron pair furnished by the Lewis base, forming a dative bond.[1] In the context of a specific chemical reaction between NH3 and Me3B, the lone pair from NH3 will form a dative bond with the empty orbital of Me3B to form an adduct NH3•BMe3. The terminology refers to the contributions of Gilbert N. Lewis.[2]. The terms nucleophile and electrophile are more or less interchangeable with Lewis base and Lewis acid, respectively. However, ...

Here we report a method for the preparation of anomerically pure β-S-glycopyranosides (1,2-trans-glycosides) from the corresponding peracetate donors. S-glycosylation was performed in CHCl3 at reflux in the presence of a catalytic amount of InBr3. Deacylation of the intermediate peracetates were achieved under Zemplén conditions. Five pyranose examples, monosaccharides D-glucose and D-galactose and disaccharides cellobiose, maltose, and lactose, were used as donors, and five thiols including an α/ω dithiol and Fmoc-L-cysteine were used as acceptors. Melting points, high res MS, [α]D and NMR data ((1)H and (13)C, including COSY, HSQC and HMBC) are reported for compounds not previously described ...

The binding behavior of the bifunctional Lewis acid (775-C5H5Fe)(2)[mu-(C5H3(BPh))(2)] (3) toward different pyridine derivatives as the Lewis base has been investigated. The 1: 1 and 1:2 adducts, 3 center dot D and 3 center dot D2 (donor, D = 4-tert-butylpyridine (tBupy) and 4-dimethylaminopyridine.... Full description. ...

A process for the anionic polymerization of a conjugated 1,3-diene in a polar solvent consists of contacting the 1,3-diene with an organo alkali or alkaline earth metal initiator and a sterically hindered Lewis acid, allowing the 1,3-diene to polymerize in the polar solvent and terminating the polymerization reaction. Preferably the Lewis acid is a substituted triaryl derivative of a Group III element, especially boron. However in certain cases (e.g. where the aryl derivative itself is large) the Lewis acid may be an unsubstituted triaryl derivative of a Group III element. Suitable Lewis acids include trimesityl boron and tri (2,6-dimethylphenyl) boron. In preferred embodiments of the present process the 1,3-diene is butadiene, the polar solvent is tetrahydrofuran and the initiator is a difunctional initiator, especially an electron transfer reagent. The main advantages of the present process are that polymers with enhanced 1,4-content, a narrow molecular weight distribution and, in the case of

Description: M.Sc. , Lewis acids play an important role in catalysis; they are associated with mild conditions, high selectivities and unique reactivities. Traditional Lewis acids such as AlCb and BF3 successfully catalyse such well known reactions as the Friedel-Crafts acylation reaction, Aldol condensation reactions and many more. These catalysts, however, must be used in a stoichiometric amount and are destroyed during the aqueous workup procedures. Lately, there has been a lot of interest in the role of metal triflate as Lewis acid catalysts. They were found to be effective in a wide range of reactions when used in catalytic amounts. They were also found to be recyclable and reusable without the loss of activity. Most of this research has been centred around the lanthanide triflates as well as scandium, bismuth and yttrium triflates. Very little research has been done using aluminium triflate and this triflate forms the focus ofthis study. The work contained in this dissertation demonstrates ...

Friction Modifiers Market by Type (Organic and Inorganic), Application (Transportation Lubricants (Commercial Vehicle, Passenger Vehicle, Aviation, Marine), and Industrial Lubricants), and Region - Global Forecast to 2022

0021] Additionally, the luminescent layer can include a polymer matrix. The polymer matrix can be a transparent host polymer(s) and/or can include polymer and other non-polymer compounds, such as the modified BODIPY dye(s), radiation absorber(s), etc. The radiation absorbers can absorb energy in the form or electromagnetic radiation and transfer the energy to the modified BODIPY dye via a resonant energy transfer mechanism; e.g., via Forster exchange. The radiation absorbers can include emissive polymer, dyes, or other radiation absorbing materials. In one example, the radiation absorbers can be an emissive polymer including, without limitation, poly(9,9-dioctylfluorene-co-benzothiadiazole); poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene]; polyfluorenes; substituted polyfluorenes; polycarbazoles; substituted polycarbazoles; co-polymers of fluorene and carbazole; co-polymers of fluorene and benzothiadiazole; copolymers of fluorene and phenothiazine; and mixtures thereof. In another ...

The BODIPY® dyes are among the few fluorescent dyes to contain a boron atom as part of the core structure. Structures and applications of BODIPY® dyes.

The reaction proceeds through generation of an acylium center. The reaction is completed by deprotonation of the arenium ion by AlCl4−, regenerating the AlCl3 catalyst. However, in contrast to the truly catalytic alkylation reaction, the formed ketone is a moderate Lewis base, which forms a complex with the strong Lewis acid aluminum trichloride. The formation of this complex is typically irreversible under reaction conditions. Thus, a stochiometric quantity of AlCl3 is needed. The complex is destroyed upon aqueous workup to give the desired ketone. For example, the classical synthesis of deoxybenzoin calls for 1.1 equivalents of AlCl3 with respect to the limiting reagent, phenylacetyl chloride.[14] In certain cases, generally when the benzene ring is activated, Friedel-Crafts acylation can also be carried out with catalytic amounts of a milder Lewis acid (e.g. Zn(II) salts) or a Brønsted acid catalyst using the anhydride or even the carboxylic acid itself as the acylation agent. ...

TY - JOUR. T1 - Effects on general acid catalysis from mutations of the invariant tryptophan and arginine residues in the protein tyrosine phosphatase from Yersinia. AU - Hoff, Richard H.. AU - Hengge, Alvan C.. AU - Wu, Li. AU - Keng, Yen Fang. AU - Zhang, Zhong Yin. PY - 2000/1/11. Y1 - 2000/1/11. N2 - General acid catalysis in protein tyrosine phosphatases (PTPases) is accomplished by a conserved Asp residue, which is brought into position for catalysis by movement of a flexible loop that occurs upon binding of substrate. With the PTPase from Yersinia, we have examined the effect on general acid catalysis caused by mutations to two conserved residues that are integral to this conformation change. Residue Trp354 is at a hinge of the loop, and Arg409 forms hydrogen bonding and ionic interactions with the phosphoryl group of substrates. Trp354 was mutated to Phe and to Ala, and residue Arg409 was mutated to Lys and to Ala. The four mutant enzymes were studied using steady state kinetics and ...

A stereodivergent synthesis of enantiopure 3,6-dihydro-2H-pyrans is presented. The addition of lithiated enol ethers to carbohydrate-derived nitrones afforded syn- or anti-configured hydroxylamine derivatives 4a-d that were cyclized under Lewis acidic conditions to yield functionalized dihydropyrans cis- or trans-5a-d containing an enol ether moiety. This functional group was employed for a variety of subsequent reactions such as dihydroxylation or bromination. Bicyclic enol ether 19 was oxidatively cleaved to provide the highly functionalized ten-membered ring lactone 20. The synthesized enantiopure aminopyrans 24, 26, 28 and 30 can be regarded as carbohydrate mimetics. Trimeric versions of 24 and 28 were constructed via their attachment to a tricarboxylic acid core. ...

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The boryl tetrahydroborole system 9 contains three independent carbon chirality centres. Therefore, there is the possibility of forming four diastereoisomers. So far our rearrangement reaction was rather stereoselective and produced the major product cis-9 with the relative stereoselectivity r-1, t-3, c-4 plus a small amount of a minor isomer which probably represents one of the other three diastereoisomers, but whose relative stereochemistry we did not know. We have now prepared and characterized the isomer trans-9 (of relative r-1, c-3, t-4 stereochemistry) by a selective isomerization process at the saturated central heterocyclic framework.. For that purpose, we treated the substituted tetrahydroborole product cis-9 [r-1, t-3, c-4] with a catalytic amount (20 mol%) of the persistent nitroxide radical TEMPO (pentane, r.t., 4 days).11,14 This reaction apparently proceeded with reversible H-atom abstraction at the activated C1 position of the heterocycle and we isolated the trans-9 epimer ...

Redox-inactive metal ions that function as Lewis acids play pivotal roles in modulating the reactivity of oxygen-containing metal complexes and metalloenzymes, such as the oxygen-evolving complex in photosystem II and its small-molecule mimics. Here we report the synthesis and characterization of non-haem iron(III)-peroxo complexes that bind redox-inactive metal ions, (TMC)FeIII-(μ,η 2:η 2-O 2)-M n+ (M n+ = Sr 2+, Ca 2+, Zn 2+, Lu 3+, Y 3+ and Sc 3+; TMC, 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). We demonstrate that the Ca 2+ and Sr 2+ complexes showed similar electrochemical properties and reactivities in one-electron oxidation or reduction reactions. However, the properties and reactivities of complexes formed with stronger Lewis acidities were found to be markedly different. In conclusion, complexes that contain Ca 2+ or Sr 2+ ions were oxidized by an electron acceptor to release O 2, whereas the release of O 2 did not occur for complexes that bind stronger Lewis acids. ...

TY - JOUR. T1 - A concise synthetic approach to optically active taxol C-ring fragment. AU - Nakada, Masahisa. AU - Kojima, Ei Ichi. AU - Iwata, Yukitaka. PY - 1998/1/15. Y1 - 1998/1/15. N2 - A concise synthetic approach to an optically active taxol C-ring fragment starting from a readily available compound is described. Lewis acid promoted-cyclization of optically active epoxy trimethylsilane 7 affords the key intermediate 8 in 69% yield (at 91% conversion). Further transformation of 8 to our taxol C-ring fragment is successfully achieved in a stereoselective manner.. AB - A concise synthetic approach to an optically active taxol C-ring fragment starting from a readily available compound is described. Lewis acid promoted-cyclization of optically active epoxy trimethylsilane 7 affords the key intermediate 8 in 69% yield (at 91% conversion). Further transformation of 8 to our taxol C-ring fragment is successfully achieved in a stereoselective manner.. UR - ...

Compounds and methods for sorbing organosulfur compounds from fluids are provided. Generally, compounds according to the present invention comprise mesoporous, nanocrystalline metal oxides. Preferred metal oxide compounds either exhibit soft Lewis acid properties or are impregnated with a material exhibiting soft Lewis acid properties. Methods according to the invention comprise contacting a fluid containing organosulfur contaminants with a mesoporous, nanocrystalline metal oxide. In a preferred embodiment, nanocrystalline metal oxide particles are formed into pellets ( 14 ) and placed inside a fuel filter housing ( 12 ) for removing organosulfur contaminants from a hydrocarbon fuel stream.

Scandium hydride, also known as scandium-hydrogen alloy, is an alloy made by combining scandium and hydrogen. Hydrogen acts as a hardening agent, preventing dislocations in the scandium atom crystal lattice from sliding past one another.

The report generally describes scandium acetate, examines its uses, production methods, patents. SCANDIUM ACETATE market situation is overviewed; scandium

Scandium International Mining Corp. (SCY) owns a 100% interest in the Nyngan Scandium Project and in the Honeybugle Scandium property in NSW, Australia.

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The reactions of the enolizable thioketone (1R,4R)-thiocamphor (= (1R,4R)-1,7,7-trimethylbicyclo[2.2.1]-heptane-2-thione; 1) with (S)-2-methyloxirane (2) in the presence of a Lewis acid such as SnCl4 or SiO2 in anhydrous CH2Cl2 led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(5), as well as the isomeric beta-hydroxy thioether 5 (Scheme 2). The analogous reactions of 1 with (RS)-, (R)-, and (S)-2-phenyloxirane (7) yielded two isomeric spirocyclic 1,3-oxathiolanes 8 and 9 with Ph at C(4), an additional isomer 13 bearing the Ph group at C(5), and three isomeric beta-hydroxy thioethers 10, 11, and 12 (Scheme 4). In the presence of HCl, the beta-hydroxy thioethers 5, 10, 11, and 12 isomerized to the corresponding 1,3-oxathiolanes 3 and 4 (Scheme 3), and 8, 9, and 13, respectively (Scheme 5). Under similar conditions, an epimerization of 3, 8, and 9 occurred to yield the corresponding diastereoisomers 4, 14, and 15, respectively (Schemes 3 and 6). The ...

SCANDIUM (REVISED) Note: This article, originally published in 1998, was updated in 2006 for the eBook edition. Overview The existence of scandium was predicted nearly ten years before it was actually discovered. The prediction was made by Russian chemist Dmitri Mendeleev (1834-1907).

PART I. A deuterium exchange analysis of 2,5-dihydroxyacetanilide (5) in the absence and presence of DHAE II was performed to test the nucleophilicity of the substrate in the absence and presence of catalyst. In addition, inhibition studies using 1,4-dihydroxybenzene were performed to determine the role that the N-acetyl side chain group plays in the formation of a stable substrate-enzyme complex. 1,4-Dihydroxybenzene was found to be a weak inhibitor, indicating that the N-acetyl functionality may play a crucial role in forming stable enzyme-substrate interactions. The synthesis of dihydroquinoline 7 was pursued to investigate the enzyme substrate interactions between DHAE and a substrate where the N-acetyl side chain has been fixed to a particular orientation. Efforts towards formation of the C6-C7 bond as a key step in the synthesis of dihydroquinoline 7 using palladium couplings, organocuprates, Lewis acid catalysts, and aza-Claisen reactions were pursued. To complement the results obtained, ...

CBiRC researchers made two important advances that further improve the economics of the previously developed process. First, a new solvent was identified that has a much higher partitioning coefficient for HMF than the previously used extracting solvent. Additionally, the HCl catalyst is nearly insoluble in this new solvent, so it more effectively stays in the aqueous phase. The second advancement is that water-stable homogeneous Lewis acid catalysts were identified, thus allowing operation of the reaction system at higher pH levels, which simplify the reactor-vessel construction materials. These advancements are the subject of a joint patent filing between two CBiRC partner institutions.. ...

кислотный катализ microheterogeneous catalysis микрогетерогенный катализ polyfunctional catalysis полифункциональный катализ photochemical catalysis фотохимический катализ fermentation catalysis ферментативный катализ acid base catalysis кислотно

The combination of well-defined acid sites, shape-selective properties and outstanding stability places zeolites among the most practically relevant heterogeneous catalysts. The development of structure-performance descriptors for processes that they catalyse has been a matter of intense debate, both in industry and academia, and the direct conversion of methanol to olefins is a prototypical system in which various catalytic functions contribute to the overall performance. Propylene selectivity and resistance to coking are the two most important parameters in developing new methanol-to-olefin catalysts. Here, we present a systematic investigation on the effect of acidity on the performance of the zeolite ZSM-5 for the production of propylene. Our results demonstrate that the isolation of Brønsted acid sites is key to the selective formation of propylene. Also, the introduction of Lewis acid sites prevents the formation of coke, hence drastically increasing catalyst lifetime. ...

Additions of one to two equivalents of Lewis acids that include magnesium salts to free-radical reduction reactions involving ester functionalized radicals and (1R,2S,5R)-menthyldiphenyltin hydride 4, bis((1R,2S,5R)-menthyl)phenyltin hydride 5, tris((1R,2S,5R)-menthyl)tin hydride 6, bis((1R,2S,5R)-menthyl)-[8-(N,N-dimethylamino)naphthyl]tin hydride 12, bis((1R,2S,5R)-menthyl)-[1-((S)-N,N-dimethylaminoethyl)phenyl]tin hydride 13 or 3α-dimethylstannyl-5α-cholestane 14 result in remarkable enantioselectivities. Examples include (S)-naproxen ethyl ester 16, produced in 74% yield and greater than 99% ee at −78°C from the bromide and 5 in the presence of MgBr2, and ethyl (R)-N-trifluoroacetyl-D-phenylglycinate 18, obtained in 78% yield and 99% ee under identical conditions. Kinetic and computational studies provide insight into the origins of these observations ...

A brief technical meaning of acidity (from the Latin acidus which means sour) is often described as the number of H+ ions that are neutralized by a base. According to a Swedish chemist, Svante Arrhenius, an acid is a substance that releases hydrogen ions (H+) in water, while a base (or alkali) is a substance that gives up hydroxide ions (OH-) when dissolved in water. You will notice from the above definition that it limits acids and bases to substances that can be dissolved in water. Subsequently, acid was defined by Bronsted and Lowry as a proton donor and base to be a proton acceptor. This definition envisaged that even substances that are insoluble in water can be acids and bases. Then there is another definition of acids that was given by Lewis, which is of a generic nature and defines a Lewis acid as an electron acceptor, and a Lewis base as an electron donor. The behaviour of acid-base systems is unlike redox reactions in that there is no change in the oxidation state or number. Acidity ...

Correct Answer: B. 2. The Aldol reaction combines two carbonyl compounds to form a new ?-hydroxy carbonyl compound. These products are known as aldols, from the aldehyde + alcohol, a structural motif seen in many of the products. The correct answer is the Aldol reaction of acetone. The newly formed bond is highlighted in red. Be able to recognize the ?-hydroxy carbonyl motif as an Aldol product.. ...

This thesis focuses on the development of methods for the activation of the hydroxyl group in non-derivatized alcohols in substitution reactions. The thesis is divided into two parts, describing three different catalytic systems.. The first part of the thesis (Chapter 2) describes nucleophilic allylation of amines with allylic alcohols, using a palladium catalyst to generate unsymmetrical diallylated amines. The corresponding amines were further transformed by a one-pot ring-closing metathesis and aromatization reaction to afford β-substituted pyrroles with linear and branched alkyl, benzyl, and aryl groups in overall moderate to good yields.. The second part (Chapters 3 and 4) describes the direct intramolecular stereospecific nucleophilic substitution of the hydroxyl group in enantioenriched alcohols by Lewis acid and Brønsted acid/base catalysis.. In Chapter 3, the direct intramolecular substitution of non-derivatized alcohols has been developed using Fe(OTf)3 as catalyst. The hydroxyl ...

This review highlights recent approaches toward polyisobutylene (PIB) by an energy efficient room temperature cationic polymerization. Special focus is laid on our own work using modified Lewis acids and nitrile-ligated metal complexes associated with weakly coordinating anions. In both cases, suitable conditions have been found for efficient production of PIB characterized by medium to low molar masses and a high content of exo double bonds as end groups-the typical features of highly reactive PIB, an important commercial intermediate toward oil and gasoline additives. These and other approaches demonstrate that the cationic polymerization of isobutylene is still not fully explored, and new innovative catalyst systems can lead to surprising results of high commercial interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 ...

Our research program uses fundamental principles of molecular design to address some of the grand challenges in the fields of small molecule activation and catalysis. We are interested in developing strategies to reversibly store energy in the form of chemical bonds, and also to rapidly convert abundant chemical (bio)feedstocks into value-added chemicals and fuels.. The overarching themes of our research program are to (a) understand how to exploit carefully positioned secondary-sphere sites to control reactivity, and (b) develop transition metal compounds to promote otherwise difficult transformations of small molecule chemical feedstocks such as N2, CO2, O2, and CO.. We are working to establish new ways by which molecular catalysts can be tuned by the incorporation of pendent functional groups within a metals secondary coordination sphere environment. We are using these appended functional groups (hydrogen bond donor/acceptors, or Lewis acid/bases) to augment reactivity of the central ...

Реферат: Modification of the oxide surface of aluminium oxide with oxalate complexes of aluminium was carried out, followed by thermal treatment for the purpose of varying the ratio between the functional groups on the surface (ОН groups, Lewis acid centres). It was established that the modification of γ-Al2O3 causes a 1.5-fold increase in the amount of adsorbed platinum (IV) complexes and the fraction of these complexes strongly bound with the surface of the support. The effect of γ-Al2O3 surface modification on the catalytic properties of the system Pt/Al2O3 was demosntrated. It was shown that an increase in the fraction of platinum forms strongly bound with the support causes an increase in the content of methylcyclopentane in the products of n-hexane isomerization and an increase in the selectivity of the formation of propylene in propane transformations ...

Abstract Alanine triazole Mn-catalyzed 1,6-conjugate coupling/aromatization of para-quinone methides was developed with good to high yields under mild conditions. This protocol provided an efficient and practical route to the synthetically interesting functionalized methines and their analogues. Preliminary mechanistic experiments revealed 1,6-conjugate addition of nucleophiles to para-quinone methides (p-QMs). The manganese was acted as the Lewis acid.. ...

The Wang support is the most widely used resin for attaching carboxylic acids for further functionalisation. Cleavage conditions for the ester anchor involve concentrated TFA or TFA/CH₂CI₂ mixtures to provide carboxylic acids or cyclization-cleavage under acidic or basic conditions. Release of an amide function by treatment with an amine in the presence of a Lewis acid was also reported. Wang resin was used to add vinyl and iodobenzoic acids via carbodiimide coupling and the products subjected to Heck conditions with alkenes or with alkynes or to Suzuki coupling with boron reagents. The Ugi multicomponent condensation reaction was conducted on Wang resin with the carboxylic acid, amine or isonitrile as the anchored functional group. On a Wang resin primary, secondary, and tertiary alcohols have been converted to 4-methoxy-benzyl ethers. As well as anchoring carboxylic acids to this resin, phenols were attached under Mitsunobu conditions, subjected to further transformations and cleaved under ...

The novel laser desorption method laser-induced liquid beam ionization/desorption (LILBID) is applied to the mass spectrometric examination of selective ion binding by natural and synthetic ionophores in methanol solutions. The ions are desorbed from a liquid jet with an IR laser pulse and then extracted perpendicularly into a reflectron time-of-flight (RE-TOF) analyzer. LILBID studies on the natural ion carriers valinomycin and monensin A are presented, as well as those on the synthetic crown ethers 18-crown-6, diaza-18-crown-6, and benzo-15-crown-5. No fragment ions are detected, and the measured ion selectivity is in good qualitative agreement with published stability constants of the complexes. The observed specific recognition of silver ions by diaza-18-crown-6 can be rationalized by the principle of hard and soft acids and bases, which predicts stable complexes when the polarizabilities of Lewis acid and base are similar. Weak, noncovalent interactions like those in the sandwich complex ...