Hypervalent iodine-mediated ring contraction reactions.
(17/99)
Hypervalent iodine reagents constitute a powerful tool in modern synthetic organic chemistry, promoting several important reactions. One such reaction is the ring contraction of cycloalkenes and cycloalkanones promoted by iodine(III) compounds, such as iodobenzene diacetate, iodosylbenzene, iodotoluene difluoride, and [hydroxy(tosyloxy)- iodo]benzene (Koser' s reagent). This review covers all the literature related to the ring contraction of cyclic ketones and olefins promoted by iodine(III) species. (+info)
L-proline catalyzed Michael additions of thiophenols to alpha,beta-unsaturated compounds, particularly alpha-enones, in the ionic liquid [bmim]PF6.
(18/99)
L-proline catalyzed additions of 13 different thiols to 11 different alpha-enone Michael acceptors in [bmim] PF(6 )are reported. Reasonable to high yields of the reaction products were isolated in most cases. (+info)
Synthesis of unsymmetrical annulated 2,2'-bipyridine analogues with attached cycloalkene and piperidine rings via sequential Diels-Alder Reaction of 5,5'-bi-1,2,4-triazines.
(19/99)
Synthesis of bisfunctionalized unsymmetrical 2,2'-bipyridines 8 or their sulfonyl derivatives 12a,b are described. They were prepared via the Diels-Alder reaction of 1-methyl-4-pyrrolidin-1-yl-1,2,3,6-tetrahydropyridine (6) with 3,3'-bis(methyl- sulfanyl)-5,5'-bi-1,2,4-triazine (1). The reaction leads to the single cycloaddition product 7 which undergoes Diels-Alder reaction with cyclic enamines 2a,b to give unsymmetrical 2,2'-bipyridine derivatives 8, consisting of the two different heterocyclic units: cycloalkeno[c]pyridine and 2,6-naphthyridine. (+info)
1,3-Dipolar cycloaddition reactions of 1-(4-phenylphenacyl)-1,10-phenanthrolinium N-ylide with activated alkynes and alkenes.
(20/99)
The 3+2 cycloaddition reaction of 1-(4-phenylphenacyl)-1,10-phenanthrolinium ylide 4 with activated alkynes gave pyrrolo[1,2- 4a][1,10]phenanthrolines 6a-d. The "one pot" synthesis of 6a,b,d from 4, activated alkenes, Et(3)N and tetrakis-pyridine cobalt (II) dichromate (TPCD) is described. The helical chirality of pyrrolophenanthrolines 6b-d was put in evidence by NMR spectroscopy. (+info)
Total synthesis of the strychnos alkaloid (+)-minfiensine: tandem enantioselective intramolecular Heck-iminium ion cyclization.
(21/99)
Development of new palladium(0)-catalyzed reactions based on novel oxidative addition mode.
(24/99)
We have developed palladium(0)/monophosphine-catalyzed trans-selective arylative, alkenylative, alkylative, and alkynylative cyclization reactions of alkyne-aldehydes and -ketones with organoboron reagents. These reactions afford six-membered allylic alcohols with endo tri- or tetra-substituted olefin groups and/or five-membered counterparts with exo olefin groups. The ratios of these products are dramatically affected by alkyne substituents as well as the phosphine ligand. The remarkable trans selectivity of the process results from the novel reaction mechanism involving 'anti-Wacker'-type oxidative addition. Although the cyclization reactions are influenced by the length of the tether between the alkyne and carbonyl group, they can be applied to a multi-component synthesis of biologically important indenes bearing three substituent groups at 1, 2, 3-positions from available o-ethynylbenzaldehyde derivatives. A two-component coupling reaction in methanol provides 1H-indenols, while a three-component reaction involving secondary aliphatic amines as the third component in DMF affords 1H-indenamines. This method allows combinatorial preparation of unsymmetrically substituted 1H-indenes that cannot be prepared via previous synthetic routes. The same catalytic system can also transform allene-carbonyl compounds into 3-cyclohexenols and -cyclopentenols with alkyl, aryl, alkenyl, alkynyl, and boryl groups at C-3. Microwave irradiation efficiently increases not only the reaction rate but also the product yield by suppressing formation of hydroarylation byproducts. Cyclization of optically active 1,3-disubstituted allene-aldehyde reveals that the reaction proceeds through not carbopalladation but 'anti-Wacker'-type oxidative addition. (+info)