Asymmetric Construction of Quaternary Carbon Centers by Regio- and Enantiocontrolled Allylzincation
摘要:
[GRAPHICS]An allylic zinc reagent bearing a chiral bisoxazoline ligand adds to a substituted cyclopropenone acetal to produce an optically active cyclopropanone acetal possessing a quaternary chiral center in high yield with 97.8-99.8% ee, The steric effects of the bulky bisoxazoline ligand overwhelm the regioselectivity inherent to the electronic property of the olefinic acceptor. High pressure exerts favorable effects on the reaction rate without affecting the high enantio- or regioselectivity.
Thermal reactions of substituted cyclopropenone acetals. Regio- and stereochemistry of vinylcarbene formation and low-temperature [3 + 2] cycloaddition
of diverse electronic character have been synthesized and examined for their thermal behavior toward water and electron-deficient olefins. The substituted cyclopropenes underwent regio- and stereoselective hydration to give acrylate derivatives via vinylcarbene species, providing new data on the regio- and stereochemistry of vinylcarbene species. The also underwent regioselective [3+2] cycloadditions
Hydrostannation of Cyclopropene. Strain-Driven Radical Addition Reaction
作者:Shigeru Yamago、Satoshi Ejiri、Eiichi Nakamura
DOI:10.1246/cl.1994.1889
日期:1994.10
cyclopropenone acetals with trialkyltinhydride takes place smoothly under radical conditions to afford a variety of 2-alkyl-3-stannylcyclopropanone acetals in high yield. Comparison of the cyclopropene with acetylenes with the aid of inter- and intramolecular competitive experiments revealed the kinetically controlled nature of the reaction of the cyclopropene reaction.
[reaction: see text] Substituted cyclopentadienone acetals (CPDAs) were synthesized by a thermal or palladium-catalyzed [3 + 2] cycloadditionreaction of a substituted cyclopropenone acetal to an electron-deficientacetylene. The synthesis afforded di-, tri-, and tetra-substituted CPDAs of considerable structural varieties that undergo Diels-Alder reaction to produce bicyclo[2.2.1]heptenes.