The opposite diastereoselectivity in the alkylation and protonation of enolates

Abstract

The conjugate addition of BuCu·BF₃ to the enoate (5) produces predominantly the syn-isomer (7) having the butyl and methyl groups syn on the carbon chain, while the methylation of the enolate derived from the ester (8) gives preferentially the other diastereoisomer, anti-(6); the diastereoselectivity can be explained by an eclipsed model.