Stereoselective Formation of Quaternary Carbon Centers: Alkylation ofα,α-Disubstituted Amide Enolates

High diastereoselectivity is achieved in the alkylation of α,α-disubstituted amide enolates to form quaternary carbon products (see scheme; LiDBB=di-tert-butyldiphenyllithium). No chelating groups are necessary for stereocontrol in either the enolate-formation or alkylation steps. In many cases, amplification of the alkylation diastereoselectivity above the isomeric ratio of the intermediate enolates is observed.