On the diastereoselectivity of alkylations of bicyclic lactams

Abstract

The diastereoselectivity in the alkylation of the enolates of bicyclic lactams 2 derived from pyroglutaminol 1a has been found to depend upon the nature of the hemiaminal ether protecting group. Although exo-alkylation has been widely reported for 2a,b,e, endo-alkylation is favoured for 2d. It is postulated that this is a result of the opening of the bicyclic structure of the enolate derived from 2d, and the consequent stereoelectronic facilitation of endo-facial attack.