High diastereofacial selectivity in the conjugate addition of phenylmagnesium bromide to acyclic α-enones with an asymmetric carbon at the γ-position

Abstract

Moderately high diastereofacial preference has been observed in the conjugate addition of phenylmagnesium bromide to the acyclic α-enones with an asymmetric carbon at the γ-position (4E,6RS)-2,2,7,7-tetramethyl-6-phenyloct-4-en-3-one (1), (2E,4RS)-5,5-dimethyl-1,4-diphenylhex-2-en-1-one (2), and (4E,6RS)-2,2-dimethyl-6-phenylhept-4-en-3-one (3). The RR,SS selectivity is practically unaffected by the addition of copper(I) salts. These results are in qualitative agreement with the selectivity predicted by a Felkin-like transition state model. The method is shown to be useful for the stereoselective preparation of acyclic ketones having two chiral centres.