摘要:
A remarkable substituent effect by a trimethylsilyl group was observed on the enantioselectivity of the tandem asymmetric epoxidation and enantiospecific ring expansion of 2-cyclopropylidene-2-(4,5-dimethoxy-2-(trimethylsiyl)phenyl)ethanol (24), affording (S)-(-)-2-(4,5-dimethoxy)-2-(trimethylsilyl)phenyl-2-(hydroxymethyl)cyclobutanone (25) in high enantiomeric excess. This feature enabled us to accomplish a concise and highly enantioselective total synthesis of(-)-mesembrine (1), providing a new and general strategy for the enantioselective synthesis of benzylic quaternary carbon centers.