N-heterocyclic carbene catalyzed formal [3+2] annulation reaction of enals: an efficient enantioselective access to spiro-heterocycles.

Abstract

A highly enantioselective N-heterocyclic carbene (NHC) catalyzed formal [3+2] annulation of α,β-unsaturated aldehydes with azaaurones or aurone generating spiro-heterocycles has been developed. The protocol represents a unique NHC-activation-based approach to access spiro-heterocyclic derivatives bearing a quaternary stereogenic center with high optical purity (up to 95% ee).