N-Heterocyclic Carbene Catalyzed Formal [3+2] Annulation Reaction of Enals: An Efficient Enantioselective Access to Spiro-Heterocycles

A highly enantioselective N-heterocyclic carbene (NHC) catalyzed formal [3+2] annulation of alpha, beta-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).