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 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). Ring, ring: A highly enantioselective formal [3+2] annulation of α,β‐unsaturated aldehydes with azaaurones or aurone is catalyzed by an N‐heterocyclic carbene (NHC) and generates spiro‐heterocycles. The protocol represents a unique NHC activation‐based approach to access spiro‐heterocyclic derivatives bearing a quaternary stereogenic center with high optical purity.