Enantioselective Diels–Alder reactions of enals and alkylidene diketones catalyzed by N-heterocyclic carbenes

An electron-withdrawing group was introduced to the α-position of chalcones, and the resulting alkylidene diketones showed new reactivities with enals under the catalysis of N-heterocyclic carbenes (NHCs). Selective activation of enals affords enolate equivalents that undergo highly enantioselective intermolecular Diels–Alder reactions with the alkylidene diketones. No products that might have resulted from typical homoenolate pathways were observed