Recent Developments for the Synthesis of Heterocycles Catalyzed by N-Heterocyclic Carbene

N-Heterocyclic carbenes (NHCs) as versatile nucleophilic organocatalysts have been extensively studied and also widely applied in organic reactions. The types of organic reactions catalyzed by N-heterocyclic carbenes are broad including benzoin condensation, Stetter reaction, a3-to-d3 umpolung, ring-opening reaction, transesterification, and ring expansion polymerization. This review reports recent developments in the synthesis of heterocycles (such as lactams, lactones, chromones, and benzofuranones) catalyzed by N-heterocyclic carbenes.