Enantioselective Medium-Ring Lactone Synthesis through an NHC-Catalyzed Intramolecular Desymmetrization of Prochiral 1,3-Diols

A highly enantioselective intramolecular annulation reaction of 1,3-diols catalyzed by a triazolium N-heterocyclic carbene (NHC) precatalyst is disclosed, affording the corresponding medium-sized lactones in moderate to good yields with high enantioselectivities. It is worth noting that this compatible catalytic system has been successfully applied to assemble a broad range of chiral medium-sized lactones, including ones with eight-, nine-, ten-, eleven-, and twelve-membered rings.