Ensembles of Metal Triflate Additives in Gold(I)-Catalyzed Formal [2 + 2 + 2] Cycloaddition of Carbonyls with Activated Terminal Alkynes: One-Pot Synthesis of 2-Pyrans.

Herein, we describe a gold(I)-catalyzed intermolecular formal [2 + 2 + 2] cycloaddition of a carbonyl compound and a propiolate. A series of highly substituted 2-pyrans are accessed regioselectively from acyclic and cyclic ketones and aldehydes with various substituted propiolates using PhPAuCl (0.1-1 mol %) with two distinct metal triflate additives [0.75-7.5 mol %; In(OTf)/Cu(OTf) for ketones, Bi(OTf)/Hf(OTf) for aldehydes]. This method should provide an opportunity for further development of synthetic access to other heterocyclic compounds.