6-endo-dig Cyclization of heteroarylesters to alkynes promoted by Lewis acid catalyst in the presence of Brønsted acid

We report a regiocontrolled 6-endo-dig cyclization of 2-(2-arylethynyl)heteroaryl esters occurred under Brønsted acidic conditions and in the presence of a catalytic amount of Lewis acids such as Cu(OTf)2, AuCl3, or (CF3CO2)Ag. A variety of heterocyclic lactones are readily prepared in excellent yields.