Base- and Copper-Catalyzed Intramolecular Cyclization for the Direct Synthesis of Dihydrofurans

A simple and convenient synthetic approach to dihydrofurans has been developed from the cyclization of 2-propynyl-1,3-dicarbonyl compounds catalyzed by potassium tert-butoxide, copper(II) trifluoromethanesulfonate and triphenylphosphine using methanol/dichloromethane as the solvent under very mild conditions. Moreover, dihydrofurans could be easily transformed into the corresponding furans in the presence of trifluoroacetic acid.