Cu(I)-Catalyzed Synthesis of Polysubstituted Furans

Significance

Reported is the efficient Cu(I)-catalyzed synthesis of tri- and tetra-substituted furans 2, 3 and 5 from bis-propargylic esters 1. The proposed mechanism involves the formation of a 2-furylcarbene complex which may be trapped with a variety of electrophiles including ethyl diazoacetate (EDA), oxygen and silanes or germanes to give furan derivatives 2, 3 and 5, respectively, in moderate to excellent yield. The reaction was found to tolerate a wide range of functionality at the alkyne terminus (R^¹) including alkyl, aryl trimethylsilyl and alkenyl groups. A number of different esters (R^²) such as acetate, propanoate, pivalate and acrylate also proved amenable to cyclization.