Copper-Catalyzed Direct Trifluoromethylation of Propiolates: Construction of Trifluoromethylated Coumarins

A novel copper-catalyzed direct trifluoromethylation of internal alkynes was developed, obtaining a series of trifluoromethylated coumarins in good yields. The cyclization was proposed to proceed via a radical mechanism under copper-catalyzed conditions with good functional group tolerance.