Copper-Catalyzed Coupling Cyclization of <i>gem</i>-Difluoroalkenes with Activated Methylene Carbonyl Compounds: Facile Domino Access to Polysubstituted Furans

A novel and efficient CuI-catalyzed synthesis of 2,3,5-trisubstituted furans was developed via coupling cyclization of gem-difluoroalkenes with active methylene carbonyl compounds such as 1,3-dicarbonyl compounds, acetoacetonitrile, and phenylsulfonylacetone with the assistance of a base. Commercial availability of substrates or reagents, good to high isolated yields, and excellent functional group compatibility make this transformation a powerful tool for the synthesis of various furans. A plausible mechanism involving the allenyl ketone is suggested.