CopperIICatalyzed CC BondForming Reactions of αElectronWithdrawing GroupSubstituted Ketene S,SAcetals with Carbonyl Compounds and a Facile Synthesis of Coumarins

A new catalytic CC bondforming reaction has been developed. Catalyzed by cheap and commercially available copperII bromide CuBr2; 10 mol%, the reactions of αelectronwithdrawing group EWGsubstituted ketene S,Sacetals with aldehydes or ketones in acetonitrile at room temperature gave a variety of densely functionalized coupling products in excellent yields 80–98%. Based on this catalytic process, coumarin derivatives were efficiently synthesized when salicylaldehydes were selected as the carbonyl components.