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Copper(II)-Catalyzed C[BOND]C Bond-Forming Reactions of α-Electron-Withdrawing Group-Substituted Ketene S,S-Acetals with Carbonyl Compounds and a Facile Synthesis of Coumarins



A new catalytic C[BOND]C bond-forming reaction has been developed. Catalyzed by cheap and commercially available copper(II) bromide (CuBr2; 10 mol%), the reactions of α-electron-withdrawing group (EWG)-substituted ketene S,S-acetals 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.