One-Pot Synthesis of Polyfunctionalized 4H-Chromenes and Dihydrocoumarins Based on Copper(II) Bromide-Catalyzed C-C Coupling of Benzylic Alcohols with Ketene Dithioacetals

The synthesis of polyfunctionalized 4H-chromenes 3 and dihydrocoumarins 4 has been developed from the same substrates. Catalyzed by copper(II) bromide (0.3 equiv.), the reactions of the easily available ketene dithioacetals 1 with 2-(hydroxymethyl)phenols 2 lead to 4H-chromenes 3 in high to excellent yields in dichloromethane solvent, whereas, 3,4-trans-disubstituted dihydrocoumarins 4 are obtained in high yields with high diastereoselectivities by prolonging the reaction time or changing the solvent from dichloromethane to acetonitrile.