Highly Regioselective α-Arylation of Coumarins via Palladium-Catalyzed CH Activation/Desulfitative Coupling

A novel regioselective α‐arylation of coumarins with readily available arenesulfonyl chlorides and sodium arenesulfinates via palladium‐catalyzed direct CH functionalizations under mild reaction conditions is described. This protocol presents an unexpected and highly regio‐controlled arylation of coumarins at C‐3 to construct interesting 3‐arylcoumarins with fascinating biological and fluorescent properties. The regioselectivity observed is in sharp contrast with that expected for the Heck reactions.