Regioselective carbonylative heteroannulation of o-iodothiophenols with allenes and carbon monoxide catalyzed by a palladium complex: A novel and efficient access to thiochroman-4-one derivatives

The palladium-catalyzed carbonylative ring-forming reactions of 2-iodothiop henol, and the corresponding substituted derivatives, with allenes and carb on monoxide are described. The reactions afford thiochroman-4-ones in good to excellent isolated yields with quite high regioselectivity. The catalyti c heteroannulation may involve regioselective addition of the sulfur moiety of the reactants on the more positive end of the allene, arylpalladium for mation, CO insertion, subsequent intramolecular cyclization, and then reduc tive elimination. The regioselectivity is probably governed by electronic e ffects.