Pd-Catalyzed Regiodivergent Hydrocarboxylation of Olefins with Oxalic Acid: A Remarkable Effect of the Counteranion on Regioselectivity.

A regioselective Pd-catalyzed hydrocarboxylation of vinyl arenes with oxalic acid is described. A wide variety of either linear or branched carboxylic acids can be readily obtained with high regioselectivities under mild reaction conditions. The reaction process is operationally simple and requires no handling of toxic CO. Besides the ligand, the counteranion of the Pd catalyst system plays an important role in the regioselectivity.