Direct Synthesis of 3‐Aryl Substituted Isocoumarins and Phthalides through Palladium Acetate Catalyzed C(sp2)−H Activation in Ionic Liquids.

A novel Pd‐catalysed oxidative coupling between benzoic acids and vinylarenes or acrylates to furnish isocoumarins and phthalides is reported. The reaction proceeds smoothly in molten tetrabutylammonium acetate via a selective C−H bond activation, with very low percentage of ligand‐free palladium acetate as the catalyst, under atmospheric pressure of oxygen. Sub‐stoichiometric amount of copper acetate is also required as a reoxidant for the palladium. [ABSTRACT FROM AUTHOR]