Modified palladium-catalyzed regioselective ortho-arylation of sp2 C-H bond substrates with a low catalyst loading

A novel and generally applicable system for ortho-arylation of a broad range of sp2 C-H bond substrates such as arylated benzoxazoles, acylated anilines, and pyridines has been developed. The arylation was performed in trifluoroacetic acid (TFA) under air by using PdCl2 as the catalyst with a low catalyst loading of 1 mol %. And it was found for the first time that the addition of weak base K3PO4 to the acidic solvent could remarkably enhance the reaction rate. The arylated products were isolated in moderate to good yields with high regioselectivity for the substrates containing a meta-substituent. This arylation is tolerant with various functional groups such as CH3, CH3O, CH3CO, Br, and Cl.