Modified palladium-catalyzed regioselective ortho-arylation of sp 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.