A simple and efficient method for the synthesis of isoquinolone and isocoumarin derivatives is reported. The method for the first time provides a one-step divergent synthesis of important isoquinolone and isocoumarin skeletons from benzoic acid by switching the coupling partners. In addition, a reliable mechanism has been proposed on the basis of experimental investigations, including kinetic isotope effect experiments, 13C labeling experiments, time-tracking experiments, and competitive experiments, as well as DFT calculation studies.