Ruthenium(IV) complexes were identified as key intermediates of C−H/O−H activations by weak O‐coordination. Thus, the annulations of sulfoxonium ylides by benzoic acids provided expedient access to diversely‐decorated isocoumarins with ample scope. Detailed experimental and computational studies provided strong support for a facile BIES‐C−Hactivation, along with cyclometalated ruthenium(IV) intermediates