Ruthenium(IV) Intermediates in C−H Activation/Annulation by Weak O ‐Coordination

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−H activation, along with cyclometalated ruthenium(IV) intermediates within a versatile ruthenium(II/IV) catalysis regime (BIES=base‐assisted internal electrophilic substitution).