Ruthenium Catalyzed ortho‐Arylation Reaction of Benzoic Acids with Arylthianthrenium Salts

Arylthianthrenium salts have become key intermediates for late‐stage functionalizations of drug‐like molecules. Ruthenium‐phosphine catalysts are now shown to enable their use as aryl sources in high‐yielding ortho‐C–H arylations of benzoic acids. The arylthianthrenium salts are converted chemo‐selectively, leaving aryl halides and boronates untouched. The carboxylate groups are uniquely effective as directing groups, ensuring exclusive ortho‐selectivity even in the presence of competing pyridine or amide groups. This makes the reaction orthogonal to cross‐couplings and conventional C‐H arylations. The carboxylate group can be removed via decarboxylation or serve as an anchor for downstream transformations. Mechanistic studies identify C–H ruthenation as the rate‐limiting step and highlight the unique efficiency of P(Cy)3 ligands.