Ruthenium Catalyzed <i>Ortho</i> ‐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.