Regioselective Functionalization of Aromatic Carboxylic Acids under Transition-Metal Catalysis

Aromatic carboxylic acids have been recognized as important building blocks in organic synthesis field because of their wide availability and easy handling. Their carboxy group is known to act as a directing group in transition–metal–catalyzed C–H functionalization. For example, ortho–substituted benzoic acids undergo iridium–catalyzed dehydrogenative coupling with alkynes at the opposite ortho–and meta–positions accompanied by decarboxylation. Exceptionally, salicylic acid couples with alkynes at the ipso– and ortho–positions to produce 5,6,7,8–tetrasubstituted 1–naphthol derivatives. 1–Naphthoic acid reacts with diphenylacetylene under rhodium catalysis at the 2–and 3–positions selectively to afford 1,2,3,4–tetraphenylanthracene. In contrast, 9–anthracenecarboxylic acid exhibits unique reactivity. Treatment of this substrate with diphenylacetylene under rhodium catalysis does not give any intermolecular coupling products at all but gives an intramolecular C–O coupling product. 9–Anthracenecarboxylic acid also undergoes palladium–catalyzed dehydrogenative coupling with styrenes at the peri position and successive Wacker–type cyclization to produce (Z)–3–benzylidenedibenzo[de,h]isochromen–1–one derivatives. © 2025 Society of Synthetic Organic Chemistry. All rights reserved.