Trifluoroacetic acid-mediated hydroarylation: Synthesis of dihydrocoumarins and dihydroquinolones

Trifluoroacetic acid mediates the hydroarylation of alkenes to afford dihydrocoumarins and dihydroquinolones in good yield. Intermolecular hydroarylation of cinnamic acids by phenols is particularly facile, which leads to the conclusion that previous reports of palladium-catalyzed hydroarylation of cinnamic acids in trifluoroacetic acid are erroneous.