Regioselective Synthesis of Isocoumarins via Iridium(III)-Catalyzed Oxidative Cyclization of Aromatic Acids with Propargyl Alcohols.

An Ir(III)-catalyzed oxidative cyclization of benzoic acids with propargyl alcohols to give substituted isocoumarins in a highly regioselective manner is described. This protocol has a broad substrate scope with high functional group tolerance. The observed isocoumarins were converted into biologically active tetracyclic indeno[2,1- c]isocoumarins by Lewis acid-mediated cyclization. A possible reaction mechanism is proposed and strongly supported by the detailed mechanistic investigation and DFT.