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.