Regioselective cyclization of 2-alkynylbenzoic acid in water for the synthesis of isocoumarin

In this work, a regioselective synthesis of isocoumarins from 2-alkynylbenzoic acid is reported. The transformations proceed smoothly with good yields in water via a metal-free radical pathway. When catalytic TBAB is employed, the reaction provides various isocoumarin derivatives according to the structures of the corresponding precursors. It is believed that TBAB serves as a phase transfer catalyst and radical initiator in the reaction. Compared to previous methodologies, the synthetic procedure reported herein provides a more environmentally benign route for the synthesis of isocoumarins.