An Efficient Route to 4‐Halophosphaisocoumarins via CuX2‐Mediated Direct Halocyclization of 2‐(1‐Alkynyl)phenylphosphonic Acid Diesters.

A series of 4-halophosphaisocoumarins were synthesized via CuX2 (X = Br, Cl) -mediated direct halocyclization of 2-(1-alkynyl)phenylphosphonic acid diesters in dichloroethane with the addition of n-Bu4NX or/and AgI in good to excellent yields. This reaction provides an effecient route to 4-halophosphaisocoumarins and represents the first example of bromo- and chlorocyclization of unsaturated phosphonic acid diesters.