Synthesis of substituted 3-iodocoumarins and 3-iodobutenolides via electrophilic iodocyclization of ethoxyalkyne diols.

A convenient and general synthesis of various 4-substituted 3-iodocoumarins and 4,5-disubstituted 3-iodobutenolides is described via an exclusive 6-endo-dig iodocyclization of 3-ethoxy-1-(2-alkoxyphenyl)-2-yn-1-ols and 5-endo-dig iodocyclization of 1-alkoxy-4-ethoxy-3-yn-1,2-diols, respectively. The reaction is carried out under very mild conditions using I2 in CH2Cl2 or toluene at room temperature. Oxygens in OMe and OMOM groups were used as efficient nucleophiles for this intramolecular cyclization to obtain the products in good to excellent yields.