Cu(OAc)2 Mediated Synthesis of 3-Sulfonyl Chromen-4-ones.

Copper acetate mediated (4 + 2) annulation of sulfonylacetylenes with salicylic acids provides sulfonyl chromen-4-ones in the presence of benzotriazol-1-yloxy tri(dimethylamino)phosphonium hexafluorophosphate (BOP, Castro's reagent) and 4-dimethylaminopyridine (DMAP) in MeNO2 at reflux for 3 h. The uses of various metal complexes and activating reagents are investigated for facile and efficient transformation. A plausible mechanism is proposed.