Copper-catalyzed synthesis of sulfonamides from nitroarenes via the insertion of sulfur dioxide

Nitroarenes are used as the coupling partners in the preparation of sulfonamides via the insertion of sulfur dioxide. A three-component reaction of arylboronic acids, nitroarenes, and potassium metabisulfite under copper catalysis proceeds smoothly, giving rise to a range of sulfonamides in good to excellent yields with broad substrate scope. Various functional groups including hydroxyl, cyano, amino, and carbonyl are all tolerated. A plausible mechanism is proposed, showing that arylsulfinate is the intermediate and the copper-assisted interaction of the nitroarene and arylsulfinate is the key step. This approach is also extended to the late-stage modification of a currently marketed drug (flutamide).