Copper Catalysed Oxidative α-Sulfonylation of Branched Aldehydes Using the Acid Enhanced Reactivity of Manganese(IV) Oxide

The oxidative coupling of secondary aldehydes and sulfinate salts is achieved using copper catalysis to form a-sulfonyl aldehydes. The use of an acidic co-solvent is important to adjust the oxidation potential of MnO2 as oxidant. A broad range of sulfonylated aldehydes is prepared, and their further functionalisation is demonstrated. A dual ionic/radical pathway mechanism is proposed.