Organophotoredox-Catalyzed Cross-Dehydrogenative Sulfonamidation of Indoles and Other Heterocycles

The visible light-triggered regioselective synthesis of 2-sulfonamidoindoles and other 2-sulfonamido heteroarenes is accomplished by the oxidative cross-dehydrogenative coupling of indoles (heteroarenes) with di-p-toluenesulfonamide or N-aryl-p-toluenesulfonamides. The reaction was catalyzed by eosin-Y through a photoredox route. Detailed mechanistic studies based on control reactions, cyclic voltammetry, and fluorescence quenching have been reported for the elucidation of the mechanistic cycle and revealed that a nitrogen-centered radical is generated, followed by regioselective addition to the heteroarene. The operationally simple, straightforward methodology and easy availability of the starting materials allow for the synthesis of a wide range of 2-amidated indoles as well as other heterocyclic compounds.