Arylsulfonic Anhydride as Thiol Surrogate for Sulfenylation of sp2 C‐H Bond Through De‐oxygenative Reduction with Neutral Ionic Liquid: Scope and Mechanistic Studies

Abstract We disclosed the dual role of neutral [Hmim]Br towards the direct conversion of arylsulfonic anhydride into arylthiol surrogate for the controlled and regioselective synthesis of 3‐sulfenylindoles from indole derivatives at rt. In addition, 2‐bromo‐3‐sulfenylindoles were synthesized in the presence of catalytic water at 50 °C in a cascade manner i. e. sulfenylation and bromination through de‐oxygenative reduction with [Hmim]Br in the absence of any additional brominating agent. The present method was also utilized for the sulfenylation of other heterocycles including azaindole, coumarin, naphthol, and pyrrole in good to excellent yields. Moreover, mechanistic investigations revealed this reaction was driven by imidazolium cation of neutral ionic liquid i. e. [Hmim]Br, which converts arylsulfonic anhydride into sulfenyl group for sulfenylation/bromination of sp 2 C−H bond wherein an acidic ionic liquid [Hmim] p TSA is released as a by‐product.