Photoinduced Multicomponent Synthesis of Sulfonylated Indole-Fused 1,4-Diazepinones Using Thianthrenium Salts

A practical photoredox-driven protocol is described for the multicomponent synthesis of sulfonylated indole-fused medium-sized N-heterocycles using readily accessible, modular thianthrenium salts together with N-indolyl phenylacrylamides and DABCO·(SO2)2. Thianthrenium salts serve as general precursors of alkyl and aryl radicals, enabling the efficient and diverse generation of alkyl or aryl sulfonyl radicals via in situ capture of sulfur dioxide while avoiding the use of highly toxic sulfonyl chlorides or sulfonyl hydrazines as sulfonyl sources. Meanwhile, a gram-scale experiment afforded the sulfonylated indole-fused 1,4-diazepinone in good yield and recovered thianthrene in high yield, demonstrating high atom and step economy via the formation of multiple C-S and C-C bonds in a single orchestrated operation.