Visible-Light-Induced Sulfonylation Cyclization to Generate Indole-Fused Medium-Sized N-Heterocycles in 2-Me-THF

A novel visible-light-induced sulfonylation cyclization to indole-fused medium-sized N-heterocycles was established under room temperature with biomass-derived 2-Me-THF as the solvent. This reaction proceeds in the absence of external photocatalyst, additive, metal salts, and base. Broad substrate scope, good functional group compatibility, and large-scale synthesis and derivatization via iodination, nitration, chlorination, cyanation, and selenylation demonstrate the utility of this protocol. A radical cyclization route was proposed based on radical inhibition experiments, visible-light irradiation on-off test, apparent quantum efficiency calculation, and UV-vis absorption spectroscopic studies.