Photo‐Induced Difluoromethylation‐Cyclization of Indoles Using Tetrazole Sulfone Reagent Under Visible Light

Polycyclic indoles are prevailed in natural products, pharmaceuticals and biologically active compounds. Herein is described photo‐induced difluoromethylation‐cyclization of N‐alkene tethered indoles to synthesis of tetrahydropyrido[1,2‐a]indole using 5‐((difluoromethyl)sulfonyl)‐1‐phenyl‐1H‐tetrazole as a CF2H radical source. This photochemical reaction tolerates an array of functional groups like ester, cyano, ketone, halide, ether, aldehyde and heteocycles. Mechanistic experiments indicated that the difluoromethyl radical and the single electron transfer were involved. Photo‐induced cascade difluoromethylation‐cyclization of N‐alkene tethered indoles was developed using tetrazole sulfone reagent as a CF2H radical precursor. A variety of indoles with ester, cyano, ketone, halide, ether, aldehyde group occurred smoothly to give the desired products in moderate yields.