Photoinduced [3 + 2] Radical Cyclization of α-Diazodifluoroethyl Sulfonium Salt with Hydrazones

Here we report a photoinduced [3 + 2] radical cyclization reaction of α-diazodifluoroethane sulfonium reagent with hydrazones to give the corresponding N-amino-4-difluoromethyl-1,2,3-triazoles. This transformation proceeds under simple blue light irradiation conditions without the need of photocatalyst. Preliminary mechanistic studies indicate that the formation of an electron donor–acceptor (EDA) complex between electron-deficient α-diazo sulfonium triflate and electron-rich hydrazone operates as the key mediator.