Metal‐Free Photochemical Radical Cyclization for the Synthesis of Pyrrolo[3,2‐c]‐quinolines with One‐Carbon Unit

An efficient and environmentally-friendly method for carbon-centered radical cyclization of olefins via visible light photoredox catalysis to afford pyrrolo[3,2-c]-quinolines, oxindoles and quinoline-2,4-diones is described. This novel reaction successfully activated the α C-H bonds in one-carbon units such as esters, chlorinated hydrocarbons and cyano compounds via HAT (hydrogen atom transfer) process by means of aryldiazonium salts. The transformation features good functional group tolerance, broad substrate scope, high atom economy, no need for transition metal or high temperature.