Efficient metal-free photochemical borylation of aryl halides under batch and continuous-flow conditions

A rapid, chemoselective and metal-free C–B bond-forming reaction of aryl iodides and bromides in aqueous solution at low temperatures was discovered. This reaction is amenable to batch and continuous-flow conditions and shows exceptional functional group tolerance and broad substrate scope regarding both the aryl halide and the borylating reagent. Initial mechanistic experiments indicated a photolytically generated aryl radical as the key intermediate.