Visible-Light-Promoted Aliphatic C-H Chlorination and Bromination Using Haloform as the Halogen Donor and Azidobenziodoxole as the Mediator

An azidobenziodoxole (BIN3)-mediated tunable radical reaction system for selective chlorination and bromination of tertiary and secondary C(sp(3)) H bonds of alkyl substrates using haloform as the halogen donor was developed. Reactions of various substrates with BIN3 under visible light irradiation without any photo or metal catalysts gave C-H chlorinated or brominated products. These reactions are selective, and compatible with many functional groups. Mechanistic studies suggest that haloform serves as the halogen atom donor and HN3 generated in situ from the reaction of BIN3 and water relays the radical chain reaction as the hydrogen atom donor. HN3 reacts with CHX2 center dot to form CH2X2 and N-3(center dot), which propagates a radical chain by abstracting a hydrogen atom of the alkane substrate.