Photochemical Dehalogenation of Aryl Halides: Importance of Halogen Bonding.

Upon UVA irradiation, aryl halides can undergo dehalogenation in the presence of bases and methanol as a hydrogen donor. This catalyst-free photochemical dehalogenation is furnished through a facile radical chain reaction under mild conditions. The chain reaction follows UVA irradiation of the reaction mixture in a transition-metal-free environment. Mechanistic studies support a chain mechanism in which initiation involves absorption by a methoxide-bromoarene complex facilitated by halogen-bonding interactions. The methoxide-bromine interaction leads to a weakened Br-C bond that is prone to facile cleavage during the initiation and propagation steps.