Catalyst-free C–H methylation of heteroarenes enabled by electron donor–acceptor complex photoactivation†

An efficient, additive- and catalyst-free, visible-light-driven radical C–H methylation of heteroarenes (including quinoxalinones, pyrazinones, quinolinones and coumarins) utilizing readily available methylamines as the methyl source has been developed. The transformation possesses the advantages of operational simplicity, mild reaction conditions and broad substrate scope. Mechanistic studies disclosed that a photoactive electron donor–acceptor (EDA) complex between methylamines and heteroarenes is crucial to this transformation.