Bioinspired transfer methylation enabled by a photoactive reagent

Radical methylation ranks among the most important yet challenging transformations in chemistry and biology, which often involves small and unstable radical intermediates, such as the methyl radical, and results in low reactivity and poor selectivity. Herein, we report a photoactive, biomimetic reagent to address some facets of these challenges by leveraging a bulky and stabilised α-aminomethyl radical, which can offer enhanced control over radical generation and transfer. Our bioinspired transfer methylation protocol enables direct and selective C(sp²)-H methylation across a wide spectrum of heteroarenes, from simple scaffolds to complex drug molecules, including the thus far elusive C4-methylation of free quinolines. Mechanistic studies reveal that the unique α-aminomethyl radical intermediate undergoes an addition-elimination sequence reminiscent of natural methyltransferases and yields balanced reactivity and selectivity.