A photo-Fenton-like (trideutero)methylation reaction of N/O heterocycles with DMSO(-d6) induced by EDA complex photocatalysis†

DMSO is a prominent and indispensable methylating agent within the realm of organic synthesis. We report an innovative strategy employing an in situ generated EDA (electron-donor–acceptor) complex as an active photocatalyst to achieve N/O heterocycle (deutero)methylation based on DMSO(-d₆). Mechanistic investigations reveal that the reaction proceeds through the synergistic action of the EDA active catalyst, water, and oxygen, inducing the formation of hydroxyl radicals in a Fenton-like process. Compared to traditional Fenton-based methylation reactions utilizing DMSO, this approach circumvents the necessity for metal catalysts and strong oxidants, thereby exhibiting significant enhancements in environmental friendliness, safety, and economy. Furthermore, a variety of N/O heterocycles, including azauracils, quinoxalinones, and coumarins, are compatible with the reaction system, which was previously unattainable in conventional Fenton methylation reactions.