Simple and Clean Photo-induced Methylation of Heteroarenes with MeOH

Heteroarene methylation utilizing a cheap and safe methylation source without involving transition metals represents an important yet challenging objective. Here, a simple and clean catalyst-free protocol for the methylation of various heteroarenes (including six-and five-membered types) is described under light irradiation. This protocol employs cheap, readily available, and abundant MeOH as both the solvent and the methylation source. It was found that adding dichloromethane (DCM) as a co-solvent could significantly increase the yield of the methylation products. Heteroarenes bearing various functional groups could be methylated and tri-deuteromethylated successfully. Deuterium labeling studies suggested that the newly generated methyl group in the products consisted of two hydrogens from the methyl group and one hydrogen from the OH group in MeOH.