We started our investigations with copper photo-catalytic conditions and PIDA for methylation reactions. Initially, using 2-chlorobenzimidazole (1) as substrate, a quick optimization gave reproducible results and high yields using readily available reagents and benign reaction conditions (see Scheme S1-5). N-Methyl-2-chlorobenzimidazole (2) was obtained in close to quantitative yield (Table , Entry 1). Control reactions revealed that the reaction conditions require inert atmosphere, as oxygen from air hampers the conversion ( With the optimized conditions in hand, we investigated the applicability of the reaction and found various N-heterocycles to be amenable under our reaction conditions. N-Heterocycles like benzimidazole, tetrazole, pyrazole, indazole, benzotriazole, and purine performed smoothly under the optimized conditions (Scheme 1). Many functional groups within the products 2 to 10, like alkyl, aryl, halide, and even nitro, are tolerated respectively. Most substrates gave competitive isolated yields between 36% and 71% compared to classical methylation with toxic methyl iodide or dimethylsulfate (see experimental section in the SI). In some cases, better regioselectivity was achieved. In our hands, electron-poor heterocycles gave higher yields and several additional substrates gave only low yields as confirmed by 1 H NMR analysis (Scheme S13). Concerning the copper source, copper(II)acetylacetonate (Cu(acac)2) and the tert-butyl analogue (tmbd) gave similar conversions (Scheme S5).