C-H activation under visible light using DDQ organo-photocatalyst: Practical, tunable and additive free

Here we present a practical, mild, selective, eco-friendly, metal-free, cost-effective, and tunable method for the photoactivation of C-H compounds using an organo photocatalyst without any additives. For this purpose, the organo photocatalyst DDQ was employed as a versatile and highly efficient catalyst for C-H bond functionalization under visible light irradiation in a straightforward reaction setup, free from additives and co-catalysts. Notably, under appropriate solvent conditions, the photooxidation of alkylarenes produced ketones, aldehydes, and carboxylic acids from corresponding starting materials. In CH3CN solvent, carboxylic acids were obtained. Interestingly over oxidation to carboxylic acid is avoided and aldehydes were produced from methyl arenes via acetal formation in CH3CN:MeOH. Furthermore, our results demonstrated that the photooxidation of 4-methoxytoluene was more efficient than that of 4-methoxybenzylalcohol. The proposed mechanism for this reaction involved the formation of a charge transfer complex between the starting material and DDQ, as indicated by UV-Vis and fluorescence spectra. Also, this method exhibited promising scalability, with 30 mmol of 4methoxytoluene being converted to 4-methoxybenzoic acid with a yield of 92 % (TON: 345).