Transition‐Metal‐Free Selective Oxidation of Heterobenzylic C─H Bond in the Presence of Other Oxidizable C─H Bonds

Abstract Direct oxidation of sp 3 C─H bond is an extremely important part of modern‐day research in both academia and industry, because of the ubiquities of C─H bond in organic and biomolecules. However, challenges remain with regard to site‐selectivity and environmental concerns, since mostly transition metals and hazardous oxidants are used. In this work, we disclose two different transition‐metal‐free oxidative approaches for the selective oxidation of heterobenzylic sp 3 C─H bond in the presence of other oxidizable C─H bonds, like benzylic C─H and more reactive C(sp 2 )─H. We initially developed a visible light‐assisted photocatalytic oxidation of the heterobenzylic C─H bond using Eosin Y (EY) as photocatalyst and K 2 S 2 O 8 as nontoxic terminal oxidant affording corresponding heteroaryl ketones. In another approach, the same reaction was performed in the absence of any photocatalyst or light, using TEMPO as the catalyst and K 2 S 2 O 8 as the oxidant. The reactions occur under ambient atmosphere, at very low temperatures, and exhibit high selectivity for the heterobenzylic C─H bond.