Metal-Free Photocatalysts for C-H Bond Oxygenation Reactions with Oxygen as the Oxidant.

Direct and selective oxygenation of C-H bonds to C-O bonds is regarded as an effective tool to generate high-value products. However, these reactions are still subject to challenges such as harsh reaction conditions, use of expensive transition metal catalysts, and involvement of stoichiometric oxidants. To avoid these, molecular oxygen would be ideal as oxidant, as the byproduct is water or hydrogen peroxide. Additionally, achieving these reactions by using metal-free catalysts would contribute to green and sustainable chemical synthesis. This Minireview summarizes recent reports on C-H oxygenation reactions with metal-free catalysts and molecular oxygen under visible-light conditions.