Photo-driven aerobic C(sp3)-H oxidation by organic photocatalysts: A recent review

Abstract

The direct oxidation and oxygenation of C(sp³)-H bonds has profound significance in synthetic chemistry for straightforwardly installing valuable C-O and CO bonds on bulk chemicals without pre-functionalization step. However, the development of highly efficient and selective catalytic methods under mild reactions remains to be a challenge due to the large bond dissociation energy as well as the competition oxidation among intramolecular C(sp³)-H bonds. Light-induced C(sp³)-H oxidation by organic photocatalysts should be a powerful tool since strong oxidative species could be achieved at the excited states at ambient temperature. In addition, this process will become more environmentally friendly when molecular oxygen, with high atom economy and eco-compatibility, is used as the terminal oxidant. During the past decade, the combination of photo irradiation and molecular oxygen or even air under metal-free condition, as a promising catalytic approach, has received increasing attention and become the method of choice for the activation of C(sp³)-H bonds. This review introduced briefly the pioneering works and listed detailed updates of the methodology development, synthetic applications especially in the late-stage modification of drugs or natural products, and mechanism studies on photo-promoted aerobic C(sp³)-H oxidation/oxygenation by organic catalysts from 2020 to 2024. And this review is divided by the type of organic photocatalysts used in the C-H activation reactions. The production of oxygenated compounds, such as ketone, aldehyde, alcohol, hydroperoxide, and lactone has been accomplished by various of organic photocatalysts alone or the synergistic catalysis with a co-catalyst as the indirect hydrogen atom abstractor. The reaction scope, limitation, challenge, and future opportunities in this field have been discussed as well.