Acyloxy, sulfate, and phosphate radicals as hydrogen atom transfer (HAT) agents for direct C(sp3)–H functionalization

Selective activation of inert and ubiquitous C(sp³)–H bonds has long been a challenging task in organic synthesis, through which chemists can directly synthesize value-added compounds from inexpensive and readily available alkane feedstocks. By means of modern photochemistry, electrochemistry, as well as traditional thermochemistry, diverse hydrogen atom transfer (HAT) protocols have been established, employing various radicals, especially oxygen-centered ones, as the HAT agents. This review focuses on three unique classes of oxygen radicals, namely acyloxy, sulfate, and phosphate radicals, which have demonstrated significant potential for achieving direct intermolecular C(sp³)–H bond functionalization via HAT pathways. By focusing on the key developments from 2014 to 2024, this review discusses the generation mechanisms, reactivity characteristics and applications of these acid-related oxygen radicals, aiming to provide researchers with insights to further advance the techniques and innovations in the future C(sp³)–H functionalization strategy development.