Thiols as Key HAT Catalysts in Photoredox Catalysis: Diversifying the Hydrofunctionalization Landscape of Unactivated Alkenes

The hydrofunctionalization of alkenes represents an atom‐ and step‐efficient approach to synthesizing value‐added molecules. While visible‐light photocatalysis offers a sustainable alternative to conventional transition‐metal systems, the functionalization of unactivated alkenes remains a significant challenge. This is primarily attributed to their low inherent reactivity, the instability of radical intermediates, and the limited availability of efficient and selective hydrogen atom transfer (HAT) catalysts. Recently, thiols have emerged as ideal HAT catalysts due to their favorable kinetics and tunable properties. By engaging in synergistic catalysis with various photocatalytic reaction modes, thiols effectively achieve the efficient and highly selective hydrofunctionalization of unactivated alkenes. This review summarizes recent advances in thiophenol‐catalyzed photoredox hydrofunctionalization of unactivated alkenes, with a focus on mechanistic elucidation and opportunities in the field.