Radical Filtration Enabled Selective C(sp3)-H Sulfinylation

The selective functionalization of inert C(sp3)-H bonds remains a central challenge in organic synthesis. Although hydrogen atom transfer (HAT) has become a powerful strategy, achieving precise control over site selectivity typically requires steric engineering or directing groups. Herein, we disclose a reversible C(sp3)-H sulfinylation system enabling highly site-selectivity governed by the thermodynamic stability of regioisomers through synergistic iron/organic photoredox catalysis. This system preferentially targets primary C(sp3)-H bonds when available, while also distinguishing among secondary C(sp3)-H sites─allowing selective functionalization of distinct positions within cyclic substrates, a level of control previously inaccessible. Mechanistic studies reveal that alkyl radical generation, SO2 capture, and sulfonyl radical reduction are all reversible processes, enabling thermodynamic equilibration to direct reactivity toward the most stable sulfinylated products.