Visible‐Light‐Mediated Activation of Remote C(sp3)‐H Bonds by Carbon‐Centered Biradical via Intramolecular 1,5‐ or 1,6‐Hydrogen Atom Transfer

In this study, we introduce a novel intramolecular hydrogen atom transfer (HAT) reaction that efficiently yields azetidine, oxetane, and indoline derivatives through a mechanism resembling the carbon analogue of the Norrish–Yang reaction. This process is facilitated by excited triplet‐state carbon‐centered biradicals, enabling the 1,5‐HAT reaction by suppressing the critical 1,4‐biradical intermediates from undergoing the Norrish Type II cleavage reaction, and pioneering unprecedented 1,6‐HAT reactions initiated by excited triplet‐state alkenes. We demonstrate the synthetic utility and compatibility of this method across various functional groups, validated through scope evaluation, large‐scale synthesis, and derivatization. Our findings are supported by control experiments, deuterium labeling, kinetic studies, cyclic voltammetry, Stern–Volmer experiments, and density functional theory (DFT) calculations.