Organophotocatalytic Site‐Selective Radical Deuteration at Sterically Hindered Benzylic Positions by Consecutive Hydrogen Atom Transfer

Abstract Site‐selective C−H bond activation or exchange labeling with hydrogen isotope are of vital importance, in particular for high‐specific‐selectivity deuteration of pharmaceuticals. While catalytic approaches relying on closed‐shell manifolds have been well documented for efficient delivery of deuterium at sterically less hindered benzylic positions, complementary strategies target sterically bulky benzylic positions remain a long‐standing challenge. We herein disclose a mild, versatile approach to achieve efficient and selective radical deuteration by merging organophotoredox catalysis and bromine radical catalysis. This open‐shell strategy provides the unparalleled ability of the convergent unification of readily available quinoxalinones and para ‐quinone methides ( p ‐QMs) and D 2 O through a simultaneous highly cross‐, regio‐, and chem‐selective radical coupling‐H/D exchange approach. Furthermore, the long‐standing challenge of the incorporation of deuterium to sterically bulky benzylic positions has been addressed through this approach.