Where Enantioselection is Set: A Mechanistic Framework for Asymmetric Hydrogen‐Atom Transfer

Abstract

Abstract Hydrogen‐atom transfer (HAT) lies at the heart of radical chemistry, yet asymmetric HAT has been difficult because the high reactivity of radicals often forces H‐transfer to proceed through early, weakly organized transition states, yielding small ΔΔG ‡ and allowing rapid racemic background pathways to compete. Recent advances across small‐molecule, metalloradical, cooperative, peptide, and enzymatic catalysis show that high enantioselectivity is attainable when the catalyst is engineered to exert stereocontrol precisely at the H‐transfer step that sets configuration. In this minireview, we organize asymmetric HAT into five regimes—donation‐controlled termination, radical‐centered control, abstraction‐controlled HAT, cooperative bimetallic catalysis, and enzyme‐mediated HAT—each specified by where chiral information is introduced during H‐transfer. Through representative cases, we illustrate how catalysts achieve enantioselection by defining radical geometry, guiding H‐delivery, enforcing selective hydrogen abstraction, or confining donor–acceptor pairs within organized chiral environments. This mechanistic framework provides a unified lens spanning synthetic and biocatalytic systems, clarifies the distinct stereochemical logics in each regime, and highlights emerging opportunities for expanding asymmetric radical chemistry through precisely orchestrated H‐atom transfer.