Redox-Neutral Thioether C–H Activation Enables Stereoselective Noncanonical Amino Acid Synthesis

The controlled generation of α-thioalkyl radicals has remained underdeveloped despite their potential in constructing C–C bonds under mild conditions, particularly in the context of asymmetric synthesis. Herein, we report a stereoselective light-driven approach that enables the one-electron oxidation and α-deprotonation of diverse thioethers, thereby accessing α-thioalkyl radicals. These fragments undergo efficient addition to a chiral N-sulfinyl imine, yielding noncanonical α-amino acid derivatives bearing sulfur substituents. The transformation exhibits broad substrate scope, including aryl, alkyl, and cyclic thioethers, and proceeds with high yields and stereoselectivity. A modular strategy enables the late-stage installation of the thioether unit onto bioactive scaffolds, demonstrating the potential of the developed technology for the functionalization of complex molecules. This work expands the synthetic utility of α-thioalkyl radicals in amino acid and peptide chemistry.