Stereoselective Synthesis of Unnatural α-Amino Acids through Photoredox Catalysis

A protocol for stereoselective C-radical addition to a chiral glyoxylate-derived sulfinyl imine was developed through visible light-promoted photoredox catalysis, providing a convenient method for the synthesis of unnatural α-amino acids. The developed protocol allows the use of ubiquitous carboxylic acids as radical precursors without prior derivatization. The protocol utilizes near-stoichiometric amounts of the imine and the acid radical precursor in combination with a catalytic amount of an organic acridinium-based photocatalyst. The mechanism for the developed transformation is discussed and the stereodetermining radical addition step was studied by the DFT calculations.