Disulfide-Bridged Peptides That Mediate Enantioselective Cycloadditions through Thiyl Radical Catalysis

An enantioselective vinylcyclopropane ring-opening/cycloaddition cascade is described. The active thiyl radical catalysts are generated in situ via UV light-promoted homolysis of cystine-based dimers. Amide-functionalization of the peptide at the 4-proline position is essential for effective asymmetric induction. Stereochemical communication is dependent on steric interactions with this substituent that are enforced by H-bonding to the peptide backbone.