Visible-Light-Enabled Enantioconvergent Synthesis of α-Amino Acid Derivatives via Synergistic Brønsted Acid/Photoredox Catalysis

Abstract

An unprecedented radical cross-coupling reaction was achieved between glycine esters and racemic α-bromoketones catalyzed by synergistic Brønsted acid/photoredox catalysis, thus serving as an efficient platform for the synthesis of highly valuable enantioenriched unnatural α-amino acid derivatives. This dual catalysis provides a powerful capability to control the reactive radical intermediate and iminium ion, thereby enabling enantioconvergent bond-formation in a highly stereochemical manner. An array of valuable enantioenriched unnatural α-amino acid derivatives bearing two contiguous stereogenic centers are readily accessible with high diastereoselectivity and excellent enantioselectivity, which include α-amino acids with a unique β-fluorinated quaternary stereocenter or its β-all-carbon counterpart. A strong chiral amplification effect was observed in this dual catalytic system.

Keywords: Brønsted acid catalysis; photoredox catalysis; radical addition; synergistic catalysis; unnatural α-amino acids.