Advances in Asymmetric Amino Acid Synthesis Enabled by Radical Chemistry

Chiral amino acids (AAs), being the main "building" blocks of the living organisms, are also an important class of organic compounds which broadly applied in synthetic chemistry, biochemistry, catalysis and the designing of new drugs. According to the industrial-commodity market, chiral non-proteinogenic AAs containing various functional groups come to the fore. To date, radical cross-coupling reactions are becoming an option as an attractive powerful tool for AA syntheses. Owing to mild reaction conditions and high functional-group tolerance, radical chemistry represents an ideal strategy for the synthesis of challenging complex non-proteinogenic AAs. Moreover, the radical cross-coupling allows introducing AA residue into drug scaffolds and natural compounds. In the present review, we wish to summarize and discuss all the reported to date methods of the asymmetric synthesis of AAs using radical chemistry by presenting a comprehensive account of the literature in this field going back to 1990. We especially emphasize on a radical chemistry approach and, exclusively, on stereoselective synthesis of various alpha-, beta-, gamma-AAs and derivatives employing a different type of radical initiators starting from AIBN and organostannes and ending with powerful photoredox catalysis. Furthermore, the mechanism of the reported reactions will be discussed.