Synthesis of Chiral β-Branched α-Amino Acids from Glycine

Significance

The asymmetric Eschenmoser-Claisen rearrangement has been used originally by Welch to synthesize chiral β-branched amino acid derivatives of 5, but the diastereomeric ratio was modest (Tetrahedron Lett. 1991, 32, 4267). Hruby and co-workers have shown that a C ₂-symmetric chiral auxiliary provides an improved diastereoselectivity to the rearrangement. The cleavage of the chiral auxiliary is done via high-yielding, simple procedures, and was demonstrated for most of the examples.