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Synthesis of Chiral β-Branched α-Amino Acids from Glycine
H. Qu, X. Gu, Z. Liu, B. J. Min, V. J. Hruby*
University of Arizona, Tucson, USA
22 November 2007 (online)
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.