Issue 2, 1988

General method for the asymmetric synthesis of α-amino acids via alkylation of the chiral nickel(II) Schiff base complexes of glycine and alanine

Abstract

Nickel(II) complexes of Schiff bases derived from (S)-o-[(N-benzylprolyl)amino] benzaldehyde and alanine (3), or (S)-O-[(N-benzylpropyl)amino]benzophenone and alanine (4), or glycine (5) have been used for the asymmetric synthesis of α-amino acids under a variety of conditions. The method of choice consists of the reaction of the corresponding complex with the appropriate alkyl halide in DMF at 25 °C using solid NaOH as a catalyst. Low diastereoselective excess (d.e.) is observed for the alkylation of complex (3) with benzyl bromide and allyl bromide. Large selectivity (80%) is observed for the alkylation of complex (4). Optically pure (R)- and (S)-α-methyl-α-amino acids [(S)-α-methylphenylalanine, (S)-α-allylalanine and (S)-O-benzyl-α-methyltyrosine] were obtained (70–90%) after the alkylated diastereoisomeric complexes had been separated on SiO2 and hydrolysed with aqueous HCl. The initial chiral reagents were recovered (80–92%). The alkylation of complex (5) gave (S)-alanine, (S)-valine, (S)-phenylalanine, (S)-tryptophan, (S)-isoleucine, (S)-2-aminohexanoic acid, and 3,4dimethoxyphenylalanine with optical yields of 70–92%. The optically pure α-amino acids were obtained after the separation of the alkylated diastereoisomeric complexes on SiO2. The stereochemical mechanism of the alkylation reaction is discussed.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 1, 1988, 305-312

General method for the asymmetric synthesis of α-amino acids via alkylation of the chiral nickel(II) Schiff base complexes of glycine and alanine

Yuri. N. Belokon, V. I. Bakhmutov, N. I. Chernoglazova, K. A. Kochetkov, S. V. Vitt, N. S. Garbalinskaya and V. M. Belikov, J. Chem. Soc., Perkin Trans. 1, 1988, 305 DOI: 10.1039/P19880000305

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