Asymmetric synthesis of amino acids using NOBIN as a phase-transfer catalyst
Typical procedure (asymmetric alkylation of (2) under phase-transfer catalysis condition): Finely ground NaOH (2 g), glycine equivalent (2) (2.1 g) and (R)-NOBIN (0.14 g) in anhydrous CH2Cl2 (30 mL) are stirred under Ar at 15-20 ºC for 3 min. Then BnBr (1 g) is added, and the mixture is stirred for 8 min. The reaction mixture is quenched by the addition of aq. AcOH (10 mL) and diluted with CH2Cl2 (30 mL). The organic layer is separated and concentrated. The residue is purified by flash chromatography on silica gel (eluent: CHCl3/acetone) to give (3) (2.3 g, 90%, 97 % ee). The crude complex (3) is crystallized from C6H6/acetone to give the enantiomerically pure product (3) (1.9 g, 74 %).
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Y. N. Belokon, K. A. Kochetkov, T. D. Churkina, N. S. Ikonnikov, O. V. Larionov, S. R. Harutyunyan, Š. Vyskočil, M. North, H. B. Kagan, Angew. Chem. Int. Ed. 2001, 40, 1948.
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