Evaluation of the Efficiency of the Chiral Quaternary Ammonium Salt β-Np-NAS-Br in the Organic-Aqueous Phase-Transfer Alkylation of a Protected Glycine Derivative

Abstract

The inherent efficiency of the N-spiro C2-symmetric chiral quaternary ammonium salt (S,S)-3 [(S,S)-β-Np-NAS-Br] has been evaluated in the representative organic-aqueous liquid-liquid phase-transfer benzylation and allylation of glycine tert-butyl ester benzophenone Schiff base (1). This revealed the practical conditions for the asymmetric synthesis of both natural and, unnatural α-amino acids, whose usefulness was demonstrated by the formal enantio-selective synthesis of antibiotic L-azatyrosine.