New optically active bis-quaternary ammonium salts were synthesized and applied to catalytic asymmtric alkylation of tert-butyl glycinate benzophenone Schiff base to provide a chiral α-amino acid derivative with 54% ee. | Journal of Chemistry, Vol. 47 (5), P. 563 - 565, 2009 Development of novel optically active Two-canter phase-transfer catalysts for enantioselective synthesis of α-amino acid Received 26 August 2008 Kazutaka Shibatomi, Fumito Kobayashi, Yuya Tsuzuki, Seiji Iwasa Department of Materials Science, Toyohashi University of Technology, Toyohashi Japan Abstract New optically active bis-quaternary ammonium salts were synthesized and applied to catalytic asymmtric alkylation of tert-butyl glycinate benzophenone Schiff base to provide a chiral α-amino acid derivative with 54% ee. Stereoselective synthesis of both nature and non-natural α-amino acids is an important subject in the field of synthetic and bioorganic chemistry. Asymmetric alkylation of glycine ester benzophenone Schiff base using chiral phase-transfer catalyst is a powerful method for this purpose (figure 1) [1]. Recently, Maruoka developed a series of chiral spiro ammonium salts 1 as efficient phase-transfer catalysts for this asymmetric alkylation (figure 2) [2]. However, a large number of reaction steps were required for the synthesis of catalysts 1. In this paper, we desribe the design and concise synthesis of novel optically active bisquaternary ammonium salts 2 (figure 2) and their application to catalytic asymmetric alkylation to provide α-amino acid derivatives. Figure 1: Approach to the synthesis of chiral α-amono acids Synthesis of (S,S,S)-2 was started from commercially available (S)-BINOL as shown in scheme 1 [3 - 7]. (S)-BINOL was converted to (S)-2,2’-bis(bromomethyl)-1,1’-binaphthyl[(S)3] according to known procedure [8]. Azidation of (S)-3 with sodium azide and following Pbcatalyzed hydrogenation provided (S)-2,2’bis(aminomethyl)-1,1’-binaphthyl [(S)-5] with quantitative yield. The reaction of (S)-5 with 2 equivalent of (S)-3 gave (S,S,S)-6 with 64% yield, and then treatment of (S,S,S)-6 with benzyl bromide afforded desired bisquanternary ammonium salts (S,S,S)-2 with 83% yield. (S,S,S)-2 .
