Pergamon Tetrahedron: Asymmetry 9 (1998) 2035–2042 TETRAHEDRON: ASYMMETRY Chiral enrichment of 2-amino-2 0 -hydroxy-1,1 0 -binaphthyl Hussein Mahmoud, Ying Han, Brent M. Segal and Lisheng Cai * Department of Chemistry, The University of Illinois at Chicago, Chicago, Illinois 60607, USA Received 19 March 1998; accepted 7 May 1998 Abstract A new synthetic procedure for the formation of 2-amino-2 0 -hydroxy-1,1 0 -binaphthyl, and a new purification procedure through the formation of Schiff bases, purification of the Schiff bases, and breakdown of the Schiff bases through amine exchange, are described. Through the new purification procedure, greater than 99% purity of the compound can be obtained easily and reliably. A set of procedures were examined to compare the efficiency and reliability to resolve 2-amino-2 0 -hydroxy-1,1 0 -binaphthyl into enantiomers. A new procedure was discovered to enrich enantiomeric excess from less than 10% to 95–99% in one step. Even a racemic mixture from an achiral procedure can be enriched to 67% e.e. in about 4% yield. The X-ray crystal structure of the racemic mixture [rhombohedral, space group Iba2, a=15.718(2) Å, b=21.703(2) Å, c=8.5398(9) Å, V =2913.2(5) Å 3 , R1=0.0705, Z=8, d calcd =1.301 g/cm 3 , F(000)=1200 e] was solved to elucidate the intriguing behavior of this compound. © 1998 Elsevier Science Ltd. All rights reserved. 1. Introduction Compared with the asymmetric ligands based on BINAP and 1,1 0 -bi-2-naphthol, 1 asymmetric ligands based on 2,2 0 -diamine-1,1 0 -binaphthyl, 2-amino-2 0 -hydroxy-1,1 0 -binaphthyl, and 2-amino-2 0 -thiol-1,1 0 - binaphthyl, are scarce, 2 but promising results have been obtained in the catalysis of Mukaiyama reactions. 2c One of the problems is the availability of the chiral starting material. There are several methods available for the synthesis or resolution of the chiral 2-amino-2 0 -hydroxy-1,1 0 -binaphthyl compound. Cross coupling of 2-naphthol and 2-naphthylamine under controlled conditions, using a combination of CuCl 2 and chiral benzylamine in methanol, generates a precipitate and solution of 46% e.e., but opposite in sign for their chirality, at 1 mmol scale. 3 After repeated recrystallization in benzene, approximately 20% of both optically pure isomers have been isolated. Since the racemic mixture of 2-amino-2 0 -hydroxy-1,1 0 -binaphthyl is available in high yield, 4 resolution into enantiomers via crystallization of diastereoisomeric salts with (1S)-(+)-10-camphorsulfonic acid has been developed. 5 In our hands, the former methods give greatly reduced e.e. on a large scale, and variable results on a * Corresponding author. E-mail: cai@uic.edu 0957-4166/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved. PII: S0957-4166(98)00203-1 tetasy 2352 Article