Highly enantioselective syntheses of chiral β-amino alcohols in the presence of chiral TiIV Schiff base complexes as catalysts

Two new chiral Schiff bases 1 and 2 were prepared by condensation of 3,3'-di-tert-butyl-5,5'-methylenebis(salicylaldehyde) and 3,3'-dimethyl-5,5'-methylenebis(salicylaldehyde) with (1R,2S)-(-)-2-aminodiphenylethanoI and were characterized by elemental analysis, H-1 NMR, C-13 NMR, IR, UV/Vis, and CD spectroscopy, optical rotation, and mass spectrometry. Highly enantios elective ring opening reactions of meso-stilbene oxide, cyclohexene oxide, cyclooctene oxide, and cis-butene oxide with anilines in the presence of several additives were carried out in the presence of Ti-IV complexes generated in situ through the interaction of Ti(OiPr)(4) with chiral Schiff bases 1 and 2 at 0 degrees C. Excellent yields (>99 %) of chiral beta-amino alcohols with high enantioselectivity lee, >99 %) were achieved in 10 h when chiral imines were used as additives. The catalyst 1-Ti(OiPr)(4) worked better than the catalyst 2-Ti(OiPr)(4) in terms of reactivity and enantioselecitivity for the epoxide ring opening reactions to produce chiral P-amino alcohols in high optical purity. The chiral catalyst used in this study was recoverable and recyclable several times with retention of its performance. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).