Highly Enantioselective Syntheses of Chiral β‐Amino Alcohols in the Presence of Chiral TiIV Schiff Base Complexes as Catalysts

Abstract

AbstractTwo 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‐aminodiphenylethanol and were characterized by elemental analysis, 1H NMR, 13C NMR, IR, UV/Vis, and CD spectroscopy, optical rotation, and mass spectrometry. Highly enantioselective 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 TiIV complexes generated in situ through the interaction of Ti(OiPr)4 with chiral Schiff bases 1 and 2 at 0 °C. Excellent yields (>99 %) of chiral β‐amino alcohols with high enantioselectivity (ee, >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 β‐amino alcohols in high optical purity. The chiral catalyst used in this study was recoverable and recyclable several times with retention of its performance. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)