Asymmetric Catalyzed Ring Opening Of Epoxides To Synthesize β-amino Alcohols

Chiralβ-amino alcohols are important structures in many natural products. They havebeen widely applied in the synthesis of chiral pharmaceutical as active intermediatecompounds, as well as in asymmetric catalyzed reactions as chiral catalysts or ligands.In this paper, two series of novel catalysts were synthesized with the (S)-binaphtholatesand (S)-salen as ligands, which were used in the enantioselective ring opening reactions ofepoxides by aromatic amines. The effect of ions cores including iron, aluminium and boronon conversions and enantioselectivities was studied. The optimal result was obtained whenthe core atom was Fe and the rate of (S)-binaphtholate and iron(Ⅲ) chloride was 2: 1. It wasfound that the properties of catalysts have tightly relationship with the alkali metals. The(S)-BINOL-Fe-Li complex was the best catalyst for ring opening of cyclopentene oxide withaniline, and the (S)-BINOL-Fe-Na complex was the best catalyst for ring opening ofcyclohexene oxide with aniline. However, the (S)-BINOL-Fe-K complex brought the lowestyield and enantioselectivity. When these reactions were carried out in different solvent, it wasshown that owing to the addition of the solvent polarity the enantioselectivity of the productswas increased obviously, but the conversion was decreased. The effect of temperature on theyield and the enantioselectivity was shown that the lower temperature resulted in the betterenantioselectivity in stead of the higher yield. The enantioselectivity and the conversioncould be increased simultaneously via increasing the content of catalyst. The effect of thenucleophilic reagents with different substituents was also investigated. Compared with aniline,N-methylbenzenamine brought the same enantioselectivity and the higher conversion.The conclusion could be drawn that the optimal condition was (S)-BINOL-Fe-Na(0.1equiv) as catalyst which was prepared by Fe: (S)-BINOL: Na=1: 2(equiv): 4(equiv),Chloroform (3 V) as solvent, at 0℃for 27 h. The product of aniline could afford 64%yield and 63% enantiomeric excess values, and the product of N-methylbenzenamine couldafford 80% yield and 63% enantiomeric exess values.