Influence of aromatic substituents, on metal(II)salen catalysed, asymmetric synthesis of α-methyl α-amino acids

被引：45
作者：
Achard, T
Belokon, YN
Fuentes, JA
North, M [1 ]
Parsons, T
机构：
[1] Kings Coll London, Dept Chem, London WC2R 2LS, England
[2] Russian Acad Sci, AN Nesmeyanov Organoelement Cpds Inst, Moscow 117813, Russia
来源：
TETRAHEDRON | 2004年 / 60卷 / 28期
基金：
英国工程与自然科学研究理事会;
关键词：
catalyst; phase-transfer; asymmetric; copper; amino-acid;
D O I：
10.1016/j.tet.2004.05.023
中图分类号：
O62 [有机化学];
学科分类号：
070303 ; 081704 ;
摘要：
The influence of substituents on both the aromatic rings of the catalyst, and the benzylidene unit of the substrate are investigated in the (salen)copper(II) catalysed asymmetric benzylation of alanine derivatives. Catalysts with electron-donating, and electron-withdrawing substituents of various sizes and at various locations on the aromatic rings of the salen ligand were prepared, but all exhibited inferior enantioselectivity to the parent (salen)copper(II) complex. In contrast, the introduction of halogenated substituents onto the aromatic ring of the N-benzylidene alanine methyl ester substrate was found to enhance the enantioselectivity of the alkylation with a para-chloro substituent giving optimal results. A new procedure for the preparation of the catalysts which avoids the need for chromatography on sephadex LH20 is reported, and the optimal catalyst obtained in this way was found to be a cobalt(salen) complex. (C) 2004 Elsevier Ltd. All rights reserved.
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收藏
页码：5919 / 5930
页数：12
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