A practical and versatile access to dihydrosalen (Salalen) ligands:: Highly enantioselective titanium in situ catalysts for asymmetric epoxidation with aqueous hydrogen peroxide
A practical and versatile access to dihydrosalen (Salalen) ligands:: Highly enantioselective titanium in situ catalysts for asymmetric epoxidation with aqueous hydrogen peroxide
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DOI：
10.1002/adsc.200700221
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发表时间：
2007-10-01
影响因子：
5.4
通讯作者：
Schaefer, Mathias
中科院分区：
文献类型：
--
作者：
Berkessel, Albrecht;Brandenburg, Marc;Schaefer, Mathias
手性和非对称salalen配体（即，单还原的Salens），带有亚胺和胺官能团。配体可以通过N-（2-羟基苄基）二胺与水杨醛的席夫碱形成原位组装，从而允许配体结构的快速和容易的变化/优化。针对钛催化非官能化烯烃不对称环氧化反应中的最佳活性和对映选择性，对两个半配体进行了位置扫描。实现了高的环氧化物产率，高达98%ee。对于一个选定的实施例，通过高分辨率质谱和X射线晶体学确定了钛络合物催化剂的组成。
A modular synthesis for chiral and non-symmetrical salalen ligands (i.e., mono-reduced salens), carrying an imine and an amine functionality has been developed. The ligands can be assembled in situ by Schiff base formation of an N-(2-hydroxybenzyl)diamine with a salicylic aldehyde, thus allowing rapid and easy variation/optimization of the ligand structure. Aiming at optimal activity and enantioselectivity in the titanium-catalyzed asymmetric epoxidation of non-functionalized olefins, a positional scanning of the two ligand halves was carried out. High epoxide yields were achieved, and up to 98 % ee. The composition of the titanium complex catalysts was determined by high resolution mass spectrometry and X-ray crystallography for one selected example.