Aqueous asymmetric Mukaiyama aldol reaction catalyzed by chiral gallium Lewis acid with trost-type semi-crown ligands
Aqueous asymmetric Mukaiyama aldol reaction catalyzed by chiral gallium Lewis acid with trost-type semi-crown ligands
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DOI：
10.1002/adsc.200505089
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发表时间：
2005-07-01
影响因子：
5.4
通讯作者：
Li, CJ
中科院分区：
文献类型：
--
作者：
Li, HJ;Tian, HY;Li, CJ
Ga（OTf）（3）与手性半冠配体（la-e）的组合产生用于芳族甲硅烷基烯醇醚与醛的水性不对称羟醛缩合反应的高效手性镓刘易斯酸催化剂。观察到配体加速效应。水对于获得高的非对映选择性和对映选择性是必不可少的。芳族烯醇醚（2 h）中的对苯基取代基起着重要的作用，使对映选择性提高到95%ee。虽然脂肪族烯醇醚的对映选择性较低，并且硅基烯酮缩醛在醇水溶液中容易水解，甲硅烷基烯酮硫代缩醛（12）与醛在镓-路易斯酸催化剂存在下的羟醛缩合反应得到β-羟基硫酯，具有合理的产率和高的非对映-（高达99：1）和对映选择性（高达96%ee）。
The combination of Ga(OTf)(3) with chiral semi-crown ligands (la-e) generates highly effective chiral gallium Lewis acid catalysts for aqueous asymmetric aldol reactions of aromatic silyl enol ethers with aldehydes. A ligand-acceleration effect was observed. Water is essential for obtaining high diastereo-selectivity and enantioselectivity. The p-phenyl substituent in aromatic silyl enol ether (2 h) plays an important role and increases the enantioselectivity up to 95% ee. Although aliphatic silyl enol ethers provided low enantioselectivities and silylketene acetal is easily hydrolyzed in aqueous alcohol, the aldol reactions of silylketene thioacetal (12) with aldehydes in the presence of gallium-Lewis acid catalysts give the beta-hydroxy thioester with reasonable yields and high diastereo- (up to 99: 1) and enantioselectivities (up to 96% ee).