Organocatalysis with cysteine derivatives: recoverable and cheap chiral catalyst for direct aldol reactions
作者:Shi Li、Xiangkai Fu、Chuanlong Wu
DOI:10.1007/s11164-011-0336-5
日期:2012.1
Highly enantioselective, recoverable and cheap cysteine derivatives have been developed with improved solubility properties in common, nonpolar organic solvents. The reactions were catalyzed using 5 mol% 1e, and the aldol products could be obtained with up to 99:1 syn/anti ratio and >99% ee. The catalyst could be easily recovered and reused, with only a slight decrease of enantioselectivity observed for five cycles. Catalyst 1e can be efficiently used in large-scale reactions with enantioselectivity being maintained at the same level, which offers great possibility for application in industry. (i) Direct aldol reactions proceeded in 1,2-dichloroethane using simple procedures. (ii) Direct S-acylation of cysteine to give organocatalysts 1a–f can be economically carried out easily in a single step from commercially available sources, with both enantiomers being readily available. (iii) 5 mol% catalyst 1e was sufficient to furnish the aldol products in excellent yields (up to 93%) and enantioselectivities (up to 99%). (iv) Catalyst 1e could be easily recovered and reused, and also can be efficiently used in large-scale reactions with enantioselectivity being maintained at the same level, which offers great possibility for applications in industry.
开发了一种高度对映选择性、可回收且廉价的半胱氨酸衍生物,其在常见的非极性有机溶剂中具有改善的溶解性特性。反应使用5 mol%催化剂1e进行催化,醛醇产物的syn/anti比率可高达99:1,对映体过量(ee)超过99%。催化剂可以轻松回收并重复使用,经过五个循环后仅观察到轻微的对映选择性降低。催化剂1e可以在大规模反应中有效使用,并维持相同水平的对映选择性,这为其在工业中的应用提供了很大可能性。(i) 直接醛醇反应在1,2-二氯乙烷中通过简单的程序进行。(ii) 半胱氨酸的直接S-酰化以获得有机催化剂1a-f,可以轻松地从商业来源通过一步经济地进行,两种对映体均易于获得。(iii) 5 mol%催化剂1e足以以优异的产率(高达93%)和对映选择性(高达99%)提供醛醇产物。(iv) 催化剂1e可以轻松回收和重复使用,并且可以在大规模反应中有效使用,保持相同水平的对映选择性,这为其在工业中的应用提供了极大的可能性。