Application of well-defined chain-end-functionalized polystyrenes with dendritic chiral ephedrine moieties as reagents for highly catalytic enantioselective addition of dialkylzincs to aldehydes
作者:Ashraf A. El-Shehawy、Kenji Sugiyama、Akira Hirao
DOI:10.1016/j.tetasy.2007.12.020
日期:2008.3
having a definite number of chiral ephedrine moieties dendritically distributed at the periphery of their hyperbranched chain-ends were evaluated as chiral catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes. These dendritic macromolecules worked well as homogeneous chiral catalysts and exhibited high catalytic activity and enantioselectivity very similar to those observed
评价了一系列定义明确的链端官能化聚苯乙烯,它们在其高支链末端的周围呈树突状分布有一定数目的手性麻黄碱部分,作为手性催化剂,用于将二烷基锌试剂对映体选择性地加成到醛中。这些树枝状大分子作为均相手性催化剂表现良好,并且表现出与相应的单体手性催化剂所观察到的非常相似的高催化活性和对映选择性。发现手性催化剂的最佳量为5mol%。观察到手性麻黄碱部分具有深远的影响,PS(Ephed)8发现在外围具有八个手性麻黄碱部分的分子优于其他树枝状手性催化剂。在将二异丙基锌添加到3-苯基丙醛中时,对映选择性达到95%的值。通过使用溶剂沉淀法可以容易地从反应溶液中回收树枝状手性催化剂,并且回收的催化剂没有显示出其催化活性或对映选择性的显着损失。