Dependence of Enantioselectivity on the Ligand/Metal Ratio in the Asymmetric Michael Addition of Indole to Benzylidene Malonates: Electronic Influence of Substrates
作者:Alexander Schätz、Ramesh Rasappan、Markus Hager、Anja Gissibl、Oliver Reiser
DOI:10.1002/chem.200800508
日期:2008.8.18
Simple bis(oxazoline) ligands, especially azabis(oxazolines), can promote the copper(II)-catalyzed Michael addition of indoles to benzylidene malonates with up to >99 % ee (ee=enantiomeric excess), provided that the ligand/metal ratio is tuned meticulously with particular regard to the electronic properties of the substrate. Despite a common paradigm followed in many asymmetric catalyses, an excess
简单的双(恶唑啉)配体,特别是氮杂双(恶唑啉),可以促进铜(II)在吲哚至丙二烯丙二酸酯中的吲哚的迈克尔加成,其ee> 99%(ee =对映体过量),前提是配体/金属比特别地,对衬底的电子特性进行微调。尽管在许多不对称催化中遵循了共同的范例,但是手性配体的过量并不总是有益的。实际上,当使用富含电子的亚苄基丙二酸酯时,必须避免任何过量的配体以达到优异的对映选择性。相反,带有吸电子基团的丙二酸酯需要过量的配体才能获得最佳ee值。光学产率与几个对位取代基的sigma(I)值的相关性显示出S型轨迹。在有添加剂的情况下,