Synthesis of Bis(oxazoline) Ligands Possessing C-5 <i>gem</i>-Disubstitution and Their Application in Asymmetric Friedel–Crafts Alkylations
作者:Steven O’Reilly、Miriam Aylward、Caoimhe Keogh-Hansen、Brian Fitzpatrick、Helen A. McManus、Helge Müller-Bunz、Patrick J. Guiry
DOI:10.1021/acs.joc.5b01767
日期:2015.10.16
A series of eight novel bis(oxazoline) ligands incorporating gem-disubstitution on one of the oxazoline rings were prepared from (S)-valine. These ligands are designed as a cost-effective alternative to similar ligands possessing an oxazolinyl C(5)-tert-butyl group derived from expensive (S)-tert-leucine. Four of the ligands possess a C(4)-gem-dimethyl group and four a C(4)-gem-diphenyl group adjacent
从(S)-缬氨酸制备了一系列八个在双恶唑啉环上掺入宝石-双取代的新颖的双(恶唑啉)配体。这些配体被设计为具有衍生自昂贵的(S)-叔亮氨酸的恶唑啉基C(5)-叔丁基的类似配体的经济有效的替代物。四个配体具有一个C(4)-gem-二甲基基团和四个与C(5)-异丙基取代基相邻的C(4)-gem-二苯基基团。配体11a – h的锌配合物,以及非C(4)-宝石双取代的类似物1a – g,在一系列系列的硝基烯烃对吲哚(至多74%ee)和2-甲氧基呋喃(至多95%ee)的Friedel-Crafts烷基化反应中有效。X射线晶体学表征了三个配体(11a – c),配体11d的二氯化铁配合物和两个二氯化锌配合物,其中一个配体为11d,第二个为双叔丁基取代的N-甲胺配体。对后者结构的直接比较清楚地说明了宝石-二甲基效应。