Synthesis and evaluation of new chiral nonracemic C2-symmetric and unsymmetric 2,2′-bipyridyl ligands
作者:Michael P. A. Lyle、Neil D. Draper、Peter D. Wilson
DOI:10.1039/b513286j
日期:——
of cyclopropanation reactions and NMR data, led to the conclusion that the 2,2'-bipyridyl ligands had the propensity to form catalytically inactive bis-ligated copper(I) species in solution that were in equilibrium with catalytically active copper(i) triflate and the desired mono-ligated copper(I) species. Moreover, it was observed that the complex of the bipyridyl ligand (R = Ph) and copper(I) chloride
一系列手性非外消旋和C2对称的2,2'-联吡啶配体(R = Me,i-Pr和Ph)的合成以及相应的不对称的2,2'-联吡啶配体(R = Me和Ph)描述。这些联吡啶配体以明显直接和模块化的方式,从容易获得的和相应的2-氯吡啶缩醛(R = Me,i-Pr和Ph)制备。在铜(I)催化的苯乙烯与重氮乙酸的乙基酯和叔丁基酯的环丙烷化反应中评估了联吡啶基配体。立体选择性以及环丙烷化反应的产率取决于所使用的联吡啶基配体和三氟甲磺酸铜的比例。苯乙烯和重氮乙酸叔丁酯与C2对称联吡啶基配体(R = i-Pr)的不对称环丙烷化反应获得了最佳结果。这以良好的非对映选择性(4∶1)和中等对映选择性(44%ee)提供了相应的反式环丙烷。X射线结构确定C2对称的2,2'-联吡啶配体(R = Ph)和氯化铜(I)之间形成的配合物表明,两个联吡啶配体已与铜(I)离子配位。该信息以及一系列环丙烷化反应的结果和NMR数据得出以下结论:2