Novel Chiral Bisoxazoline Ligands with a Biphenyl Backbone: Preparation, Complexation, and Application in Asymmetric Catalytic Reactions
作者:Yoshitane Imai、Wanbin Zhang、Toshiyuki Kida、Yohji Nakatsuji、Isao Ikeda
DOI:10.1021/jo9915978
日期:2000.6.1
solution. Interestingly, when the ligands 1 were coordinated with a metal ion, only one of the two possible diastereomer complexes, an (S,aS,S)-complex, can be formed depending on the combination of the ligand and the metal ion. Thus, copper(I) afforded only the (S,aS,S)-complexes with all ligands 1, while zinc(II), palladium(II), and silver(I) afforded the (S,aS, S)-complexes as the sole product only
新型C(2)对称手性双恶唑啉配体1可以轻松地从对映体纯的2-氨基醇和非手性2,2'-联苯二羧酸通过相应的酰胺和甲磺酸酯作为中间体制备。由于这些配体在联苯主链上仅带有两个邻位取代基,因此联苯轴不固定,并且这些配体的两个非对映异构体在溶液中处于平衡状态。有趣的是,当配体1与金属离子配位时,取决于配体和金属离子的组合,只能形成两种可能的非对映异构体络合物之一,即(S,aS,S)络合物。因此,铜(I)仅提供具有所有配体1的(S,aS,S)复合物,而锌(II),钯(II)和银(I)提供(S,aS,S)复合物作为只有1b的唯一产品,其在恶唑啉环上具有庞大的叔丁基基团,以及两种非对映体配合物与1a,c,d的混合物。用这些配体成功地进行了铜(I)催化的重氮乙酸酯对苯乙烯的不对称环丙烷化反应,并提供了良好的对映体选择性。