Acetyl-BINOL as mimic for chiral β-diketonates: a building block for new modular ligands
作者:Robert von Rönn、Jens Christoffers
DOI:10.1016/j.tet.2010.11.037
日期:2011.1
six-membered chelates with transition metal ions. The second hydroxy-function was submitted to esterification with several carboxylic acids bearing another donor function, thus, new tridentate chiral ligands were obtained. Out of this library the l-proline-α-acetyl-(S)-BINOL-ester was identified to be most effective for the titanium-mediated addition of Et2Zn to PhCHO yielding the respective secondary
α-乙酰基-(S)-BINOL是通过邻位锂化和随后的乙缩醛保护的(S)-BINOL乙酰化制备的。该化合物的β-羟基酮部分在本文中是β-二酮酸酯的结构模拟物,并与过渡金属离子形成六元螯合物。将第二羟基官能团与带有另一种给体功能的几种羧酸进行酯化反应,从而获得了新的三齿手性配体。从该文库中,鉴定出1-脯氨酸-α-乙酰基-(S)-BINOL-酯对于钛介导的Et 2 Zn向PhCHO的添加最有效,从而产生相应的仲醇,ee最高可达93%,这比使用(S)-BINOL本身。除了对溶剂的依赖性(最好使用MeCN)外,正确选择抗衡离子也很重要:三氟乙酸根与溴离子的阴离子交换显着提高了对映选择性。