Asymmetric Henry reaction catalyzed by C2-symmetric tridentate bis(oxazoline) and bis(thiazoline) complexes:: Metal-controlled reversal of enantioselectivity
Asymmetric Henry reaction catalyzed by C2-symmetric tridentate bis(oxazoline) and bis(thiazoline) complexes:: Metal-controlled reversal of enantioselectivity
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DOI：
10.1021/jo050097d
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发表时间：
2005-04-29
影响因子：
3.6
通讯作者：
Xu, JX
中科院分区：
文献类型：
--
作者：
Du, DM;Lu, SF;Xu, JX
具有二苯胺主链的 C-2-对称三齿双（恶唑啉）和双（噻唑啉）配体已在 α-酮酯与不同路易斯酸的催化不对称亨利反应中进行了研究。它们的CU(OTf)(2)配合物提供S对映体，而Et2Zn配合物提供R对映体，两者都具有较高的对映选择性（高达85% ee）。通过将路易斯酸中心从 Cu(II) 更改为 Zn(II)，使用相同的手性配体实现了不对称亨利反应中对映选择性的逆转。结果表明，C-2-对称三齿手性配体中的NH基团在控制Henry产物的产率和对映选择性方面起着非常重要的作用。
C-2-symmetric tridentate bis(oxazoline) and bis(thiazoline) ligands with a diphenylamine backbone have been investigated in the catalytic asymmetric Henry reaction of a-keto esters with different Lewis acids. Their CU(OTf)(2) complexes furnished S enantiomers, while Et2Zn complexes afforded R enantiomers, both of them with higher enantioselectivities (up to 85% ee). Reversal of enantioselectivity in asymmetric Henry reactions was achieved with the same chiral ligand by changing the Lewis acid center from Cu(II) to Zn(II). The results show that the NH group in C-2-symmetric tridentate chiral ligands plays a very important role in controlling both the yields and enantiofacial selectivity of the Henry products.