Fu Yu, Guo Xun-Xiang, Zhu Shou-Fei, Hu Ai-Guo, Xie Jian-Hua, Zhou Qi-Lin
State Key Laboratory and Institute of Elemento-organic Chemistry, Nankai University, Tianjin 300071, China.
J Org Chem. 2004 Jul 9;69(14):4648-55. doi: 10.1021/jo049655z.
Novel chiral monodentate phosphorus ligands, SIPHOS, were conveniently synthesized from 1,1'-spirobiindane-7,7'-diol. The Rh complexes of SIPHOS can catalyze the hydrogenation of alpha-dehydroamino esters in mild conditions, providing alpha-amino acid derivatives in up to 99% ee. Enamides and beta-dehydroamino esters can also be hydrogenated in good to excellent enantioselectivities (up to 99% and 94% ee, respectively). The SIPHOS ligand with smaller alkyl groups on the N-atom afforded higher enantioselectivity. The X-ray analysis of single crystal showed that the structure of Rh/SIPHOS catalyst is Rh(COD)((S)-SIPHOS-Me)(2), which clarified the configuration of the catalyst with the monodentate chiral phosphorus ligand in Rh-catalyzed asymmetric hydrogenation. A positive nonlinear effect in the relationship of the optical purities of ligand and product was observed in the hydrogenation of dehydroamino acid derivatives. The kinetic study of hydrogenation showed that the reaction is zero order in the concentration of substrate and first order in the concentration of Rh catalyst and the hydrogenation pressure. The rate of hydrogenation decreased when the Rh/L ratio changed from 1:1 to 1:4.
新型手性单齿磷配体SIPHOS可由1,1'-螺二茚满-7,7'-二醇方便地合成。SIPHOS的铑配合物能在温和条件下催化α-脱氢氨基酸酯的氢化反应，提供对映体过量高达99%的α-氨基酸衍生物。烯酰胺和β-脱氢氨基酸酯也能以良好至优异的对映选择性进行氢化反应（分别高达99%和94% ee）。氮原子上具有较小烷基的SIPHOS配体具有更高的对映选择性。单晶X射线分析表明，Rh/SIPHOS催化剂的结构为[Rh(COD)((S)-SIPHOS-Me)(2)]⁺，这阐明了在铑催化的不对称氢化反应中具有单齿手性磷配体的催化剂的构型。在脱氢氨基酸衍生物的氢化反应中，观察到配体和产物的光学纯度关系存在正非线性效应。氢化反应的动力学研究表明，该反应对底物浓度为零级，对铑催化剂浓度和氢化压力为一级。当Rh/L比从1:1变为1:4时，氢化速率降低。
