A new class of versatile chiral-bridged atropisomeric diphosphine ligands: remarkably efficient ligand syntheses and their applications in highly enantioselective hydrogenation reactions.
A new class of versatile chiral-bridged atropisomeric diphosphine ligands: remarkably efficient ligand syntheses and their applications in highly enantioselective hydrogenation reactions.
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DOI：
10.1021/ja0602694
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发表时间：
2006-04
影响因子：
15
通讯作者：
L. Qiu;F. Kwong;Jing Wu;W. Lam;Shu-sun Chan;Wing-Yiu Yu;Yue‐Ming Li;Rongwei Guo;Zhongyuan Zhou-Zhongyuan
中科院分区：
文献类型：
--
作者：
L. Qiu;F. Kwong;Jing Wu;W. Lam;Shu-sun Chan;Wing-Yiu Yu;Yue‐Ming Li;Rongwei Guo;Zhongyuan Zhou-Zhongyuan
通过对映体选择性的Ullmann偶联和关环反应合成了一系列手性双膦配体PQ-Phos。联芳基双膦二氧化物的Ullmann偶联反应具有高效的中心-轴向手性转移，非对映体过量> 99%。这种底物导向的非对映体联芳基偶联反应是前所未有的制备手性二膦二氧化物，我们的方法排除了繁琐的决议程序通常需要制备对映体纯的二膦配体。在相应的不对称关环反应中也发现了手性识别效应。桥接两个芳基单元的手性系链产生了对映体分化所必需的构象刚性支架;配体支架的微调（例如，二面角）可以通过改变手性系链的链长来实现。制备了对映体纯的Ru-和Ir-PQ-Phos配合物，并将其应用于α-和β-酮酯（C=O键还原）、2-（6 ′-甲氧基-2 ′-萘基）丙烯酸、烷基取代的β-脱氢氨基酸（C=C键还原）和N-杂芳族化合物（C=N键还原）的催化对映体选择性氢化。一个优秀的水平的对映体选择性（高达99.9%ee）已达到催化反应。此外，还发现配体二面角对Ir催化的N-杂环化合物的不对称氢化反应有显著的影响。
A series of chiral diphosphine ligands denoted as PQ-Phos was prepared by atropdiastereoselective Ullmann coupling and ring-closure reactions. The Ullmann coupling reaction of the biaryl diphosphine dioxides is featured by highly efficient central-to-axial chirality transfer with diastereomeric excess >99%. This substrate-directed diastereomeric biaryl coupling reaction is unprecedented for the preparation of chiral diphosphine dioxides, and our method precludes the tedious resolution procedures usually required for preparing enantiomerically pure diphosphine ligands. The effect of chiral recognition was also revealed in a relevant asymmetric ring-closure reaction. The chiral tether bridging the two aryl units creates a conformationally rigid scaffold essential for enantiofacial differentiation; fine-tuning of the ligand scaffold (e.g., dihedral angles) can be achieved by varying the chain length of the chiral tether. The enantiomerically pure Ru- and Ir-PQ-Phos complexes have been prepared and applied to the catalytic enantioselective hydrogenations of alpha- and beta-ketoesters (C=O bond reduction), 2-(6'-methoxy-2'-naphthyl)propenoic acid, alkyl-substituted beta-dehydroamino acids (C=C bond reduction), and N-heteroaromatic compounds (C=N bond reduction). An excellent level of enantioselection (up to 99.9% ee) has been attained for the catalytic reactions. In addition, the significant ligand dihedral angle effects on the Ir-catalyzed asymmetric hydrogenation of N-heteroaromatic compounds were also revealed.