Catalytic asymmetric dihydroxylation of olefins with reusable OsO(4)(2-) on ion-exchangers: the scope and reactivity using various cooxidants.
Catalytic asymmetric dihydroxylation of olefins with reusable OsO(4)(2-) on ion-exchangers: the scope and reactivity using various cooxidants.
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DOI：
10.1021/ja017889j
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发表时间：
2002-04
影响因子：
15
通讯作者：
B. Choudary;N. Chowdari;K. Jyothi;M. Kantam
中科院分区：
文献类型：
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作者：
B. Choudary;N. Chowdari;K. Jyothi;M. Kantam
本文采用离子交换技术，以树脂和二氧化硅为载体，以层状双氢氧化物和季铵盐为离子交换剂，制备了交换型OsO（4）催化剂。特别选择具有不同特性和相反离子选择性的离子交换剂以产生可以在不对称二羟基化反应中使用各种助氧化剂操作的最佳非均相催化剂。考察了不同组成的LDH-OsO（4）催化剂在反式二苯乙烯不对称双羟基化反应中的催化活性。为克服LDH-OsO（4）的问题而设计的Resin-OsO（4）和SiO（2）-OsO（4）在以K（3）Fe（CN）（6）和分子氧为助氧化剂的烯烃不对称二羟基化反应中确实表现出一致的活性和对映选择性。与小林的多相体系相比，树脂-OsO（4）是一种非常有效的催化剂，可用于芳香族、脂肪族、无环、环状、单、二和三取代烯烃的双羟基化，以高产率和对映选择性得到手性邻二醇，而与所用的助氧化剂无关。树脂-OsO（4）通过简单的过滤定量回收，并重复使用多次，具有一致的活性。非均相锇催化剂的高结合能力使得能够使用等摩尔比的配体与锇以在不对称二羟基化中给出优异的对映选择性，这与其中总是使用过量摩尔量的昂贵手性配体与锇的均相锇体系相反。手性配体（DHQD）（2）PHAL具有非常大的尺寸，这是获得更高ee的先决条件，只有位于载体表面的OsO（4）（2-）才有可能络合。
Exchanger-OsO(4) catalysts are prepared by an ion-exchange technique using layered double hydroxides and quaternary ammonium salts covalently bound to resin and silica as ion-exchangers. The ion-exchangers with different characteristics and opposite ion selectivities are specially chosen to produce the best heterogeneous catalyst that can operate using the various cooxidants in the asymmetric dihydroxylation reaction. LDH-OsO(4) catalysts composed of different compositions are evaluated for the asymmetric dihydroxylation of trans-stilbene. Resin-OsO(4) and SiO(2)-OsO(4) designed to overcome the problems associated with LDH-OsO(4) indeed show consistent activity and enantioselectivity in asymmetric dihydroxylation of olefins using K(3)Fe(CN)(6) and molecular oxygen as cooxidants. Compared to the Kobayashi heterogeneous systems, resin-OsO(4) is a very efficient catalyst for the dihydroxylation of a wide variety of aromatic, aliphatic, acyclic, cyclic, mono-, di-, and trisubstituted olefins to afford chiral vicinal diols with high yields and enantioselectivities irrespective of the cooxidant used. Resin-OsO(4) is recovered quantitatively by a simple filtration and reused for a number of cycles with consistent activity. The high binding ability of the heterogeneous osmium catalyst enables the use of an equimolar ratio of ligand to osmium to give excellent enantioselectives in asymmetric dihydroxylation in contrast to the homogeneous osmium system in which excess molar quantities of the expensive chiral ligand to osmium are invariably used. The complexation of the chiral ligand (DHQD)(2)PHAL, having very large dimension, a prerequisite to obtain higher ee, is possible only with the OsO(4)(2-) located on the surface of the supports.