Enantioselective epoxidation of olefins using novel chiral binuclear Mn(Ⅲ)-Schiff-base complexes with built-in phase-transfer capability
会议名称：《甘肃省化学会第二十四届年会》
会议日期：2005年
学科分类：081704[工学-应用化学] 07[理学] 08[工学] 0817[工学-化学工程与技术] 070303[理学-有机化学] 0703[理学-化学]
摘 要：Chiral epoxides are of great interest for the synthesis of chiral intermediates in the pharmaceutical and agrochemical field . Therefore, the design of new chiral catalysts for enantioselective epoxidation of alkenes constitutes an important strategy for the synthesis of those chiral Pharmaceuticals and fine chemicals . Among several catalytic systems, the Jacobsen epoxidation had emerged as a powerful method for the asymmetric oxidation of unfunctionalized olefins,almost at the same lime, Katsuki and his colleagues had developed another set of salen -Mn (III) complexes which containing two extra stereogenic axes. Soon after these key findings, a number of reports appeared describing efforts to expand this catalytic system. We are interested in the synthesis and catalytic activity of novel dimeric salen ligands and their Mn(III) complexes based on some previous results, and furthermore, we found these dimeric salen-Mn(III) complexes have certain built-in phase-transfer capability under biphasic reaction condition(H2O/CH2Cl2, NaCIO as oxidant). In our present study, pyridine N-oxide, 1,4-dioxane and HMPA had been used as proximal ligand respectively, and they all stabilized the catalytically active intermediate Mn (V)-oxo and imparted the requisite activity and selectivity in the catalysts. For example, even water-soluble O-coordinating ligand (1,4-dioxane, 10mol%, catalyst 1) do the same work (epoxidation of indene with conversion 80%, e.e. 52%, time 4h). This feature maybe attributed to the built-in phase-transfer capability of these complexes, because they have two active metal sites on the catalysts and make the transportation of HOC1 from water phase to organic phase more conveniently. The structure of catalyst 1: