Chiral 2,6-bis(oxazolinyl)pyridine-rare earth metal complexes as catalysts for highly enantioselective 1,3-dipolar cycloaddition reactions of 2-benzopyrylium-4-olates.
Chiral 2,6-bis(oxazolinyl)pyridine-rare earth metal complexes as catalysts for highly enantioselective 1,3-dipolar cycloaddition reactions of 2-benzopyrylium-4-olates.
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DOI：
10.1021/jo049007f
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发表时间：
2005-01
期刊：
影响因子：
--
通讯作者：
H. Suga;Kei-ichi Inoue;S. Inoue;A. Kakehi,;M. Shiro
中科院分区：
文献类型：
--
作者：
H. Suga;Kei-ichi Inoue;S. Inoue;A. Kakehi,;M. Shiro
Rh（2）（OAc）（4）催化邻甲氧羰基-α-重氮苯乙酮分解生成的2-苯并吡喃-4-醇盐在1，3-偶极环加成反应中获得了显著的对映选择性。该反应使用手性2，6-双（恶唑啉基）吡啶（Pybox）-稀土金属三氟甲磺酸盐配合物作为手性刘易斯酸催化剂。Sc（III）-Pybox-i-Pr配合物（10 mol %）催化的苄氧基乙醛衍生物的反应顺利进行，选择性地生成内加合物，对映选择性高达93%ee。对于与丙酮酸苄酯的反应，Sc（III）-Pybox-i-Pr络合物（10摩尔%）在三氟乙酸（10摩尔%）的存在下有效地催化反应，以产生具有高非对映体和对映体选择性（94%ee）的外加合物。该催化体系被有效地应用于与其他几种α-酮酯的反应，具有高的外型和对映选择性（高达95%ee）。与羰基化合物的反应相反，Yb（III）-Pybox-Ph络合物（10摩尔%）被发现在与3-丙烯酰基-2-恶唑烷酮的反应中有效地获得非对映选择性地产生的外环加合物的高对映选择性（96%ee）。
Significant levels of enantioselectivity were obtained in 1,3-dipolar cycloadditions of 2-benzopyrylium-4-olate generated from the Rh(2)(OAc)(4)-catalyzed decomposition of o-methoxycarbonyl-alpha-diazoacetophenone. This reaction utilized chiral 2,6-bis(oxazolinyl)pyridine (Pybox)--rare earth metal triflate complexes as chiral Lewis acid catalysts. The reactions with several benzyloxyacetaldehyde derivatives catalyzed by a Sc(III)--Pybox-i-Pr complex (10 mol %) proceeded smoothly to yield endo-adducts selectively with high enantioselectivity (up to 93% ee). For the reaction with benzyl pyruvate, the Sc(III)-Pybox-i-Pr complex (10 mol %) catalyzed the reaction effectively in the presence of trifluoroacetic acid (10 mol %) to yield an exo-adduct with both high diastereo- and enantioselectivity (94% ee). This catalytic system was efficiently applied to the reactions with several other alpha-keto esters with high exo- and enantioselectivities (up to 95% ee). In contrast to the reaction with carbonyl compounds, Yb(III)--Pybox-Ph complex (10 mol %) was found to be effective to obtain high enantioselectivity (96% ee) of diastereoselectively produced exo-cycloadduct in the reaction with 3-acryloyl-2-oxazolidinone.