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首页> 外文期刊>Chemistry: A European journal >Control of enantioselectivity with flexible biaryl axes: Terpene-based alkylzinc catalysts in enantioselective dialkylzinc additions
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Control of enantioselectivity with flexible biaryl axes: Terpene-based alkylzinc catalysts in enantioselective dialkylzinc additions

机译：用灵活的联芳基轴控制对映选择性：对映选择性二烷基锌加成中的基于萜烯的烷基锌催化剂

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摘要

New enantiopure pyridyl alcohols are efficiently accessible through few synthetic steps from commercially available terpenes, that is, (+)-fenchone, (-)-menthone and (-)-verbenone as well as 2,6-diphenylpyridine. These chelating pyridyl alcohols exhibit flexible pyridyl-phenylene axes, which give rise to P and M conformers. Alkylzincation of the hydroxy groups eliminates equilibria of the conformers and generates alkylzinc complexes with adjusted biaryl axes, as it is demonstrated by NMR studies. These alkylzinc catalysts perform well in the addition of dimethylzinc or diethylzinc to benzaldehyde with yields up to 99% and ee's up to 95%. The adjusted pyridylphenylene conformations in the ligands now control enantioselectivities of the catalysts, which were also analysed by computations at the DFT level. Fixing the biaryl axis: New chiral pyridyl terpenols are derived from 2,6-diphenylpyridine by means of short synthetic routes. The chiral biaryl axes of the metal-free alcohols are conformationally free, almost without any preferences for P or M arrangements. The chiral information of the terpene units is effectively transferred to the pyridylphenylene biaryl axes only if zinc is implemented, giving well-defined conformations in the enantioselective catalyst (see scheme).
机译：新的对映体纯的吡啶醇可以通过几个合成步骤从市售的萜烯中高效地获得，即，（+）-去氢酮，（-）-薄荷酮和（-）-马酮酮以及2,6-二苯基吡啶。这些螯合的吡啶基醇表现出柔性的吡啶基-亚苯基，从而产生P和M构象异构体。 NMR研究表明，羟基的烷基锌化消除了构象异构体的平衡，并生成了具有调整后的联芳基轴的烷基锌络合物。这些烷基锌催化剂在将二甲基锌或二乙基锌添加到苯甲醛中时表现良好，收率高达99％，ee高达95％。现在在配体中调节的吡啶基亚苯基构象控制了催化剂的对映选择性，这也通过在DFT水平上的计算来分析。固定联芳基轴：新的手性吡啶基萜烯醇是通过短合成路线衍生自2,6-二苯基吡啶的。不含金属的醇的手性联芳基轴是无构象的，几乎不偏爱P或M排列。仅在使用锌的情况下，萜烯单元的手性信息才能有效地转移到吡啶基亚苯基联芳基轴上，从而在对映选择性催化剂中得到定义明确的构象（参见方案）。

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