Fu Aiping, Li Hongliang, Yuan Shuping, Si Hongzong, Duan Yunbo
Institute for Computational Science and Engineering, Laboratory of New Fiber Materials and Modern Textile, Qingdao University, Qingdao, Shandong 266071, China.
J Org Chem. 2008 Jul 18;73(14):5264-71. doi: 10.1021/jo800089q. Epub 2008 Jun 13.
The effects of different amino acid catalysts on the stereoselectivity of the direct intermolecular aldol reactions between alpha-hydroxyketones and isobutyraldehyde or 4-nitrobenzaldehyde have been studied with the aid of density functional theory methods. The transition states of the crucial C-C bond-forming step with the enamine intermediate addition to the aldehyde for the proline and threonine-catalyzed asymmetric aldol reactions are reported. B3LYP/6-31+G** calculations provide a good explanation for the opposite syn vs anti diastereoselectivity of these two kinds of amino acid catalysts (anti-selectivity for the secondary cyclic amino acids proline, syn-selectivity for the acyclic primary amino acids like threonine). Calculated and observed diastereomeric ratio and enantiomeric excess values are in good agreement.
借助密度泛函理论方法，研究了不同氨基酸催化剂对α-羟基酮与异丁醛或4-硝基苯甲醛之间直接分子间羟醛反应立体选择性的影响。报道了脯氨酸和苏氨酸催化的不对称羟醛反应中，关键的C-C键形成步骤（烯胺中间体加成到醛上）的过渡态。B3LYP/6-31+G**计算很好地解释了这两种氨基酸催化剂相反的顺式与反式非对映选择性（对二级环状氨基酸脯氨酸为反式选择性，对无环伯氨基酸如苏氨酸为顺式选择性）。计算得到的非对映体比例和对映体过量值与实验观测值吻合良好。
