Szefczyk Borys, Andruniów Tadeusz, Sokalski W Andrzej
Institute of Physical & Theoretical Chemistry, Wrocław University of Technology, Wybrzeze Wyspiańskiego 27, 50-370, Wrocław, Poland.
J Mol Model. 2008 Aug;14(8):727-33. doi: 10.1007/s00894-008-0289-9. Epub 2008 Mar 11.
Hetero-Diels-Alder (HDA) reaction of methyl glyoxylate with buta-1,3-diene has been investigated using multireference methods (complete active space SCF and multi-reference perturbation theory) and compared with several single-reference methods (including DFT) often used in calculations of catalysed [4+2] cycloadditions. Concerted and stepwise mechanisms, found in the literature, are compared. It is shown, that the stepwise mechanism may be a result of choosing unbalanced active space. Such choice leads to very close singlet and triplet states in the intermediate geometry - an artificial effect, that disappears if properly balanced active space is used (here, we use active space of 12 orbitals and 12 electrons). Conclusions concerning the mechanism and usefulness of the applied methodology are drawn, which might be important for theoretical investigation of stereoselectivity and specificity of catalysts for the HDA reaction.
已使用多参考方法（完全活性空间自洽场和多参考微扰理论）研究了乙醛酸甲酯与1,3 - 丁二烯的杂环狄尔斯-阿尔德（HDA）反应，并与催化[4+2]环加成计算中常用的几种单参考方法（包括密度泛函理论）进行了比较。对文献中发现的协同和分步机理进行了比较。结果表明，分步机理可能是选择了不平衡活性空间的结果。这种选择导致中间几何构型中的单重态和三重态非常接近——这是一种人为效应，如果使用适当平衡的活性空间（此处，我们使用12个轨道和12个电子的活性空间），这种效应就会消失。得出了关于所应用方法的机理和实用性的结论，这对于HDA反应催化剂的立体选择性和特异性的理论研究可能很重要。
