An ab initio study of facial selectivity in the Diels-Alder reaction
An ab initio study of facial selectivity in the Diels-Alder reaction
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DOI：
10.1021/jo9712815
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发表时间：
1998-01-09
影响因子：
3.6
通讯作者：
Burnell, DJ
中科院分区：
文献类型：
--
作者：
Xidos, JD;Poirier, RA;Burnell, DJ
在从头算HF/6-31G*水平上，可靠地预测了5-取代1，3-环戊二烯与各种亲双烯化合物的Diels-Alder反应中的表面选择性。与反加成反应相比，正加成反应的活化能范围较大，与环戊二烯自身的活化能基本一致。将活化能划分为双烯变形、双烯变形和双烯-双烯相互作用能表明，决定表面选择性的主要因素是将二烯变形为其过渡态几何构型所需的能量。预测了5-氟、5-羟基和5-氨基-1，3-环戊二烯向其SYN过渡态构型的变形比环戊二烯本身的变形所需的能量更少，这与这些双烯与SYN加成的实验观察相一致。首次提出了从头算空间因子的定义，它与SYN活化能有很好的相关性。这表明，这些双烯的表面选择性主要是由于双烯上的亲双烯基团和平面不对称基团之间的空间位阻。然而，当亲二烯基团是1，2，4-三唑啉-3，5-二酮时，我们也发现了与反应氮的显著的孤对-孤对相互作用。
Facial selectivities in the Diels-Alder reactions of 5-substituted 1,3-cyclopentadienes with a variety of dienophiles are predicted reliably at the ab initio HF/6-31G* level. The ranges of activation energies for syn addition are large relative to those for anti addition, which are all similar to the activation energy for cyclopentadiene itself. Partitioning the activation energy Into diene deformation, dienophile deformation, and diene-dienophile interaction energies shows that the major factor in determining facial selectivity is in the energy required to deform the diene into its transition state geometry. Deformation of the 5-fluoro-, 5-hydroxy- and 5-amino-1,3-cyclopentadienes into their syn transition state geometries is predicted to require less energy than deformation of cyclopentadiene itself, which is in accord with experimental observation of syn addition with these dienes. The first definition of an ab initio steric factor is presented which correlates very well with syn activation energies. This indicates that facial selectivity with these dienes is primarily due to steric hindrance between the dienophile and the plane-nonsymmetric groups on the diene. However, we have also identified a significant lone pair-lone pair interaction with the reacting nitrogens when the dienophile is 1,2,4-triazoline-3,5-dione.