The reactions of five‐membered cyclodiene derivatives with itaconic anhydride could proceed via four plausible pathways: two pathways involving initial Diels–Alder cycloaddition reactions followed by lactonization, and two pathways involving direct ring‐opening esterification reactions followed by intramolecular Diels–Alder cycloaddition, all to afford five‐ and six‐membered norbornene lactones, which are key intermediates in the synthesis of biologically interesting molecules as well as polymers such as polyelectrolytes. There are several regio‐, enantio‐, peri‐, and stereo‐chemical possibilities in these reactions, leading to several potential pathways, and these pathways are studied with density functional theory calculations in this work. The results reveal that the initial Diels–Alder reaction pathways have lower activation barriers than esterification reaction pathways. Generally, the activation barriers for the formation of S‐enantiomers are lower compared with the formation of R‐enantiomers. The reactions are stereo‐selective toward endo‐cycloadducts over exo‐cycloadducts, and this is as a result of steric interaction. The analysis of the electrophilic (P_k⁺) and nucleophilic (P_k⁻) Parr functions at the reactive centers shows that the cycloaddition will happen in such a way as to unite the atoms with the highest molecular orbital coefficients because this would lead to the greatest stabilization, and this is in good agreement with the energetic trends and the experimental outcome.

中文翻译：

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五元环二烯衍生物与衣康酸酐对降冰片烯内酯形成反应的区域，对映体，对映体和立体选择性

五元环二烯衍生物与衣康酸酐的反应可通过四个可能的途径进行：两个途径涉及最初的Diels-Alder环加成反应，然后进行内酯化；两个途径涉及直接开环酯化反应，然后进行分子内Diels-Alder环化反应，所有提供五元和六元的降冰片烯内酯，它们是合成生物学上感兴趣的分子以及聚合物（例如聚电解质）的关键中间体。这些反应中存在几种区域，对映体，周边和立体化学的可能性，从而导致了几种潜在的途径，并且在这项工作中使用密度泛函理论计算研究了这些途径。结果表明，最初的Diels–Alder反应途径比酯化反应途径具有较低的活化障碍。通常，与R-对映体的形成相比，S-对映体的形成的激活障碍要低。反应是对内环加合物的立体选择性高于对环外加合物的立体选择性，这是空间相互作用的结果。亲电分析（P_ķ ⁺）和亲核（P _ķ ^- ）在反应中心示出了环加成将以这样一种方式，以团结具有最高分子轨道系数的原子，因为这将导致最大的稳定化发生帕尔功能，这是在与能量趋势和实验结果良好吻合。