In quantum chemical calculations, the Diels–Alder (DA) cycloaddition reaction of furan with maleic anhydride favors the endo‐isomer kinetically in the gas phase. This preference, however, changes in favor of the exo‐isomer on inclusion of solvent effects. For example, in acetonitrile, the exo‐isomer was calculated to form twice as fast as the endo‐isomer at room temperature, an observation that corroborates well with the experiments. The free energy change of the reaction is such that it allows faster reversal of the endo‐isomer to the reactants in an equilibrium process and, thus, the predominance of the more stable exo‐isomer eventually. The reaction of furan with maleimide is similar to that with maleic anhydride. However, it predominantly favors endo‐selectivity at temperatures below 320 K, which is also in excellent agreement with the experimental studies of temperature dependence of this DA reaction. Further, a gedanken calculation of the DA reaction of furan with cyclopropene has been investigated to delineate the effect of the retro‐pathway on stereoselectivity.

中文翻译：

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呋喃与马来酸酐和马来酰亚胺的Diels-Alder环加成反应的溶剂和温度驱动的立体选择性

在量子化学计算中，呋喃与顺丁烯二酸酐的Diels-Alder（DA）环加成反应在气相动力学上有利于内异构体。但是，这种优先选择改变了包含溶剂效应的外向异构体。例如，在乙腈中，计算出在室温下外消旋异构体的形成速度是内消旋异构体的两倍，这一观察结果与实验相符。反应的自由能变化使得它可以在平衡过程中更快地将内消旋异构体逆转为反应物，从而最终使更稳定的外消旋异构体占优势。呋喃与马来酰亚胺的反应类似于与马来酸酐的反应。但是，它主要有利于在低于320 K的温度下进行内选择性，这也与该DA反应的温度依赖性的实验研究非常吻合。此外，已经研究了呋喃与环丙烯的DA反应的gedanken计算，以描述逆向途径对立体选择性的影响。