Abstract Effect of formal one and two CH/P exchange(s) on tandem Cope rearrangement and [2 + 2] cycloaddition of cis-1,2-diethylnylcyclopropane and its mono-hetero analogues has been investigated theoretically in the gas phase at the DFT (B3LYP/6-31+G(d)) level. The activation free energy for the first step, i.e., Cope rearrangement decreases successively on replacing one and two CH moieties of cis-1,2-diethylnylcyclopropane and its mono-hetero analogues with P atom(s), which could be rationalized on the basis of weaker C = P π bond than C = C π bond. However, this trend is not maintained in the second step, i.e. [2 + 2] cycloaddition of the initially formed intermediate; instead, the activation free energy for monophospha- and diphospha- analogues is slightly higher, which may be attributed to the lesser stability of monophospha- and diphosphacyclobutene rings than cyclobutene. The CASSCF calculations indicate that except the intermediates generated from the Cope rearrangement of cis-diethynylthiirane and cis-bis(phosphaethynyl)cyclopropane which are expected to follow concerted mechanism for the [2 + 2] cycloaddition, in all other cases, apparently, there is no preference for the concerted or stepwise mechanism. Inclusion of the dispersion correction in the DFT functional does not cause significant changes in energetics. Graphical Abstract

中文翻译：

---

形式CH/P交换对顺式1,2-二乙基环丙烷及其单杂类似物串联Cope重排和[2+2]环加成的影响

摘要 正式的一和二 CH/P 交换对顺式 1,2-二乙基环丙烷及其单杂类似物的串联 Cope 重排和 [2 + 2] 环加成的影响已在 DFT 气相中进行了理论上的研究。 (B3LYP/6-31+G(d)) 级别。第一步的活化自由能，即 Cope 重排在用 P 原子取代顺式 1,2-二乙基环丙烷及其单杂类似物的一个和两个 CH 部分时连续降低，这可以在基础上合理化C = P π 键比 C = C π 键弱。然而，这种趋势在第二步中并未保持，即最初形成的中间体的 [2 + 2] 环加成；相反，单磷酸和双磷酸类似物的活化自由能略高，这可能是由于单磷杂环丁烯环和双磷杂环丁烯环的稳定性低于环丁烯。CASSCF 计算表明，除了顺式二乙炔基硫醚和顺式双（磷炔基）环丙烷的 Cope 重排产生的中间体预计遵循 [2 + 2] 环加成的协同机制，在所有其他情况下，显然，不偏爱协调或逐步机制。在 DFT 泛函中包含色散校正不会引起能量学的显着变化。图形概要 CASSCF 计算表明，除了顺式二乙炔基硫醚和顺式双（磷炔基）环丙烷的 Cope 重排产生的中间体预计遵循 [2 + 2] 环加成的协同机制，在所有其他情况下，显然，不偏爱协调或逐步机制。在 DFT 泛函中包含色散校正不会引起能量学的显着变化。图形概要 CASSCF 计算表明，除了顺式二乙炔基硫醚和顺式双（磷炔基）环丙烷的 Cope 重排产生的中间体预计遵循 [2 + 2] 环加成的协同机制，在所有其他情况下，显然，不偏爱协调或逐步机制。在 DFT 泛函中包含色散校正不会引起能量学的显着变化。图形概要