Mechanism of the Intramolecular Hexadehydro-Diels-Alder Reaction.
Mechanism of the Intramolecular Hexadehydro-Diels-Alder Reaction.
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DOI：
10.1021/acs.joc.5b01356
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发表时间：
2015-12-04
期刊：
影响因子：
--
通讯作者：
Kuwata KT
中科院分区：
文献类型：
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作者：
Marell DJ;Furan LR;Woods BP;Lei X;Bendelsmith AJ;Cramer CJ;Hoye TR;Kuwata KT
理论分析的分子内的六脱氢-狄尔斯-桤木（HDDA）反应，验证了对先前和新测量的动力学数据的一些不同的拴系炔-diynes的机制，表明该反应在一个高度异步的方式进行。速率决定步骤是在最接近系链的炔末端形成键，其涉及表现出实质性双自由基特征的过渡态结构。然后反应是否继续以协同方式或逐步方式闭合剩余的键（即，具有插入中间体）取决于在剩余末端炔位置上的取代基。HDDA反应的计算建模是复杂的显着的双自由基字符出现沿着反应坐标，这导致不稳定性限制单重态Kohn-Sham密度泛函理论（DFT）和耦合簇理论的基础上的Hartree-Fock参考波函数。一个一致的图片出现，但是，从比较破缺对称DFT计算和二阶微扰理论的基础上完整的活性空间自洽场（CASPT 2）计算。
Theoretical analysis of the mechanism of the intramolecular hexadehydro-Diels–Alder (HDDA) reaction, validated against prior and newly measured kinetic data for a number of different tethered yne-diynes, indicates that the reaction proceeds in a highly asynchronous fashion. The rate-determining step is bond formation at the alkyne termini nearest the tether, which involves a transition-state structure exhibiting substantial diradical character. Whether the reaction then continues to close the remaining bond in a concerted fashion or in a stepwise fashion (i.e., with an intervening intermediate) depends on the substituents at the remaining terminal alkyne positions. Computational modeling of the HDDA reaction is complicated by the significant diradical character that arises along the reaction coordinate, which leads to instabilities in both restricted singlet Kohn-Sham density functional theory (DFT) and coupled-cluster theory based on a Hartree-Fock reference wave function. A consistent picture emerges, however, from comparison of broken-symmetry DFT calculations and second-order perturbation theory based on complete-active-space self-consistent-field (CASPT2) calculations.