Bonded to Carbon or Nitrogen? This is a Question on the Regioselectivity in Hyperconjugative Aromaticity
Bonded to Carbon or Nitrogen? This is a Question on the Regioselectivity in Hyperconjugative Aromaticity
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与碳或氮键合？
DOI：
10.1021/acs.joc.8b02996
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Jun Zhu
中科院分区：
文献类型：
--
作者：
Tingting Sun;Ping Guo;Qiong Xie;Liang Zhao;Jun Zhu
在化学中，区域选择性是化学键形成或断裂的一个方向优先于所有其他可能的方向。尽管在各种反应中已经得到了广泛的研究，但由于合成目标产物的挑战性，超共轭芳香性在主族体系或过渡金属体系上的区域选择性仍然是难以捉摸的。在这里，我们报告一个联合的理论和实验研究这个问题。理论计算预测，吸电子基团更喜欢连接到sp3杂化的碳原子上，而不是连接到吲哚中的氮原子上。对于供电子基团，与sp3杂化的碳或氮原子键合的两种异构体几乎是等能的。当同时考虑吲哚五元环中sp2-和sp3-杂化的碳和氮原子时，与sp3-杂化的碳原子键合的多金取代基的异构体比与sp3-杂化的氮原子键合的多金取代基的异构体在热力学上更稳定。这一预测得到了实验观察的合理验证。键离解能比芳香性更能合理化这种偏好。研究结果有助于实验工作者设计和实现更多的新型超共轭芳香化合物。
In chemistry, regioselectivity is the preference of one direction of chemical bond making or breaking over all other possible directions. Although it has been extensively investigated in various reactions, the regioselectivity of hyperconjugative aromaticity on either main group systems or transition metal ones.remains elusive due to the challenge of synthesizing the target products. Here we report a joint theoretical and experimental study on this issue. Theoretical calculations predicted that electron-withdrawing groups prefer an attachment to the sp3-hybridized carbon atom rather than the nitrogen atom in indoliums. For the electron-donating groups, the two isomers bonded to the sp3-hybridized carbon or nitrogen atom are almost isoenergetic. When both sp2- and sp3-hybridized carbon and nitrogen atoms in the five-membered ring of indoliums are considered, the isomer with the polyaurated substituents bonded to the sp3-hybridized carbon atom is thermodynamically more stable than that with the polyaurated substituents bonded to the sp3-hybridized nitrogen atom. This prediction is reasonably verified by experimental observation. Bond dissociation energy is found to be more important than aromaticity in rationalizing.such a preference. Our findings could help experimentalists to design and realize more novel hyperconjugative aromatics.