Influence of Endo- and Exocyclic Heteroatoms on Stabilities and 1,3-Dipolar Cycloaddition Reactivities of Mesoionic Azomethine Ylides and Imines
Influence of Endo- and Exocyclic Heteroatoms on Stabilities and 1,3-Dipolar Cycloaddition Reactivities of Mesoionic Azomethine Ylides and Imines
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DOI：
10.1021/acs.joc.7b01928
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发表时间：
2017-10-20
影响因子：
3.6
通讯作者：
Houk, K. N.
中科院分区：
文献类型：
--
作者：
Champagne, Pier Alexandre;Houk, K. N.
使用密度泛函理论计算在 M06-2X/6-311+G-(d,p)/M06-2X/6-31G-(d) 水平上研究了 24 个介离子偶氮甲碱叶立德和亚胺的几何形状、稳定性和 1,3-偶极环加成反应活性。计算出的结构强调了如何用两种更精确的共振结构来取代常用的“芳香族”共振形式。通过各种均质方案评估了偶极子的稳定性，并且与这些非芳香族化合物一致。乙烯或乙炔的活化自由能范围为 11.8 至 36.6 kcal/mol。在每种偶极子类型中，预测的环加成反应性与反应能量和各种取代基提供的共振稳定能量相关。内环 (X) 杂原子按 O > NH 与 S 一致的顺序增加 1,3-偶极子的反应性，而环外 (Y) 取代基按 CH2 > NH > O > S 的顺序增加 1,3-偶极子的反应性。畸变/相互作用分析表明，不同取代的 1,3-偶极子之间的反应性差异是由畸变驱动的，而甲亚碱叶立德和亚胺之间的差异与较低的相互作用有关亚胺与亲偶极子的能量。
The geometries, stabilities, and 1,3-dipolar cycloaddition reactivities of 24 mesoionic azomethine ylides and imine were investigated using density functional theory calculations at the M06-2X/6-311+G-(d,p)/M06-2X/6-31G-(d) level. The computed structures highlight how the commonly used "aromatic" resonance form should be replaced by two more accurate resonance structures. Stabilities of the dipoles were assessed by various homodesmotic schemes and are consistent with these compounds being nonaromatic. The activation free energies with ethylene or acetylene range from 11.8 to 36.6 kcal/mol. Within each dipole type, the predicted cycloaddition reactivities correlate with the reaction energies and the resonance stabilization energies provided by the various substituents. Endo cyclic (X) heteroatoms increase the reactivity of the 1,3-dipoles in the order of O > NH congruent to S, whereas exocyclic (Y) substituents increase it in the order of CH2 > NH > O > S. Distortion/interaction analysis indicated that the difference in reactivity between differently substituted 1,3-dipoles is driven by distortion, whereas the difference between azomethine ylides and imines is related to lower interaction energies of imines with the dipolarophiles.