Mechanistic Aspects on [3+2] Cycloaddition (32CA) Reactions of Azides to Nitroolefins: A Computational and Kinetic Study
Mechanistic Aspects on [3+2] Cycloaddition (32CA) Reactions of Azides to Nitroolefins: A Computational and Kinetic Study
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[3 2] 叠氮化物与硝基烯烃的环加成 (32CA) 反应的机理：计算和动力学研究
DOI：
10.1002/chem.202202294
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Ferreira, Marco A. B.
中科院分区：
文献类型：
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作者：
Kawamura, Meire Y.;Alegre‐Requena, Juan V.;Barbosa, Thaís M.;Tormena, Cláudio F.;Paton, Robert S.;Ferreira, Marco A. B.
硝基烯烃的[3+2]环加成已经成为由叠氮化物合成1，2，3-三唑的选择性和无催化剂的替代方案。我们描述的环加成/rearomatization反应序列的机理研究。DFT计算揭示了通过异步TS进行的限速环加成步骤，对1，5-三唑具有高动力学选择性。动力学研究揭示了一个二级速率定律，并在天然丰度下测量了13 C动力学同位素效应，在β-硝基苯乙烯的α和β碳的共轭烯烃中心1.0158和1.0216处具有显著的正常效应。畸变/相互作用-活化应变和能量分解分析表明，主要的区域异构体途径受益于更早和更少畸变的TS，而分子间相互作用项主导了1，5-环加合物的偏好。此外，主要的区域异构体还具有更有利的静电和色散项。此外，虽然静态DFT计算表明了一种协调但高度一致的Ei-型HNO 2消除机制，但准经典直接动力学计算揭示了动态中间体的存在。
[3+2] cycloadditions of nitroolefins have emerged as a selective and catalyst‐free alternative for the synthesis of 1,2,3‐triazoles from azides. We describe mechanistic studies into the cycloaddition/rearomatization reaction sequence. DFT calculations revealed a rate‐limiting cycloaddition step proceeding via an asynchronous TS with high kinetic selectivity for the 1,5‐triazole. Kinetic studies reveal a second‐order rate law, and13C kinetic isotopic effects at natural abundance were measured with a significant normal effect at the conjugated olefinic centers of 1.0158 and 1.0216 at the α and β‐carbons of β‐nitrostyrene. Distortion/interaction‐activation strain and energy decomposition analyses revealed that the major regioisomeric pathway benefits from an earlier and less‐distorted TS, while intermolecular interaction terms dominate the preference for 1,5‐ over 1,4‐cycloadducts. In addition, the major regioisomer also has more favorable electrostatic and dispersion terms. Additionally, while static DFT calculations suggest a concerted but highly asynchronousEi‐type HNO2elimination mechanism, quasiclassical direct‐dynamics calculations reveal the existence of a dynamic intermediate.