Ríos-Gutiérrez Mar, Darù Andrea, Tejero Tomás, Domingo Luis R, Merino Pedro
Department of Organic Chemistry, University of Valencia, Dr. Moliner 50, E-46100 Burjassot, Valencia, Spain.
Org Biomol Chem. 2017 Feb 21;15(7):1618-1627. doi: 10.1039/c6ob02768g. Epub 2017 Jan 25.
The [3 + 2] cycloaddition (32CA) reaction between nitrones and ketenes has been studied within the Molecular Electron Density Theory (MEDT) at the Density Functional Theory (DFT) MPWB1K/6-311G(d,p) computational level. Analysis of the conceptual DFT reactivity indices allows the explanation of the reactivity, and the chemo- and regioselectivity experimentally observed. The particular mechanism of this 32CA reaction involving low electrophilic ketenes has been elucidated by using a bonding evolution theory (BET) study. It is determined that this reaction takes place in one kinetic step only but in a non-concerted manner since two stages are clearly identified. Indeed, the formation of the second C-O bond begins when the first O-C bond is already formed. This study has also been applied to predict the reactivity of nitrones with highly electrophilic ketenes. Interestingly, this study predicts a switch to a two-step mechanism due to the higher polar character of this zw-type 32CA reaction. In both cases, BET supports the non-concerted nature of the 32CA reactions between nitrones and ketenes.
在密度泛函理论（DFT）的MPWB1K/6 - 311G(d,p)计算水平下，运用分子电子密度理论（MEDT）对硝酮与烯酮之间的[3 + 2]环加成（32CA）反应进行了研究。通过对概念性DFT反应性指数的分析，可以解释该反应的反应性以及实验观察到的化学选择性和区域选择性。利用键演化理论（BET）研究阐明了这种涉及低亲电性烯酮的32CA反应的具体机理。确定该反应仅在一个动力学步骤中发生，但方式并非协同，因为可以清楚地识别出两个阶段。实际上，第二个C - O键的形成在第一个O - C键已经形成时就开始了。该研究还被用于预测硝酮与高亲电性烯酮的反应性。有趣的是，由于这种zw型32CA反应具有更高的极性特征，该研究预测反应会转变为两步机理。在这两种情况下，BET都支持硝酮与烯酮之间32CA反应的非协同性质。
