School of Chemistry and Molecular Biosciences , The University of Queensland , St Lucia , 4067 Queensland , Australia.
J Org Chem. 2019 May 17;84(10):5997-6005. doi: 10.1021/acs.joc.8b03236. Epub 2019 Feb 13.
By drawing analogies from the dimerization of cyclopentadiene, a novel reaction pathway bifurcation is uncovered in the cycloaddition of oxidopyrylium ylides and butadiene. Analysis of the potential energy surface (at the M06-2X/6-311+G(d,p) level of theory) in combination with Born-Oppenheimer molecular dynamics simulations (M06-2X/6-31+G(d)) demonstrate that both the (4 + 3)- and (5 + 2)-cycloaddition products are accessed from the same transition state. Key indicators of a pathway bifurcation (asynchronous bond formation, and a second transition state for the interconversion of the products) are also observed. The absence of a post-transition state bifurcation in the related oxidopyridinium systems of Krenske and Harmata is rationalized. Finally, the isosymmetry of the oxidopyrylium and cyclopentadiene molecular orbitals as well as the presence of "secondary orbital interactions" are emphasized as the common source of nonstatistical behavior. Application of these principles will allow for the rapid identification of new reaction pathway bifurcations.
通过类比环戊二烯的二聚反应，揭示了氧化吡喃鎓叶立德与丁二烯环加成反应中一种新的反应途径分岔。通过势能面分析（在 M06-2X/6-311+G(d,p)理论水平）结合 Born-Oppenheimer 分子动力学模拟（M06-2X/6-31+G(d)）表明，（4 + 3）-和（5 + 2）-环加成产物都可以从同一个过渡态得到。还观察到了途径分岔的关键指标（异步键形成和产物互变的第二个过渡态）。Krenske 和 Harmata 的相关氧化吡啶鎓体系中不存在过渡后分岔的情况得到了合理的解释。最后，强调了氧化吡喃鎓和环戊二烯分子轨道的等对称性以及“次级轨道相互作用”的存在，它们是非统计行为的共同来源。这些原则的应用将允许快速识别新的反应途径分岔。
