Zhang Hong, Thøgersen Mathias Kirk, Jamieson Cooper S, Xue Xiao-Song, Jørgensen Karl Anker, Houk Kendall N
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, 90095, USA.
College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China.
Angew Chem Int Ed Engl. 2021 Nov 15;60(47):24991-24996. doi: 10.1002/anie.202109608. Epub 2021 Oct 18.
The Diels-Alder reactions of tropolone and its conjugate base with N-methylmaleimide have been explored computationally and experimentally. Previous studies of the [4+2] cycloaddition under basic conditions show that both endo- and exo-products are obtained in similar, but variable amounts. Density functional theory (ωB97X-D) explorations of potential energy surfaces, and molecular dynamics trajectories show that the reaction involves an ambimodal transition state for the reaction of the ammonium tropolonate with N-methylmaleimide, and that similar amounts of endo- and exo-products are obtained. The thermal reaction, studied experimentally in detail here for the first time, is predicted to form the endo-adduct through an ambimodal transition state. The exo-adduct can be formed from the same transition state, but requires a hydrogen shift, that hinders this reaction dynamically. Longer reaction times give a small excess of the exo-product, which is thermodynamically more stable.
已通过计算和实验方法对托酚酮及其共轭碱与N-甲基马来酰亚胺的狄尔斯-阿尔德反应进行了研究。先前在碱性条件下对[4+2]环加成反应的研究表明，内型和外型产物的生成量相近，但存在一定变化。对势能面的密度泛函理论（ωB97X-D）探索以及分子动力学轨迹表明，该反应涉及托酚酮铵盐与N-甲基马来酰亚胺反应的双峰过渡态，并且内型和外型产物的生成量相近。本文首次对热反应进行了详细的实验研究，预计该热反应通过双峰过渡态形成内型加合物。外型加合物可由相同的过渡态形成，但需要氢迁移，这在动力学上阻碍了该反应。反应时间延长会使外型产物略有过量，外型产物在热力学上更稳定。
