Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 60, Issue 47, Pages 24991-24996Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202109608
Keywords
cycloaddition reactions; molecular dynamics; periselectivity
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Funding
- National Science Foundation [NSF CHE-1764328]
- Fundamental Research Funds for the Central Universities the Natural Science Foundation of China [20720190042]
- China Scholarship Council (CSC)
- Villum Investigator grant [25867]
- Aarhus University
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This study investigates the Diels-Alder reactions of tropolone and its conjugate base with N-methylmaleimide through computational and experimental approaches. The results reveal that the reaction forms both endo- and exo-products in similar, but variable amounts under basic conditions, with the endo-product being thermodynamically more stable. Computational explorations suggest the reaction involves an ambimodal transition state, and longer reaction times lead to a slight excess of the exo-product.
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 (omega B97X-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.
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