How Ionization Catalyzes Diels-Alder Reactions

Pascal Vermeeren, Trevor A. Hamlin*, F. Matthias Bickelhaupt

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The catalytic effect of ionization on the Diels-Alder reaction between 1,3-butadiene and acrylaldehyde has been studied using relativistic density functional theory (DFT). Removal of an electron from the dienophile, acrylaldehyde, significantly accelerates the Diels-Alder reaction and shifts the reaction mechanism from concerted asynchronous for the neutral Diels-Alder reaction to stepwise for the radical-cation Diels-Alder reaction. Our detailed activation strain and Kohn-Sham molecular orbital analyses reveal how ionization of the dienophile enhances the Diels-Alder reactivity via two mechanisms: (i) by amplifying the asymmetry in the dienophile's occupied π-orbitals to such an extent that the reaction goes from concerted asynchronous to stepwise and thus with substantially less steric (Pauli) repulsion per reaction step; (ii) by enhancing the stabilizing orbital interactions that result from the ability of the singly occupied molecular orbital of the radical-cation dienophile to engage in an additional three-electron bonding interaction with the highest occupied molecular orbital of the diene.

Original languageEnglish
Article numbere202200987
Number of pages9
JournalChemistry - A European Journal
Volume28
Issue number40
Early online date20 Apr 2022
DOIs
Publication statusPublished - 15 Jul 2022

Bibliographical note

Funding Information:
We thank The Netherlands Organization for Scientific Research (NWO) and the Dutch Astrochemistry Network (DAN) for financial support.

Publisher Copyright:
© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.

Keywords

  • activation strain model
  • density functional calculations
  • Diels-Alder reaction
  • radical chemistry
  • reactivity

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