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Article

Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory

Department of Organic Chemistry, University of Valencia, Dr. Moliner 50, Burjassot, E-46100 Valencia, Spain
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Author to whom correspondence should be addressed.
Academic Editor: Roberto Cammi
Chemistry 2021, 3(3), 834-853; https://doi.org/10.3390/chemistry3030061
Received: 23 June 2021 / Revised: 23 July 2021 / Accepted: 26 July 2021 / Published: 3 August 2021
(This article belongs to the Special Issue 2021 Profile Papers by Chemistry' Editorial Board Members)
The intramolecular ionic Diels–Alder (IIDA) reactions of two dieniminiums were studied within the Molecular Electron Density Theory (MEDT) at the ωB97XD/6-311G(d,p) computational level. Topological analysis of the electron localization function (ELF) of dieniminiums showed that their electronic structures can been seen as the sum of those of butadiene and ethaniminium. The superelectrophilic character of dieniminiums accounts for the high intramolecular global electron density transfer taking place from the diene framework to the iminium one at the transition state structures (TSs) of these IIDA reactions, which are classified as the forward electro density flux. The activation enthalpy associated with the IIDA reaction of the experimental dieniminium, 8.7 kcal·mol−1, was closer to that of the ionic Diels–Alder (I-DA) reaction between butadiene and ethaniminium, 9.3 kcal·mol−1. However, the activation Gibbs free energy of the IIDA reaction was 12.7 kcal·mol−1 lower than that of the intermolecular I-DA reaction. The strong exergonic character of the IIDA reaction, higher than 20.5 kcal·mol−1, makes the reaction irreversible. These IIDA reactions present a total re/exo and si/endo diastereoselectivity, which is controlled by the most favorable chair conformation of the tetramethylene chain. ELF topological analysis of the single bond formation indicated that these IIDA reactions take place through a non-concerted two-stage one-step mechanism. Finally, ELF and atoms-in-molecules (AIM) topological analyses of the TS associated with the inter and intramolecular processes showed the great similarity between them. View Full-Text
Keywords: intramolecular ionic Diels–Alder reactions; molecular electron density theory; dieniminiums; superelectrophiles; global electron density transfer intramolecular ionic Diels–Alder reactions; molecular electron density theory; dieniminiums; superelectrophiles; global electron density transfer
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MDPI and ACS Style

Domingo, L.R.; Ríos-Gutiérrez, M.; Aurell, M.J. Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory. Chemistry 2021, 3, 834-853. https://doi.org/10.3390/chemistry3030061

AMA Style

Domingo LR, Ríos-Gutiérrez M, Aurell MJ. Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory. Chemistry. 2021; 3(3):834-853. https://doi.org/10.3390/chemistry3030061

Chicago/Turabian Style

Domingo, Luis R., Mar Ríos-Gutiérrez, and María J. Aurell 2021. "Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory" Chemistry 3, no. 3: 834-853. https://doi.org/10.3390/chemistry3030061

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