Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Unveiling the Ionic Diels-Alder Reactions within the Molecular Electron Density Theory

Version 1 : Received: 26 May 2021 / Approved: 27 May 2021 / Online: 27 May 2021 (13:56:43 CEST)

A peer-reviewed article of this Preprint also exists.

Domingo, L.R.; Ríos-Gutiérrez, M.; Aurell, M.J. Unveiling the Ionic Diels–Alder Reactions within the Molecular Electron Density Theory. Molecules 2021, 26, 3638. Domingo, L.R.; Ríos-Gutiérrez, M.; Aurell, M.J. Unveiling the Ionic Diels–Alder Reactions within the Molecular Electron Density Theory. Molecules 2021, 26, 3638.

Journal reference: Molecules 2021, 26, 3638
DOI: 10.3390/molecules26123638

Abstract

The ionic Diels-Alder (I-DA) reactions of a series of six iminium cations with cyclopentadiene have been studied within the Molecular Electron Density Theory (MEDT). The superelectrophilic character of iminium cations,  > 8.20 eV, accounts for the high reactivity of these species participating in I-DA reactions. The activation energies are found between 13 and 20 kcal·mol-1 lower in energy than those associated to the corresponding Diels-Alder (DA) reactions of neutral imines. These reactions are low endo selective as a consequence of the cationic character of the TSs, but highly regioselective. Solvents have poor effects on the relative energies, and an unappreciable effect in the geometries. In dichloromethane the activation energies increase slightly as a consequence of the better solvation of the iminium cations than the cationic TSs. ELF topological analysis of the bonding changes along the I-DA reactions shows that they are very similar to those in polar DA reactions. The present MEDT study makes it possible establishing that the global electron density transfer (GEDT) taking place at the TSs of I-DA reactions, and not steric (Pauli) repulsions such as have been recently proposed, are responsible for the features of these type of DA reactions.

Subject Areas

ionic Diels-Alder reactions; Molecular Electron Density Theory; iminium cations; superelectrophiles; global electron density transfer, asynchronicity.

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