A molecular electron density theory study of the enhanced reactivity of aza aromatic compounds participating in Diels–Alder reactions

2020 ◽  
Vol 18 (2) ◽  
pp. 292-304 ◽  
Author(s):  
Luis R. Domingo ◽  
Mar Ríos-Gutiérrez ◽  
Patricia Pérez
Keyword(s):  
Electron Density ◽  
Aromatic Compounds ◽  
Activation Energies ◽  
Diels Alder ◽  
Aromatic Character ◽  
Molecular Electron ◽  
Molecular Electron Density Theory

The change of C–H by N: in these aromatic compounds decreases the ring electron density (RED), thus decreasing the activation energies of the aza Diels–Alder reactions mainly by the loss of the aromatic character of the reagents.

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

2021 ◽  
Author(s):  
Luis R. Domingo ◽  
Mar Ríos-Gutiérrez ◽  
María J. Aurell
Keyword(s):  
Electron Density ◽  
Topological Analysis ◽  
Activation Energies ◽  
High Reactivity ◽  
Diels Alder ◽  
Electron Density Transfer ◽  
Molecular Electron ◽  
Iminium Cations ◽  
Molecular Electron Density Theory ◽  
Density Transfer

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.

scholarly journals A Molecular Electron Density Theory Study of the Competitiveness of Polar Diels–Alder and Polar Alder-ene Reactions

Molecules ◽  
2018 ◽  
Vol 23 (8) ◽  
pp. 1913 ◽  
Author(s):  
Luis R. Domingo ◽  
Mar Ríos-Gutiérrez ◽  
Patricia Pérez
Keyword(s):  
Electron Density ◽  
Diels Alder ◽  
Structural Isomers ◽  
Ene Reactions ◽  
Aromatic Character ◽  
Molecular Electron ◽  
Molecular Electron Density Theory ◽  
Electrophilic Character ◽  
Selective Formation ◽  
Very High

The competitiveness of the BF3 Lewis acid (LA) catalyzed polar Diels–Alder (P-DA) and polar Alder-ene (P-AE) reactions of 2-methyl-1,3-butadiene, a diene possessing an allylic hydrogen, with formaldehyde has been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. Coordination of BF3 LA to the oxygen of formaldehyde drastically accelerates both reactions given the high electrophilic character of the BF3:formaldehyde complex. As a consequence, these reactions present a very low activation enthalpy—less than 2.2 kcal·mol−1—thus becoming competitive. In dioxane, the P-AE reaction is slightly favored because of the larger polar character of the corresponding transition state structure (TS). In addition, the Prins reaction between hexahydrophenanthrene and the BF3:formaldehyde complex has also been studied as a computational model of an experimental P-AE reaction. For this LA-catalyzed reaction, the P-DA reaction presents very high activation energy because of the aromatic character of the dienic framework. The present MEDT study allows establishing the similarity of the TSs associated with the formation of the C–C single bond in both reactions, as well as the competitiveness between P-AE and P-DA reactions when the diene substrate possesses at least one allylic hydrogen, thus making it necessary to be considered by experimentalists in highly polar processes. In this work, the term “pseudocyclic selectivity” is suggested to connote the selective formation of structural isomers through stereoisomeric pseudocyclic TSs.

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

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3638
Author(s):  
Luis R. Domingo ◽  
Mar Ríos-Gutiérrez ◽  
María José Aurell
Keyword(s):  
Electron Density ◽  
Topological Analysis ◽  
Activation Energies ◽  
High Reactivity ◽  
Diels Alder ◽  
Electron Density Transfer ◽  
Molecular Electron ◽  
Iminium Cations ◽  
Molecular Electron Density Theory ◽  
Density Transfer

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, ω > 8.20 eV, accounts for the high reactivity of these species participating in I-DA reactions. The activation energies are found to be between 13 and 20 kcal·mol−1 lower in energy than those associated with 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 on the geometries. In acetonitrile, the activation energies increase slightly as a consequence of the better solvation of the iminium cations than the cationic TSs. Electron localization function (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 establishes 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 types of DA reactions.

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

Chemistry ◽  
2021 ◽  
Vol 3 (3) ◽  
pp. 834-853
Author(s):  
Luis R. Domingo ◽  
Mar Ríos-Gutiérrez ◽  
María José Aurell
Keyword(s):  
Electron Density ◽  
Electronic Structures ◽  
Activation Enthalpy ◽  
Topological Analysis ◽  
Chair Conformation ◽  
Diels Alder ◽  
Molecular Electron ◽  
One Step ◽  
Molecular Electron Density Theory ◽  
Step Mechanism

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 diastereo selectivity, 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.

scholarly journals A molecular electron density theory study of the participation of tetrazines in aza-Diels–Alder reactions

RSC Advances ◽  
2020 ◽  
Vol 10 (26) ◽  
pp. 15394-15405 ◽  
Author(s):  
Luis R. Domingo ◽  
Mar Ríos-Gutiérrez ◽  
Patricia Pérez
Keyword(s):  
Electron Density ◽  
Diels Alder ◽  
Molecular Electron ◽  
Molecular Electron Density Theory ◽  
Electron Withdrawing Substituents

The electron-withdrawing substituents on the tetrazine favour aza-Diels–Alder reactions towards nucleophilic ethylenes, but they do not react with electrophilic ethylenes.

A Study of the Effects of the Lewis Acid Catalysts on Oxa‐Diels‐Alder Reactions through Molecular Electron Density Theory

2020 ◽  
Vol 5 (17) ◽  
pp. 5341-5348 ◽  
Author(s):  
Saeedreza Emamian ◽  
Luis R. Domingo ◽  
Seyed Javad Hosseini ◽  
Safa Ali‐Asgari
Keyword(s):  
Electron Density ◽  
Lewis Acid ◽  
Diels Alder ◽  
Acid Catalysts ◽  
Lewis Acid Catalysts ◽  
Molecular Electron ◽  
Molecular Electron Density Theory

On the Catalytic Effects of the Thiazolium Salt in the Oxa-Diel-Alder Reaction between Benzaldehyde and Danishefsky’s Diene: A Molecular Electron Density Theory Study

2021 ◽  
Author(s):  
Mar Ríos-Gutiérrez ◽  
Patricia Perez ◽  
Luis R. Domingo ◽  
Jorge Soto-Delgado
Keyword(s):  
Ionic Liquid ◽  
Electron Density ◽  
Alder Reaction ◽  
Diels Alder ◽  
Molecular Electron ◽  
Molecular Electron Density Theory ◽  
Danishefsky's Diene ◽  
Catalytic Effects

The oxa-Diels-Alder (ODA) reaction of benzaldehyde with the Danishefsky diene in the presence of [thiazolium][Cl] salt, as a model of an ionic liquid, has been studied within Molecular Electron Density...

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