Intramolecular Diels-Alder reactions of pyrimidines and a computational study toward their structure and reactivity

1992 ◽  
Vol 57 (11) ◽  
pp. 3000-3007 ◽  
Author(s):  
Werner A. W. Stolle ◽  
August E. Frissen ◽  
Antonius T. M. Marcelis ◽  
Henk C. Van der Plas
Keyword(s):  
Computational Study ◽  
Diels Alder

On the Mechanism of Au‐catalyzed Enynamide‐Yne Dehydro‐Diels‐Alder Reactions: An Experimental and Computational Study

2021 ◽  
Author(s):  
David Fabian León Rayo ◽  
Young J. Hong ◽  
Dominic Campeau ◽  
Dean J. Tantillo ◽  
Fabien Gagosz
Keyword(s):  
Computational Study ◽  
Diels Alder

A computational study towards the reactivity of 2-(2-ethynylphenyl-X-)pyrimidines in intramolecular Diels-Alder reactions.

Tetrahedron ◽  
1991 ◽  
Vol 47 (9) ◽  
pp. 1753-1764 ◽  
Author(s):  
W.A.W. Stolle ◽  
A.T.M. Marcelis ◽  
H.C. van der Plas
Keyword(s):  
Computational Study ◽  
Diels Alder

Origins of the diastereoselectivity in hydrogen bonding directed Diels–Alder reactions of chiral dienes with achiral dienophiles: a computational study

2011 ◽  
Vol 9 (23) ◽  
pp. 8079 ◽  
Author(s):  
Sesil Agopcan ◽  
Nihan Çelebi-Ölçüm ◽  
Melek Nihan Üçışık ◽  
Amitav Sanyal ◽  
Viktorya Aviyente
Keyword(s):  
Hydrogen Bonding ◽  
Computational Study ◽  
Diels Alder

QTAIM–DI–VISAB computational study on the Diels–Alder reaction of cyclopentadiene — On the nature of the so-called secondary orbital interactions

2008 ◽  
Vol 86 (7) ◽  
pp. 737-744 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Wojciech Sokol
Keyword(s):  
Computational Study ◽  
Transition States ◽  
Alder Reaction ◽  
Diels Alder ◽  
Physical Organic Chemistry ◽  
Hydrogen Atoms ◽  
Endo Isomer ◽  
Orbital Interactions ◽  
Physical Organic ◽  
Diels Alder Reaction

We have undertaken a QTAIM–DI–VISAB computational study of the dimerization of cyclopentadiene (1), the archetypal example of a Diels–Alder reaction that has been studied experimentally and computationally. Secondary orbital interactions (SOIs) that have gained acceptance in the interpretation of stereoselectivities seen in many cycloaddition reactions have been used to account for the fact that the endo isomer was the kinetic product of the reaction. To this point, “classical” MO analyses along with a variety of arbitrarily assigned solid and dashed lines (solid lines and bold dashes for “primary” interactions and dashed and dotted lines to differentiate between different SOI schemes) have been used in an attempt to describe the bonding of the transition states. Yet, the existence of SOIs has been challenged. Our interest in applying QTAIM to fundamental chemical problems in physical organic chemistry, with the goal of refining our knowledge of the bonding in transition-states and ground-state molecules while obviating the need to use a variety of confusing arbitrarily assigned dashed and dotted lines, led us to a QTAIM–DI–VISAB computational study of the endo and exo dimerizations of 1 at the DFT B3PW91 and MPW1PW91 levels. We have characterized the bonding interactions between cyclopentadiene rings in the various transition states and show that “normal” bonds are present where SOIs have been considered to exist. There is no need to use different types of dashed and dotted lines. An analysis of the changes in atom energies revealed that the significant destabilization of the carbon atoms in achieving the TSs (potentially leading to a very high barrier) is ameliorated by a stabilization of the hydrogen atoms leading to the relatively low barrier for the D–A reaction.Key words: cyclopentadiene dimerization, bispericyclic transition states, DFT calculations, QTAIM–DI–VISAB analysis, bonding, atom energy analysis.

scholarly journals A Computational Study of the Relative Aromaticity of Pyrrole, Furan, Thiophene and Selenophene, and Their Diels-Alder Stereoselectivity

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Computational Study ◽  
Lone Pair ◽  
Alder Reaction ◽  
Diels Alder ◽  
Size Mismatch ◽  
Aromatic Character ◽  
Diels Alder Reaction ◽  
Ground State Structures ◽  
Better Than

The collinearity of terminal <i>p</i> orbitals of a diene with that of a dienophile is required for an effective overlap to result in s bond formation during the Diels-Alder reaction. The ease of the DA reaction of a cyclic diene with a given dienophile, therefore, must also depend on the distance between the termini of the diene. A distance larger than the unsaturated bond of the dienophile is expected to raise the energy of activation. This scenario has been amply demonstrated from the study of reactions of several dienes, some designed to serve the purpose, with different dienophiles. The five-ring heterocycles pyrrole, furan, thiophene and selenophene possess varying aromatic character for the varied resonance participation of the heteroatom lone pair with ring p bonds. The aromaticity decreases in the same order due to: (a) the increasing s<sub>C-X</sub> (X = heteroatom) bond length lifts the bond uniformity required for ring current, hence aromaticity, such as in benzene and (b) size-mismatch of the interacting lone pair orbital and the ring <i>p</i> orbitals, especially in thiophene and selenophene, both allowing poor overlap in the ground state structures. It is demonstrated that increase alone in the activation energies of the DA reactions of pyrrole, furan, thiophene and selenophene cannot be considered a measure of relative aromaticity as often done and even theoretically attempted in many ways to prove just that. The separation of the termini of the diene has a much larger role in the determination of activation energy, especially in thiophene and selenophene, than their aromaticity profile. There cannot be a measure better than the relative intensity of heteroatom lone pair overlap with ring p bonds, giving rise to a six-electron like system in following Hückel’s 4n+2 rule, to assess the relative aromaticity.

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