Structural Studies on α-Pyrone Cycloadducts. Manifestation of the Early Stages of CO2 Extrusion by retro Hetero-Diels - Alder Reaction

2009 ◽  
Vol 62 (5) ◽  
pp. 407 ◽  
Author(s):  
Jesse Roth-Barton ◽  
Yit Wooi Goh ◽  
Asimo Karnezis ◽  
Jonathan M. White
Keyword(s):  
Normal Values ◽  
Alder Reaction ◽  
Diels Alder ◽  
Structural Studies ◽  
State Structure ◽  
Transition State Structure ◽  
Early Stages ◽  
Diels Alder Reaction ◽  
Decarboxylation Reaction ◽  
Ground State Structures

Structures of the α-pyrone (pyran-2-one) cycloadducts 4–8 show deviations of some bond distances from their normal values, consistent with manifestation of the early stages of the retro hetero-Diels–Alder decarboxylation reaction in the ground state structures. Thus the bridgehead C–O(CO) and C–CO(O) bonds are lengthened and the bridging C–O bond is shortened. The degree of lengthening of the C–O(CO) and C–CO(O) bonds is similar, whereas in the calculated transition state structure there is significant asymmetry in the extent of C–CO(O) and C–O(CO) bond breaking.

Structure Correlation Study of Some Diels–Alder Cycloadducts of Anthracene

2009 ◽  
Vol 62 (5) ◽  
pp. 419 ◽  
Author(s):  
Yit W. Goh ◽  
Jonathan M. White
Keyword(s):  
Correlation Study ◽  
Alder Reaction ◽  
Diels Alder ◽  
Ground State Structure ◽  
State Structure ◽  
Structural Effects ◽  
Early Stages ◽  
Diels Alder Reaction ◽  
Structure Correlation ◽  
Qualitative Relationship

Crystal structures of some Diels–Alder cycloadducts of anthracene and a variety of dienophiles reveal structural effects consistent with the manifestation of the early stages of the retro Diels–Alder reaction in the ground state structure. The symmetrical cycloadducts 3 and 4 reveal a qualitative relationship between structure and reactivity, whereas the cycloadducts of 9-methoxyanthracene show structural effects suggestive of the early stages of an asynchronous retro Diels–Alder reaction.

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.

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.

The Diels-Alder Reaction of 2-Ethenyl-1,4-Benzodioxin: A New and Simple Synthesis of Bisaryl Ethers

Synlett ◽  
1989 ◽  
Vol 1989 (01) ◽  
pp. 30-32
Author(s):  
Thomas V. Lee ◽  
Alistair J. Leigh ◽  
Christopher B. Chapleo
Keyword(s):  
Alder Reaction ◽  
Diels Alder ◽  
Simple Synthesis ◽  
Diels Alder Reaction

The intermolecular anthracene-transfer in a regiospecific antipodal C60 difunctionalization

2020 ◽  
Author(s):  
Radu Talmazan ◽  
Klaus R. Liedl ◽  
Bernhard Kräutler ◽  
Maren Podewitz
Keyword(s):  
Noncovalent Interactions ◽  
Interaction Model ◽  
Alder Reaction ◽  
Diels Alder ◽  
Stacking Interactions ◽  
Pi Stacking ◽  
Diels Alder Reaction ◽  
Double Decker ◽  
Anthracene Molecule ◽  
New Strategies

We analyze the mechanism of the topochemically controlled difunctionalization of C60 and anthracene, where an anthracene molecule is transferred from one C60 monoadduct to another one under exclusive formation of equal amounts of C60 and the difficult to make antipodal C60 bisadduct. Our herein disclosed dispersion corrected DFT studies show the anthracene transfer to take place in a synchronous retro Diels-Alder/Diels-Alder reaction: an anthracene molecule dissociates from one fullerene under formation of an intermediate, while already undergoing stabilizing interactions with both neighboring fullerenes, facilitating the reaction kinetically. In the intermediate, a planar anthracene molecule is sandwiched between two neighboring fullerenes and forms equally strong "double-decker" type pi-pi stacking interactions with both of these fullerenes. Analysis with the distorsion interaction model shows that the anthracene unit of the intermediate is almost planar with minimal distorsions. This analysis sheds light on the existence of noncovalent interactions engaging both faces of a planar polyunsaturated ring and two convex fullerene surfaces in an unprecedented 'inverted sandwich' structure. Hence, it sheds light on new strategies to design functional fullerene based materials.<br>

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