Kinetics of the Cope rearrangement of a 3,4-diphenylhexa-1,5-diene

Lutz, Raymond P.; BERG, H. A. J.

doi:10.1021/jo01307a038

Cited by 16 publications

(4 citation statements)

References 2 publications

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“…Many Cope rearrangements proceed at markedly higher temperatures than the 11 a to 7 a conversion . The closely related rac ‐3,4‐diphenyl‐1,5‐hexadiene to trans , trans ‐1,6‐diphenyl‐1,5‐hexadiene rearrangement was reported to take place at about 100 °C . Therefore, we assume essential participation of the B(C 6 F 5 ) 2 substituent in the Cope rearrangement of 11 a .…”

Section: Methodssupporting

confidence: 94%

Borane‐Induced Dimerization of Arylallenes

et al. 2018

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A series of arylallenes react with HB(C6F5)2 in a 2:1 molar ratio to give the tail‐to‐tail 1,6‐diaryl‐2‐boryl‐hexa‐1,5‐diene coupling products. The reaction of the phenylallene substrate with HB(C6F5)2 was shown to initially give the 2‐boryl‐3,4‐diphenyl‐1,5‐hexadiene head‐to‐head coupling product which then rearranged, by a thermally induced Cope rearrangement, into the final product.

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Section: Methodssupporting

confidence: 94%

Borane‐Induced Dimerization of Arylallenes

et al. 2018

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“…They assumed that the parent Cope reaction might float between concerted cyclic and a biradical mechanism and that substituted cases are more likely to proceed via biradicals 39,40. These results have been confirmed by Wehrli et al,41 Lutz,42 and Gajewski and Conrad43 in the 1970s and 1980s. The conclusion drawn had been that the TS changes from virtually synchronous and aromatic for the parent system to a stepwise pathway with a real intermediate in 2,5‐disubstituted cases such as in 2,5‐diphenyl‐1,5‐hexadiene.…”

Section: Historical Survey Of the Cope Rearrangementmentioning

confidence: 74%

The Cope rearrangement—the first born of a great family

Graulich

2011

WIREs Comput Mol Sci

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This review takes the experimental and theoretical discussions on the Cope rearrangement as the basis to emphasize its tight connection to many closely related pericyclic reactions. The Cope reaction, which is rather simple in a formal sense, has led to a plethora of mechanistic discussions to determine the nature of biradical-like intermediates or transition structures. After intense experimental and theoretical investigations starting in the late 1960s, the Cope rearrangement turned out to be a multifaceted reaction with a 'chameleonic' nature, ranging from homoaromatic transition structures to biradical intermediates in substituted cases, and six-electron transition states in the parent system. Additionally, the Cope rearrangement served as an excellent example to probe theoretical methods for the computations of a variety of pericyclic reactions. However, the relationship of the Cope rearrangement with analogous reactions has been hampered by the notion that pericyclic reactions typically are assumed to proceed in a concerted fashion. Only in the past 10 years, the Cope reaction, with its 1,5hexadiene unit, emerged as the structural and mechanistic prototype of a large family, including sigmatropic, cycloaddition, and other electrocyclic reactions as well as thermal rearrangements of polyunsaturated systems, enediynes, eneyneallenes, and many others. The recurrent and interconnecting motif in this family of reactions is the questions regarding cyclic aromatic transition states and the possible involvement of biradical intermediates.

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“…However, substrate modifications can significantly reduce the barrier to rearrangement. The accelerating effects of phenyl and electron-withdrawing groups, in particular, at the 2,5-positions, are well documented. − In addition, strain release in the divinylcyclopropane rearrangement greatly accelerates the Cope process, with reactions often occurring at ambient temperature. , Similarly, the anionic oxy-Cope incorporates a C-3 alkoxide that weakens the adjacent 3,4-bond and allows for room-temperature reactions − and below . These latter examples also have the advantage of overcoming the lack of a natural forward equilibrium found in the parent substrate, 1,5-hexadiene.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of an Organocatalytic Cope Rearrangement Involving Iminium Intermediates: Elucidating the Role of Catalyst Ring Size

Sanders

Jun

et al. 2020

J. Am. Chem. Soc.

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The mechanism of the organocatalytic Cope rearrangement is elucidated through a combined computational and experimental approach. As reported previously, hydrazides catalyze the Cope rearrangement of 1,5-hexadiene-2-carboxaldehydes via iminium ion formation, and seven- and eight-membered ring catalysts are more active than smaller ring sizes. In the present work, quantum mechanical computations and kinetic isotope effect experiments demonstrate that the Cope rearrangement step, rather than iminium formation, is rate-limiting. The computations further explain how the hydrazide catalyst lowers the free-energy barrier of the Cope rearrangement via an associative transition state that is stabilized by enehydrazine character. The computations also explain the catalyst ring size effect, as larger hydrazide rings are able to accommodate optimal transition-state geometries that minimize the unfavorable lone-pair repulsion between neighboring nitrogen atoms and maximize the favorable hyperconjugative donation from each nitrogen atom into neighboring electron-poor sigma bonds, with the seven-membered catalyst achieving a nearly ideal transition-state geometry that is comparable to that of an unconstrained acyclic catalyst. Experimental kinetics studies support the computations, showing that the seven-membered and acyclic hydrazide catalysts react 10 times faster than the six-membered catalyst. Unraveling the mechanism of this reaction is an important step in understanding other reactions catalyzed by hydrazides, and explaining the ring size effect is critical because cyclic catalysts provide a constrained scaffold, enabling the development of asymmetric variants of these reactions.

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Kinetics of the Cope rearrangement of a 3,4-diphenylhexa-1,5-diene

Cited by 16 publications

References 2 publications

Borane‐Induced Dimerization of Arylallenes

Borane‐Induced Dimerization of Arylallenes

The Cope rearrangement—the first born of a great family

Mechanism of an Organocatalytic Cope Rearrangement Involving Iminium Intermediates: Elucidating the Role of Catalyst Ring Size

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