Cope and related rearrangements

The Cope rearrangement is the reversible, thermal [3,3]-sigmatropic rearrangement of 1,5-dienes.  

Over the course of the last 68 years since the landmark discovery of this reaction, the Cope rearrangement has captivated the entire organic chemistry community, including the physical and theoretical organic chemists enthralled by the subtle details of its mechanism, and the synAetic chemists, who have used the Cope and its variants, as extremely powerful tools for the stereoselective construction of a diverse array of organic products. 

When first reported by Cope and Hardy, similarities between this and the Claisen rearrangement were immediately recognized, and it was thus hypothesized that the reaction proceeds through a concerted, intramolecular, cyclic transition state. To confirm this mechanism, a series of experiments were conducted which strongly supported Cope s initial postulate. 

Following acceptance of the concerted, cyclic mechanism, the exact nature of the transition state was discovered by Doering and Roth in 1962. Their studies demonstrated that while the reaction proceeds through either a chair-like or boat-like transition state, if both are possible, the chair-like transition state is kinetically favored.  

While the Cope rearrangement is considered to be a concerted [3,3]-sigmatropic rearrangement, it displays a unique response to attached substituents, which suggest the involvement of biradical intermediates. 

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Nowicki, J. Claisen, Cope and related rearrangements in the synthesis of flavor and fragrance compounds. Molecules [online computer file] 2000, 5, 1033-1050. 

For example, see the review Rearrangements Proceeding Through No Mechanism Pathways The Claisen, Cope, and Related Rearrangements" by Rhoads, S. J. in de Mayo, P., Ed. Molecular Rearrangements, Vol. 1 Wiley-Interscience New York, 1963 pp. 655-706. 

Numerous mechanistic studies have been done with the aim of elucidating the subtler details of the Cope and related mechanisms. However, this review focuses on the synthetic aspects of the Cope and related rearrangements, and thus, readers interested in these mechanistic explorations are directed to other reviews of this topic. ... 

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