Claisen, Cope and related rearrangements

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. 

The synthetic utility of this process can be seen by evaluating the examples in Table 2. For example, because the cyclopropane serves as a pseudo alkene and because the [1.5] shift requires a six-memb ed transition state, it relates conceptually to the Cope and Claisen rearrangements. The 7,8-unsaturated carbonyl compounds in Table 2 are those that would otherwise be obtained via Claisen or orthoester Claisen rearrangements, which are normally effected under strongly acidic or strongly basic conditions (Scheme 3). 

The rearrangement of modified glycals provides novel strategies to the preparation of C-glycosides. Such reactions involve the sigmatropic mechanisms associated with both Cope and Claisen reactions. In this section, these and related reactions are presented. 

The various [3,3]-sigmatropic reactions related to the Cope and Claisen rearrangements have proved to be very useful for stereoselective formation of carbon-carbon bonds. 

The Claisen rearrangemenC is a thermal rearrangement of allyl aryl ethers and allyl vinyl ethers respectively. It may be regarded as the oxa-version of the closely related Cope rearrangement. Claisen has discovered this reaction first on allyl vinyl ethers 1, and then extended to the rearrangement of allyl aryl ethers 2 to yield o-allylphenols 3 ... 

According to the Woodward-Hoffmann rales, five concerted transition states are possible for the Claisen as well as the closely related Cope rearrangements chair, boat, twist, cross and plane (Table 6). Only the chair and boat TS have to be considered, as twist, cross and plane are antarafacial-anta-rafacial processes and require highly elevated temperatures. - For the correct prediction of product stereochemistry it is nevertheless crucial to know the preference for chair- or boat-like transition state in the actual 3,3-sigmatropic shift. 

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