A thermal Cope rearrangement is a concerted [3,3]-sigmatropic shift, suprafacial on both allyl fragments. Use the preferred chair-like transition state and track the two cis methyl groups into the newly formed terminal alkene geometries. This gives one E and one Z alkene, structure III. Thus C; I and II instead have matching end geometries.
More Pericyclic Reactions and Photochemistry: Electrocyclic, cycloaddition and sigmatropic reactions. Diels-Alder reaction, Claisen and Cope rearrangements and their applications in organic synthesis. FMO method of analysis. Woodward-Hoffmann rules. Photochemistry of alkenes, arenes and carbonyl compounds. Photo-oxidation and photo-reduction. Di-π-methane rearrangements, Norrish type-I and II reactions. Paternό-Büchi reaction, Photo- Curtius and Wolff rearrangements. Barton and Hofmann-Lӧffler-Freytag reactions. questions
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