Non-Concerted Cope Rearrangement

✍ Scribed by Wolfgang R. Roth; Rolf Gleiter; Volker Paschmann; Ulrich E. Hackler; Gerd Fritzsche; Holger Lange

• Book ID: 102658360
• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 618 KB
• Volume: 1998
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/(sici)1099-0690(199806)1998:6<961::aid-ejoc961>3.0.co;2-b

✦ Synopsis

The observation of practically identical activation parameters for the Cope rearrangement 2 Ǟ 6 and its "frustrated" counterpart 1 Ǟ 5 indicates a two-step mechanism for the reaction 2 Ǟ 6. Direct proof of this interpretation comes from trapping experiments, which demonstrate the intermediate formation Recently, the syntheses, properties and reactions of the highly strained polyenes 1؊4 have been reported. For the Cope rearrangement leading to 6؊8, a two-step mechanism must be considered in view of the highly strained nature of starting materials and the products, respectively. In 1,5hexadiene, the non-concerted pathway is destabilized by 59.7 Ϫ33.5 ϭ 26.2 kcal•mol Ϫ1 ; this could not be counterbalanced by the introduction of radical stabilizing substituents because a comparable stabilization was also observed for the concerted route.