title: Cascade Rearrangement of 5-Cyclopentylidenecyclooctanones.
abstract: Acid-catalyzed rearrangement of 5-cyclopentylidenecyclooctanone derivatives 9a-c was examined to obtain polyspiropolyquinanes 11a-c, considered to have a unique helical structure, through cascade rearrangement pathways consisting of continuous transannular cyclization followed by successive 1,2-alkyl shifts. The substrates were prepared easily by use of the Wittig or McMurry reaction. Reaction of the 5-cyclopentylidenecyclooctanone (9a) with acid gave the expected dispirotriquinane ketone 11a in high yield. The precise mechanism was elucidated by a deuterium-labeling experiment. In the case of the ketone 9b, having another spiroannulated cyclopentane ring attached on 9a, the trispirotetraquiane 11b was not obtained but the bis-propellane-type tetrahydrofuran 25 was produced exclusively. The 5-(5'-cyclopentylidenecyclooctylidene)cyclooctanone (9c) afforded the polycyclic compounds 27-31, depending on the acid used, instead of the desired tetraspiropentaquinane 11c. The structures of the products were determined by NMR spectral data including 2D (13)C INADEQUATE spectra and X-ray crystallographic analyses. The unexpected rearrangement pathways are also discussed.
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan.
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Kakiuchi
authors.forename: Hideki
authors.initials: H
authors.lastname: Okada
authors.forename: Nobuko
authors.initials: N
authors.lastname: Kanehisa
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kai
authors.forename: Hideo
authors.initials: H
authors.lastname: Kurosawa