title: Five-membered ring annelation in [2.2]paracyclophanes by aldol condensation.
abstract: Under basic conditions 4,5,12,13-tetraacetyl[2.2]paracyclophane (9) cyclizes by a double aldol condensation to provide the two aldols 12 and 15 in a 3:7 ratio. The structures of these compounds were obtained from X-ray structural analysis, spectroscopic data, and mechanistic considerations. On acid treatment 12 is dehydrated to a mixture of the condensed five-membered [2.2]paracyclophane derivatives 18-20, whereas 15 yields a mixture of the isomeric cyclopentadienones 21-23. The structures of these elimination products are also deduced from X-ray and spectroscopic data. The sequence presented here constitutes the simplest route so far to cyclophanes carrying an annelated five-membered ring.
authors.affiliation: Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Hopf
authors.affiliation: Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany.
authors.forename: Swaminathan Vijay
authors.initials: SV
authors.lastname: Narayanan
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Postfach 3329, D-38106 Braunschweig, Germany.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Jones
keywords: X-ray analysis; aldol condensation; cyclopentadienones; cyclophanes; multibridged cyclophanes; stereochemistry