title: Novel synthesis of benzalacetone analogues of naphth[a]azulenes by intramolecular tropylium ion-mediated furan ring-opening reaction and X-ray investigation of a naphth[1,2-a]azulene derivative.
abstract: [reaction: see text] Benzalacetone analogues of naphth[1,2-a]azulene (8), naphth[2,1-a]azulene (13), and naphth[2,3-a]azulene (18) were synthesized from 2-(5-methyl-2-furyl)-1-tropylionaphthalene (7), 1-(5-methyl-2-furyl)-2-tropylionaphthalene (12), and 2-(5-methy-2-furyl)-3-tropylionaphthalene (17), respectively. The synthetic method is based on furan ring-opening reaction by the intramolecular electrophilic attack of a tropylium ion. Single-crystal X-ray work on the naphth[1,2-a]azulene derivative (8) revealed that its tetracyclic system exhibited deformation from planarity similar to that of benzo[c]phenanthrene (tetrahelicene). A centrosymmetric associated dimer structure, just like the molecules of carboxylic acids but via C=O...H-C hydrogen bonds, was found in the crystal. Reduction of bond-length alternation in the seven-membered ring was also found.
authors.affiliation: Department of Chemistry, Faculty of Science, Kobe University, Rokkodai, Nada, Japan. kyama@kobe-u.ac.jp
authors.forename: Kimiaki
authors.initials: K
authors.lastname: Yamamura
authors.forename: Shizuka
authors.initials: S
authors.lastname: Kawabata
authors.forename: Takatomo
authors.initials: T
authors.lastname: Kimura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Eda
authors.forename: Masao
authors.initials: M
authors.lastname: Hashimoto