title: An efficient novel synthesis of beta-(azuleno[1,2-b]benzothienyl)- and beta-(azuleno[2,1-b]benzothienyl)-alpha,beta-unsaturated ketones by the tropylium ion-mediated intramolecular furan ring-opening reaction and X-ray investigation of methyl ketone derivative.
abstract: Intramolecular reaction of 2-tropylio-3-(5-substituted 2-furyl)benzothiophenes (3), prepared from the corresponding 2-cycloheptatrienyl-3-(5-substituted 2-furyl)benzothiophenes (2), afforded the beta-(azuleno[1,2-b]benzothienyl)-alpha,beta-unsaturated ketones (4), which are otherwise difficult to obtain, in moderate yields. The reaction involves a ring-opening process of the furan ring by intramolecular attack of the tropylium ion onto the 2-position of the furan ring. Similarly, beta-(azuleno[2,1-b]benzothienyl)-alpha,beta-unsaturated ketones (8) were obtained from the corresponding 3-tropylio-2-(5-substituted 2-furyl)benzothiophenes (7) albeit in lower yields. The molecular and crystal structures of the methyl ketone derivative, 8a, are discussed on the basis of X-ray structure analysis.
authors.affiliation: Department of Chemistry, Faculty of Science, Kobe University, Nada, Kobe 657-8501, Japan.
authors.forename: Kimiaki
authors.initials: K
authors.lastname: Yamamura
authors.forename: Yuuko
authors.initials: Y
authors.lastname: Houda
authors.forename: Masao
authors.initials: M
authors.lastname: Hashimoto
authors.forename: Takatomo
authors.initials: T
authors.lastname: Kimura
authors.forename: Makoto
authors.initials: M
authors.lastname: Kamezawa
authors.forename: Takehiko
authors.initials: T
authors.lastname: Otani