title: Synthesis and two-electron redox behavior of diazuleno[2,1-a:1,2-c]naphthalenes.
abstract: The Diels-Alder reaction of di-2-azulenylacetylene with tetraphenylcyclopentadienone afforded 7,8,9,10-tetraphenyldiazuleno[2,1-a:1,2-c]naphthalene in one pot via autoxidation of the presumed 1,2-di-2-azulenylbenzene derivative. In contrast, a similar reaction of bis(1-methoxycarbonyl-2-azulenyl)acetylene with tetraphenylcyclopentadienone gave the 1,2-di-2-azulenylbenzene derivative. The following cyclodehydrogenation reaction of the benzene derivative with iron(III) chloride afforded diazuleno[2,1-a:1,2-c]naphthalene 6,11-bismethoxycarbonyl derivative. The redox behavior of these novel diazuleno[2,1-a:1,2-c]naphthalenes was examined by cyclic voltammetry (CV). These compounds exhibited two-step oxidation waves at +0.22 to +0.71 V upon CV, which revealed the formation of a radical cation and dication stabilized by the fused two azulene rings under the electrochemical oxidation conditions. Since the 1,2-di-2-azulenylbenzene derivative was oxidized at higher oxidation potentials (+0.83 and +1.86 V), the fusion of the two azulene rings to naphthalene increased electron-donating properties because of the formation of a closed-shell dicationic structure. Formation of the radical cation was characterized by UV-vis spectroscopy under the electrochemical oxidation conditions, although no evidence was obtained for the presumed dication under the conditions of the UV-vis spectroscopy measurement.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. ito@funorg.chem.tohoku.ac.jp
authors.forename: Shunji
authors.initials: S
authors.lastname: Ito
authors.forename: Akiko
authors.initials: A
authors.lastname: Nomura
authors.forename: Noboru
authors.initials: N
authors.lastname: Morita
authors.forename: Chizuko
authors.initials: C
authors.lastname: Kabuto
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Seiko
authors.initials: S
authors.lastname: Maejima
authors.forename: Kunihide
authors.initials: K
authors.lastname: Fujimori
authors.forename: Masafumi
authors.initials: M
authors.lastname: Yasunami