title: Diazadioxa[8]circulenes: planar antiaromatic cyclooctatetraenes.
abstract: In this paper we describe a new class of antiaromatic planar cyclooctatetraenes: the diazadioxa[8]circulenes. The synthesis was achieved by means of a new acid-mediated oxidative dimerization of 3,6-dihydroxycarbazoles to yield the diazadioxa[8]circulenes in high yields. The synthetic protocol appears to be general, and is a one-pot transformation in which two C-C bonds and two C-O bonds are formed with the loss of two molecules of water. We also present a detailed characterization of the optical and electrochemical properties of this new class of stable planar cyclooctatetraenes. The properties of the diazadioxa[8]circulenes are compared with the properties of isoelectronic tetraoxa[8]circulenes and azatrioxa[8]circulenes. We discuss the antiaromatic nature of the planar central cyclooctatetraene moiety. The antiaromatic nature of the planar cyclooctatetraenes was studied by using computational methods (NICS calculations), and these calculations reveal that the central eight-membered ring has antiaromatic character.
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø (Denmark), Fax: (+45) 35320212.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hensel
authors.forename: Denis
authors.initials: D
authors.lastname: Trpcevski
authors.forename: Christopher
authors.initials: C
authors.lastname: Lind
authors.forename: Rémi
authors.initials: R
authors.lastname: Grosjean
authors.forename: Peter
authors.initials: P
authors.lastname: Hammershøj
authors.forename: Christian B
authors.initials: CB
authors.lastname: Nielsen
authors.forename: Theis
authors.initials: T
authors.lastname: Brock-Nannestad
authors.forename: Bjarne E
authors.initials: BE
authors.lastname: Nielsen
authors.forename: Magnus
authors.initials: M
authors.lastname: Schau-Magnussen
authors.forename: Boris
authors.initials: B
authors.lastname: Minaev
authors.forename: Gleb V
authors.initials: GV
authors.lastname: Baryshnikov
authors.forename: Michael
authors.initials: M
authors.lastname: Pittelkow
keywords: aromaticity; density functional calculations; electrochemistry; fluorescence; heterocycles