Ferrocenylmethylene-bridged calix[4]azulene derivative 3 and bis(1-azulenyl)ferrocenylmethane derivative 4 were obtained by the reaction of 6-tert-butylazulene (6) with ferrocenecarbaldehyde (7) in acetic acid. The new bis(1-azulenyl)ferrocenylmethylium ion 5⁺ was also generated by the hydride abstraction reaction of the corresponding hydro derivative 4 with DDQ. The novel ferrocene-substituted calix[4]azulene derivative 3 exhibit a reversible one-step multi-electron oxidation upon cyclic voltammetry.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Preparation of thienylazulenes 3–6 was established by the palladium-catalyzed cross-coupling reaction of the corresponding haloazulenes with thienylmagnesium ate complexes, which were readily prepared from the corresponding bromothiophenes. The reaction of 3–6 with several sulfoxides in the presence of Tf₂O, followed by treatment with triethylamine afforded the corresponding 1,3-bis(methylthio)- and 1,3-bis(phenylthio)-2- and 6-thienylazulenes 7–12 in good yields. Redox behavior of the novel azulene derivatives with 2- and 3-thienyl-substituted 3–12 was examined by cyclic voltammetry and differential pulse voltammetry, which revealed amphoteric redox behavior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Electrophilic ipso-substitution reactions between 1,3,6-tri-tert-butylazulene (2) and several electrophilic reagents were examined. Friedel–Crafts and Vilsmeier reactions of 2 gave the corresponding ipso-substitution products in moderate to excellent yields. One of the ipso-substitution products, 1,6-di-tert-butyl-3-formylazulene (5), was converted in high yield into the synthetically more useful azulene derivative 1,6-di-tert-butylazulene (1) by decarbonylation on treatment with pyrrole in acetic acid. Treatment of 2 with N-[(trifluoromethyl)sulfonyl]pyridinium trifluoromethanesulfonate (TPT) unexpectedly afforded 1-trifluoromethylthioazulene 10 and 1(8H)-azulenone 11. Compound 2 also reacted with tetracyanoethylene (TCNE) to give an excellent yield of cycloaddition product 13, rather than the ipso-substitution reaction product.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)