Synthesis and redox behavior of 1,3-bis(methylthio-) and 1,3-bis(phenylthio)azulenes bearing 2- and 3-thienyl substituents by palladium-catalyzed cross-coupling reaction of 2- and 6-haloazulenes with thienylmagnesium ate complexes

Preparation of thienylazulenes3-6 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.