Dibenzofurans featuring a 2,2'-biazulene framework were prepared in good yields by Brønsted acid-promoted annulation of 2,3-di(1-azulenyl)benzofurans in 100% H3PO4. The NMR, UV-Vis, and fluorescent spectroscopies were used to investigate the...
A series of benz[a]azulenes reacted with pyridinium hydrobromide perbromide (PHBPB) in hydrous tetrahydrofuran yielding the corresponding benz[a]azulenequinones in moderate yields. The detailed structure of the benz[a]azulenequinone derivative obtained was clarified by single crystal X-ray analysis.
The preparation of bis(3-methylthio-1-azulenyl)phenylmethyl cations and 1,4-phenylenebis[bis(3,6-di-tert-butyl-1-azulenyl)methyl] dications was accomplished by the hydride abstraction of the corresponding hydride derivatives, which were synthesized by the acid-catalyzed condensation of 1-azulenyl methyl sulfide with benzaldehyde and terephthalaldehyde with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. The intramolecular charge transfer among the azulene ring and the methylium moieties of these cations and dications was investigated by UV–Vis spectroscopy and electrochemical analyses. The pKR+ values of the cations were examined for their thermodynamic stability spectrophotometrically. The voltammetry experiments of these cations revealed their reversible reduction waves on their cyclic voltammograms. Moreover, a notable spectral change of cations was observed by spectroelectrochemistry during electrochemical reduction conditions.
Brønsted acid‐mediated intramolecular cyclization of 2‐amidoazulene derivatives, prepared by the reaction of 1‐cyano‐2‐aminoazulene derivatives with perfluoroalkyl acid anhydrides, resulted in the formation of 2‐perfluoroalkylazuleno[2,1‐d]pyrimidin‐4(3H)‐ones. Heating of these products in phosphoryl chloride led to 4‐chloro‐2‐perfluoroalkylazuleno[2,1‐d]pyrimidines. We also evaluated the reactivity of these pyrimidin‐4(3H)‐ones and pyrimidine derivatives toward the electrophilic and nucleophilic substitution reactions, revealing that a variety of functional groups can be incorporated into these derivatives. The NMR studies, NICS calculations, and single‐crystal X‐ray structure analyses revealed structural features including the bond‐length alternation of the azuleno[2,1‐d]pyrimidin‐4(3H)‐ones and pyrimidine derivatives.
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