Liviu Birzan

Azulene-1-azopyridine 1′-oxides

The coupling between diazonium salts obtained from the three aminopyridine 1-oxides and azulene allowed the synthesis in good yield of the corresponding azulene-1-azopyridine 1 0 -oxides, which were characterised. The reduction and the methylation of the products were studied. The last two reactions allowed to synthesize azulene-1-azo-2 0 -pyridine and its alkylpyridinium salts, unavailable on other way. The UV–vis spectra of azulene-1-azopyridines were compared with those of the corresponding N-oxides and pyridinium salts. For the N-oxides the solvatochromic effect was evidenced. # 2003 Elsevier Science Ltd. All rights reserved.

AZULENE-1-AZOPYRIDINES. SYNTHESIS AND N-ALKYLATION AT PYRIDINE MOIETY

ABSTRACT Azulene-1-azo-(3′- and 4′-pyridines) were synthesised from azulenes and diazotized aminopyridines. The mechanism for the generation of the diazonium salt was discussed. The obtained azulene-1-azo pyridines were alkylated with alkyl, benzyl and allyl halides.

1-Phenylselanylazulenes: synthesis and selenium atom oxidation

The phenylselanylation of azulene with PhSeCl or PhSeBr was reported. Clean electrophilic substitution of azulene in positions 1 and/or 3 occurred with the first reagent whereas with PhSeBr a complex mixture of products was generated suggesting a radicalic mechanism. The influence on the reaction route of the substituent attached at position 1 of azulene, or of the alkyl positions in alkylated azulenes was investigated. 1-Phenylselanylazulene and 1,3-bis(phenylselanyl)azulene were oxidized using sodium metaperiodate. The oxidation took place at selenium atom and afforded azulenes substituted with PhSe(O) and/or PhSe(O2) groups in positions 1 and/or 3. The magnetic and electronic spectra as well as the electrochemical oxidation and reduction potentials of the obtained products were recorded and the results were briefly discussed.Graphical abstract.

Synthesis and reactions of N-(azulen-1-ylmethylene)arylamines

N-(Azulen-1-ylmethylene)arylamines, 5, were obtained in a fast quantitative conversion and high yield from the condensation of the corresponding azulene-1-carbaldehydes with aromatic amines without solvent. The reactions of the Schiff bases obtained, 5, were compared to those of the corresponding azo compounds 1a which have already been studied. The lack of regioselectivity in the oxidation of 5 with anhydrous FeCl3 at both the azulenyl and at the aryl moiety, in contrast with the oxidation of compounds 1a which react mainly at the aryl, is in agreement with the differences of the calculated Fukui one electron reactivity index squared (IR2) for the reactive positions in these molecules. From the calculated net charge for different positions in the molecules, a regioselective course for the electrophilic halogenation with CuCl2 for both compounds 1a and 5 (at C3 in the azulene moiety) can be foreseen. However, the Schiff bases were chlorinated also at the aromatic ring; an explanation was proposed for this behaviour.

Synthesis of azulenic compounds substituted in the 1-position with heterocycles

The review proposes an overview of the important general routes for the achievement of 1-heteroarylazulenes using both azulene substitution by heterocycles and azulenic cyclic construction pathways. With strong electrophilic heterocyclic derivatives, the electrophilic substitution takes place while concerted route is adopted for medium and low reactive heterocyclic substrates. Particular attention has been paid to the heterocycles construction from the functional groups attached to azulenic 1-position.Graphical abstract

On the electrochemical behavior of selanyl azulenes

The electrochemical behavior of substituted 1-phenylselanyl azulenes has been established by cyclic, differential pulse, and rotating disk electrode voltammetric methods. The redox potentials and the number of electrons exchanged in the main redox processes have been examined in connection with the electronic effects of their substituents. Controlled potential electrolyses have been performed in order to point out the products associated to the redox peaks. A mechanism to explain the redox processes has been proposed.

Thermodynamics of interactions between lead(II) and cadmium(II) ions and azulene-based complexing polymer films

In order to understand the essential processes/interactions between the metal ions and modified electrodes which are based on complexing polymeric films, access to thermodynamic characteristics is compulsory. The paper enlarges the information concerning the sorption of metal ions within complexing polymer films, particularly based on azulene, which can be involved in metal detection sensors. Interactions between lead(II) or cadmium(II) ions and complexing polymer films have been studied using chemical preconcentration–anodic stripping method. The films have been obtained by controlled potential electrolysis in millimolar solutions of 4-azulen-1-yl-2,6-bis(2-thienyl)pyridine (L) in acetonitrile. PolyL films affinities towards these metal ions have been quantified at different temperatures by means of sorption isotherms. Parameters for sorption of lead(II) and cadmium(II) ions within polyL films have been calculated for Freundlich, Langmuir and Redlich–Peterson isotherms. The best fit was obtained when using Langmuir isotherm. The results evidence that lead ions are better sorbed than cadmium within polyL film. Thermodynamic parameters for the chemical sorption of lead(II) and cadmium(II) ions within polyL films have been calculated.

Electrochemistry of functionalized azo azulenes

The electrochemical study of certain azulene bis azo derivatives meta or para substituted is connected to the potential applications (enhanced NLO coefficients [1] and electrochromic behaviour) of this type of compounds. New compounds were studied by cyclic (CV) and differential pulse voltammetry (DPV), in TBABF4 0.1 M, CH3CN or CH3CHCl2 in order to find some rules regarding the influence of substituents position versus azo groups on the redox behaviour of azulene and azo groups. These electrochemical methods allowed establishing the oxidation and reduction processes characteristic for this type of compounds. Comparisons with common azo derivatives lead to conclusions regarding the enhanced azulene electro-reactivity in respect with aromatic structures [2]. The presence of two azo groups, especially when are para orientated, increases the polarization of the molecule, fact that facilitates the electrochemical generation of radical-ions. The presence of the alkyl substituents modifies both the electron density and the planarity of the azulene moiety toward the rest of the molecule. The modification of the glassy carbon electrodes with the polyazulene films was tested in view of obtaining new electrode materials [3]. The modulation of the structure parameters lead to important changes in the polymerization process being connected to the redox potentials and concentration in the synthesis solution. The formation of substituted poly-azo-azulene films was accomplished through electrochemical oxidation by scanning or controlled potential electrolysis. Conductive or isolating films have been obtained on glassy carbon, using CH3CN or CH3CHCl2 as solvents and 0.1 M TBAP or TBABF4 as supporting electrolytes [2], starting from differently substituted bis azo azulenes.

Synthesis and properties of 4-(3-substituted azulen-1-yl)-2,6-diphenylpyridines

The syntheses of 4-azulen-1-yl-2,6-diphenylpyridines substituted at the azulene C-3 moiety with electron donating or withdrawing groups, are reported. When electron-donating groups (EDG) are present, the reaction of the corresponding pyranylium perchlorates and ammonium acetate takes place. Because of the difficulties in the generation of pyranylium salts with electronwithdrawing groups (EWG), the corresponding pyridines are obtained by a PdCl2-promoted substitution of halogen in 4-chloro-2,6-diphenylpyranylium salt, with an azulene derivative followed by an in situ replacement of oxygen with nitrogen. The physical and chemical properties of the pyridines obtained are discussed.