The electrochemical features of these derivatives were also examined by voltammetry and spectroelectrochemical experiments. The electronic properties of the thiophene-fused heptalenes obtained by this study were characterized by UV/Vis and fluorescence spectroscopy and theoretical calculations. The structural feature of the heptalene derivatives was elucidated by single-crystal X-ray structural analysis. In this paper, we describe a synthesis of thiophene-fused heptalene derivatives from the readily accessible starting materials, i.e., azulenothiophenes. Although thiophene-fused heptalene derivative 3 has already been reported as described above, preparation of much simpler derivatives should be essential for better understanding the nature of these series. In these researches, we have reported the synthesis, optical and electrochemical properties of azulenothiophene derivatives 23, 26, 27, 28 that become good precursors for the thiophene-fused heptalenes. In recent years, we have investigated the novel synthetic methods for various azulene derivatives and explored their distinctive reactivity 16, 17, 18, 19, 20, 21, 22, 23, 24, 25.

However, there are few examples of the synthesis of heptalenes by the reaction of ring-fused azulene derivatives with DMAD, and the properties of the ring-fused heptalene derivatives have hardly been evaluated, although a number of azulene derivatives may become a promising precursor for the heptalene synthesis. have reported the synthesis and reactivity of several fused-heptalenes including benzene-fused derivatives 6, 7, 8, 9, 10, 11, 12, 13, 14, 15. The reaction of benzoazulene with DMAD gives benzene-fused heptalene derivative 2b, which is demonstrated by Yasunami et al. reported the cycloaddition reaction of azulene itself with DMAD to afford heptalene derivative 1b with two-ester functions 4. In addition to the above synthetic procedures, preparation of the heptalene skeleton is established by using the reaction of azulene derivatives with dimethyl acetylenedicarboxylate (DMAD). Recently, Fukazawa, Yamaguchi, and their colleagues have achieved the synthesis of kinetically stabilized heptalene 3 fused by four thiophenes by reductive cyclization of bisdehydroannulene with sodium metal, as well as its dianion (Fig. established the preparation of benzo-fused heptalene 2a, but 2a is still unstable and the synthetic protocol requires a multi-step pathway 2. In 1961, the first synthesis of parent heptalene 1a was reported by Dauben Jr. Therefore, a number of synthetic methods for the heptalene derivatives have appeared in the literature. Fascinated by such unique properties, many researchers have studied the synthesis and characterization of various heptalene derivatives. Heptalene produces the stabilized aromatic dication and dianion with 10π- and 14π-electrons by two-electron oxidation and reduction, respectively. Heptalene has a fused structure of two cycloheptatrienes which is one of the non-aromatic bicyclic molecules with a 12π-electronic structure.

Bruker apex iii -ii