Synthesis of thiophene-fused heptalenes by cycloaddition of azulenothiophenes with dimethyl acetylenedicarboxylate

Heptalene has a fused structure of two cycloheptatrienes which is one of the non-aromatic bicyclic molecules with a 12π-electronic structure. We report herein the synthesis of thiophene-fused heptalene derivatives from the corresponding azulenothiophenes via cycloaddition reaction with dimethyl acetylenedicarboxylate. Their structure was clarified by single-crystal X-ray structural analysis. The electronic properties of the thiophene-fused heptalenes obtained by this study were characterized by UV/Vis and fluorescence spectroscopy measurements. The electrochemical features of these derivatives were also examined by voltammetry and spectroelectrochemical experiments.