Wittig-reactions of thieno[2′,3′:1,2]benzo[4,5-b]thiophene-2,6-dicarboxaldehyde (8a) with “mono- and bis-Wittig-salts” 12a–c and 9a–c poly(thieno[2′,3′:1,2]benzo[4,5-b]thiophene-2,6-diylvinylenearylenevinylene)s 10a–c and some model compounds 13a–c were obtained. Analogous reactions of 4,8-dimethoxythieno[2′,3′:1,2]benzo[4,5-b]thiophene-2,6-dicarboxaldehyde (8b) gave the corresponding poly(4,8-dimethoxythieno[2′,3′:1,2]benzol[4,5-b]thiophene-2,6-diylvinylenearylenevinylene)s 11a–c and their model compounds 14a–c. Wittig-reactions of benzo[b]thiophene-2-carboxaldehyde (15) with “mono- and bis-Wittig-salts” gave model compounds 16a–c and 17a, c. A new synthesis of thieno[2′,3′:1,2]benzo[4,5-b]thio-phene (4) was worked out. 4,8-Dimethoxythieno[2′,3′:1,2]benzo[4,5-b]thiophene (7) and dicarboxaldehydes 8a and 8b were synthesized for the first time. The structures of all compounds were confirmed by elemental analyses, IR and electronic spectra, those of the model compounds additionally by mass spectra, and in case of sufficient solubility by 1H NMR spectra. The electrical conductivities of all polymers and their model compounds were investigated.