Reaction of 1,3,4,6-tetrakis(alkylthio)-2λ4δ2-thieno[3,4-c]thiophenes with trifluoroacetic acid and with Vilsmeier reagent, and synthesis of new 2λ4δ2-thieno[3,4-c]thiophene derivatives

Abstract

2λ⁴δ²-Thieno[3,4-c]thiophenes 1a, 1c and 1d possessing t-butylthio substituents reacted with trifluoroacetic acid to give the thione derivatives 3a, 3′c and 3′d through the intermediary formation of a proton adduct, 1H-thieno[3,4-c]thiophenium trifluoroacetates, followed by cleavage of the Bu^t–S bond. Treatment of the thione 3a with sodium hydride and then an alkyl iodide gave 2λ⁴δ²thieno[3,4-c]thiophenes 1c and 5–7. The reaction of 2λ⁴δ²-thieno[3,4-c]thiophenes 1a–e with trifluoroacetic acid and water resulted in the formation of thieno[3,4-c] thiophen-1(3H)-ones 9–12. Compounds 1a and 1b reacted with Vilsmeier reagent to give mono- and di-formyl-substituted 2λ⁴δ²-thieno[3,4-c]thiophenes 15a, 15b and 16b. Furthermore, formyl-substituted derivatives 15a and 16b reacted with malononitrile, ethyl cyanoacetate, and N,N-dimethylhydrazine to give the condensed compounds 17–21.