Peculiar Features of the Reduction of Keto Group in the Synthesis of Mono- and Dialkyl-Substituted Benzo[b]benzo[4,5]thieno[2,3-d]thiophene

Mono- and dioctyl-substituted benzo[b]benzo[4,5]thieno[2,3-d]thiophenes C8-BTBT and C8-BTBT-C8 that are widely used as organic semiconductors in the manufacture of various organic electronic devices have been synthesized in two steps, by Friedel–Crafts acylation of benzo[b]benzo[4,5]thieno[2,3-d]­thiophene (BTBT) and subsequent reduction of the ketone group(s). Taking into account that the limiting stage in the synthesis of such compounds is the reduction stage, different methods for the reduction acyl-substituted BTBT derivatives have been studied and probable reduction mechanisms have been proposed. The best results in the keto group reduction stage have been obtained with the use of hydrazine hydrate as reducing agent.