Synthesis of 2,5-asymmetrically substituted 3,4-diaminothieno[2,3-b]thiophenes by domino reaction.

A convenient one pot synthesis of 2,5-asymmetrically substituted thieno[2,3-b]thiophenes is developed. The method is based on consecutive domino reactions (SN2 reaction → Thorpe-Ziegler reaction) using malononitrile and carbon disulfide as starting materials with the generation of potassium 2,2-dicyanoethene-1,1-bis(thiolate) in a solution. The high yield of the target thienothiophenes was achieved using the Ziegler dilution effect.