A New Route to Annulated Oligothiophenes

A new convenient method for the construction of thiophene-annulated thieno[2,3-b]thiophenes has been proposed. The key step of the method is ring closure of 10H-bisthienodithiocin-10-one by strong bases. The syntheses of two previously unknown annulated oligothiophenes, thieno[2,3-b]thieno[3‘,2‘:4,5]thieno[3,2-d]thiophene (1a) and thieno[3,2-b]thieno[2‘,3‘:4,5]thieno[3,2-d]thiophene (1b), have been described to illustrate the success of the method.