Application of bis(iminophosphorane) in heterocyclic synthesis: New entries to symmetrically or unsymmetrically substituted thieno[2,3-d:5,4-d']dipyrimidine-4,5(3H,6H)-diones

The bis(carbodiimides) obtained from bis-aza-Wittig reactions of bis(iminophosphorane) with 2 equiv of aromatic isocyanates were reacted with secondary amine to give symmetrically substituted 2,7-diaminothieno[2,3-d:5,4-d']dipyrimidine-4,5(3H,6H)-dione. Further reaction of iminophosphoranes with aromatic isocynates and various nucleophile generated unsymmetrically substituted thieno[2,3-d:5,4-d']dipyrimidine-4,5(3H,6H)-diones in good yields.