Synthesis of new 1,2,4-oxadiazolidin-5-ylthiophenes and thienopyrimidine derivatives by aza-Wittig reaction using a thienyl carbodiimide

Azidation of aminothiophene derivative 1 afforded the corresponding azido derivative 2. The latter reacted with triphenylphosphine to afford iminophosphorane derivatives 3. Reacting 3 with phenylisocyanate gave the highly reactive carbodiimide intermediate 4, which was reacted with different nitrones to afford new 1,2,4-oxadiazolidin-5-ylidene-aminothiophenes 5a–c. Treatment of 4 with absolute EtOH at room temperature gave methyleneamino-5-(methylthio)thiophene 7, (methylthio)-3-(3-phenylureidothiophene)-2-carboxylate 8 or thienopyrimidine 9 and 10 at refluxing temperature. Finally reaction of carbodiimide intermediate 4 with different secondary amines gave the new thienopyrimidines 11a–c.