Efficient synthesis of 5,6-dihydrothieno[3′,2′:4,5]thieno[2,3-d]pyrimidin-4(3H)-ones via an iminophosphorane

5,6-Dihydrothieno[3′,2′:4,5]thieno[2,3-d]pyrimidin-4(3H)-ones 6 were synthesized in yields of 71–87% by a consecutive method, which includes aza-Wittig reaction of iminophosphorane 3 with aromatic isocynate to give carbodiimide 4 and subsequent reaction of 4 with various amines, phenols or alcohols in the presence of catalytic amount of sodium ethoxide or solid potassium carbonate.