New Efficient Synthesis of 2-Substituted Benzothieno[3,2-d]pyrimidin-4(3H)-ones via a Tandem Aza-Wittig Reaction

Abstract

1-Aryl-3-[2-(ethoxycarbonyl)benzothien-3-yl]carbodiimides 4, obtained from aza-Wittig reactions of iminophosphorane 3 with aryl isocyanates, reacted with secondary amines, phenols, or alkanols in the presence of a catalytic amount of potassium carbonate or sodium alkoxide to give 2-substituted benzothieno[3,2-d]pyrimidin-4(3H)-ones 6 in good yields. The reaction of carbodiimides 4 with primary amines RNH2 (R ≠ H, Me) in the presence of sodium ethoxide selectively produced one regioisomer 8 via a base-catalyzed cyclization mechanism. However, a different regioisomer 9 was obtained when primary amines RNH2 (R = H, Me) were used in the absence of sodium ethoxide via a direct cyclization mechanism.