4-Chlorothieno [2, 3-d] pyrimidines were prepared by the chlorination of 4-oxo-3, 4-dihydrothieno [2, 3-d] pyrimidines with phosphoryl chloride. 4-Oxo-3, 4, 5, 6, 7, 8-hexahydro [1]-benzo- and 4-oxo-6-phenylthieno [2, 3-d] pyrimidine were synthesized by the cyclization of 2-acylaminothiophene-3-carboxamide derivatives with base. 2-Methyl-4-oxo-3, 4-dihydrothieno [2, 3-d] pyrimidine was prepared by the treatment of 2-methyl-4-trichloromethylthieno [2, 3-d] pyrimidine with sodium hydroxide in aqueous methanol. A series of 4-alkylamino-and 4-arylaminothieno [2, 3-d] pyrimidines were synthesized by the nucleophilic substitution of 4-chlorothieno [2, 3-d] pyrimidines with various amines. These compounds were evaluated for antifungal activity against Piricularia oryzae. The preventive effects on Rice blast, Sheath blight, and Cucumber powdery mildew were also determined by pot tests.
