Facile synthesis and biological activities of novel fluorine-containing pyrido[4,3-d]pyrimidines

Fourteen novel 3-substituted-5-methyl-4-methylene-7-alkylsulfanyl-3,4-dihydro-pyrido[4,3-d]pyrimidine-8-carbonitriles, compounds 4a–n, were designed and synthesized via a facile regioselective cyclization process. The intermediate 2 reacted with triethyl orthoformate (molar ratio is 1:4) in the presence of acetic anhydride to give formamidate 3, which was cycled to 4 regioselectively upon addition of different amines at mild condition. The structures of compounds 4a–n were confirmed by IR, 1H NMR, MS and elemental analysis. The preliminary bioassay indicated that some compounds possess significant herbicidal activity against the roots of rape and barnyard grass, especially when the fluorine atom was introduced to the para position of the substitutents on pyrimidine ring; some compounds showed fungicidal activities against Rhizoctonia solani, Botrytis cinereapers, Gibberella zeae, Dothiorella gregaria, Colletotrichum gossypii as well, and the introduction of fluorine has negative effect on the antifungal activities.