Acid-catalysed ring-cleavage of some pyrimidine derivatives

Abstract

Reduction of ethyl 4-(o-nitrophenylthio)pyrimidine-5-carboxylate with iron powder in aqueous acetic acid results in cleavage of the pyrimidine ring to give ethyl α-(aminomethylene)benzothiazole-2-acetate. Acid treatment of ethyl 4-(o-aminophenylthio)pyrimidine-5-carboxylate, synthesised by an alternative route, gives the same benzothiazole derivative through an isolable formylaminomethylene compound. A similar reduction of ethyl 4-(o-nitrophenoxy)pyrimidine-5-carboxylate does not cause pyrimidine ring-cleavage, but rearrangement of the expected primary amino-compound occurs to give ethyl 4-(o-hydroxyanilino)pyrimidine-5-carboxylate. Ethyl 4-(o-aminoanilino)pyrimidine-5-carboxylate forms benzimidazole derivatives on treatment with acid. A possible mechanism for these changes is described.