It could be established that the reaction between hydrazine
and enamines, formed from ethyl 2(or 3)-aminopyridine-3(or 2)carboxylates and diethyl ethoxymethylenemalonate or ethyl ethoxymethylenecyanoacetate, afforded 3-aminopyrido(2,3-d)pyrimidin-
4(3H)one or 3-aminopyrido(3,2-d)pyrimidin-4(3H)one, respectively.
Similarly, these aminopyridinecarboxylates condense with N,N-
dimethylformamide dimethylacetal and react further with
hydrazine to give the same bicyclic compounds