Pyrimidine reactions. Part XVIII. The conversion of 4-methoxy-5-nitropyrimidine into 3-amino-4-nitropyrazole by hydrazine

4-Methoxy-5-nitropyrimidine reacts with ethanolic hydrazine hydrate below 0° to give 4-hydrazino-5-nitropyrimidine which is converted by an excess of hydrazine hydrate at 25° into 3-amino-4-nitropyrazole. The mechanism, unprecedented in transformations of pyrimidines into pyrazoles, is discussed.The nitropyrazoles undergo hydrogenation to ortho-diamines which condense with α-dicarbonyl compounds to give pyrazolo[3,4-b]pyrazine and appropriate derivatives. Assigned structures are consistent with the measured u.v., i.r., 1H n.m.r., and mass spectra, and with ionization constants.