The reaction of phenylmalononitrile with hydrazine. Synthesis and properties of 3,5-diamino-4-phenylpyrazole, 2-amino-3-phenylpyrazolo[1,5-a] pyrimidine, and related compounds

3,5-Diamino-4-phenylpyrazole was prepared by the reaction of phenylmalononitrile with hydrazine hydrate. This hitherto unknown polyfunctional heterocycle reacted with acetylacetone, ethyl acetoacetate, 5-oxobutyraldehyde, malonaldehyde, diethyl (ethoxymethylene)malonate, and mesityl oxide to give derivatives of 2-aminopyrazolo[1,5-a]pyrimidine. The free amino-group in the bicyclic system tends to react, in the presence of hydrochloric acid, with 1,3-dicarbonyl compounds to yield either 3-oxobut-1-enylamino side chains or a trimethine chain linkage between two aminopyrazolo[1,5-a]pyrimidine nuclei. The symmetric delocalized structure of the latter compounds was confirmed by a spectral study. In the case of diethyl (ethoxymethylene)malonate the amino-group gave a Michael addition product. Reaction with anisaldehyde followed by the reaction with (chlorocarbonyl)phenylketen led to a paraionic diazapentalene derivative.