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-dicarbonyI compounds to yield either 3-oxobut-lenylamino side chains or a trimethine chain linkage between two aminopyrazolo[lI5-a] pyrimidine nuclei. The symmetric delocalized structure of the latter compounds was confirmed by a spectral study. In the case of diethyl (ethoxymethy1ene)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.
Different substituted anhydro-l-hydroxy-3-oxopyrazolo[l,2-a]pyrazolium hydroxides were prepared by the reaction of 1,3-dicarbonyl compounds with derivatives of 4-phenyl-3,5-dihydroxypyrazole. These diazapentalene derivatives belong to a new series of 4 cyclic betaines which are named "paraionic" heterocycles. The effects of substituents on the stability of both the anionic and the cationic rings were kinetically studied. Selective cleavage of either the aiiionic or the cationic ring was achieved by varying the conditions of the reaction with morpholine. Electron releasing groups on the cationic ring and electron attracting groups on the anionic ring enhance the stability of the bicyclic system. They also cause a hypsochromic shift of the visible light absorption.
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