Reactions with β-cyanoethylhydrazine—I : A route for the preparation of pyrazolo[1.5-a]pyrimidines and pyrrolo[1.2-b]pyrrazoles

Abstract

Malononitrile ( 1) reacts with β-cyanoethylhydrazine ( 2) to yield 5-amino-4-cyano-1-β-cyanoethyl-3-cyanomethyl-pyrazole ( 3). Treatment of 3 with 1% NaOH solution results in the formation of 3-cyano-2-cyanomethyl-4,5,6,7-tetrahydropyrazolo[1.5-a] pyrimine ( 6). On the other hand, when 3 was refluxed with acetic acid-hydrochloric acid mixture, the pyrido[3:4:3′:4′]pyrazolo[1.5-a] pyrimidine ( 10) was formed. 1,2-Dihydro-5-hydroxy-3-phenylazopyrazolo[1.5-a] pyrimidine ( 16) was obtained by cyclization of 3,5-dianimo-1-(β-cyanoethyl)-4-phenylazopyrazole ( 18), which, in turn, was obtained by the action of 2 on phenylazomalononitrile ( 17). Ethoxymethylenemalononitrile ( 20) reacts with 2 to yield 3-amino-4-cyano-1-β-cyanoethyl)-pyrazole ( 21). Compound 21 was readily cyclized into the pyrrolo[1.2-b]pyrazole derivative 25 by the action of either 3% NaOH solution or conc sulphuric acid.