Synthesis of (3-Aroyl-2-aryl-4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrol-1-yl)acetonitriles and Their Reaction with Hydrazine Hydrate

Three-component reaction of methyl 4-aryl-2,4-dioxobutanoates with aromatic aldehyde and 2-aminoacetonitrile sulfate in glacial acetic acid in the presence of anhydrous sodium acetate afforded previously unknown (3-aroyl-2-aryl-4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrol-1-yl)acetonitriles. The reaction involved intermediate formation of Schiff base, followed by Michael-type addition of the dioxo ester to the C=N bond and cyclization of the addition product, methyl 3-aroyl-4-aryl-4-(cyanomethylamino)-2-oxobutanoate. The cyclization product reacted with hydrazine hydrate at the aroyl carbonyl group to give the corresponding hydrazone which was converted in 1,4-dioxane to the cyclic form, [3,4-diaryl-6a-hydroxy-6-oxo-3a,4,6,6a-tetrahydropyrrolo[3,4-c]pyrazol-5(1H)-yl]acetonitrile, without elimination of the second water molecule. When the reaction of (3-aroyl-2-aryl-4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrol-1-yl)acetomtriles with hydrazine hydrate was carried out in boiling acetic acid, [3,4-diaryl-6-oxo-2,6-dihydropyrrolo[3,4-c]pyrazol-5(4H)-yl]acetonitriles were obtained as a result of dehydration of initially formed [3,4-diaryl-6a-hydroxy-6-oxo-3a,4,6,6a-tetrahydropyrrolo[3,4-c]pyrazol-5(1H)-yl]acetonitriles as shown by special experiment. The structures of [6a-hydroxy-6-oxo-3,4-diphenyl-3a,4,6,6a-tetrahydropyrrolo[3,4-c]pyrazol-5(1H)-yl]acetonitrile and [4-(4-methoxyphenyl)-6-oxo-3-phenyl-2,6-dihydropyrrolo[3,4-c]pyrazol-5(4H)-yl]acetonitrile were determined by X-ray analysis.