Reaction of methyl 3-aroyl-1-aryl-4,5-dioxo-4,5-dihydro-1H-pyrrole-2-carboxylates with arylhydrazines. synthesis of isomeric 5-arylcarbamoyl-4-aroyl- and 5-aryl-4-aryloxamoyl-1H-pyrazoles

Regiodivergent Synthesis of 3,4- and 4,5-Disubstituted N-Methylpyrazoles from 4-Acyl-1H-pyrrole-2,3-dione and Methylhydrazine

“… a With (a) β-enamino ketone, , (b) BED, − (c) 4-acyl-1 H -pyrrole-2,3-dione, and (d) secondary BED by in situ generation of 4-acyl-1 H -pyrrole-2,3-dione intermediate. …”

“…The product formed from these reactions depends on the nature of the substituents present, especially in 4- and 5-positions of the heterocyclic ring. 4-Acyl-1 H -pyrrole-2,3-diones react with arylhydrazines by the attack on carbon-5, followed by an attack on carbonyl carbon C4′ and C3 (in this case, preceded by the cleavage of the ring), resulting in a mixture of regioisomers (Scheme c). On the other hand, to the best of our knowledge, the reaction of 4-acyl-1 H -pyrrole-2,3-diones with methylhydrazine has not been reported so far.…”