Stereoselective ring opening of dimethyl 5-aryl-2,3-dihydro-3,3 dimethyl-1-oxo-1H,5H-pyrazolo[1,2–a]pyrazole-6,7-dicarboxylates with hydrazine hydrate. Synthesis of rel-(4'R,5'S)-3-[5-aryl-3,4bis (hydrazino-carbonyl)]-4,5-dihydro-1H-pyrazol-1-yl)-3-methylbutanohydrazides

Reactions of dimethyl 5-aryl-2,3-dihydro-3,3-dimethyl-1-oxo-1H,5H-pyrazolo[1,2–a]pyrazole6,7-dicarboxylates 3a–e with excess of hydrazine hydrate gave propanohydrazides 5a–e in 70– 99% yields. The ring opening of pyrazolo[1,2–a]pyrazole-6,7-dicarboxylates 3a–e proceeded stereoselectively, furnishing the rel-(4'R,5'S)-isomers of 3-[5-aryl-3,4-bis(hydrazinocarbonyl)4,5-dihydro-1H-pyrazol-1-yl)-3-methyl-butanohydrazides 5a–e. The X–ray structure of 5a was determined.