Cyclic and acyclic products from the reactions between methyl 3-oxo­butanoate and aryl­hydrazines

The mol­ecules of methyl 3-(2-nitro­phenyl­hydrazono)­butan­oate, C₁₁H₁₃N₃O₄, (I), and methyl 3-(2,4-dinitro­phenyl­hydrazono)butanoate, C₁₁H₁₂N₄O₆, (II), both prepared from methyl 3-oxobutanoate and the corresponding nitro­phenyl­hydrazine, exhibit polarized mol­ecular electronic structures; in each of (I) and (II), the mol­ecules are linked into chains by a single C-H...O hydrogen bond. The mol­ecules of 5-hydroxy-3-methyl-1-phenyl-1H-pyrazole, C₁₀H₁₀N₂O, (III), prepared by the reaction of methyl 3-oxobutanoate and phenyl­hydrazine, are linked into chains by a single O-H...N hydrogen bond. The reaction between methyl 3-oxobutanoate and 3-nitro­phenyl­hydrazine yields 5-hydr­oxy-3-methyl-1-(3-nitro­phen­yl)-1H-pyrazole, (IV), which when crystallized from acetone yields 4-isopropyl­idene-3-methyl-1-(3-nitro­phen­yl)-1H-pyrazol-5(4H)-one, C₁₃H₁₃N₃O₃, (V).