1-Pyrazolin-3-one (Ia) and its 5, 5-dimethyl derivative (Ib) were prepared in good yield by oxidation of the corresponding pyrazolidin-3-one derivatives (Va) and (Vb) with lead tetra- acetate at low temperature. Reactions of (Ia and b) with various nucleophiles were examined. Hydroxide, alkoxides, alcohols, and amines attack initially at the carbonyl carbon atom; ring cleavage then gives intermediate carbanions (III), which are either protonated ...
[Hansen, John F.; Kim, Yong In; McCrotty, Stephen E.; Strong, Scott A.; Zimmer, Douglas E. Journal of Heterocyclic Chemistry, 1980 , vol. 17, p. 475 - 479]