Abstract A synthesis of 1-aminopyrazolin-5-ones (I) by chloramine attack on the 2- benzylpyrazolones (IVd-e) has been accomplished. Nucleophilic substitution reactions of aminopyrazolones (I) are investigated; with 1, 4-diketones, N, N'-pyrrolylpyrazolones (XVIIa- c) are obtained. Chlorination of acetylaminopyrazolones (VII) led to the corresponding 1- amino-5-chloropyrazoles (XXI) via the isolable pyrazolo [3, 2-b] oxadiazoles (XIX).
