1-Phenyl and 1-methyl derivative of 3-methyl-5-pyrazolone were prepared quantitatively via ascalable solvent-free reaction of corresponding hydrazine derivative with ethyl acetoacetate. Differentmechanisms have been proposed for the reaction of hydrazine derivatives (methyl or phenyl) with ethylacetoacetate and also the tautomeric aspects of the targeted compounds have been discussed.

Synopsis: ¹³C NMR and quantitative proportional amount of different tautomeric forms of 1,3-dimethyl-5-pyrazolone in DMSO-d₆.

The synthesis of (5-chloro-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl) methanone (IV) asthe key intermediate in the preparation of zolazepam is reconsidered. The previous report for the preparationof this compound consist of acylation of 5-chloro-1,3-dimethylpyrazole (prepared from chlorination of 1,3-dimethyl-5-pyrazolone) by 2-fluorobenzoyl chloride (II). Herein, the preparation of (IV) via chlorination of(5-hydroxy-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl) methanone (III) which was prepared by acylationof 1,3-dimethyl-5-pyrazolone (I) by II is investigated. Different aspects of each step (reaction conditions, sideproducts and workup procedure) were considered and the products and side products were characterized via ¹H NMR, ¹³C NMR and GC-MS techniques.

The synthesis of (5-chloro-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl) methanone (IV), as the key intermediate in the preparation of zolazepam, via chlorination of (5-hydroxy-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl) methanone (III) which was prepared by acylation of 1,3-dimethyl-5-pyrazolone (I) by II is reconsidered. Different aspects of each step (reaction conditions, side products and workup procedure) were considered and the products and side products were characterized via ¹H NMR, ¹³C NMR and GC-MS techniques.