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.