The 2-acetyl-5-methyl-2,4-dihydro-3H-pyrazol-3-one 2 prepared via acetylation of 5-methyl-1H-pyrazol-3-one 1 was
reacted with aromatic aldehydes in 1:1 and 1:3 ratio to give chalcone derivatives 3a-c and the tri-condensed product 6. Chalcone
derivative 3a was condensed with hydrazine hydrate and hydroxylamine hydrochloride to give the corresponding bis pyrazole
4 and the oxime 5 derivatives, respectively. Also, it was reacted with bromine in 1:1 and 1:2 ratio to give the mono 7 and the
dibromo 10 derivatives, respectively. Reaction of the monobromo derivative 7 with hydrazine hydrate and thiourea gave the
pyrazolotriazine 8 and the 2-(thiazol-4-yl)-3-pyrazolone 9 derivatives, respectively. Compound 1 was reacted with chloroacetyl
chloride to give the 2-(2-chloroacetyl)pyrazolone 11 derivative, which on reaction with hydrazine hydrate, urea and thiourea
gave the 2-aminoglycyl pyrazolone 12 and the urea and thiourea derivatives 13a,b. Furthermore, reaction of compound 1 with
formaldehyde/piperidine, benzene sulfonyl chloride and chloroacetyl chloride gave the Mannich product 14, the 2-
phenylsulfonyl pyrazolone 15 and the bis pyrazolone 16. All new compounds were prepared using both conventional and
microwave techniques. Elemental analyses together with spectroscopic data including IR, 1H-NMR in addition to 13C-NMR
and mass spectra submit proofs for the chemical structures for all compounds. Some of the new pyrazolone derivatives showed
antimicrobial activities.