Synthesis and Antimicrobial Evaluation of Some Chalcones and Their Derived Pyrazoles, Pyrazolines, Isoxazolines, and 5,6-Dihydropyrimidine-2-(1 H )-thiones

Chalcones were synthesized by a base catalyzed Claisen-Schmidt condensation reaction. Bromination of chalcones afforded the dibromo derivatives. Monobromo derivatives could be obtained by treating the corresponding dibromochalcones with dry benzene in the presence of triethylamine. Pyrazole derivatives were obtained by refluxing of dibromochalcones with phenylhydrazine or 2,4-dinitrophenylhydrazine in dry pyridine. Chalcones were treated with hydrazine hydrate or phenyl hydrazine in ethanol to afford Δ ²-pyrazolines and N-phenyl-Δ ²-pyrazolines. Condensation of chalcones with hydroxylamine hydrochloride or thiourea in ethanolic sodium hydroxide solution gave 4,5-dihydroisoxazoles and 5,6-dihydropyrimidine-2-(1H)-thiones. The prepared compounds were tested for antimicrobial activity against four different bacterial species displaying different degrees of antibacterial activities or inhibitory actions.