Synthesis and Antimicrobial Screening of Some Novel Chromones and Pyrazoles with Incorporated Isoxazole Moieties

Abstract

The title compounds 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h and 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h have been synthesized from β‐diketones and chromones, respectively, having 5‐methyl‐3‐phenylisoxazole moiety. Substituted 2‐acetylphenyl 5‐methyl‐3‐phenylisoxazole‐4‐carboxylate 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h were converted into 1‐(2‐hydroxyphenyl)‐3‐(5‐methyl‐3‐phenylisoxazole‐4‐yl)propane‐1,3‐dione 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h by Baker–Venketaraman transformation. Further, the cyclodehydration of diketone 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h with glacial acetic acid in conc. HCl at reflux gave corresponding substituted 2‐(5‐methyl‐3‐phenylisoxazole‐4‐yl)‐4H‐chromen‐4‐one 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h. The corresponding 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h react with hydrazine hydrate in presence of glacial acetic acid in ethanol at reflux to furnish 2‐(5‐5(5‐methyl‐3‐phenylisoxazole‐4‐yl)‐1H‐pyrazole‐3‐yl)phenol 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h. The structures of all newly synthesized compounds have been confirmed by IR, 1H NMR, mass spectral data, as well as elemental analysis. The synthesized compounds have been screened for their antimicrobial activity. Some of the compounds show better antimicrobial activity as compared with the reference drugs Streptomycin, Ampicillin, Gentamycin, Cefixime, and Ketoconazole.