Synthesis, characterization and herbicidal activity of isoxazole derivatives for control of barnyard grass in rice

A series of 20 isoxazole derivatives were synthesized using alkoxy/halo acetophenones and N, Ndimethylformamide dimethylacetal. These compounds were characterized by various spectroscopic techniques, viz, ¹H NMR, ¹³C NMR and LC-HRMS and evaluated for their herbicidal activity against barnyard grass (Echinochloa crus-galli). In vivo herbicidal bioassay revealed that compound 5r (5-(3-Fluoro-2-hydroxylphenyl) isoxazole) was found to be most active against E. crus-galli (weed control index (WCI) = 53.9%), followed by compound 5a (2-(isoxazol-5-yl)-5-(methoxy) phenol, WCI = 52.9%). These results showed that the compound 5r can be considered as a potential herbicidal agent. The pot experiment indicated that this compound control barnyard grass rapidly with a good tolerance for rice seedlings after post-emergence and soil application.