Design, synthesis, and bioactivities of novel pyridazinone derivatives containing 2‐phenylthiazole or oxazole skeletons

Abstract

AbstractA series of novel pyridazinone derivatives were designed and synthesized by replacing 4‐(tert‐butyl)phenyl moiety of pyridaben with 2‐phenylthiazole or oxazole fragments via activity substructure connecting approach. The structures of all target compounds were characterized through NMR, MS, and elemental analysis. Bioassay results exhibit that most compounds showed potent bioactivities against Aphis fabae, Tetranychus urticae, Erysiphe graminis, and/or Puccinia polysora. Among the newly synthesized compounds, 2‐(tert‐butyl)‐4‐chloro‐5‐(((2‐phenylthiazol‐4‐yl)methyl)thio)pyridazin‐3(2H)‐one (12b) displays remarkable insecticidal activity against A fabae. Its LC50 value (2.73 mg/L) is better than that of pyridaben (5.46 mg/L), although inferior to that of imidacloprid (0.51 mg/L). In addition to its extraordinary insecticidal activity, compound 12b also exerts 96.9% fungicidal activities against P polysora at 500 mg/L in vivo, significantly superior to that of pyridaben (50.0%), while slightly lower than that of tebuconazole (100%). This article discusses the synthesis, bioassay results, and structure‐activity relationship of this series of novel pyridazinone derivatives.