In the search for new antifungal agents, a series of isoxazoles (D) and isoxazolines (E) analogs were designed and synthesized. The 2,3-dihydro-2,2-dimethyl-7-benzofuranol was used as the raw material, and the chalcone derivatives were obtained by methylation, acetylation, and hydroxyaldol condensation. Notably, the isoxazoles (D) and isoxazolines (E) were obtained via a one-pot 3 + 2 cycloaddition reaction for the first time, and the reaction mechanism was explored preliminarily. The synthesized compounds were verified using 1H NMR, 13C NMR and HRMS. The antifungal activity results showed that the isoxazoles and isoxazolines both have good activity against Pseudoperonospora cubensis. Among them, compounds D2 and E2 have excellent inhibitory activities of 80% and 95% at 100 mg/L, respectively, which are almost comparable to the positive control fluopicolide.
Tianle et al. (Sun,) studied this question.