In order to find new compounds with high activity, 20 1,2,3-benzotriazin-4-one thioether (sulfone) derivatives containing oxadiazole fragments were designed and synthesized. The results of in vitro antibacterial activity assay showed that 6-chloro-3-(5-ethylsulfonyl)-1,3,4-oxadiazo-2-ylmethyl)benzo[d][1,2,3]triazin-4(3H)-one (7c) had a good inhibitory effect on Sclerotinia sclerotiorum with an EC₅₀ value of 3.84 mg/L, which was comparable to that of the control agent hymexazol (5.43 mg/L). The toxicity of 7c (1.81 mg/L) against Rhizoctonia solani was comparable to that of carbendazim (1.09 mg/L), and significantly higher than that of the control agent hymexazol (45.70 mg/L). At the concentrations of 100 and 200 mg/L, the protective effects of compound 7c against Rhizoctonia solani were 78.51% and 84.48%, and the curative effects of compound 7c were 60.34% and 78.91%, respectively. At low concentrations, the curative effect was comparable to that of carbendazim (61.53%). At a concentration of 100 mg/L, some compounds had certain in vitro activities against Caenorhabditis elegans and Bursaphelenchus xylophilus, and the LC₅₀ value of 3-(5-ethylthio)-1,3,4-oxadiazo-2-ylmethyl)benzo[d][1,2,3]triazin-4(3H)one (6a) against C. elegans was 3.96 mg/L, which was better than that of fosthiazate (57.39 mg/L) and comparable to that of fluopyram (4.68 mg/L). However, the virulence of compound 6a (50.28 mg/L) against B. xylophilus was lower than that of fosthiazate (24.68 mg/L) and fluopyram (0.57 mg/L). The target compounds synthesized have high fungicidal activity and certain nematicidal activity, which can provide a reference for the study of new 1,2,3-benzotriazine-4-one derivatives.

Key words: 1,2,3-benzotriazin-4-one, oxadiazole, thioether, sulfone, fungicidal activity, nematocidal activity