3-Benzoyl-4-hydroxycoumarin derivatives were designed by combination of coumarin and triketone structure. Twenty one target compounds were synthesized. Their structures were elucidated by ¹H NMR, ¹³C NMR and HRMS techniques. Furthermore, the structure of 3-(2,4-dichlorobenzoyl)-7-methoxyl- 4-hydroxycoumarin (15) was determined by X-ray single crystal diffraction. Their herbicidal activities against Brassica campestris and Echinochloa crus-galli were eualuated. The results indicated that the target compounds pocessed similar activity with 4-hydroxycoumarin, only active toward Brassica campestris. The addition of benzoyl group to 4-hydroxycoumarin could enhance their activities against Brassica campestris to some extent. 3-(2-Nitro-4-mesylbenzoyl)-4-hydroxycoumarin (21) displayed better in-vitro activ-ity against Brassica campestris than mesotrione, with 87.6% inhibition under 10 μg/mL. But it showed worse in-vivo activity than mesotrione. Target compounds showed no bleaching ac-tion, displaying a different mode of action with triketone herbicides. Since compound 21 was active selectively to Brassica campestris, it could be a leading compound for developing selective herbi-cide.

Key words: coumarin, synthesis, crystal structure, herbicidal activity