Synthesis and Herbicidal Activity of New Pyrazole-4-carboxamide Derivatives

A series of novel 3-(substituted alkoxy)pyrazole-4-carboxamide derivatives were synthesized, and their herbicidal activity against various weeds and crop safety were examined under flooded conditions. The herbicidal activity was primarily influenced by the substituent at the 3-position of the pyrazole ring. The benzyloxy group, the meta-position of which was substituted with an electron-withdrawing group, particularly with a trifluoromethyl group, was most efficient in enhancing the bleaching activity. The level of activity also varied with the N-substituent of the carbamoyl group, with N-ethoxycarbamoyl group providing the best combination of herbicidal activity and selectivity. Among the compounds synthesized, N-ethoxy-1-methyl-3-(3-trifluoromethylbenzyloxy)pyrazole-4-carboxamide (KPP-297), which showed good herbicidal activity against various annual lowland weeds and excellent crop safety at just of 100 g a.i./ha, was considered to be the most promising rice herbicide.