Synthesis and herbicidal activity of sulfonanilides having a pyrimidinyl-containing group at the 2′-position

A novel series of sulfonanilides having a pyrimidinyl-containing group at the 2′-position was prepared and their herbicidal activities against paddy weeds and selectivity against rice plants were assessed. The structure-activity relationships were probed by substitution of the sulfonyl group, bridge and benzene ring. Among the sulfonamides, difluoromethyl compound showed comparatively high activity and a broad spectrum to control weeds, including Echinochloa oryzicola. The most preferable substitution position on the benzene ring was in the 6-position and the lower alkyl group showed high herbicidal activity and a broad weed control spectrum, and among the compounds tested, the methoxymethyl group was the best. In respect of the bridge moiety, the hydroxyl group was the best. Among the compounds examined, 2′-[(4,6-dimethoxypyrimidin-2-yl)(hydroxy)methyl]-1,1-difluoro-6′-(methoxymethyl)methanesulfonanilide, applied at rates between 4 to 16 g a.i./ha, showed excellent pre-emergence herbicidal activity with a broad spectrum against grass, sedge and broadleaf weeds without injury to rice plants.