Enantioselective Herbicidal Activity of Chiral α-Methylbenzylphenylureas against Cyperaceae and Echinochloa Paddy Weeds.

Optically active α-methylbenzylphenylureas were synthesized and tested for their herbicidal activities against barnyardgrass and Cyperaceae paddy weeds in a greenhouse to evaluate the cross intergenus phytotoxicity between rice and barnyardgrass and the enantioselective phytotoxicity to the weeds. Several compounds controlled the growth of the weeds, and a suitable enantiomer for successful weed control was dependent on the type of weed and on the substituent at the aniline moiety. The (R)-2-isoPr and (R)-2-tert-Bu derivatives significantly controlled barnyardgrass and both annual and perennial Cyperaceae paddy weeds. The (R)-2-Et and (R)-2-CF3 derivatives showed the strong herbicidal activity against perennial Cyperaceae paddy weeds, while the (S)-enantiomers of the unsubstituted and fluoro derivatives were active against barnyardgrass. The enantioselectivity of the most potent compounds was high.