Abstract: Aseries of 1-aryl-2-phenyl-3-methyl-3-isopropyl-1,4,2-diazaphospholidin-5-one 2-oxides(2a_2o)have been synthesized by the Mannich type reaction of substituted phenyl ureas, phenyldichlorophosphine and 3-methyl-2-butanone, and their structures were confirmed by elemental analysis, NMR, IR and MS. On the basis of NMR analyses, we found that the cis isomers, in which the bigger group isopropyl and the phenyl group linked with the phosphorus atom are at the opposite side, are generated preferably in the reaction. The results of preliminary bioassay show that compounds 2 possess an excellent herbicidal activity selectively against rape. The structure herbicidal activity relationship(SAR) has also been discussed. Their herbicidal activities for the same substituent at different positions and those for different substituents at the same position are compared.

Key words: 1,4,2-Diazaphospholidin-5-one-2-oxides, Synthesis, Herbicidal activity, Struc-ture herbicidal activity relationship