Synthesis and insecticidal/acaricidal activity of novel 3-(2,4,6-trisubstituted phenyl)uracil derivatives

A series of novel 3-(2,4,6-trisubstituted phenyl)uracil derivatives has bee n synthesised and assayed for insecticidal/acaricidal activity; The assay i ndicated certain requirements for optimal insecticidal activity, which can be summarised as follows: (a) the substituents on the phenyl ring should po ssess hydrophobicity and electron-withdrawing properties, and the sum of th eir volumes determines the level of activity; (b) the substituent at the Ci -position on the uracil ring should also possess electron-withdrawing prope rties and hydrophobicity, together with the correct volume; (c) the 6-posit ion on the uracil ring should be unsubstituted for activity against Nephote ttix cincticeps and Epilachna vigintioctopunctata, but substituents with le ngth C3 to C4 may be optimal for activity against Tetranychus urticae; (d) certain substituents at the 5-position of the uracil ring give activity aga inst E vigintioctopunctata and T urticae, but not against N cincticeps; (e) a thiocarbonyl group at the a-position of the uracil ring is less effectiv e than a carbonyl group. Of the compounds assayed, 3-(2,6-dichloro-4-trifluoromethylphenyl) showed h igh activity against all the species assayed. (C) 2000 Society of Chemical Industry.