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A series of novel 4,5-dihydropyrazole-5-thiones (DHPs) was synthesised by treating the corresponding dihydropyrazolones with Lawesson's reagent and evaluated for miticidal activity against two-spotted spider mites (Tetranychus urticae Koch). Of these, 3-(4-chlorophenyl)-4,4-dimethyl-1-phenyl-4, 5-dihydropyrazole-5-thione, 3-(4-chlorophenyl)-4-ethyl-4-methyl-l-phenyl-4,5-dihydropyrazole-5-thione, 3-(4-chlorophenyl)-1-phenyl-4,5-dihydropyrazole-5-thione-4-spirocyclopentane and 4,4-dimethyl-l-phenyl-3-(4-trifluoromethylphenyl)-4,5-dihydropyrazole-5-thione were highly active (pEC,, > 4-0) and were more effective than the miticide dicofol (pEC,, = 3.879), which has traditionally been used for the control of phytophagous mites. Structure-activity relationship (SAR) studies were performed on each position of the pyrazole ring of DHPs. The results indicated that the unsubstituted phenyl, 4-substituted phenyl and thioxo groups on the 1-, 3-and 5-positions of DHPs respectively were required for activity. Quantitative SAR studies using physicochemical parameters of substituents and the capacity factor k' as a hydrophobicity index suggested that: (a) the activities of all types of DHPs examined were mainly dominated by hydrophobicity, (b) the bulkiness of 4-substituents of the 3-phenyl ring favoured the activity and (c) the log k' optimum for all DHPs was 1.675, equivalent to a log Po, value of c. 5.0.

: A series of novel 6-(1,2,4-triazol-4-yl) chromone and -1-thiochromone (benzo [b]thiazin-4-one) derivatives was obtained by cyclisation via thiosemicarbazides which were prepared by reaction of hydrazines and the corresponding isothiocyanates. Their fungicidal activity was evaluated against the rice blast fungus Pyricularia oryzae. Of this series, 2,5,8-trimethyl-6-(1-propyl-5-thioxo-3-triÑuoromethyl-1,2,4-triazol-4-yl) chromone, 6-(1-butyl-5-thioxo-3-triÑuoro-methyl-1,2,4-triazol-4-yl)-2,5,8-trimethylchromone, 6-(1-hexyl-3-methyl-5-thioxo-1,2,4-triazol-4-yl)-2,5,8-trimethylchromone and 6-(1-allyl-5-thioxo-3-triÑuoro-methyl-1,2,4-triazol-4-yl)-2,5,8-trimethylchromone were highly active (pEC 50 [ StructureÈactivity relationship studies using the capacity factor k@ as a 6É0). hydrophobicity index suggested that the log k@ optimum for 2,5,8-trimethylchromone and -1-thiochromone derivatives was around 1É0, equivalent to a log value of c. 4É4. 1998 SCI P ow ( Pestic. Sci., 52, 309È320 (1998)