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A series of twenty substituted 3,4-dihydropyrimidine derivatives were prepared and characterized by TLC, IR, 1H NMR, 13C NMR spectroscopic data and elemental analysis. These were screened for insecticidal activity by the film residue method against the pulse beetle (adzuki bean weevil, Callosobruchus chinensis). 4-(2′-Chlorophenyl)-6-phenyl-3,4-dihydropyrimidine-2(1H)-thione (LC50 0.00201 mg/cm2), 4-(2′-chlorophenyl)-6-p-tolyl-3,4-dihydropyrimidine-2(1H)-thione (LC50 0.00122 mg/cm2), 4-(4′-methoxyphenyl)-6-(4″-methylphenyl)l-3,4-dihydropyrimidine-2(1H)-thione (LC50 0.00164 mg/cm2), 4-(4′-chlorophenyl)-6-(4″-methoxyphenyl)-3,4-dihydropyrimidine-2(1H)-thione (LC50 0.00175 mg/cm2) were found to be more effective than dichlorvos (2,2-dichlorovinyl dimethyl phosphate, LC50 0.00243 mg/cm2), a commercial insecticide recommended for managing Callosobruchus chinensis.

A series of twenty 3,5-disubstituted isoxazoles were synthesized (using conventional and microwave methods) by the reaction of substituted chalcones with hydroxylamine hydrochloride and characterized by TLC, IR, 1H NMR, 13C NMR spectroscopic data and elemental analysis. The compounds were screened for insecticidal activity against the pulse beetle, Callosobruchus chinensis. Compounds 1a (LC50 36 mg L−1), 1d (LC50 110 mg L−1), 2c (LC50 93 mg L−1) and 5b (LC50134 mg L−1) were more effective than the recommended organophosphorous insecticide dichlorvos (2,2-dichlorovinyl dimethyl phosphate) (LC50 155 mg L−1). These compounds provide a lead for designing new substances endowed with insecticidal activity.