Design, synthesis, and biological evaluation of various α-substituted benzylpyrroles based on the structures of insecticidal chlorfenapyr and natural pyrrolomycins.

On the basis of the structures of chlorfenapyr and dioxapyrrolomycin, a series of 2-benzylpyrroles with a hydroxyl, an alkyloxy, an acyloxy, an alkylsulfanyl, or an oxime moiety at the α-position of benzyl were designed and synthesized. Their insecticidal, acaricidal, and fungicidal activities were extensively investigated. The structure-activity relationship showed that benzylpyrroles bearing shorter α-alkyloxy groups gave better activities against most of the insect species; the alkylation of pyrrole usually gave increased activity. Among all compounds, (4-bromo-2-(α-(2,2,2-trifluoroethoxy)-4-chlorobenzyl)-1-(ethoxymethyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile) (5'j) exhibited the most outstanding insecticidal activities against oriental armyworm (IC₅₀=10 mg L⁻¹), diamondback moth (0.07 mg L⁻¹), corn borer (50 mg L⁻¹), and mosquito (0.04 mg L⁻¹), which are very close to those of chlorfenapyr (5, 0.08, <25, and <0.025 mg L⁻¹, respectively). In addition, some compounds also exhibited a broad or selective fungicidal spectrum.