Synthesis and insecticidal activity of lipophilic amides. Part 3: Influence of chain length and terminal group in N-(2-methylpropyl)-2,4-dienamides

Increasing the alkylene chain length in N-(2-methylpropyl)-ω-phenylalka-2,4-dienamides revealed in addition to the active compounds reported earlier a second peak of activity, but only against mustard beetles, with the tridecadienamide. Similar extension in the methyl-terminated series gave much weaker peaks, at different lengths for the two test species. Results with terminal vinyl compounds were intermediate, and indicated a specific functional role in the lethal process for the terminal unsaturation, with a possible contribution to steric flexibility and physical property optimisation from the longer chains. Synthetic samples of pellitorine and pipercide, natural products to which insecticidal activity has been ascribed, were only very weakly active in the present tests, but compounds with other groups on the ends of chains nearer the optimum length were more active.