Synthesis and insecticidal activity of lipophilic amides. Part 4: The effect of substituents on the phenyl group of 6‐phenylhexa‐2,4‐dienamides

Substituted phenylacetaldehydes, made by homologation of the benzaldehydes by Wittig condensation with a methoxymethylene ylid, were condensed under Wadsworth‐Emmons conditions to give the substituted N ‐(2‐methylpropyl)‐6‐phenylhexa‐2,4‐dienamides. Electron withdrawing substituents favoured the formation of the unwanted 3,5‐diene isomer. Insecticidal activity was lowered by most substituents examined, but was retained or even enhanced by halogen atoms at the m ‐ or p ‐positions. At the m ‐position, activity decreased as size of halogen increased.