Synthesis and insecticidal activity of 3-(haloalkyl-1,3-dienyl)-2,2-dimethylcyclopropanecarboxylates

New 2,2‐dimethylcyclopropanecarboxylic acids bearing halogenated 1,3‐alkadienyl substituents at position 3 of the cyclopropane ring were synthesised and the insecticidial activities of their 3‐phenoxybenzyl and α‐cyano‐3‐phenoxybenzyl esters against housefly (Musca domestica), Colorado potato beetle (Leptinotarsa decemlineata) and Egyptian cotton leafworm (Spodoptera littoralis) were determined. The activity of these compounds varied according to the relative position of the halogen substituents on the diene chain. The observed changes of activity with the structure of the side chain are discussed in terms of the coplanarity of the conjugated double bonds.