1-alkylcyclopropanecarboxylates: An extension of pyrethroid structure—activity relationships

1-Alkylcyclopropanecarboxylic acids are synthesised by thermolysis of 1-pyrazolines prepared by 1,3-dipolarcycloadditions of diazoalkanes. The insecticidal and acaricidal activities of 14 pyrethroid esters of these acids are considered in relation to the influence of steric and metabolic factors on activity. 1-Alkyl compounds are less active than esters with no alkyl group at position 1, contrary to expectations, and also less active than the corresponding 2-alkyl esters.