Esters of cis or trans-3[2-(E/Z)-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethlcyclopro panecarboxylic acid, or mixtures thereof, which are useful as insecticides or as intermediaes of pyrethroid insecticides may be prepared by the dehydrohalogenation of corresponding esters of cis/trans-3(2,2-dichloro-3,3,3-trifluoropropyl)-2,2-dimethylcyclopropa necarb oxylic acid with a catalytic amount of a cyclic amidine in the presence of a stoichiometric amount of an alkali metal or alkaline earth metal base, or combinations thereof and a polar aprotic solvent. The use of cyclic amidines as dehydrohalogenation catalysts permits reactions to be carried out at lower temperatures, shorter reaction times, and with reduced unwanted by-products compared with prior art methods using metal bases alone.