There is disclosed a process for the preparation of a lower alkyl ester of 3-(2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclopropane carboxylic acid which comprises the steps of (a) reacting a compound of formula: CF.sub.3 --CXCl--CH(OH)--CH.dbd.C(CH.sub.3).sub.2 (I) wherein X is chloro or bromo, with a tri-lower-alkyl orthoacetate containing up to four carbon atoms in each alkyl groups in the presence of at least a catalytic amount of an acid catalyst at an elevated temperature for a sufficient time to obtain a compound of formula: CF.sub.3 --CXCl--CH.dbd.CH--C(CH.sub.3).sub.2 --CH.sub.2 CO.sub.2 R (III) wherein R is an alkyl group containing up to four carbon atoms, and (b) treating said compound of formula (III) with at least one molar equivalent of a base to obtain said alkyl ester of 3-(2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclopropane carboxylic acid. The products are useful as intermediates for insecticides.