A process has been discovered for selective preparation of isomers and enantiomers of 2,2-dimethyl-3-(2,2-dihalovinyl)cyclopropane carboxylic acids. In this process an adduct of an alkyl 3,3-dimethyl-4-pentenoate and a substituted 2-oxazolidone is reacted with a substituted dihalomethane compound. The resulting compound is cyclized, dehydrohalogenated and hydrolyzed to yield the desired product. These cyclopropane carboxylic acids are useful precursors for pyrethroid insecticides.