A process for the preparation of 2-(2',2',2',-trihalogenoethyl)-4-halogenocyclobutan-1-ones of the formula ##STR1## in which one of the radicals R.sub.1 and R.sub.2 is methyl and the other is hydrogen or methyl, or R.sub.1 and R.sub.2 together are an alkylene group having 2 to 4 carbon atoms, and X and Y are each chlorine or bromine, comprising reacting a 2,4,4,4-tetrahalogenobutyric acid chloride in the presence of an organic base with an ethylene compound which is disubstituted in 1-position by the radicals R.sub.1 and R.sub.2, as defined above, to form a 2-(2',2',2'-trihalogenoethyl)-2-halogenocyclobutan-1-one and then rearranging the latter, in the presence of a catalyst, into a 2-(2',2',2'-trihalogenoethyl)-4-halogenocyclobutan-1-one of the above formula; said 2-(2',2',2'-trihalogenoethyl)-4-halogenocyclobutan-1-ones being valuable intermediates for the preparation of 2-(2',2'-dihalogenovinyl)-cyclopropanecarboxylic acid and its insecticidally active esters; as well as the 2-(2',2',2'-trihalogenoethyl)-4-halogenocyclobutan-1-ones of the above formula and the intermediates utilized for their preparation.