VERFAHREN ZUR HERSTELLUNG VON CYCLOPROPAN-DERIVATEN

The invention relates to a process for the preparation of a compound of the general formula (formula I> in which R and R in each case independently of one another represent a hydrogen atom or an alkyl group having up to 10 carbon atoms or R and R together represent an alkylene group having 2 to 5 carbon atoms, or an alkali metal salt or alkaline earth metal salt of this compound, which comprises reacting an ester of the general formula (formula II> in which R and R have the abovementioned meaning and R represents an optionally substituted alkyl group, with a hypochlorite or hypobromite of an alkali metal or an alkaline earth metal in the presence of water. The compounds of the formula I are intermediates for a specific isomerisation process which is suitable for preparing insecticidally active pyrethroid compounds.