A novel process for the preparation of compounds in all their possible isomeric forms of the formula ##STR1## wherein R is selected from the group consisting of hydrogen, alkyl of 1 to 18 carbon atoms, an easily cleavable derivative of the alcohol R-OH and a residue of an alcohol used in the pyrethrinoid series and when Y is --COOR' or --COSR', W is hydrogen and W is halogen when Y is --COOR' and R' is selected from the group consisting of hydrogen, optionally unsaturated alkyl of 1 to 18 carbon atoms and optionally substituted with at least one functional group, aryl optionally substituted with at least one functional group and heterocycle optionally substituted with at least one functional group and when W is hydrogen, the double bond has Z configuration and when W is halogen, the double bond has the E configuration comprising reacting a compound of the formula ##STR2## wherein R has the above definition with a compound of the formula ##STR3## wherein W and Y have the above definitions and A is alkylene of 1 to 18 carbon atoms attached to the two oxygen atoms fixed on the phosphorus atom to obtain a compound of formula I with the double bond having the Z configuration when W is hydrogen and having the E configuration when W is halogen, the cyclopropane and the carboxyl of Y being in both cases in the cis position with respect to the double bond and novel intermediates.