Process for preparing cis-chrysanthemic acid

Claim 1

A process for preparing cis-chrysanthemic acid of the formula (I) ##EQU1## which comprises preparing a trans-δ-hydroxydihydrochrysanthemic acid ester of the formula (V) ##EQU2## wherein A represents C 1 -C 4 alkyl or benzyl by either hydrolyzing an ester of trans-δ-halogenodihydrochrysanthemic acid of the formula (VI) ##EQU3## wherein X is a halogen atom under neutral conditions maintained by the presence of calcium carbonate or magnesium carbonate or by hydrolyzing a trans-δ-halogenodihydrochrysanthemic acid of the formula (VIII) ##EQU4## wherein X is a halogen atom under neutral conditions maintained by the presence of calcium carbonate or magnesium carbonate with further esterifying said hydrolyzed acid with an alcohol of the formula A-OH wherein A is defined above in the presence of a mineral acid at about room temperature, reacting said trans-δ-hydroxydihydrochrysanthemic acid ester of the formula (V) with more than an equimolar amount of a strong base selected from the group consisting of alkali metal alkoxide, alkali metal hydride, alkali metal amide and alkali metal in the presence or absence of an inert solvent at a temperature ranging from 100° C to 200° C to prepare a mixture of cis-chrysanthemic acid of the formula (I) and iso-cis-chrysanthemic acid of the formula (III) ##EQU5## treating said mixture with water in the presence of an acid catalyst, in the presence or absence of an inert solvent to convert iso-cis-chrysanthemic acid of the formula (III) selectively to cis-dihydrochrysanthemolactone of the formula (II) ##EQU6## and separating the acid part from the neutral part by adding an aqueous alkaline agent to the resulting mixture and removing the lactone of the formula (II) as the neutral part according to an ordinary method.