LACTOBACILLIC ACID 17 



which are useful for purification purposes, methods for the 

 synthesis of the cis cyclopropane fatty acids had to be de- 

 vised which precluded the formation of mixtures of stereo- 

 isomers. Thus, an intermediate of unquestionable cis con- 

 figuration had to be prepared which would lend itself to 

 conversion into the desired long-chain cyclopropane fatty 

 acids without any risk of cis-trans inversion during the 

 process. 



Cyclopropane-<:/5-l,2-diacetic acid, a compound not previ- 

 ously described, seemed ideally suited for this purpose, 

 since methods are available for its conversion into the 

 desired long-chain acids, and since the separation of its 

 carboxyl groups from the centers of asymmetry eliminates 

 the possibility for cis-trans inversions. Our route (23) to 

 cyclopropane-aVl,2-diacetic acid (Fig. 1.9) involves reaction 

 of equimolar proportions of cyclohexa-l,4-diene (I) with 

 dibromocarbene according to the method of Doering (24) 

 to give the intermediate (II) which is readily converted by 

 oxidation into (III). Cyclopropane-d5-l,2-diacetic acid is 

 obtained in good yields when (III) is subjected to hydro- 

 genolysis over a Raney nickel catalyst in presence of potas- 

 sium hydroxide. The method of synthesis employed and 

 the fact that cyclopropane-<:/5-l,2-diacetic acid, identical with 

 the acid prepared by the above described scheme, can be 

 obtained from cyclopropane-c?5-l,2-dicarboxyIic acid (25) 

 leaves no doubt regarding the stereochemical configuration 

 of this compound. For conversion into long-chain fatty 

 acids, the carboxyl ends of cyclopropane-c/5-l,2-diacetic acid 

 are elongated through suitable manipulations (26, 27). For 

 construction of the hydrocarbon end (Fig. 1.10), the diacetic 

 acid (I) is converted into the monomethyl ester, and the 

 acid chloride of the latter (II) is reacted with a suitable 

 alkylcadmium reagent to form the keto acid (III), which is 



