Preparation and properties of gem-dichlorocyclopropane derivatives of long-chain fatty esters.

Methyl oleate (18:1) and linoleate (18:2) were readily transformed to the corresponding gem-dichlorocyclopropane derivatives in high yield, using triethylbenzylammonium chloride as the phase-transfer catalyst in the presence of aqueous NaOH and CHCl3. Reaction of dichlorocarbene with methyl 12-hydroxystearate furnished methyl 12-chlorostearate (49%) and 12-O-formylstearate (19%). The hydroxy group in methyl ricinoleate was protected (O-tetrahydropyran-2'-yl) prior to dichlorocyclopropanation of the ethylenic bond. Removal of the protecting group allowed the hydroxy group to be converted to a chloride, O-acetyl, azido or O-formyl function. Treatment of methyl ricinoleate with thionyl chloride, followed by the reaction with dichlorocarbene gave the corresponding 12-chloro-dichlorocyclopropane derivative. The dichlorocyclopropane derivative of oleic acid was transformed to a C19 allenic fatty acid when treated with t-butyl lithium. However, the remaining dichlorocyclopropane derivatives containing an additional functional group in the alkyl chain, failed to yield the corresponding allenic derivatives. All derivatives were characterized by a combination of spectroscopic and chromatographic techniques, including infrared, 1H nuclear magnetic resonance (NMR), and 13C NMR spectroscopy.