Abstract
Methyl santalbate (methyl trans-11-octadecen-9-ynoate) from Sandal wood seed oil, Santalbum alum) was epoxidized to methyl trans-11,12-epoxy-octadec-9-ynoate ( 1). Treatment of compound 1 with tetrabutylammonium dihydrogentrifluoride, and boron trifluoride etherate gave the corresponding anti- ( 2a) (57%) and syn- ( 2b) (35%) fluorohydrin derivatives, respectively. These reactions were regio- and stereoselective in nature. The structures of the anti- and syn- isomers were confirmed by NMR spectroscopy. Ring opening of the epoxy system of compound 1 with lithium chloride gave the anti-chlorohydrin derivative ( 3) (89%). Oxidation of either compound 2a or 2b gave the same fluoro-keto acetylenic fatty ester ( 4) (75%), and compound 3 on chromic acid oxidation yielded the corresponding chloro-keto acetylene ( 5) (73%). Isomerization of compounds 4 and 5 with potassium carbonate in dichloromethane furnished the requisite fluoro-allenic ( 6) (63%, methyl 11-fluoro-12-oxo-9,10-octadecadienoate) and chloro-allenic ( 7) (80%, methyl 11-chloro-12-oxo-9,10-octadecadienoate) C 18 fatty esters. All products were confirmed by a combination of spectrometric and spectroscopic techniques.
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