Novel Syntheses of Isomers of Damascenone from Ethyl 2,6,6-Trimethyl-4-oxo-2-cyclohexene-1-carboxylate

摘要

Three isomers of damascenone, odorous terpenic ketones, have been synthesized conveniently from a same starting material, ethyl 2,6,6-trimethyl-4-oxo-2-cyclohexene-1-carboxylate( 1), which was easily available by the acid-catalyzed condensation of mesityl oxide or acetone with ethyl acetoacetate. メ -Damascenone(7) was prepared by converting the enone ester 1 into the corresponding tosylhydrazone(4), followed by treating with 4 molar equiv of allyllithium. モ-Damascenone(12) was synthesized by chemoselective reduction of 1 with sodium borohydride/cerium chloride to give corresponding allylic alcohol 8, conversion of 8 into acetate 9, and thermal decomposition of 9 with DBU to afford ethyl モ-safranate(10), followed by reaction with an excess amount of allyllithium. ャ-Damascenone(15) was obtained by dehydration of 8 with boric acid to furnish ャ -safranate(13), followed by treatment with 2 molar equiv of allyllithium.