1980 年 28 巻 11 号 p. 3265-3274
Total syntheses of (±)-phomenone (5a), (±)-3-epiphomenone (12), (±)-ligularenolide (27), and (±)-furanoligularanone (34) are described. Dehydration of 6 followed by epoxidation gave the epoxide (8), which was treated with lithium diethylamide to afford the alcohol (9). Epoxidation of 9 gave the α-epoxide (10), which was deketalized to give the diketone (11) Reduction of 11 with NaBH4 gave (±)-3-epiphomenone (12) as a major product. Stereoselective synthesis of (±)-5a starting from 7 was examined. Deketalization of 7 gave the triene-dione (13) which was reduced with NaBH4 to afford the alcohols 14a and 14b. Epoxidation of 3α-ol (14a) gave the epoxide (15), which was treated with lithium diethylamide to afford the diol (16). Epoxidation of 16 with hydrogen peroxide gave (±)-phomenone (5a) regio- and stereoselectively. Treatment of 17 with lithium diisopropylamide followed by condensation with methyl pyruvate gave the hydroxy ester (19), which was treated with acetic acid to give the ketone (24). 24 was thioketalized to give 25, which was treated with p-toluenesulfonic acid to afford the unsaturated lactone (26). 26 was transformed to (±)-ligularenolide (27) and (±)-tetrahydroligularenolide (28) in good yield. Condensation of 17 with acetol pyranyl ether followed by catalytic hydrogenation gave 33. Treatment of 33 with p-toluenesulfonic acid gave (±)-furanoligularanone (34), which was transformed to (±)-3β-furanoligularanol (36).
