Synthetic Studies on dl-Aspterric Acid, a Carotane-Type Sesquiterpene. II. Synthesis of dl-Aspterric Acid(Organic,Chemical)

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Total synthesis of dl-aspterric acid (1) has been accomplished. Robinson annulation of the keto ester (2) with methyl vinyl ketone, followed by reduction with LiAlH_4 and oxidation with MnO_2, afforded the enone alcohol (4), which was converted to the hydroxy-ether (6) via three steps (I_2-Ag_2O, AgOAc, and alkaline hydrolysis). Successive treatment of 6 with tert-butyldimethylsilyl chloride, tert-BuOK-MeI, NaBH_4, Ac_2O-pyridine and 5% HC1 afforded the hydroxy acetate (18). The hydroxy acetate (18) was converted to the hydroxy ketone (20) via catalytic hydrogenation under medium pressure, Jones oxidation, and alkaline hydrolysis. Treatment of 20 with PCl_5 gave the norketone (21), which is the degradation product of 1. The dimethylacetal (25) of 20 was treated with Me_3SiCN-SnCl_2 to give the methoxy cyanides A (26) and B (27). The major methoxy cyanide B (27) was successively treated with KOH, Me_3SiCl-NaI, Ac_2O, and 5% HCl to give the monoacetate (31), which was finally converted to 1 via ring contraction with PCl_5 and alkaline hydrolysis.
社団法人日本薬学会の論文
1987-04-25