9 薬用人参サポゲニンの合成研究 : 光励起ニトロベンゼン誘導体によるリモート酸化とその応用

抄録

The synthesis of dammaranediol-II(VI) from hydroxyhopanone(III) has already been reported. In an attempt toward the synthesis of 20(S)-protopanaxadiol(I) from VI, the introduction of a hydroxy function to C-12 of the dammarane skeleton has been studied. A solution of p-nitrobenzoate(XI) of 3-epi-dammaranediol-I(X) in tert.BuOH was irradiated for 40 hr and the products were saponified to give octakisnordammarane-3α,17β-diol(XII). From the crude irradiation products, 2-methyl-6-heptanone(XIII) was isolated and identified. Whereas, the irradiation of p-nitrophenylacetate(XIV) of 3-epi-dammarandeiol-II(IX) under the similar condition followed by saponification yielded the 12α-hydroxy compound(XV). p-Nitro-phenylacetate of X also afforded the 12α-hydroxy compound by the similar sequence of the reaction. In case of β-(p-nitrophenyl)propionate of IX, the similar hydroxylation reaction was observed but production of the compounds other than XV was increased. The 12α-hydroxy compound(XV) thus obtained was converted to betulafolienetriol(XVI) and 20(S)-protopanaxadiol(I) furnishing the synthesis of the Ginseng sapogenin.