Diastereoselective reaction of
2,3-O-isopropylidene-D-ribose with allylmagnesium
chloride gave a 5∶1 mixture of triols 4 and 5, which were then
converted to nitrones 8 and 9. Intramolecular nitrone cycloaddition gave
the isoxazolidines 10 and 11, which on acetylation gave the
corresponding acetates 12 and 13 which were separated by repeated
crystallisation. The major adduct 12 was converted to
(-)-5-epi-shikimic acid 2. Reaction of the ribonolactone
derivative 20 with allylmagnesium chloride gave the hemiacetal 21.
Reduction of compound 21 with DIBAL afforded exclusively the diol 22,
which was desilylated to give the triol 5. Similar chemistry to that
employed for the synthesis of (-)-5-epi-shikimic acid 2
with the diol 5 resulted in the synthesis of (-)-shikimic acid
1.
2,3-O-异亚丙基-
D-核糖与烯
丙基氯化镁发生非对映选择性反应,生成 5∶1 的三醇混合物 4 和 5,然后转化为硝酮 8 和 9。分子内的硝酮环化反应生成
异噁唑烷 10 和 11,乙酰化反应生成相应的
乙酸盐 12 和 13,通过反复结晶分离。主要加合物 12 转化为 (-)-5- 表
莽草酸 2。
核糖酸内酯衍
生物 20 与烯
丙基氯化镁反应生成
半缩醛 21。 化合物 21 与二
乙酰胆碱还原生成二元醇 22,二元醇 22 经过脱
硅反应生成三元醇 5。用二元醇 5 合成(-)-5-表
莽草酸 2 的
化学反应与合成(-)-
莽草酸 1 的
化学反应类似。