Diastereoselective Reduction of Hemiacetals Derived from 2,3-<i>O</i>-Isopropylidene Derivatives of Carbohydrate Lactones
作者:Shende Jiang、Gurdial Singh、Richard H. Wightman
DOI:10.1246/cl.1996.67
日期:1996.1
corresponding hemiacetals which, by choice of hydride reagents, can be reduced stereoselectively to give products with a syn-(threo-) relationship between the new chiral centre and that at C-2 of the lactone.
Enantiospecific synthesis of (−)-5-epi-shikimic acid and (−)-shikimic acid
作者:Shende Jiang、Kevin J. McCullough、Boualem Mekki、Gurdial Singh、Richard H. Wightman
DOI:10.1039/a700389g
日期:——
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.