ENANTIOSPECIFIC SYNTHESIS OF (-)-5-EPI-SHIKIMIC ACID AND (-)-SHIKIMICACID

Diastereoselective reaction of 2,3-O-isopropylidene-D-ribose with ally lmagnesium chloride gave a 5:1 mixture of triols 4 and 5, which were t hen converted to nitrones 8 and 9. Intramolecular nitrone cycloadditio n gave the isoxazolidines 10 and 11, which on acetylation gave the cor responding acetates 12 and 13 which were separated by reheated crystal lisation. The major adduct 12 was converted to (-)-5-epi-shikimic acid 2. Reaction of the ribonolactone derivative 20 with allylmagnesium ch loride gave the hemiacetal 21. Reduction of compound 21 with DIBAL aff orded 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 (-)-shiki mic acid 1.