Retro synthetic Analysis and Strategy

Although compound 14 may be preferred at equilibrium, C-l in isomer 18 is particularly susceptible to nucleophilic attack because it is much less hindered than either C-2 or C-3 in 14. Once 18 is produced, it reacts selectively with hydroxide ion to give triol 19. The irreversible conversion of 18 to triol 19 drives the equilibrium process forward. 

From a stereochemical point of view, compound 35 is rather complex, for it possesses four contiguous oxygen-bearing stereocenters. Nonetheless, compound 35 is amenable to a very productive retro-synthetic maneuver. Indeed, removal of the epoxide oxygen from 35 furnishes trans allylic alcohol 36 as a potential precursor. In the synthetic direction, SAE of 36 with the (+)-dialkyl tartrate ligand would be expected to afford epoxy alcohol 35, thus introducing two of the four contiguous stereocenters in one step. 

The most crucial stage in the synthesis has been reached. The goal of constructing the L-hexoses from allylic alcohols 36 and 44 can be achieved only in the event that the two diastereotopic olefin 

NaOAc 2. Ac20, NaOAc 3. NaOMe, MeOH 

Seebach, D. Weidmann, B. Wilder, L. In Modern Synthetic Methods 1983, Scheffold, R Ed., Otto Salle Verlag Frankfurt, 1983, p. 324. 

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