Dihydroxylation of methyl ( E)-2,3-dideoxy-4,5:6,8-di- O-isopropylidene- l- xylo-oct-2-ene-4-ulofuranosonate ( 1) with osmium tetraoxide took place with high diastereoselectivity to give a 7:1 mixture of methyl 4,5:6,8-di- O-isopropylidene- α- l- glycero- d- galacto- ( 2) and - d- ido-oct-4-ulofuranosonate ( 3). When 1 was dihydroxylated in the presence of dihydroquinine and dihydroquinidine p-chlorobenzoate, an appreciable increase and decrease, respectively, in the 2/ 3 ratio was observed. Compound 2 was transformed into its 2,3-di- O-methyl derivative 4 which was deisopropylidenated to methyl 2,3-di- O-methyl- α- l- glycero- d- galacto-oct-4-ulopyranosonate ( 5) and subsequently degraded to dimethyl 2,3-di- O-methyl-(+)- l-tartrate ( 6). On the other hand, compounds 2 and 3, separately, were isopropylidenated to the corresponding 2,3:4,5:6,8-tri- O-isopropylidene derivatives 7 and 8, which were reduced with LiAlH 4 to the related 2,3:4,5:6,8-tri- O-isopropylidene- α- l- glycero- d- galacto- ( 9) and - d- ido-oct-4-ulofuranose ( 10). Finally, compounds 9 and 10 were deisopropylidenated to the corresponding l- glycero- d- galacto- ( 11) and l- glycero- d- ido-oct-4-ulose ( 12).