The stereoselective synthesis of novel 4-octulose derivatives

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 LiAlH4 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).