Synthesis of 4-octuloses from a derivative of (D)-fructose

Reaction of 2,3:4,5-di-O-isopropylidene-beta-D-arabino-hexos-2-ulo-2,6-pyranose (1) with (methoxycarbonylmethylene)triphenylphosphorane in either dichloromethane or methanol gave methyl (E)-2,3-dideoxy-4,5:6,7-di-O-isopropylidene-beta-D-arabino-oct-2-ene-4-ulo-4,8-pyranosonate (2) or a 1:2.3 mixture of 2 and its Z-isomer (3), respectively. Bishydroxylation of 2 with osmium tetraoxide gave a mixture of methyl 4,5:6,7-di-O-isopropylidene-beta-D-glycero-D-galacto- (4) and -D-glycero-D-ido-oct-4-ulo-4,8-pyranosonate (5) which were carefully resolved by column chromatography. Compound 4 was transformed into its 2,3-di-O-methyl derivative (6) which was deacetonated to 7 and subsequently degraded to dimethyl 2,3-di-O-methyl-(+/-)-L-tartrate (8). On the other hand, acetonation of a mixture of 4 and 5 gave the corresponding tri-O-isopropylidene derivatives (9) and (10). Compounds 4 and 5 were reduced with LiAlH4 to the related 4,5:6,7-di-O-isopropylidene-beta-D-glycero-D-galacto- (11) and -beta-D-glycero-D-ido-oct-4-ulo-4,8-pyranose (12). Treatment of 11 and 12 with acetone/PTSA/CuSO4 only produced the acetonation at the C-2,3 positions. Finally, compounds 11 and 12 were deacetonated to the corresponding D-glycero-D-galacto- (15) and D-glycero-D-ido-oct-4-ulose (16).