Total Asymmetric Syntheses of 1,5-Dideoxy-1,5-Iminooctitols and 1,2,6,7,8-Pentahydroxyindolizidines

(1R,4R,5S,6S,7S)-4-exo-[(1'S,2'R)-1'-Hydroxy-2',3'-(isopropylidenedioxy) propyl]-6-exo,7-exo-(isopropylidenedioxy)-2,8-dioxabicyclo[3.2.1]octan-3 -one ((+)-5) and its diastereomer (1S,4S,5R,6R,7R)-(1'R,2'R)-(-)-30 derived from (R)-2,3-O-isopropylideneglyceraldehyde and (+/-)-5-exo,6-exo-(isopropylidenedioxy)-7-oxabicyclo[2.2.1]hept-2-one were alcoholyzed with benzyl alcohol in CCl4 (CsF as base) into the corresponding 5-C-(benzyloxycarbonly)-5-deoxyoctofuranoses (+)-9 and (-)-31 which were converted via Curtius rearrangements into (-)-1,5-dideoxy-1,5-imino-D-erythro-D-talo-octitol ((-)-20) and its D-threo-L-talo isomer (+)-36, respectively, Alcoholyses of (+)-5 and (-)-30 with benzyl alcohol in DMSO in the presence of CsF or K2CO3 led to the epimerized benzyl esters (-)-10 and (-)-38, respectively, which were converted into (-)-1,5-didoexy-1,5-imino-D-erythro-6-allo-octitol ((-)-27) and its D-threo-D-allo isomer (+)-42. The 1,5-dideoxy-1,5-iminooctitols were converted into the corresponding 1,2,6,7,8-pentahydroxyindolizidines in a single step.