Synthesis of a polyhydroxyquinolizidine bearing a polyhydroxylated carbon side-chain

The lithium enolate of (-)-6-endo-chloro-5-exo-(phenyl-seleno)-7-oxabicyclo [2.2.1]heptan-2-one ((-)-4) added to (+)-(3aR, 4aR,7aR,7bS)-3a,4a,7a,7b-tet rahydro-6,6-dimethyl[1,3]dioxolo[4,5]furo[2,3-d]isoxazole-3-carbaldehyde (( +)-5) giving a major aldol (+)-6 in 90% yield that was converted into (+)-( 1R,4R,5R, 6S,7R)-4-exo-(4-bromobenzenesulfonyloxy)-6-exo-{(S)-[(tert-butyl) dimethylsilyloxy]-[(3aR,4aR,7aR,7bS)-3a,4a,7a,7b-tetrahydro-6,6-dimethyl[1, 3]dioxolo[4,5]furo [2,3-d]isoxazol-3-yl]methyl}-7-endo-(methoxymethoxy)-2,8 -dioxabicyclo[3.2.1]octan-3-one ((+)-15). Methanolysis of (+)-15, followed by reduction and protection steps provided (-)-1,4-anhydro-3-{6S-5-[(benzyl oxy) carbonyl]amino-5-deoxy-beta-L-idohexofuranos-6-C-yl}-3-deoxy-2,6-bis-O -(methoxymethyl)-alpha-D-galactopyranose((-)-21). Acidic treatment of(-)-21 followed by catalytical hydrogenation generated (-)-(1R,2R,3S,7R,8S,9S,9aS )-1,3,4,6,7,8,9a-octahydro-8-[(1'R,2'R)-1',2',3'-trihydroxypropyl]-2H-quino lizine-1,2,3,7,9-pentol((-)-2) characterized as its octaacetate (+)-26.