Synthesis of Alpha-(1-]2)-, Alpha-(1-]3)-, Alpha-(1-]4)-, and Alpha-(1-]5)-C-Linked Disaccharides through 2,3,4,6-Tetra-O-Acetylglucopyranosyl Radical Additions to 3-Methylidene-7-Oxabicyclo[2.2.1]Heptan-2-One Derivatives

The ''naked sugar'' (+)-1 (1R,2S,4R)-2-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl (1S')-camphanate) has been converted into (+)-(1R,4R,5R,6R)-3-methylidene-5-exo,6-exo(isopropylidenedioxy)-7-oxabi cyclo[2.2.1]heptan-2-one ((+)-3) and (-)-(1S,4R,5R,6R)-5-exo-(benzeneselenyl)-6-endo-chloro-3-methylidene-7-o xabicyclo[2.2.1]heptan-2-one ((-)-26). Reductive addition of 2,3,4,6-tetra-O-acetylglucopyranosyl radical onto (+)-3 and (-)-26 were highly stereoselective giving exclusively 3-endo-(glucosylmethyl)-7-oxabicyclo[2.2.1]heptan-2-one derivatives. The anomeric selectivity (alpha-C-glucoside vs beta-C-glucoside) was 5.5:1 with (+)-3 and 8:1 with (-)-26. The C-glucosides so-obtained were transformed into alpha-(1 --> 2)-, alpha-(1 --> 3)-, alpha-(1 --> 4)-, and alpha-(1 --> 5)-C-linked disaccharide derivatives which combine alpha-D-glucopyranose with L-altro-hexonolactone, L-manno-hexonolactone, L-mannose, and L-(talo-hexofuranosid)uronic acid, respectively.