Unsaturated sugars I. Decarboxylative elimination of methyl 2,3-di- O-benzyl-α- D-glucopyranosiduronic acid to methyl 2,3-di- O-benzyl-4-deoxy-β- L- threo-Pent-4-enopyranoside

Abstract

Decarboxylative elimination of methyl 2,3-di- O-benzyl-α- D-glucopyranosiduronic acid ( 1) with N,N-dimethylformamide dineopentyl acetal in N,N-dimethylformamide gave methyl 2,3-di- O-benzyl-4-deoxy-β- L- threo-pent-4-enopyranoside ( 3). Debenzylation of 3 was effected with sodium in liquid ammonia to give methyl 4-deoxy-β- L- threo-pent-4-enopyranoside ( 4). Hydrogenation of 3 catalyzed by palladium-on-barium sulfate afforded methyl 2,3-di- O-benzyl-4-deoxy-β- L- threo-pentopyranoside ( 5), whereas hydrogenation of 3 over palladium-on-carbon gave methyl 4-deoxy-β- L- threo-pentopyranoside ( 6). An improved preparation of methyl 4,6- O-benzylidene-α- D-glucopyranoside is also described.