Abstract
Formation of 3,4,6-tri-O-benzyl-2-nitro-D-galactal (3) was readily accomplished starting from tri-O-benzyl-D-galactal (1) by acetyl nitrate addition to 2 and base-promoted acetic acid elimination. Addition of alcohols to 3 under conditions of base catalysis afforded 2-deoxy-2-nitrogalactopyranosides 4a–e in high yields; high α-selectivity was obtained with strong bases, whereas weaker bases furnished mainly the corresponding β-galactopyranosides. Chemoselective nitro group reduction in these glycosides was successfully carried out in the case of disaccharide 4cα using Raney nickel as catalyst, thereby affording after N-acetylation the corresponding 2-acetylamino-2-deoxy derivative 5cα.
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