1-C-(2′-Oxoalkyl) glycosides as latent α,β-unsaturated conjugates. Synthesis of aza-C-glycosides by an intramolecular hetero-Michael addition

1-C-(2′-Oxoalkyl)-5-azido-5-deoxy-glycofuranosides were used as latent substrates for intramolecular hetero-Michael addition. Reduction of the azido groups by catalytic hydrogenation followed by base treatment produced 2′-ester and 2′-ketone aza-C-glycopyranosides. The conjugation addition was stereoselective in favor of aza-C-glycosides with equatorial substitutions at the pseudo anomeric center.