Monomeric hexofuranoses having an acetylimino group in the hemiacetal ring

Acetolysis of methyl 4-acetamido-4-deoxyhexopyranosides of gluco and galacto configuration yields not only the corresponding 4-acetamido-4-deoxy-pyranoses, but also ring contraction products, i.e., 4-acetamido-1,2,3,5,6-penta-O-acetyl-4-deoxy-D-gluco- and -D-galactofuranose, respectively, with the ease of acetolysis and product distribution depending on the configuration at C-4. Mechanistic implications with respect to the formation of acylic and cyclic intermediates are discussed.