Concise synthesis of 1-deoxy-4-O-β-d-galactopyranosyl-d-nojirimycin avoiding a glycosylation step

2′,6′-Di-O-benzyl-2,3:5,6:3′,4′-tri-O-isopropylidenelactose dimethyl acetal was used as starting material for the preparation of the until now unknown 4-O-β-d-galactopyranosyl-d-xylo-hexos-5-ulose derivatives 7–9, through selective C-5 oxidation of its partially deprotected derivatives 4–6. Hydrolysis of 7–9 with aq. CF3COOH led to deprotected 1,5-dicarbonyl disaccharides 11–12, diastereoselectively transformed without purification into 1-deoxy-4-O-β-d-galactopyranosyl-d-nojirimycin derivatives in about 60% yield, through a double reductive amination reaction.