Stereodivergent De Novo Synthesis of Branched Amino Sugars by Lewis Acid Promoted Rearrangement of 1,2-Oxazines
F. Pfrengle, D. Lentz, H.-U. Reissig – 2009
Well concealed: 1,2-oxazines such as 1 rearrange under Lewis acidic conditions to bicyclic products of type 2, which can be incorporated into oligosaccharides as protected amino sugar equivalents. Subsequent reductive steps provide unusual oligosaccharides 3 having C2-branched 4-amino sugar units. Most of the reactions proceed with excellent stereocontrol and allow the synthesis of a collection of stereoisomers.