Pyranosides with 2,3‐ trans Carbamate Groups: Exocyclic or Endocyclic Cleavage Reaction?

Pyranosides with 2,3‐ trans carbamate groups exhibit high 1,2‐ cis selectivity in glycosylation reactions. Using glycosyl donors with N ‐benzyl 2,3‐ trans carbamate groups, an anti‐ H elicobacter pylori oligosaccharide was synthesized in an efficient manner. Moreover, pyranosides with 2,3‐ trans carbamate groups readily undergo anomerization from the β to the α configuration under mild acidic conditions via endocyclic cleavage. Acyclic cations generated during the endocyclic cleavage reaction were captured using reduction and intramolecular F riedel– C rafts reaction. By exploiting this anomerization, multiply aligned 1,2‐ trans glycosyl bonds can be transformed to 1,2‐ cis glycosyl bonds in a single operation.