Endocyclic cleavage reactions of pyranosides have been recognized as rare events in glycoscience. The pyranosides with 2,3-trans carbamate/carbonate group are easily anomerized from the β- to the α-direction via endocyclic cleavage reaction. Evidence of endocyclic reaction was shown by reduction and Friedel-Crafts reaction of acyclic cation. Significant substituent effect was observed at the carbamate nitrogen, especially and Ac group. By using the isomerization reaction via endocyclic reaction, several 1,2-cis aminosaccharides were prepared from the 1,2-trans glycosides. [chemical formula]