2,3-trans-carbamate- and -carbonate-carrying pyranosides were very easily anomerised from the ß to the a direction in the presence of a Lewis acid compared to other pyranosides. This reaction is caused by endocyclic cleavage of the pyranosides. Evidence for endocyclic cleavage of conformationally restricted pyranosides in the chair form was obtained by intra- and intermolecular FriedelCrafts reactions, chloride addition, and reduction of the generated cation. On the other hand, pyranosides with the distorted conformation were never cleaved in an endocyclic manner.
- Cleavage reactions
- Friedel-crafts reaction