Pyranosides containing a 2,3-trans carbamate group exhibit high 1,2-cis selectivity in glycosylation reactions. Furthermore, they are easily anomerized from the 1,2-trans to the 1,2-cis form via endocyclic cleavage reaction, in which the bond between the anomeric carbon and O5 oxygen is cleaved to afford an acyclic cation. The anomerization occurred under mild acidic conditions. The endocyclic cleavage reaction was confirmed by trapping the acyclic cation by reduction and intramolecular Friedel–Crafts reactions. A significant substituent effect on the carbamate nitrogen was observed, and complete anomerization of the acetyl group substituent was observed. The anomerization of multiple 1,2-trans glycosyl bonds via endocyclic cleavage reaction afforded 1,2-cis glycosyl bonds via a single step reaction under mild acidic conditions.
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