text: Transglycosylation, which involves the reversible transfer of a sugar moiety from one heterocyclic base to another, is effective for the conversion of pyrimidine nucleosides to purine nucleosides. Most other transglycosylation reactions are low yielding due to a small thermodynamic difference between equilibrating nucleosides.
  Deoxyribose-derived electrophiles are unable to form the cyclic cation 1; as a result, the stereoselective synthesis of deoxyribonucleosides is more difficult than the synthesis of ribonucleosides. One solution to this problem involves the synthesis of a ribonucleoside, followed by protection of the 3- and 5-hydroxyl groups, removal of the 2'-hydroxyl group through a Barton deoxygenation, and deprotection.