Protecting Group\nControl of Hydroxyketone-Hemiketal\nTautomeric Equilibrium Enables the Stereoselective Synthesis of a\n1<i>′</i>‑Azido <i>C</i>‑Nucleoside

The synthesis of 1<i>′</i>-azido <i>C</i>-nucleosides is described to expand the set of azide-functionalized\nnucleosides for bioorthogonal applications and as potential antiviral\ndrugs. Lewis acid-promoted azidation of a nucleoside hemiketal resulted\nin the formation of a tetrazole through a Schmidt reaction manifold.\nConformational control to prevent ring–chain tautomerism enabled\nefficient 1<i>′</i>-azidation with complete β-diastereoselectivity.\nThe unique reactivity and further derivation of the 1<i>′</i>-azido <i>C</i>-nucleosides are also reported.