Switching between X -Pyrano-, X -Furano-, and Anhydro- X -pyranoside Synthesis (X = C, N) under Lewis acid Catalyzed Conditions.

A variety of C -glycosides can be obtained from the fluoroarylborane (B(C ₆ F ₅ ) ₃ ) or silylium (R ₃ Si ⁺ ) catalyzed functionalization of 1-MeO- and per-TMS-sugars with TMS-X reagents. A one-step functionalization with a change as simple as the addition order and/or Lewis acid and TMS-X enables one to afford chiral synthons that are common ( C -pyranosides), have few viable synthetic methods ( C -furanosides), or are virtually unknown (anhydro- C -pyranosides), which mechanistically arise from whether a direct substitution, isomerization/substitution, or substitution/isomerization occurs, respectively.