ABSTRACT
Several workers have reversed the natural character of the anomeric carbon atom from electrophilic to nucleophilic and trapped these nucleophiles with appropriate carbon electrophiles to produce C-glycosides. Vinyl anions of glycals have also seen utility in the preparation of C-glycoside compounds. Sinay and collaborators published three consecutive papers dealing with the reductive lithiation of anomeric sulfones to yield anomeric anions that were then trapped with suitable electrophiles to give a variety of C-glycosides. The anionic approaches described thus far result in the preparation of C-glycosides either with oxygenation at the first carbon atom on the carbon aglycone by reaction with a carbonyl compound or by Michael type additions to provide C-glycosides with oxygenation on C-3. The insertions retain the starting stereochemistry of the glycosylmanganese pentacarbonyl complexes and generally give good yields of C-glycosides. Transition metal anomeric complexes have also begun to emerge as useful precursors for C-glycoside preparation.
