Addition of Electrophilic Radicals to 2-Benzyloxyglycals: Synthesis and Functionalization of Fluorinated α-C-Glycosides and Derivatives

A new method for the synthesis of fluorinated -C-glycosides is described. The reactions between highly electrophilic radicals (fluorinated or unfluorinated) and a 2-benzyloxyglucal or galactal provide 2-keto-D-arabino- or 2-keto-D-lyxo-hexopyranosides through an addition/fragmentation process. Sodium borohydride mediated or Meerwein-Ponndorf-Verley (MPV) reduction of these compounds provides -C-glycosides that feature appropriate anchoring groups for further synthetic elaboration. The presence of CF(2)CO(2)iPr or CF2Br groups at the pseudo-anomeric position allows efficient reduction/olefination or Br/Li-exchange/nucleophilic-addition sequences. These transformations open the way for the synthesis of fluorinated C-glycosidic analogues of glycoconjugates.