Stereoselective Synthesis of C,C-Glycosides from exo-Glycals Enabled by Iron-Mediated Hydrogen Atom Transfer.

We describe herein a convenient strategy for the construction of C,C-glycoside building blocks via the intermediacy of tertiary pseudoanomeric radicals. Application of an iron-mediated hydrogen atom transfer/Michael-Giese coupling enables the anomeric quaternization of readily available exo-glycals with good to complete stereocontrol in the pyranose and furanose series. Carefully optimized conditions allow the use of challenging trisubstituted derivatives prone to undergo further elaboration to stable neoglycoconjugates. Preliminary results for direct C-disaccharide synthesis are also discussed.