Ligand-Controlled Stereoselective Synthesis of 2-Deoxy-β-C-glycosides by Cobalt Catalysis.

2-Deoxy-β-C-glycosides represent an important class of carbohydrates that are present in many bioactive molecules. However, owing to the lack of substituents at the C2 position, the stereoselective synthesis of 2-deoxy-β-C-glycosides is highly challenging. Herein, we report a ligand-controlled stereoselective C-alkyl glycosylation reaction to access 2-deoxy-β-C-alkyl glycosides from readily available glycals and alkyl halides. This method exhibits broad substrate scope and excellent diastereoselectivity under very mild conditions. In addition, unprecedented stereodivergent synthesis of 2-deoxy-C-ribofuranosides is achieved using different chiral bisoxazoline ligands. Mechanistic studies suggest that hydrometallation of the glycal with the bisoxazoline-ligated Co-H species may be the turnover-limiting and stereodetermining step of this transformation.