Copper Reactivity Can be Tuned to Catalyse the Stereoselective Synthesis of 2-Deoxy Glycosides from Glycals

We demonstrate that tuning the reactivity of Cu by the choice of oxidation state and counterion leads to the activation of both “armed” and “disarmed” type glycals towards direct glycosylation leading to the a-stereoselective synthesis of deoxyglycosides in good to excellent yields. Mechanistic studies show that CuI is essential for effective catalysis and stereocontrol and that the reaction proceeds through dual activation of both the enol ether as well as the OH nucleophile.