Hypervalent Chalcogenonium H-Bonding Organocatalysis for the Direct Stereoselective Synthesis of Deoxyglycosides

The use of trisubstituted selenonium salts as organocatalysts for the direct and stereoselective synthesis of deoxyglycosides from hemiacetals is described. The reaction conditions are mild and compatible with various functionalities and has a broad substrate scope including examples of 1-hydroxy deoxy-galactoside and glucoside substrates. Mechanistic investigations suggest that the reaction proceeds via a step-wise process involving the he hemiacetal donor, OH acceptor and catalyst, whereby the chalcogen catalysts mediates the key H+ transfer step. This study opens a new avenue for the development of nonmetallic acid/base catalysis for the stereoselective synthesis of complex glycosides.