Dynamic Kinetic Stereoselective Glycosylation via Rh and Chiral Phosphoric Acid-Cocatalyzed Carbenoid Insertion to the Anomeric OH Bond for the Synthesis of Glycoconjugates.

Chemical synthesis of glycoconjugates is essential for studying the biological functions of carbohydrates. We herein report an efficient approach for the stereoselective synthesis of challenging α-linked glycoconjugates via a Rh /chiral phosphoric acid (CPA)-cocatalyzed dynamic kinetic anomeric O-alkylation of sugar-derived lactols via carbenoid insertion to the anomeric OH bond. Notably, we observed excellent anomeric selectivity, excellent diastereoselectivity, broad substrate scope, and high efficiency for this glycosylation reaction by exploring various parameters of the cocatalytic system. DFT calculations suggested that the anomeric selectivity was mainly determined by steric interactions between the C2-carbon of the carbohydrate and the phenyl group of the metal carbenoid, while π/π interactions with the C2-OBn substituent on the carbohydrate substrate play a significant role for diastereoselectivity at the newly generated stereogenic center.