Anion-Binding-Mediated Reductive Etherification Enables Alkylation of Sugar Hydroxyls in the Presence of Esters

The selective introduction of ether-protecting groups in the presence of esters remains a longstanding challenge in carbohydrate chemistry. Herein, we report an anion-binding-mediated reductive etherification strategy for the efficient alkylation of carbohydrate hydroxyl groups using chlorodimethylsilane and catalytic Schreiner thiourea. This method shows broad functional group tolerance, including esters, acetals, and silyl ethers, and is further demonstrated in the synthesis of the trimannoside motif.