Sequential Regiodivergent Polyol Sulfonylation and Functionalization Enable Precise Engineering of Carbohydrates

Substituent functionalization of unprotected and partially protected carbohydrates with controlled regioselectivity remains challenging due to the difficulty in differentiating hydroxyl groups with similar reactivities. This study presents an efficient protocol for site-specific modification through a "two-stage," regiodivergent polyol tagging and functionalization strategy. To achieve effective tagging, we developed two complementary Ag₂CO₃-ligand-based regimes that enable the regioselective sulfonylation of cis-diol and trans-diol in carbohydrates, controlled by simply toggling the presence of a [Pd] catalyst. Competition experiments and DFT simulations elucidated the underlying dual mechanisms accounting for the regioselectivity. [Pd] catalyst complexes to cis-diol as a bidentate ligand, enhancing the differentiated electrophilicities through stereoelectronic effects and preferentially activating the equatorial C3-OH groups. Conversely, without [Pd], the Ag-(I) complex switches the reaction position, directing sulfonylation to the axial hydroxyl within 1,2-cis-diol, a position that is typically kinetically inert under conventional conditions. And the Ag-(I) complex preferentially coordinates to cis-1,2-substituents on the sugar ring and selectively activates the C2-OH group. The sulfonylated products serve as versatile synthons for the following structural derivations and chemical glycosylations, facilitating efficient access to structurally unique rare sugars, deoxy- and aminosugar analogues, and complex oligosaccharides. This dual-catalytic approach provides a robust platform for precision carbohydrate engineering, advancing the synthesis of biologically relevant oligosaccharides and glycoconjugates.