Synergistic Boronic Acid and Photoredox Catalysis: Synthesis of C-Branched Saccharides via Selective Alkylation of Unprotected Saccharides.

Here we present a regio- and stereoselective alkylation approach for unprotected saccharides using synergistic boronic acid and photoredox catalysis. Targeting the equatorial C-H bond of the cis-1,2-diol motif, this method employs MeB(OH)2 as a catalyst. Mechanistic investigations indicate that the formation of a tetracoordinate boron species, resulting from the interaction between the cyclic boronic diol ester and a free hydroxyl group in the saccharide, is critical to this transformation. Notably, this method enables efficient late-stage modification of complex carbohydrates, such as raffinose and the drug digoxin, expanding opportunities for carbohydrate functionalization.