Mechanochemical Production of Oligosaccharide Alcohols via Borohydride‐Mediated Activation and Reductive Stabilization

Oligosaccharides are valuable functional carbohydrates, yet their selective synthesis from abundant polysaccharides remains challenging because uncontrolled hydrolytic processes lead to over‐hydrolysis and degradation. Here, we report a borohydride‐mediated mechanochemical strategy for the selective conversion of polysaccharides into oligosaccharide alcohols. Borohydride plays two key roles in the process: boron species form cyclic borate esters with carbohydrate hydroxyl groups under mechanochemical conditions to activate glycosidic linkages, while hydride species reduce anomeric hemiacetals to suppress repolymerization and stabilize depolymerized intermediates. This coupled activation‐stabilization mechanism enables microcrystalline cellulose depolymerization with up to 92% efficiency and 89% oligosaccharide alcohol selectivity. The process is also applicable to poplar sawdust, sugarcane bagasse, and corncob, affording 76%–84% yields. The resulting oligosaccharide alcohols exhibit intrinsic protein‐stabilizing performance comparable to that of commercial stabilizers. These findings provide mechanistic insights into boron‐mediated mechanochemistry for biomass valorization, and offer convenient access to oligosaccharide alcohols.