The influence of boric acid on the acetylation of aldoses: ‘one-pot’ syntheses of penta-O-acetyl-β-D-glucofuranose and its crystalline propanoyl analogue

Chemical Synthesis of Furanose Glycosides

“…2). Success depends upon the monosaccharide having a threo arrangement of the hydroxyl groups at C3 and C4 (i.e., glucose, idose, mannose, gulose, xylose or lyxose), and the highest yields of the peracylated furanose derivatives were obtained with glucose, idose and xylose (53,54). This stereochemcial requirement is due to the formation of a borate intermediate (22), which is possible only when the O3 and O5 hydroxyl groups are on the same side of the ring.…”

“…Furneaux and coworkers have demonstrated that peracylated furanose derivatives can be formed from certain hexoses and pentoses via a two-step, one-pot process involving first treatment with boric acid followed by acetolysis ( Fig. 7) (53). The resulting species can be used directly in the formation of glycoside bonds by treatment with an alcohol and a Lewis acid, or converted to other glycosyl donors (Fig.…”

Boron acids as protective agents and catalysts in synthesis

“…As indicated in Section 1.2, boric acid has found less frequent application as a protective agent in organic synthesis than boronic acids. However, despite the water solubility and the complex equilibria that exist with sugar borate esters, Rendle et al 45 have recently employed boric acid in the efficient synthesis of penta-O-acetyl-and penta-O-propanoyl-β--glucofuranose (Scheme 13). This is an example of a boron acid being used to lock a reactant in one isomeric form rather than being used as a protecting agent.…”

Kinetically Controlled Fischer Glycosidation under Flow Conditions: A New Method for Preparing Furanosides

“…The simple and efficient syntheses of furanosides remain an important issue 3 even though various synthetic methods have been reported, including the kinetically controlled cyclization of dithioacetals in alcohol, 4 perbenzoylation of arabinose and galactose at high temperatures, 5 reduction of D-galactono-1,4-lactone with disiamylborane, 6 acetylation of hexoses and pentoses in the presence of boric acid, 7 and the selective activation of the anomeric position using 2,4,6-trichloro-1,3,5-triazine-activated DMSO. 8 Here, we achieved a concise synthesis of furanosides via kinetically controlled Fischer glycosidation.…”