Equimolar oxymercuration of D-glucal triacetate with mercuric perchlorate and its application to the synthesis of 2′-deoxy disaccharides

Abstract

A search for appropriate reaction conditions for the equimolar methoxymercuration of D-glucal triacetate was made by using various mercuric salts, bases, and reaction solvents. Under optimum conditions with mercuric perchlorate, sym-collidine, and acetonitrile, D-glucal triacetate underwent methoxymercuration with an equimolar amount of methanol to afford methyl 3,4,6-tri- O-acetyl-2-deoxy-2-perchloratomercuri-β- D-glucopyranoside ( 1, 26%) and its α- D- manno isomer ( 2, 49%). Equimolar oxymercuration of D-glucal triacetate with partially protected sugars, followed by subsequent demercuration of the products with sodium borohydride, afforded α- and β-linked 2′-deoxy disaccharide derivatives in moderate yields. The partially protected sugars used were 1,2,3,4-tetra- O-acetyl-β- D-glucopyranose and 1,2:3,4-di- O-isopropylidene-α- D-galactopyranose, and the corresponding products were O-(3,4,6-tri- O-acetyl-2-deoxy-α- D- arabino-hexopyranosyl)-(1→6)-1,2,3,4-tetra- O-acetyl- D-glucopyranose( 4, 23%) and its β-linked isomer ( 5, 11%) from the former, and O-(3,4,6-tri- O-acetyl-2-deoxy-α- D- arabino-hexapyranosyl)-(1→6)-1,2:3,4-di- O-isopropylidene-α- D-galactopyranose ( 9, 29%) and its β-linked isomer ( 10, 10%) from the latter. Deacetylation of these 2′-deoxy disaccharides was effected with methanolic sodium methoxide, but deacetonation was unsuccessful owing to simultaneous cleavage of the glycosidic linkage.