Protected glycosides and disaccharides of 2-amino-2-deoxy- d-glucopyranose by ferric chloride-catalyzed coupling

Abstract

The ferric chloride-catalyzed glycosylation of hydroxy compounds by protected 2-acylamino-2-deoxy-β- d-glucopyranose 1-acetates is described. In addition to known glycosides from the reaction of alcohols with 2-acetamido-1,3,4,6-tetra- O-acetyl-2-deoxy-β- d-glucopyranose ( 3), allyl (and other alkyl) β-glycosides were obtained from the N-benzoyl, N-phenoxyacetyl, N-methoxyacetyl, N-chloroacetyl, and N-phthaloyl congeners of 3. The latter compounds, except for the N-phthaloyl derivative, gave oxazolines in the absence of an alcoholic reactant. Compound 3 and the related N-benzoyl, N-chloroacetyl, N-acetyl-3,4,6-tri- O-benzyl, and N-acetyl-4- O-acetyl-3,6-di- O-benzyl derivatives were coupled to one or more protected sugars to form protected, β-linked disaccharides. Coupling at the 6-positions of acceptors proceeded smoothly and gave 67–80% yields. For successful coupling at positions 3 and 4, long reaction times and multiple additions of glycosyl donor were required, and yields ranged from 60% to as low as 30%. 1,3,4,6-Tetra- O-acetyl-2-(chloroacetamido)-2-deoxy-β- d-glucopyranose appeared to be the most reactive glycosyl donor in this series. The reaction of 2-methyl-(3,4,6-tri- O-acetyl-1,2-dideoxy-α- d-glucopyrano) [2,1- d]-2-oxazoline (derived from 3) with allyl alcohol was catalyzed by ferric chloride, and oxazolines were detected as intermediates in some of the glycosylations of protected sugars.