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

The ferric chloride-catalyzed glycosylation of hydroxy compounds by protected 2-acylamino-2-deoxy-beta-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-beta-D-glucopyranose (3), ally (and other alkyl) beta-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, beta-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-beta-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-alpha-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.