Maltoside selective acetylation

Selective acetylations of D-mannose and D-xylose have been carried out. The former with 5.7 mol Ac20-Na0i gave 60% penta-acetate and 29% 1,2,3,6-tetra-0-acetyl-Q ,j3-D-mannopyranose. The latter with 5.3 mol AcjO-NaOAc yielded 27% tetra-acetate and 7.2% l,2,4-tri-0-acetyl-/3-D-xylopyranose. Benzyl /3-maltoside with 20 mol AcaO at r.t. during 10 days gave 10% hepta-acetate, and 71% 2,6,2, 3, 4, 6 -hexa-acetate which was characterized by methyla-tion followed by deacetylation and n.m.r. ... 

The importance of sugar sulfonates as synthetic intermediates has been widely recognized.77,78 Selective methanesulfonylation and p-toluenesulfonylation of maltose and its derivatives has been studied. Umezawa and coworkers used sequential p-toluenesulfonylation and acetylation to obtain crystalline l,2,3,2, 3, 4 -hexa-0-acetyl-6,6 -di-0-p-tolylsulfonyl-/3-maltose in 45% yield.79 Dimolar methanesulfonylation of methyl /3-maltoside followed by acetylation afforded crystalline methyl 2,3,2, 3, 4 -penta-0-acetyl-6,6 -di-0-(methylsulfonyl)-/3-maltoside. The mother liquor also yielded a small proportion of a... 

Selective p-toluenesulfonylation of methyl 4, 6 -0-benzylidene-/3-maltoside with 2 molar equivalents of the reagent in pyridine, followed by acetylation, gave a mixture of a major and a minor product, from which methyl 2,3,2, 3 -tetra-0-acetyl-4, 6 -0-benzylidene-6-0-p-tolylsulfonyl-/3-maltoside was isolated in 66% yield.81 Interestingly, a similar attempt at selective p-toluenesulfonylation of benzyl 4, 6 -0-benzylidene-/3-maltoside with a view to obtaining the 6-O-p-tolylsul-fonyl derivative failed.46 The presence of a bulky aglycon in the /3-ano-meric position apparently exerts a marked steric effect upon substitution at 0-6. 

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