Mannopyranosides selective hydrolysis

Methylation (methyl iodide-silver oxide) of methyl 3-0-benzyl-4,6-0-benzyl-idene-a-D-mannopyranoside (prepared by selective benzylation of the equatorial hydroxy-group of methyl 4,6-O-benzyhdene-a-D-mannopyranoside) followed by hydrogenolysis and hydrolysis with acid has provided a convenient synthesis of 2-0-methyl-D-mannose. 3-O-Methyl- and 3,6-di-O-methyl-D-galactose have been synthesized by straightforward procedures from methyl P-D-galactopyrano-... 

Exposure to mercury(II) bromide and 2,4collidine converted acetylated gly-cosyl halides to 1,2-orthoesters. Formation of orthoesters under kinetic control (ketene dimethylacetal, pTsOH, DMF) gave 4,6-derivatives 64-66 from d-glucose, D-mannose and methyl a-D-glucopyranoside, respectively, and product 67 from methyl 4,6-0-isopropylidene-a-D-mannopyranoside. Mild acid hydrolysis of 67 gave specifically the 2-0-acetate. This method has been applied to the selective acetylation of monoisopropylidenated furanoses an example is given in Scheme 3. ... 

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