Reactions of the Glycosyl Fluorides

Similar reactions have been observed with 8-D-galactopyranosyl fluoride and a-D-mannopyranosyl fluoride. In this latter example, the epoxide ring in the supposed intermediate [(8)] would not be favorably located for internal-glycoside formation with the C-6-hydroxyl group the only observed product is methyl a-D-mannopyranoside (9). 

Depending on the alkoxide concentration, either the methyl jS-D-glucoside (12) or the anhydride (13) arises from 2-deoxy-2-p-toluenesulfonamido-i8-D-glucopyranosyl fluoride (10). - The presumed intermediate imine [(H)] has not been isolated. 

When the methanolic alkoxide is replaced by an aqueous solution of an inorganic base (preferably barium hydroxide), completely analogous reac- 

For the glycosyl fluorides, those reactions which do not involve participation are normally much slower than those which may proceed through cyclic intermediates (5, 8, 11, and 15). Two situations may force the glycosyl fluorides to react with bases without participation of the neighboring group. The C-2 function may be cis to the fluorine atom at C-1 or, if the relation is irons, may bear no removable proton. 

In the first case, typical reactions are the formation of the methyl fi-D-glucoside from a-D-glucopyranosyl fluoride and of its 2-amino-2-deoxy derivative from 2-amino-2-deoxy-a-D-glucopyranosyl fluoride, on treatment with sodium methoxide in methanol. The products from the reaction of aqueous bases with the glycosyl fluorides depend on the concentration of alkali. At low concentrations, the normal hydrolysis products are formed. At higher concentrations of base, if the proper (trans) steric relation exists between C-6 and the fluorine atom at C-1, anhydro compounds are formed, as in (21) from (20). 

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