Studies of specifically fluorinated carbohydrates. Part III. A new method for the addition of the elements of "BrF" and of "IF" to unsaturated carbohydrate derivatives

A smooth addition of the elements of "BrF", to D-glucal triacetate (1), occurs when bromine is reacted with 1 in the presence of silver monofluoride and a suitable solvent. This reaction affords a major product 2-bromo-2-deoxy-α-D-mannopyranosyl fluoride triacetate, together with smaller quantities of 2-bromo-2-deoxy-α-D-glucopyranosyl fluoride triacetate and the corresponding β-D-anomer. The structures of these products have been elucidated by fluorine and proton magnetic resonance studies, and confirmed by several independent syntheses. The same three products are obtained when "BrF" is generated insitu from N-bromosuccinimide and HF; however, under these conditions 2-deoxy-α-D-arabino-hexopyranosyl fluoride triacetate is also formed in ca. 7% yield. The Br2/AgF reagent has also been reacted with several 3,4-dihydro-2H-pyran derivatives and with other glycals. In all cases the major product(s) corresponds to the trans addition of "BrF". Similar results are obtained for the addition of the elements of "IF" to all of the above derivatives.