D-Mannopyranosyl fluoride

Ci2HieBrF07 3,4,6-Tri-0-acetyl-2-bromo-2-deoxy-a-D-mannopyranosyl fluoride DMANPR10 31 367... 

On treatment of tri-O-acetyl-D-glucal with chlorine and silver fluoride,198 all four possible isomers were formed tri-0-acetyl-2-chloro-2-deoxy-a-D-mannopyranosyl fluoride (16%), tri-0-acetyl-2-chloro-2-deoxy-/3-D-mannopyranosyl fluoride (16%), tri-0-acetyl-2-chloro-2-deoxy-a-D-glucopyranosyl fluoride (6%), and tri-O-acetyl-2-chloro-2-deoxy-/3-D-glucopyranosyl fluoride (62%). These product ratios differ significantly from those of the corresponding bromofluorination and iodofluorination reactions of tri-O -ace tyl-D-glucal,43,53 and this behavior has been discussed198 in terms of the differences observed between the addition of bromine (or iodine) and chlorine to tri-O-acetyl-D-glu-cal, and the nature of the chlorination reaction itself. 

The addition of the elements of IF with silver fluoride/iodine toD-glucal triacetate - leads to similar results to the corresponding bromofluorination (Section 1.2.1.3.2.). The three products are 3,4,6-tri-0-acetyl-2-deoxy-2-iodo-a-D-mannopyranosyl fluoride (5, 60 Vo), 3,4.6-tri-0-acetyl-2-deoxy-2-iodo-/l-D-glucopyranosyl fluoride (6, 34%), and 3,4,6-tri-0-acctyl-2-deoxy-2-iodo-a-D-glucopyranosyl fluoride (7,6 %). lodofluorination with hydrogen fluoride/At-iodosuccinimide gives the same three fluorides 5/6/7 in 71, 3 and 23 Vo yield. 

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). 

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