Glucal fluoride

Introduction of F2 into 3,4,6-tri-O-acetyl-D-glucal (61) in CCI3F (Freon 11) at —78° in a manner used for the non-labeled compound (so-called cold synthesis) gave a 4 1 mixture of 3,4,6-tri-0-acetyl-2-deoxy-2-[ F]fluoro-a-D-gluco- (574) and ) -D-manno-pyranosyl fluorides (575),... 

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. 

Finally, halogens can be introduced by electrophilic addition to a double bond (Scheme 3.4b). For example, the reaction of glucal with xenon difluoride in the presence of a catalytic amount of BF3 OEt2 gives a 2-deoxy-2-fluoro-glucosyl fluoride as a mixture of anomers.19... 

Tri-( -benzoyl-D-glucal is hydrofluorinated with hydrogen fluoride at — 70 C for 20 hours to yield 3,6-di-0-benzoyl-2-deoxy-a-D-n7)o-hexopyranosyl fluoride (5). ... 

A method using silver(I) fluoride and chlorine is sufficiently mild for the isolation of the chlorine fluoride adducts in good yield, whereas the combination of IV-chlorosuccinimide and hydrogen fluoride gives no fluorinated products. The reaction of chlorine with a suspension of D-glucal triacetate and silver(I) fluoride in an acetonitrile/benzene solution is unusual in that it gives all four possible 3,4,6-tri-0-acetyl-2-chloro-2-deoxy-D-glycopyranosyl fluorides... 

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. 

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