Glucal bromine addition

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. 

Somewhat surprisingly, particularly in view of the proposed means of formation of the glycosid-3-ulose derivative 2,1,5-anhydro-2,3,4,6-tetra-O-benzoyl-D-arah/no-hex-1 -enitol (tetra-O-benzoyl-2-hydroxy-D-glucal) does not undergo bromination at the allylic C-3 atom the only products isolated following attempted photobromination with N-bromosucdnimide were two dibromides produced by addition reactions.50... 

The addition of bromine to 2,3,4,6-tetra-0-acetyl-(2-hydroxy-D-glucal) conforms closely to that required by one double bond. Maurer1 found values which were some 4 to 8 % low. However, the analysis is complicated by evolution of hydrogen bromide and rapid discoloration of the... 

An anomaly1 regarding the nature of addition of hydrogen bromide to tri-O-acetyl-D-glucal, which arose from Fischer s claim that a stable carbon-bromine bond was present in the product, has now apparently been resolved. From the reaction products obtained by conducting the addition in acetic acid, 4,6-di-0-acetyl-3-bromo-2,3-dideoxy-a-D-arafotno-hexose (6, X = Br) was isolated in crystalline... 

Recent publications in this field have reported a thorough investigation of the addition of bromine and chlorine to tri-O-acetyl-n-glucal and -D-galactal, and the isolation, after thin-layer chromatographic separation, of the a-ji-gluco and a-D-manno products of chlorination of tri-O-acetyl-n-glucal. ... 

Secondary halogen esters are also known. The addition of bromine to D-glucal 3,4,6-triacetate (p. 401) produces 3,4,6-tri-0-acetyl-2-bromo-2-deoxy-D-glucopyranosyl bromide (14 ). Methyl 4,6-dichloro-4,6-dideoxy-ct-D-glucopyranoside 2,3-sulfate was obtained by the action of sulfuryl chloride on methyl a-D-glucopyranoside 150),... 

The results obtained in electrophilic additions of bromine (and other electrophiles) to 3,4,6-tri-O-benzyl-D-glucal 29 have been recently reexamined [21]. 

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