Glucal chlorination product

Unidentified chlorination product of 2,3,4,6-tetra-0-acetyl-(2-hydroxy-D-glucal) 136... 

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. 

Besides the D-glucose derivative just described, three other crystalline dichlorides have been prepared from 2-hydroxyglycals, namely, the dichlorides from 2,3,4,6-tetra-0-benzoyl-(2-hydroxy-D-glucal)10 (yield, 22%), 2,3,6,2, 3, 4, 6,-hepta-0-acetyl-(2-hydroxycellobial)IS (yield, 30%), and 2,3,4-tri-0-benzoyl-(2-hydroxy-D-xylal)12 (yield, 17%). The 2,3,4,6-tetra-0-benzoyl-l,2-dichloro-l-deoxy-D-hexose prepared from the first of these by short chlorination in benzene reacted with sodium acetate in hot, glacial acetic acid. The crystalline product was assigned the structure of l-0-acetyl-3,4,6-tri-0-benzoyl-D-glucosone10 since it is not converted to kojic acid by pyridine-acetic anhydride (see below). A benzoyl group has been lost. 

In a previous Section it was noted that the hydrolysis product from chlorinated 2,3,4,6-tetra-0-benzoyl-(2-hydroxy-D-glucal) and several substances derived therefrom also underwent conversion to di-O-benzoylkojic acid. 

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... 

Addition of dichlorocarbene, produced by treatment of ethyl tri-chloroacetate with sodium methoxide, to 3,4,6-tri-O-methyl-D-glucal gave, apparently, one product (gas-chromatographic analysis) in 82% yield. By stereochemical analogy with epoxidations, the product was considered to be l,5-anhydro-2-deoxy-l,2-C-(dichloromethylene)-3,4,6-tri-O-methyl-D-g/j/cero-D-ido-hexitol (21). Demethylation was brought about with boron trichloride at—70°, to give atriol from which a crystalline tribenzoate was obtained and reaction with lithium aluminum hydride caused reductive cleavage of the carbon-chlorine bonds.36 A similar addition was applied to 3,4-unsaturated furanosyl compound (see p. 247). 

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. ... 

The adducts of tri-O-acetyl-n-glucal with bromine or chlorine react with aryl Grignard compounds, to give products which, by analogy with those... 

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