Reactions of the Bromine-containing Products

Not enough data are available for the complete assessment of the chemical reactions undergone by the products of photobromination of carbohydrate derivatives, but the following observations permit an appreciation of the current state of knowledge of their chemistry and of the potential of these compounds as synthetic intermediates. 

Ohrui and coworkers82 exploited the highly selectively deuterated sugars available from the bromo compounds by, for example, synthesizing a- and / -(l- 6)-linked hexose disaccharides with deuterium incorporated selectively within the methylene group involved in the interunit linkage, thereby 

One of the few efficient reactions to have been reported of 5-bromohexose derivatives is the acetolysis [mercury(II) acetate in acetic acid] of methyl tetra-0-acetyl-5-bromo-/ -D-glucopyranuronate (10), which affords the crystalline methyl 5-acetoxy-tetra-O-acetyl-a-L-idopyranuronate (126) this was assigned the inverted configuration at C-5 on the grounds of a major optical rotational change during its formation. Likewise, methyl tetra-0-acetyL/f-L-xy/o-hexulopyranosonate (127) is obtained in excellent yield from the bromide 8, and it, too, is dextrorotatory and is produced from a levorotatory bromide, conceivably by way of a cyclic 4,5-acetoxonium ion. Compound 127 also differs in expected ways from its known C-5 epimer, and, on deprotection, affords L-ascorbic acid.21 28 

Hydrolysis studies of (5S)-tetra-0-acetyl-5-bromo-/ -D-xylopyranose (28) showed it to be much less susceptible than is tri-O-acetyl-a-D-xylopyranosyl bromide, presumably because the acetoxyl group at C-l inhibits the partici- 

There was particular interest in the analogous reactions of 1-Oacetyl-2,3,5-tri-0-benzoyl-4-bromo-/ -D-ribose (37), because of the potential to prepare from it compounds related to nucleocidin, which is a 4 -fluoroaden-osine derivative having antitrypanosomal activity. With silver fluoride in acetonitrile, this bromide also reacted mainly with inversion of configuration, and gave the l-lyxo fluoride 140 (53% isolated yield), whereas, with silver tetrafluoroborate, much more of the more interesting 1-0-acetyl-2,3,4-tri-0-benzoyl-4-fluoro-/ -D-ribose (141) was obtained.38 

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