Photobromination, 1,6-anhydro

The negative results obtained on photobromination of 1,6-anhydro-2-0-benzoyl-3,4-0-isopropylidene-/ -D-galactose and its 3,4-0-cyclohexylidene analog are more difficult to rationalize, especially as the authors used W-bro-... 

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 functionalization at C-6 of 1,6-anhydro sugars using the previously described photobromination process allows the synthesis of chirally deuterated hydrosy methyl groups in the glucopyranose series [34] (Scheme 15). Similar sequences can be used in the galacto [35] and ribo series [36]. 

R. J. Ferrier and R. H. Fumeaux, Photobromination of carbohydrate derivatives. 6. Functionalization at C-6 of 2,3,4-tri-0-acetyl-1.6-anhydro-/i-i)-glucopyranosc, Aust. J. Chem., 33 (1980) 1025-1036 for other references, see L. Somsak and R. J. Ferrier, Radical-mediated bromination at ring positions of carbohydrates, Adv. Carhohydr. Chem. Biochem., 49 (1991) 37-92. 

Interestingly, the photobromination of 1,6-anhydro sugars (levoglucosan) developed by Perrier s group (54-57) proceeds stereo- and regioselectively by substitution of H-6. 

Radical chlorination (SOjClj, AIBN) of tetra-O-acetyl-p-D-glucopyranosyl azide produced the S-chloro compound 15, whereas use of NBS in place of SOjClj gave a product via bromination at C-l. The reaction of a 1-bromo-l-chloroglucopyranosyl derivative with tributyltin hydride in the presence of acrylonitrile is discussed in Chapter 2, and use of the 6-bromo compound, that results from photobromination of tri-O-acetyl-1,6-anhydro-(3-D-glucopyranose, in substitution and oxidation reactions is mentioned in Chapters 5,7, and 16. 

Treatment of 1,6-anhydro-3,4-di-0-acetyl-2- -tosyl- -D-gluco-pyranose with hydrogen bromide in acetic acid yields the glycosyl bromide (26). Photobromination at the "pro-anomeric centre" of... 

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