Carbohydrates selective halogenation

The selective replacement of hydroxyl groups in carbohydrates by halogen has mainly been achieved by the use of (a) sulfuryl chloride, (b) reagents based on phosphorus compounds, and (c) reagents of the... 

An enantiospecific synthesis of negstatin I (52) was accomplished efficiently with a sequence involving two C-imidazolide anion transformations. The first was coupling of a suitably protected carbohydrate intermediate with N-tritylimidazole. Direct monobromination of imidazole (51a, X = Y = H) was not feasible, except by selective halogen-metal exchange and reprotonation of dibromo intermediate (51b, X = Y = Br) [95TL6721], Introduction of the pendant acetic acid function was accomplished by C-allylation of 51c. 

Our next goal was to prepare the iodide 41 (Scheme 12). Although the carbohydrate literature abounds with examples of alkyl glycosides and oligosaccharides having been selectively halogenated at C(6), most of... 

For a detailed discussion of the methods for the selective halogenation of carbohydrates, see Boons, G.J., Hale, K.J. Organic Synthesis with Carbohydrates" Blackwell Science Oxford, 2000, Chapter 3, 56. 

A survey of regio-, stereo-, and chemo-selective reactions in carbohydrate chemistry includes discussion of phase transfer reactions in partial substitution reactions, selective halogenation... 

OH — X. Pi. carbohydrate hydroxyl group can be replaced by halogen (bromine, chlorine, iodine) by treatment in DMF with 2 eq. each of triphenylphosphine and an N-halosuccinimidc. The by-products are succinimide and triphenylphosphine oxide. Yields are generally high. Primary hydroxyl groups can be selectively replaced in the presence of secondary hydroxyl groups. 

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