Use of glycosyl bromides

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

Reactivity Patterns and Some Useful Reactions of Glycosyl Bromides 68... 

Bromotrimethylsilane has proven to be useful for a wide variety of applications most of them being reviewed.5 8 Other recent applications are mild cleavage of oxiranes,9 the synthesis of glycosyl bromides,10 the selective cleavage of tetrahydro-2,5-dimethoxyfuran and tetrahydro-2,6-dimethoxy-pyran,11 the cleavage of esters and ethers,12 and the synthesis of benzyl bromides.13... 

The use of glycosyl chlorides, bromides, and even fluorides are all commonplace in the formation of glycosidic bonds. Glycosyl iodides, owing to their inherent instability, have not been used as frequently nevertheless, they are powerful glycosyl acceptors. Glycosyl iodides have been exploited synthetically for the very reason that makes them difficult to handle—namely, the high reactivity they possess. 

Gagne and coworkers showed that Giese additions of glycosyl bromides 128 to a,p-unsaturated carbonyl compounds 129 can be successfully performed using reductive photoredox catalysis (Fig. 33) [191]. Double addition of 129 competed to a considerable extent under standard conditions, indicating that reduction of the... 

Glycosyl fluorides are too unreactive to be activated under standard Koenigs-Knorr conditions, and, for this reason, their use as glycosyl donors was explored relatively late, after the development of glycosyl bromides. They were introduced in 1981 [103], and glycosyl fluorides are currently among the most frequently used donors. 

Glycosylation of glycosyl bromide or chloride using heavy metal KO ROH O... 

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