Halides glycosyl-halides

In the case of indazoles the reaction of indazole, 5-nitroindazole or 6-nitroindazole with glycosyl halides and mercury(n) cyanide gives exclusively 2-glycosylindazoles (670), (673) and (675) (7QJHC1435). Similarly, the reaction of 1-trimethylsilyl derivatives of indazole, 3-cyanoindazole, 4-nitroindazole, 5-nitroindazole and 6-nitroindazole with 2,3,5-tri-O-acetyl-D-ribofuranosyl bromide gives only, or preferentially, the 2-ribofuranosyl derivatives (670)-(674) 7QJHC117, 70JHC1329). 

Compounds in which the anomeric hydroxy group is replaced by a halogen atom are named as glycosyl halides. Pseudohalides (azides, thiocyanates etc.) are named similarly. 

From Acylated Glycosyl Halides by Reaction with Thiolate Anion. 181... 

IV. In situ Generation of Glycosyl Halides from Thioglycosides. 184... 

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... 

In the halide-assisted method,25 a glycosyl halide (normally bromide) with a nonparticipating 2-substituent and with the thermodynamically more stable axial orientation at C-l is treated with an excess of the corresponding halide anion by the addition of a soluble tetraalkylammonium salt. This sets up an equilibrium between the axial and the (much less stable) equatorial glycosyl halide. The lat-... 

In this classic41 and general method, an acylated glycosyl halide reacts with a thiolate anion to produce a 1-thioglycoside, usually with 1,2-trans configuration. With alkyl thiolates, re-acylation is normally required following this treatment. 

An acylated glycosyl halide, such as a 2,3,4,6-tetra-O-acetyl derivative, is treated with thiourea. The resulting pseudothiouronium salt is hydrolyzed with aqueous potassium carbonate to give the 2,3,4,6-tetra-0-acetyl-l-thio-(3-D-glucopyranose,48 which then is alkylated. 

Fischer projection of acyclic form, 56-57 glycosides, 132-135 C-glycosyl compounds, 139-140 N-glycosyl derivatives, 137-139 glycosyl halides, 136-137 glycosyl residues, 125 isotopic substitution and isotopic labelling, 91 me so forms, 59 optical rotation, 59 parent structure choice, 53... 

Because of the high C - F bond energy, glycosyl fluorides are stable in comparison to the other glycosyl halides, and this character has attracted much attention. They have been prepared in many different ways. One of them, rather classical, is through addition of the elements of HF (for example, HF in benzene ), BrF, or IF to per-O-acylated glycals. ... 

Glycosylations utilizing the aforedescribed glycosyl fluorides are described next. In 1981, Mukaiyama and coworkers attempted to prepare 1,2-cw-glycosides by utilizing the relatively stable (as compared with other glycosyl halides) 2,3,4,6-tetra-0-benzyl-)8-D-glucopyranosyl fluoride (47)5)... 

Tetramethylguanidinium azide, an azide salt that is readily soluble in halogenated solvents, is a useful source of azide ions in the preparation of azides from reactive halides such as a-haloketones, a-haloamides, and glycosyl halides.74... 

The /3-d configuration was assigned40 to 82 on the basis of the trans rule,83 as exemplified by the reaction of glycosyl halides with heavy-metal salts of heterocyclic bases.833 Unambiguous chemical proof was secured from the transformation of the nitrile into the corresponding acid (21). 

Glycosyl halides, a very important group of carbohydrate derivatives, are commonly prepared14 from per-O-acylated sugars by reaction with hydrogen halides or halides of aluminum or titanium. The selection of the method depends mainly on the anomeric configuration of the substrate, the kind of its O-acyl groups, and the stability of the product to be prepared. 

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