1-Thioglycosides preparation

Dithiocetals, thioglycosides preparation, 181 DNA, disaggregation, ultrasonic irradiation, 11 Double bonds, unsaturated monosaccharides,... 

Thiols, thioglycosides preparation, 183 2,3,4-Tri-O-ethylamylose, structure, 412 Triple bonds, unsaturated monosaccharides, 95-96... 

In contrast, cleavage of alkyl and also aryl thioglycosides with dimethyl(meth-ylthio)sulfonium tetrafluoroborate takes place with total inversion of configuration [9] (equation 12) The latter reagent is commercially available or easily prepared as a crystalline nonhygroscopic solid [10]. All the three above-mentioned reagents... 

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... 

A great variety of methods for the preparation of alkyl and aryl 1-thioglycosides of aldoses have been described30-31 ... 

Partial hydrolysis of dithioacetals has been found useful for the preparation of anomers not obtained by the foregoing methods and also for preparation of fu-ranosidic 1-thioglycosides. 

This preparation, specifically of acylated aryl thioglycosides, is carried out by reaction of, for instance, a 2,3,4,6-tetra-O-acety 1-1 -thio-P-D-glucopyranose with a di-azonium salt, followed by thermal decomposition of the intermediate diazo product. 

Nicolaou and coworkers reported a new method for preparing glyco-syl fluorides (38) from phenyl thioglycosides (37) by treatment with di-ethylaminosulfur trifluoride (DAST)-A -bromosuccinimide (NBS), or HF-pyridine-NBS, the phenylthio group of the thioglycosides being initially activated by NBS. Thus prepared were compounds 39, 40, and 42 (see Table I) and 3,4-C)-carbonyl-2,6-dideoxy-3-C-methyl-L-n Z)ohexo-pyranosyl, 2-azido-2,6-dideoxy-3,4-0-isopropylidene-D-altropyranosyl,... 

Glycosylation of thioglycosides.1 1-Thioglycosides when activated with 1.5 equiv. of C,H,SeOTf, prepared in situ from QH SeCl and AgOTf, react at 0° to -40° with alcohols to form glycosides in 60-95% yield. The reaction is generally p-selective. 

P-Mannosides are difficult to introduce because the axial C-2 substituent of a mannosyl donor sterically and electronically disfavors nucleophilic attack from the P-face. P-Mannosides have been obtained by the direct substitution of a-glycosyl triflates, which are conveniently prepared by the treatment of an anomeric sulfoxide with triflic anhydride (Tf20) or thioglycosides with NIS (Scheme 4.3a)... 

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