1-Thioglycosides thiols

Fully acetylated hexopyranoses react with thiols in the presence of Lewis acids, such as BF3-Et20.32,33 The reaction is faster with 1,2-trans acetates than with the corresponding 1,2-cij ones and 1,2-trans products predominate. Alkyl, alkenyl, and aryl thioglycosides are produced by this method. Variations on this method include the use of trimethylsilyl34 or stannyl derivatives35 of the thiols. 

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

Fluorodcsulfurizations of thiols,311 phenyl thioglycosides,290 1,2-dithiolans.312 aromatic dithiocarboxylic acids,399 or orthothioesters313 in hydrogen fluoride systems with N-chloro-or N-bromosuccinimide as a coagcnt are facile methods for the generation of monofluorides, gem-difluorides, and trifluoromethyl derivatives, e.g. formation of 11,311 12,312 13,313 and... 

Thioglycosides have been prepared on solid phase by glycosylation of thiols with various types of glycosyl donor. Carbohydrate-derived thioethers have been used either to link carbohydrates to thiol-functionalized supports [9,26,78,79] or as glycosyl donors for the preparation of glycosides on solid phase (see Section 16.3.3). 

An anomeric acetate is efficiently displaced by a thiol under the influence of an acidic catalyst, and this is probably presently the most used and efficient way to produce thioglycosides of simple mercaptans, especially on a large scale. The standard procedure is to react a peracetylated aldose dissolved in dichloromethane with a slight excess of thiol using a hard Lewis acid as promoter, which generally gives a high yield of mainly the 1,2-trans product ( Scheme i) [11]. 

Early studies employing hydrogen chloride as catalyst on perbenzoylated sugars showed complicated product mixtures [1,30], while Lewis acid-catalyzed mercaptolysis of peracetylated monosaccharides afforded the corresponding thioglycosides in good yields [31,32,33], However, from a preparative point of view (smell, work-up), the present use of a solvent and only a small excess of thiol is definitely an advantage. 

Deoxy functions in the sugar ring also increase the acid lability of the glycoside. Thus, was the methyl glycoside of daunosamine (2,3,6-trideoxy-3-amino-L-/yjt o-hexopyranose) efficiently transformed into the corresponding aryl thioglycoside by treatment with a thiol and BF3-etherate (O Scheme 23) [96]. The reaction was highly a-selective. 

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