Triflates glycoside synthesis

The glycals are easily converted into the 1,2-dihalo-derivatives, which in principle can act as glycosyl donors. However, these derivatives have not found wide application in glycoside synthesis, mainly because of the low facial selectivity in the initial addition of the electrophilic species [143-145]. In an example of a successful application, 2-deoxy-2-bromo-a-D-glucopyranosyl bromide [146] has been shown to give predominantly the 2-deoxy-P-D-glucopyranosides in silver-triflate-promoted reactions with alcohols. 

A. Hasegawa, M. Ogawa, H. Ishida, and M. Kiso, a-Predominant glycoside synthesis of Af-acetylneuraminic acid with the primary hydroxyl group in carbohydrates using dimethyl-(methylthio)sulfonium triflate as a glycosyl promoter, J. Carbohydr Chem. 9 393 (1990). 

Glycoside synthesis from 2-pyridylthio glycosides is also possible with 0-benzyl-protected donors in the presence of methyl iodide [20], silver triflate [21 ], or mercuric salts [10,13,22], The versatility of this leaving group has also been demonstrated in the synthesis of C-glycosides [23 J. 

Srivastava and Schuerch [112] and Dessings et al. [113]. reported on the potential utility of 1,2-O-stannylene acetals in /3-wianno-glycoside synthesis. Recently, Hodosi and Kovac established a highly efficient /3-mannosylation process involving alkylation of a 1,2-O-stannylene acetal with the triflate derived from an aglycon [ 114] (O Scheme 39). A remarkable feature of this method is its extreme simplicity. Even free mannose can be used as a precursor of... 

Synthesis of Monosaccharide Derivatives.—New approaches to the synthesis of glycosides, including the alkoxylation of N-furanosyl-lactams, the reaction of l-0-acetyl-2,3,5-tri-0-benzoyl-P-D-ribofuranose with cyclic amide acetals derived from vicinal diols (see Vol. 10, p. 16), the Lewis acid-catalysed alcoholysis of sugars with an activated anomeric centre (see Vol. 10, p. 11), and the glycosidation of glycopyranosyl halides catalysed by silver trifluoromethanesulphonate (triflate), have been reviewed. A general review of carbonyl compounds has also dealt with some aspects of glycoside synthesis. 

Thiopyridyl glycosides, and related esters with metal activators, have been used appreciably in glycoside synthesis. Now the glycosyl carboxylate (2) has been found to allow high yields and a ratios of 4 1 and 1 4 when used with unsubstituted alcohols and copper(II) triflate in ether or tin(II) triflate in acetonitrile, respectively (Scheme 1). °... 

Dimethyl (methylthio)sulfonium Triflate as a Promoter for Creating Glycosidic Linkages in Oligosaccharide Synthesis... 

We have found that the secret to a successful synthesis of the alkenyl glycosides 64 lies in obtaining the pure -acetate 65 [47]. Condensation of the acetate 65 with the appropriate alkenol,in the presence of a small amount (5-20 mol% depending on the scale) of trimethylsilyl triflate, gave the alkenyl glycosides 64 in excellent yield. Oxidation of the alkene 64 with dimethyldioxirane, followed by deacetylation, then gave the putative enzyme inhibitors 60. 

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