Synthesis of glycosyl fluorides

Synthesis of Glycosyl Fluoride Donors 2.1.2.1 Fluorinating Reagents... 

Trifluorozincbromide reagent (CF3ZnBr) is employed for the synthesis of glycosyl fluorides from glycosyl bromides. When 2,3,4,6-tetra-O-acetyl-a-D-glycopyranosyl... 

Figure 2.4 Synthesis of glycosyl fluorides from 1,2-anhydro sugars and glycal derivatives.

This Section deals with the methods of preparation of glycosyl fluorides generally (for the synthesis of glycosyl fluorides by addition reactions to glycals, see Section 11,6), and gives a number of examples from the types of glycosyl fluorides that have been prepared. 

Silver tetrafluoroborate in ether or toluene has also been used for the synthesis of glycosyl fluorides. Peracetylated 2-chloro-2-deoxy-D-gluco- and -mannopyranosyl fluorides have been prepared by treatment of the corresponding chlorides with the aforementioned reagent.50,51 Products of kinetic control were obtained when diethyl ether was used as the solvent, whereas products of thermodynamic control were obtained when toluene was used instead. Peracetylated... 

Carboxylates are stable to anhydrous hydrogen fluoride,30 but as described above, how ever, hemiacetal esters are readily cleaved and fluorinated by anhydrous hydrogen fluoride or 70% hydrogen fluoride/pyridine, this method has been widely applied in the synthesis of glycosyl fluorides from glycosyl esters for reviews see refs 29, 34, 277-279. 288, 289. Furthermore, p-toluene- or methanesulfonates (but not trifluoroacetates) of primary alcohols arc fluorinated by nucleophilic substitution using tctrabutylammonium hydrogen fluoride. This procedure is less suitable for secondary alcohols because of the considerable number of elimination products 306 for example, formation of 1 compared to 2.306... 

A method for the synthesis of glycosyl fluorides 11 starting from the glycosyl chlorides 10 with silver(I) tetrafluoroborate proceeds under very mild, homogeneous conditions.72,73 The ratio of isomers formed is dependent on the solvent used. The results are summarized in Table 14.72,73... 

Not within the scope of this section are the synthesis of a-fluoro sulfides from dithioace-tals, their reduction to alkyl fluorides, and the synthesis of glycosyl fluorides from (phenyl-sulfanyl)glycosides. ... 

A newer field of application of Swarts fluorination in carbohydrate chemistry is the synthesis of glycosyl fluorides from the corresponding bromides [46] (Scheme 2.16.). 

Scheme 2,62 Synthesis of glycosyl fluorides with 70% HF-pyridine from different activated precursors [134, 135],...

Another method for the synthesis of glycosyl fluorides consists of 1,3-dipolar cycloaddition of glycosyl azides with di-f-butyl acetylenedicarboxylate and subsequent treatment of the triazole derivatives with HF-pyridine. ... 

Rosenbrook W, Riley DA, Lartey PA (1985) A new method fra- the synthesis of glycosyl fluorides. Tetrahedron Lett 26 3-4... 

Notes and discussion. This procedure is used to form a glycosyl fluoride from a hemiacetal and as such is the original and most straightforward use of DAST in the synthesis of glycosyl fluorides. The product is an anomeric mixture, but there appears to be some solvent dependence of the stereochemical outcome of the reaction, with more polar solvents giving a greater degree of selectivity. 

The stereoselective preparation of 6-deoxy-6,6,6-trifluorohexopyranoses has been reviewed, and the use of such derivatives in liquid crystals is mentioned in Chapter 3. Some substitution reactions at the anomeric centre of l-deoxy-l,l,l-trifluoro-2-ulose derivatives included synthesis of glycosyl fluorides 9 from the corresponding 1-0-mesylates. ... 

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