Sulfonyloxy group

The benzylidene derivative above is used, if both hydroxyl groups on C-2 and C-3 are needed in synthesis. This r/vzns-2,3-diol can be converted to the sterically more hindered a-cpoxide by tosylation of both hydroxy groups and subsequent treatment with base (N.R. Williams, 1970 J.G. Buchanan, 1976). An oxide anion is formed and displaces the sulfonyloxy group by a rearside attack. The oxirane may then be re-opened with nucleophiles, e.g. methyl lithium, and the less hindered carbon atom will react selectively. In the following sequence starting with an a-glucoside only the 2-methyl-2-deoxyaltrose is obtained (S. Hanessian, 1977). 

Displacement of a sulfonyloxy group by fluorine can be achieved by tctra-butylpbosphonium fluoride and its mono- and dihydrofluonde under mild conditions and in good yields [I4 (equation 30)... 

Removal of the 2 -sulfonyloxy group of 859 in a basic medium, followed by reaction with metal halides (LiBr and Nal) or hydrogen halides (HCl-1,4-dioxane, HBr-acetone, or0.1% HFin l,4-dioxane-AlF3)gave, byway of the 2,2 -anhydro intermediate 861, the 2 -halo derivatives 862-865. The 2 -deoxy analog 866 and l-(6-deoxy-6-fluoro- ff-D-mannopyranosyl)thy-mine were also prepared from 864 (R = H) and 861 (R = H), respectively. l-(4-Deoxy-4-fluoro-y -D-glucopyranosyl)thymine was obtained by the condensation method. A different kind of nucleoside, 5-(5-deoxy-5-fluoro-2,3-0-isopropylidene-a-D-ribofuranosyl)-l,3-dimethyluracil has also been prepared. ... 

Displacement of the 1 -chlorosulfate group in compound 55 has been achieved by the use of a dipolar, aprotic solvent. When compound 55 was heated in hexamethylphosphoric triamide at 95°, it gave, after chromatography on silica gel, 2,3,4,3, 4 -penta-0-benzoyl-6,l, 6 -trichloro-6,l, 6 -trideoxysucrose (56) in 63% yield.78 The yield of 56 was raised to 88% when compound 55 was treated with sodium chloride in hexamethylphosphoric triamide for 24 h at 95°. It is of interest that a similar displacement of the sulfonyloxy group at C-l has so far been unsuccessful. 

These results support the earlier observation (see Section VII, 1) that the reactivity of sulfonyloxy groups in sucrose sulfonates for Sn2 reaction is in the order C-6 > C-6 > C-4 > C-l. ... 

With certain exceptions, primary fluorination of carbohydrate derivatives is very facile. Fluoride displacement of sulfonyloxy groups by potassium, or cesium, fluoride in 1,2-ethanediol and a variety of other solvents has frequently been used. Tetrabutylammonium (sometimes tetraethylammonium) fluoride in dipolar, aprotic solvents (mainly ace-... 

Several fluoro analogs of ketoses have been reported 1,6-dideoxy-1,6-difluoro-D-fructose was readily obtained from 2,3-O-isopropyli-dene-l,6-di-0-p-tolylsulfonyl-)3-D-fructofuranose by treatment with potassium fluoride in 1,2-ethanediol under a stream of carbon dioxide.96 Surprisingly, although the 6-sulfonyloxy group would be expected to be more reactive than the 1-sulfonyloxy group,97-99 no selectivity was observed. The failure to obtain 1-deoxy-l-fluoro-D-fructopyranose96 from 2,3 4,5-di-0-isopropylidene-l-0-(methylsulfonyl) (or p-nitro-phenylsulfonyl)-/3-D-fructopyranose or phenyl 3,4,5-tri-O-acetyl-l-O-(methylsulfonyl)-/3-D-fructopyranoside by treatment with potassium or sodium fluoride in 1,2-ethanediol, N,N-dimethylformamide, or form-amide at elevated temperatures may be attributed to the fact that nu-... 

HSAB principle, because it is a hard base. Acetonitrile was also shown to give the highest ratio of substitution to elimination in comparative displacements of a secondary sulfonyloxy group of the alkyl chain of stearic acid in a number of solvents.136... 

As might be expected, no displacement of the sulfonyloxy group was observed when 1,2 4,5-di-0-isopropylidene-3-0-p-tolylsulfonyl-/3-D-fructo- or -psico-pyranose was treated with fluoride under a variety of conditions.130,131... 

Replacement of sulfonyloxy groups by hydrogen is also achieved by refluxing the methanesulfonyl and p-toluenesulfonyl esters of alcohols with sodium iodide and zinc dust in wet dimethoxyethane. Evidently iodine displaces sulfonyloxy group and is replaced by hydrogen by means of zinc. Yields range from 26% to 65% [700] (Procedure 33, p. 213). 

The difference in reactivity of primary and secondary sulfonyloxy groups towards replacement by iodine was originally the basis of a method for distinguishing between primary and secondary hydroxyl groups in cyclic sugar molecules [see, J. W. H. Oldham and J. K. Rutherford,/. Amer. Chem. Soc., 54, 366 (1932)]. 

In a preliminary step, adjacent ester groups undergo initial hydrolysis or alcoholysis, by the base, to the oxide anion. This step is reasonable for carboxylic esters, which are rapidly hydrolyzed under the conditions usually employed, but is rather more surprising for sulfonic esters, which are usually hydrolyzed only slowly by the nucleophilic attack on sulfur required for this reaction. With these disulfonic esters, the ease of hydrolysis has been explained by the inductive effect of the adjacent sulfonyloxy group.7... 

It is of interest that methyl 4,6-0-benzylidene-2,3-di-0-p-tolylsul-fonyl-a-D-galactopyranoside, epimeric with 8 at C-4, is unreactive at room temperature, in contrast to 8 this behavior may be attributed to the 3-0Ts-4-0 interaction arising in the transition state. On refluxing, displacement of the 3-sulfonyloxy group occurs, to give the D-... 

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