Sulfonyloxy group displacement

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)... 

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. 

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-... 

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). 

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-... 

Investigations by Hough and coworkers134 have shown that 4-sulfonyloxy groups of aldopyranose derivatives can be displaced rather readily with thiocyanate and iodide ions this constitutes a potential route to 4-deoxy sugars. 

The foregoing method of preparation of sugar thiocyanates109,110 by Sn2 displacement of a sulfonyloxy group has been reported by many workers.111 143 Displacement of sugar sulfonate groups by various nucleo-... 

Nucleophilic displacement of the 4-trifloxy group of 327 required only 12 h at 80°, and provided thiocyanate 262 in 85% yield, whereas the methyl-sulfonyloxy group at C-4 in 261 required 42 h at 140°, and provided the thiocyanate 262 in 68% yield, in contrast to previous reports.118 121... 

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