Tetra-O-acetyl-a-D-glucosyl bromide

An amount of 40 g. of 2,3,4,6-tetra-O-acetyl-a-D-glucosyl bromide is warmed with 12 g. of diethylamine in 20 ml. of dry benzene at 60° until dissolved. (Benzene is often replaced by chloroform, and the initial warming is often omitted.) After 32 hours at room temperature, the reaction mixture is extracted with dry ether, and the diethylamine hydrobromide is removed by filtration. The filtrate is washed once with dilute sulfuric acid and twice with water and is dried over calcium chloride. After evaporation of the ether under diminished pressure, the residue is dissolved in the least possible amount of hot alcohol. Crystallization occurs after the addition, with stirring, of petroleum ether to the cooled solution. Yield of crude 2,3,4,6-tetra-0-acetyl-(2-hy-droxy-D-glucal), 17 g. (51% of the theoretical). Itecrystallization is effected from hot water or from ethanol with the addition of water to turbidity.1 2... 

Thus, a 50-g. sample of tetra-O-acetyl-a-D-glucosyl bromide in 150 ml. of dry acetonitrile containing 50 g. of anhydrous silver fluoride is shaken for 1 hr. The mixture is filtered and the filtrate is evaporated under diminished pressure at a bath temperature of 35 , with precautions to exclude moisture. The residue is dissolved in ether and cooled. Subsequently, crystallization is completed by the addition of petroleum ether. A 50% yield of tetra-0-acetyl- 8-D-glucopyranosyl fluoride is obtained. 

Key A = 2,3,4,6-tetra-O-acetyl- -D-glucose B = 2,3,4,6-tetra-O-acetyl-a-D-glucosyl bromide. 

The best yield recorded for a,(8-trehalose octaacetate is 40%, obtained by Sharp and Stacey in 1951. The compound resulted from shaking 2,3,4,6-tetra-0-acetyl-(8-D-glucosyl fluoride with silver carbonate, An-hydrone, and iodine in chloroform for 48 hours. The same compound was obtained from 2,3,4,6-tetra-0-acetyl-(3-D-glucose treated in chloroform with phosphorus pentaoxide. A disaccharide was not produced by the action of sodium on 2,3,4,6-tetra-O-acetyl-a-D-glucosyl bromide at 90-100°. 

Reactive halogen on carbohydrates was readily replaced by cobalt tetracarbonyl anion in ether solution. As an example, treatment of tetra-O-acetyl-a-D-glucopyranosyl bromide (80) with sodium cobalt tetracarbonyl in ether under 15 atmospheres of anhydrous carbon monoxide for 2 days at room temperature, followed by addition of triphenylphosphine, gave an almost quantitative yield of 2,3,4,6-tetra-0-acetyl-/8-D-glucosyl cobalt tricarbonyl triphenylphosphine... 

The first poly-O-acetylaldosyl azide was synthesized by Bertho by treating tetra-O-acetyl-a-D-glucopyranosyl bromide with a metal azide. In addition to the aldosyl azide derivatives that are known (see Table IV), derivatives of 2-amino-2-deoxy-D-glucosyl azide have been prepared - (see Table V). If the trans hydroxyl group at C-2 is not acetylated, an intermediate epoxide of the type suggested for the aldosyl fluorides can form, and the azide obtained has the. same anomeric configuration as the original halide, as. shown by the formulas. The acetylated azides, like the... 

A mixture of methyl 4,6-0-benzylidene-a-D-glucoside, Ag-carbonate, Drierite, and dry methylene chloride stirred 0.5 hr. under anhydrous conditions, iodine and 1.25 molar equivalents of tetra-O-acetyl-a-D-glucopyranosyl bromide added, and stirred 19 hrs. at room temp. methyl 4,6-0-benzylidene-2-0-(2,3,4,6-tetra-0-acetyl- -D-glucosyl)-a-D-glucoside (Y 40%) suspended in acetic anhydride stirred with a soln. of 4% coned. H2SO4 in acetic anhydride until dissolved after 10 min., allowed to stand 4 hrs. at 25°, the soln. of the crude product in methanol treated with 1.5 A Ba-methoxide, and kept 4 hrs. at room temp. sophorose (Y 76% as the monohydrate). B. Coxon and H. G. Fletcher, Jr., J. Org. Chem. 26, 2892 (1961). 

An improvement in the synthesis of the tri-O-acetyl-D-galactal was noted when the reaction of tetra-O-acetyl-a-D-galactopyranosyl bromide with zinc-acetic acid was carried out at -1S°C at which temperature less hydrolysis and acetolysis of the carbon-bromine bond occurred. Tri-O-acetyl-D-glucal may be obtained from 3,4,6-tri-0-acetyl-2-bromo-2-deo -D-glucosyl phenylthionocarbonate. Racemic (4) has been resolved by the... 

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