Synthesis of deoxyhalogeno sugars. Displacement of the (trifluoromethanesulfonyl)oxy (triflyl) group by halide ion

Abstract

Cholestenone. The literature method7 was modified by using aluminum isopropoxide in place of aluminum terf-butoxide. A solution of 21 g of freshly distilled aluminum isopropoxide in 130 mL of benzene was added to a solution of 30 g of cholesterol in 350 mL of benzene and 250 mL of acetone. After the mixture was refluxed for 48 h, the product was isolated as described7 to give 18 g of cholestenone, mp 80-81.5 °C (lit.7 mp 78.5-80.5 °C).The filtrate was subjected to recycling which raised the overall yield to 85-90%. 24-Hydroxychol-4-en-3-one Acetate (I). Cholestenone (0.50 g) was dissolved at 0 °C in a solution of 19.5 mL of CF3COOH, 10.5 mL of 96% H2SO4, and 1.0 mL of 50% aqueous H202. After being stirred for 4 h at 0 °C, the solution was quenched by slow addition to ice-water. A hexane extract was washed with 5% NaHC03 and dried over MgS04.After removal of solvent in vacuo at 25 °C, the residue was dissolved in a solution of 50 mL of acetic acid, 2 mL of water, and 1.0 g of sodium acetate. The solution was refluxed for 18 h under N2, cooled, and diluted with 100 mL of water. A hexane extract was washed with 5% Na2C03 and dried over MgS04. Removal of solvent in vacuo at 25 °C gave 0.15 g of crystalline acetate (I). A GC analysis indicated that it was 70% pure with the remainder being unreacted cholestenone.The impure I was chromatographed on 10 g of 28-200 mesh silica gel, using 65:35 hexane-ether. Cholestenone eluted before

The rapid synthesis of deoxyfluoro sugars using tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF)

“…Base-catalyzed elimination reactions with triflyl derivatives are uncommon (44,45), but have been observed in certain furanoid (44,46) and, very recently, in pyranoid (34a, c) ring systems (see also Table 1). Eliminations in glycopyranosides occurred (34a, c) under conditions that decreased the ease of nucleophilic substitution (34a, 47).…”

The hex-5-enose degradation: zinc dust cleavage of 6-deoxy-6-iodo-α-D-galactopyranosidic linkages in methylated di- and trisaccharides

“…Two recent methods for halogenation at C-6 involve the saccharides where polymer chain may formation of highly reactive sulfonates followed by halide additional restrictions. Displacement by iodide ion was chosen displacement under mild conditions (3,4). These reactions as the reaction least likely to be accompanied by competing elimination (3,4).…”

“…' Presented in part at the Canadian Institute of Chemistry Conference, Montreal, Quebec, June [3][4][5][6]1984, and at the 12th…”

Modular Furanoside Phosphite‐Phosphoroamidites, a Readily Available Ligand Library for Asymmetric Palladium‐Catalyzed Allylic Substitution Reactions. Origin of Enantioselectivity

“…Compounds 3, 8 and 12 are easily made in a few steps from the corresponding dxylose or d-glucose. [8,9,10] These compounds (3, 8 and 12) were chosen as intermediates for the preparation of ligands because they will easily allow incorporation of the various elements that will enable us to study the position of the phosphoroamidite (at either C-5 or C-3) as well as the configuration of C-3. Compounds 3, 8 and 12 were treated with sodium azide to produce the desired azides 4, [11] 9 [12] and 13 [10] [Scheme 1, step (d)].…”

“…[8] (b) ref. [9] (c) ref. [10] Allylic Substitution of rac-1,3-Diphenylprop-2-en-1-yl Acetate S1 using Dimethyl malonate and Benzylamine as Nucleophiles…”