Showing papers on "Glycal published in 1973"

The synthesis of fluorinated carbohydrates

Abstract: Three types of reaction are of particular value in the synthesis of fluoro sugars, namely, nucleophilic displacements with fluoride salts, epoxide cleavage reactions, and glycal addition reactions. These reactions have been developed to the point where effective syntheses of a wide range of fluoro sugars can be planned on a rational basis. Nucleophilic displacement usually involves the treatment of sulphonates with fluoride salts. Reagents of the type tetrabutylammonium fluoride-dipolar aprotic solvent are particularly effective for the displacement of secondary sulphonates. An understanding of the steric and polar factors which can adversely influence the displacement of carbohydrate secondary sulphonates and of competing reaction pathways usually allows the evaluation of this route in designing effective syntheses of fluoro sugars. Selection of ring size (furanose, pyranose, septanose derivatives) is an important parameter in synthesis design. The cleavage of carbohydrate epoxides to give Trans-fluorohydrins can be effected with reagents such as HF or KHF2. The reactions usually occur stereo-specifically and predictably if the epoxide ring is part of a rigid molecular system such as 1, 6-anhydrohexopyranose. The reagent CF3OF, which is an effective source of electrophilic fluorine, readily adds to O-acetylated glycals to give 2-deoxy-2-fluoro derivatives. 2-Deoxy-2-fluoro-D-glucose can be converted into 3,4,6-tri-O-acetyl-2-fluoro-D-glucal and thence by treatment with CF3OF, into ‘2,2-difluoro-D-glucose.’

The synthesis of fluorinated carbohydrates

Abstract: Three types of reaction are of particular value in the synthesis of fluoro sugars, namely, nucleophilic displacements with fluoride salts, epoxide cleavage reactions, and glycal addition reactions. These reactions have been developed to the point where effective syntheses of a wide range of fluoro sugars can be planned on a rational basis. Nucleophilic displacement usually involves the treatment of sulphonates with fluoride salts. Reagents of the type tetrabutylammonium fluoride-dipolar aprotic solvent are particularly effective for the displacement of secondary sulphonates. An understanding of the steric and polar factors which can adversely influence the displacement of carbohydrate secondary sulphonates and of competing reaction pathways usually allows the evaluation of this route in designing effective syntheses of fluoro sugars. Selection of ring size (furanose, pyranose, septanose derivatives) is an important parameter in synthesis design. The cleavage of carbohydrate epoxides to give Trans-fluorohydrins can be effected with reagents such as HF or KHF2. The reactions usually occur stereo-specifically and predictably if the epoxide ring is part of a rigid molecular system such as 1, 6-anhydrohexopyranose. The reagent CF3OF, which is an effective source of electrophilic fluorine, readily adds to O-acetylated glycals to give 2-deoxy-2-fluoro derivatives. 2-Deoxy-2-fluoro-D-glucose can be converted into 3,4,6-tri-O-acetyl-2-fluoro-D-glucal and thence by treatment with CF3OF, into ‘2,2-difluoro-D-glucose.’