Synthesis of aryl-2-deoxy-d-lyxo/arabino-hexopyranosides from 2-deoxy-1-thioglycosides

The synthesis of either anomers of aryl 2-deoxy-D-glycopyranosides from 2-deoxy-1-thioglycosides is reported. The alpha-anomers form as the major product when thioglycosides react with differently substituted phenols and naphthols, in the presence of N-iodosuccinimide/triflic acid. On the other hand, reaction of the thioglycosides with bromine initially, followed by reaction with aryloxy anions lead to aryl 2-deoxy-beta-D-glycosides with high specificities.

A stereoselective synthesis of 6,6,6-trifluoro-l-daunosamine and 6,6,6-trifluoro-l-acosamine

A short synthesis of 6,6,6-trifluoro-L-acosamine 15 and 6,6,6-trifluoro-L-daunosamine 19 has been accomplished. The pyranose ring system of these carbohydrate analogues was formed by a hetero-Diels-Alder reaction of vinylogous imide 11 and ethyl vinyl ether which gave adduct 12a in 40% yield. Hydroboration gave 13 and subsequent hydrogenolytic removal of the (R)-2-phenylethyl chiral auxiliary gave ethyl 6,6,6-trifluoro-L-acosaminide 14. Acid hydrolysis furnished target 15. Glycoside 13 was N-trifluoroacetylated to give 16, the structure was confirmed by single crystal X-ray diffraction. The C-4 stereochemistry of 16 was inverted by Swern oxidation of the 4-OH group, and subsequent borohydride reduction to give 17. Hydrogenolytic removal of the auxiliary gave ethyl-6,6,6-trifluoro-L-daunosaminide 18. Acid hydrolysis provided 19.

A Straightforward and Flexible [4 + 2] Route to β-C-Naphthyl-2-deoxy-glycosides through Tandem Hydroboration-Ketal Reduction: De Novo Access to C-Naphthyl-6-fluoro and 6,6-Difluoro 2-Deoxyglycosides

[reaction: see text] Under standard hydroboration-oxidation conditions, the dihydropyrans 4 underwent a highly stereocontrolled tandem reaction, involving the expected hydration of the double bond together with the reduction of the ketal moiety. This unprecedented transformation gives rise to a short, [4 + 2]-based synthetic route to (+/-)-beta-C-naphthyl-2-deoxyglycosides 5, which allows a significant structural and functional diversity at C-6. We thus described the first synthesis of (+/-)-C-aryl-6-fluoro and -6,6-difluoro olivosides, via the allylic mono- and difluorides produced by regioselective fluorination of, respectively, hydroxyalkyl and oxoalkyl dihydropyran derivatives.

C-Difluoromethylene-containing, C-trifluoromethyl and C-perfluoroalkyl carbohydrates. Synthesis by carbohydrate transformation or building block methods

The synthetic methods for preparing carbohydrates bearing a C-branched substituent of the type CF2-Y, with Y = F, Y = CnF(2n + 1) or Y = a carbon-attached or heteroatom-attached nonfluorinated residues, are reviewed. Both direct introduction of C-branched fluorinated substituents (direct trifluoromethylation, perfluoroalkylation or difluoromethylenation) and building block methods from fluorinated synthons are considered.