Glycopyranosylations

The Gewald reaction was utilized to prepare glycopyranosyl thiophene C-... 

Acylated glycosyl thiocyanates are made by treatment of acylated glycopyranosyl halides with potassium thiocyanate.30 Reaction at —40° with a Grignard reagent affords alkyl or aryl 1-thioglycosides.54... 

Noyori and coworkers found that tetrafluorosilane or trimethylsilyl tri-flate catalyzes the condensation of appropriately protected glycopyranosyl fluorides with trimethylsilyl ethers or alcohols. The strong affinity of silicon for fluorine was considered to be the driving force for this reaction. In the case of Sip4, attack of a nucleophile on the glycosyl cation-SiFj ion-pair intermediate was anticipated. Thus, condensation of 2,3,4,6-tetra-O-benzyl-a- and - -D-glucopyranosyl fluorides (47a and 47fi) with methyl... 

The preparation of 3,5-bis(/3-D-glycopyranosyl)-l,2,4-thiadiazoles has been accomplished via the oxidation of the corresponding acylated C-(/3-D-glycopyranosyl)thioformamides with potassium and sodium dithionite. The synthesis is completed by a Zemplen deacylation. This is an interesting extension to a type A synthesis which has previously only been suitable for arylthioamides <2001T5429>. 

Trifluorozincbromide reagent (CF3ZnBr) is employed for the synthesis of glycosyl fluorides from glycosyl bromides. When 2,3,4,6-tetra-O-acetyl-a-D-glycopyranosyl... 

Scheme 5 Stereoselective 1,2-cis-glycosylations with chiral auxiliaries at C-2 of glycopyranosyl donors.

An example of synthesis of a thiodisaccharide exploiting procedure (a) is reported in Fig. 23. Saponification of glycopyranosyl thioacetate 48 generated the thio-anion 49 which displaced a triflate in position 4 of galacto-derivative 50, generating the thiodisaccharide 51.52... 

The recent discovery that acetylated glycopyranosyl bromides may be reduced in high yields with lithium aluminum hydride to the corresponding 1,5-anhydroglycitols661 represents an improvement over the reductive desulfurization process and will doubtless make this class of compound even more readily available in the future. 

The signs of geminal, F H coupling-constants (in contrast to those of geminal, iH-1H coupling-constants) are absolutely positive. They were determined for derivatives of glycopyranosyl fluorides, 75,292,293 2-deoxy-2-fluoro-D-gluco- and -manno-pyranosyl fluorides,71... 

In a study of the infrared spectra of acetylated and benzoylated gly-copyranosyl fluorides, it was found that, with few exceptions, such compounds exhibit an absorption band at 802-748 cm-1 if the fluorine atom is axial, whereas no such absorption band is observed if the fluorine atom is equatorial therefore, it is necessary to know the conformation of the molecule before the anomeric configuration can thus be determined.45 It is possible that reinterpretation of some of these observed absorptions may be necessary, because some of the conformations of some of the glycopyranosyl fluorides are now known to exist in the conformation opposite to that originally anticipated without proof, because of the strong anomeric effect of a fluorine substituent (see Section III,2e). 

Glycopyranosyl halides react with ethyl acetoacetate and pentan-2,4-dione under soliddiquid phase-transfer catalytic conditions, using potassium phosphate as the base, providing the C-alkylated derivatives (40-60%) ]94],... 

Reaction of glycopyranosyl halides with activated methylene groups... 

Biodegradation of poly(sodium carboxylate) containing a glycopyranosyl group, Poly(sodium carboxylate)s containing... 

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