Glycopyranosyl donors

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

Since encounter complexes of alcohol donors and glycopyranosyl oxacarbenium ions were not found, nor were CIPs of partially ionized glycopyranosyl donors, it is hypothesized that including solvent molecules in such studies is necessary. Such studies may require methodology development, but are included here since these are extrapolations of existing studies. 

To prepare glycopyranosyl donors having chiral protecting groups at 0-2, to assess if the 0-2 syn preference can be used productively to either increase reactivity or enhance stereoselectivity. 

Directing Ejfect of Potentially Participating Groups at Remote Positions of Glycopyranosyl Donors Other than Mannopyranosyl Donors... 

O-glycosidation between O-silylated glycosyl acceptors and several 1-substituted sugars, glycopyranosyl or furanosyl silyl ethers [79a], fluorides [80], phosphates [81], and trichloroacetimidates [82a] has been examined to develop other efficient and stereoselective procedures catalyzed by silicon Lewis acids. The trichloroacetimidate glycosyl donors are fairly reliable and were used for the synthesis of eanelioside GD by Ogawa (Fig. l)[82b]. 

Takeuchi, K, Mukaiyama, T, Trityl tetrakis(pentafluorophenyl)borate catalyzed stereoselective glycosylation using glycopyranosyl fluoride as a glycosyl donor, Chem. Lett, 555-556, 1998. 

Hashimoto, S, Umeo, K, Sano, A, Watanabe, N, Nakajima, M, Ikegami, S, An extremely mild and stereocontroUed construction of l,2-/ra w-p-glycosidic linkages capitalizing on benzyl-protected glycopyranosyl diethyl phosphites as glycosyl donors. Tetrahedron Lett., 36, 2251-2254, 1995. 

Cyclic thiophosphates (35) of 1,2-O-isopropylidene-a-D-glucofuranose have been obtained from the corresponding 3,5,6-bicyclic thiophosphate by treatment with various nucleophiles. 6-Deoj -6-sulphono-o-D glucopyranosyl phosphate has been prepared as shown in Chapter 11, Scheme 5 the synthesis of individual enantiomers and racemates of mvo-inositol mono-, di-, and tri-phosphates is covered in Chapter 18, and the use of glycopyranosyl phosphates as gfyco I donors is referred to in Chapter 3. 

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