Glycosylations regioselective

An alternative stereoselective synthesis of chiral heterocycles based on carbohydrate-induced stereodifferentiation includes nucleophilic addition reactions on heterocyclic systems already bound to the carbohydrate auxiliary. An example of this strategy has been shown by stereoselective addition of Grignard reagents to carbohydrate-linked 4-pyridones [61]. For this purpose, trimethylsiloxypyridine was glycosylated regioselectively using pivaloyl-protected glycosyl fluorides. 

Scheme 4.74 Sialyl xanthate in regioselective and stereoselective glycosylations [398].

Relevance of NPOEs to the Regioselectivity in the Glycosylation of Primary Versus Secondary Hydroxyls... 

Diol 159 was chosen as a model for probing regioselective glycosylation with armed and disarmed thioglycosides 160 and 163, and NPOE 108. The results obtained were not anticipated (Scheme 5.35b-d). 

Scheme 5.35 The issue of regioselectivity in the glycosylation of primary versus secondary hydrosyls.

Iterative Regioselective Clycosylations of Unprotected Glycosyl Donors and Acceptors... 

Table 5.7 Regioselectivity in intramolecular glycosylations via prearranged glycosides.

Some authors exemplified different regioselectivity on glycosylations of various O- and thio-p-D-glycopyranosides (phenyl, benzyl, phenylethyl, phenylthio, benzylthio, etc.), including a C-glycosyl compound.29... 

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