Thioglycosides direct activation

Hycosylation. Hindered thioglycosides are activated by PhSOTf and the process permits the direct formation of p-mannopyranosides. 

Figure 4.1 Direct activation of thioglycosides without neighbouring group participation.

Common problems in oligosaccharide synthesis not directly related to the method of direct activation of thioglycoside donors, such as for example transacylations or formation of orthoesters, when using 2-0-participating groups, or glycal or 1,6-anhydro derivative formation of the donor can, of course, also be encountered [90, 110]. 

As is the case with most glycosylation reactions, i.a. because of their complexity, no truly thorough mechanistic investigation has been performed on the direct activation of thioglycosides. An obvious general mechanism (Scheme 19), very similar to the one suggested for other types of glycosylation reactions, in which the soft... 

As iodine is a milder thioglycoside activator than IDCP, we have been able to directly monitor iodine-promoted thioglycoside activation, epimerization, and gly-cosylation reactions by H NMR spectroscopy.41,44 We have been able to show that... 

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