0-Pentenyl glycosides selective activation

It was reported that selective activation of the SBox glycosyl donors over SEt and O-pentenyl glycoside acceptors can also be achieved in the presence of AgOTf... 

Building on the observations of Kahne and Takahashi, Chenault and Castro relied on the selective activation of an isopropenyl glycoside donor with TMSOTf, followed by subsequent activation of a second n-pentenyl glycoside with NIS/TESOTf.12 This one-pot glycosylation offers proof of the concept that Fraser-Reid s glycosides can be incorporated into one-pot syntheses. (See Scheme 11.7.)... 

TV-Bromosuccinirnide (NBS) and NIS are the most widely used electrophiles to activate -pentenyl glycosides. Catalytic amounts of acids such as TfOH or trieth-ylsilyl triflate (TESOTf) are introduced to speed up the generation of bromonium or iodonium ions [43], The stereochemical outcome depends, as usual, on whether a participating group exists at C2. An alternative promoter is iodonium dicollidine perchlorate (IDCP), whose lower reactivity allows it to selectively activate certain disarmed n-pentenyl glycosides [44],... 

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