Remote intramolecular glycosylation

The use of bis-ester tethers in remote intramolecular glycosylation has been investigated by a number of groups. In contrast to the short tethers used by Stork, Hindsgaul, and Ogawa, these more remote tethers provide a much less predictable outcome and as a result they remain less synthetically useful. Another difference between the short tethers and remote bis-ester tethers is that the reacting alcohol functionality is not masked in the tether but is already free to react as soon as the anomeric center is activated. 

Scheme 10-84 Remote tethers are less useful for stereoselective intramolecular glycosylation.

Crich and co-workers reported that the remote participation of esters at the 0-3 position of allopyranosyl donors is possible in glycosylations based on the trapping experiment, in which the anomeric oxocarbenium ion intermediate generated by the activation of thioalloside 132 was trapped by the intramolecular nucleophilic attack of the tert-butoxycarbonyl (Boc) group at the 0-3 axial position to afford stable cyclic carbonate 133 (Scheme 21) [65],... 

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