Stereoelectronic effects determine oxacarbenium vs β-sulfonium ion mediated glycosylations
Thomas J Boltje1, Jin-Hwan Kim, Jin Park
1Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, Georgia 30602, USA.
Abstract:
Activation of a glycosyl donor protected with a 2-O-(S)-(phenylthiomethyl)benzyl ether chiral auxiliary results in the formation of an anomeric β-sulfonium ion, which can be displaced with sugar alcohols to give corresponding α-glycosides. Sufficient deactivation of such glycosyl donors by electron-withdrawing protecting groups is, however, critical to avoid glycosylation of an oxacarbenium ion intermediate. The latter type of glycosylation pathway can also be suppressed by installing additional substituents in the chiral auxiliary.
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