In pursuing step economy-oriented carbohydrate synthesis in solution phase for rapid access to oligosaccharides, we have recently developed a simple glycosylation approach employing only allyl glycosides as building blocks. In a one-pot fashion, an allyl glycoside is isomerized to the corresponding prop-1-enyl glycoside and its subsequent activation with NIS/TfOH in the presence of an allyl glycoside acceptor leads to the formation of a new allyl glycoside. The new protocol could markedly simplify carbohydrate synthesis and improve overall synthetic efficiency. Studies have been carried out to elucidate the mechanism of this new glycosylation reaction. The reaction mechanism proves to be quite complicated. Upon activation of the anomeric prop-1-enyl group isomerized from an allyl group, both the desired new glycoside and addition-reaction byproducts can be produced. TfOH has a dual role in the reaction; it promotes the conversion of the addition-reaction products to the desired new glycoside through multiple competing pathways.

Step economy oriented carbohydrate synthesis with allyl glycoside building blocks

243rd National Meeting (2012)

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