Recent results in synthetic glycochemistry with iron salts at Orsay-Gif
Résumé
This review particularly emphasizes synthetic applications resulting from cascade or one-pot transformations and a glycosylation reaction promoted by ferric salts. These easy to handle, cheap and environment-friendly salts have been examined for their ability to induce, as a Lewis acid, fast carbohydrate-based modifications in our laboratories at Orsay and Gif sur Yvette. A short synthetic route to the dihydropyran framework of anti-influenza constructs is reported by coupling the Petasis three-component condensation to an iron(iii)-promoted one-pot cascade of deprotection – C–C double bond isomerization – cyclization - oxazoline formation. We also show that iron(iii) chloride hexahydrate is most appropriate to catalyze a one-pot regioselective protection of mono- and disaccharides. This iron(iii) catalysis renders multi-step routes, such as chemical oligosaccharide syntheses, faster. In the last section, we report a catalytic glycosylation method particularly simple and straightforward leading to the important β-d-GlcNAc motif, in which the more electrophilic iron(iii) triflate activates the readily available peracetate of N-acetyl-β-d-glucosamine. This glycosylation does not necessarily require the formation of the mandatory oxazolinium intermediate.