Reactions of N-, S- and O-Nucleophiles with 3,4,6-Tri-O-benzyl-D-glucal Mediated by Triphenylphosphane Hydrobromide versus Those with HY Zeolite

Direct C–N bond formation has been accomplished by reaction of 1,5‐anhydro‐3,4,6‐tri‐O‐benzyl‐2‐deoxy‐D‐arabino‐hex‐1‐enitol (3,4,6‐tri‐O‐benzyl‐D‐glucal) with N‐nucleophiles, using triphenylphosphane hydrobromide as catalyst in dichloromethane or THF. 2‐Deoxy‐S‐ and ‐O‐glycosides have also been prepared with thiols, sterols, flavonoids, alcohols and sugars as nucleophiles, with α‐stereoselectivity. Sterically demanding reagents such as sterols, flavonoids, sugars and an indole give only the α‐anomer in dichloromethane, while the purine nucleosides in THF were obtained as anomeric mixtures whilst maintaining the α‐stereoselectivity. This procedure has led to an easy and straightforward synthesis of a variety of biomolecules, in moderate to high yield, with the first use of triphenylphosphane hydrobromide for N‐ and S‐glycosylation. An alternative method for C–O and C–S bond formation uses HY zeolite to promote theFerrier rearrangement of 3,4,6‐tri‐O‐benzyl‐D‐glucal to give exclusively the corresponding 2,3‐unsaturated α‐O‐ and α‐S‐glycosides in moderate yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)