Ferric sulfate hydrate-catalyzed O-glycosylation using glycals with or without microwave irradiation

We have developed a novel glycal-based O-glycosylation reaction, in which the substrates are not only peracetyl glycals but also perbenzyl glucals to afford the corresponding 2,3-unsaturated-O-glycosides via Ferrier rearrangement. The reaction of the perbenzyl glucal with various alcohols catalyzed by ferric sulfate hydrate (Fe-2(SO4)(3)center dot xH(2)O) was successfully carried out to give 2,3-unsaturated D-O-glucosides with exclusive a-selectivity and no formation of addition products 2-deoxy hexopyranosides was observed. It is the first report on peralkyl glycal efficiently undergoing Ferrier rearrangement instead of addition of alcohols catalyzed by Lewis acids. Fe-2(SO4)(3)center dot xH(2)O is an effective, convenient, and environmentally benign heterogeneous catalyst. It has low catalytic loading and recyclable without significant loss of activity. (c) 2007 Elsevier Ltd. All rights reserved.