Study On Preparation Of2,3-unsatureted Glycosides With Type Ⅰ Ferrier Rearrangement

2,3-Unsaturated glycosides or pseudoglycosides are recognized as important chiral intermediates in the synthesis of biologically active compounds and functional materials such as oligosaccharides, modified carbohydrates, nucleosides and glycopeptides blocks. One of the most useful procedures to achieve2,3-unsatureted glycosides directly and efficiently is Type I Ferrier Rearrangement, in which glycals are reacted with nucleophiles promoted by acid catalyst. This reaction was proposed to proceed through a cyclic allylic oxocarbonium intermediate which was formed via departure of the leaving group on the C-3position of glycal via the action of the acid catalyst, followed by the nucleophilic substitution on the C-1position via quasi-equatorial orientation.A wide range of Lewis acid catalysts and other catalysts have been investigated to promote such glycosidation. However, some of these reaction systems sufferred from the disadvantages in terms of large excess of nucleophile, stiochiometric amounts of catalyst, harsh reaction conditions, which leading to extensive work up. Therefore, there still is of interest to find new efficient catalyst for milder and more efficient synthetic process with good anomeric selectivity by using stiochiometric amount of nucleophile under low catalyst load.We investigated the Type I Ferrier Rearrangement reaction systems by using Lewis acid iron(III) triflate or Bronsted acids TfOH-SiO2as new efficient catalyst. The reaction systems were optimized and a series of nucleophiles were reacted with glucal donor affording2,3-unsaturated-glycosides in high yield and good anomeric selectivity under mild conditions.