Preparation Of 2,3-Unsaturated Pseudoglycosides With Ferrier Rearrangement Promoted By Tm（OTf）₃ As A Highly Efficient Catalyst

2,3-Unsaturated glycosides are of great importance in the synthesis of biologically active molecules and new functional materials as chiral intermediates since the regio- and stereo-varieties that they provide for the subsequent transformations. As one of the most useful procedures to achieve 2,3-unsatureted glycosides directly and efficiently, Ferrier Rearrangement was widely investigated and a variety of reagents have been used to promote this reaction, including Bronsted acids, Lewis acids, as well as other reagents such as oxidants, etc. Due to their unique properties and high catalytic activity, lanthanide salts as catalyst in Ferrier Rearrangement have recently gained more and more applications, among which there could be mentioned Dy(OTf)3, Er(OTf)3, Yb(OTf)3, Y(OTf)3, and Sm(OTf)3, etc. In our continuing efforts to search for more efficient catalyst for Ferrier Rearrangement,we found thulium triflate is a highly efficient catalyst for our purposes. Here we wish to report our result.First of all, reaction condition optimization was performed. For the thulium salts,among TmF3, TmCl3, Tm(NO3)3·6H2O, Tm(OAc)3?xH2O and Tm(OTf)3 we found Tm(OTf)3 was the most efficient. For the reaction solvent, among the tested acetonitrile, methylene dichloride, tetrahydrofuran, acetone and toluene, acetonitrile gave the highest conversion under the catalysis of Tm(OTf)3. For the reaction temperature, shortest reaction time and highest yield were obtained at 40 oC. Therefore,the established reaction conditions are mild.Under the established reaction conditions, 2,3-unsaturated glycosides were synthesized from glucal and rhamnal with various O-, S-, N-, and C-nucleophiles. By using Tm(OTf)3 as catalyst, an efficient procedure for the preparation of2,3-unsaturated-glycosides has been established. A series of O-, S-, N- and C-2,3-unsaturated-glucosides were obtained from 2,4,6-tri-O-acetyl-D-glucal or3,4-Di-O-acetyl-6-deoxy-L-glucal in good yield and high anomeric selectivity.