Sm(OTf)3 as a highly efficient catalyst for the synthesis of 2,3-unsaturated O- and S-pyranosides from glycals and the temperature-dependent formation of 4-O-acetyl-6-deoxy-2,3-unsaturated S-pyranosides and 4-O-acetyl-6-deoxy-3-alkylthio glycals

By using Sm(OTf)3 as the catalyst, synthesis of 2,3-unsaturated-glycosides has been performed. A series of 2,3-unsaturated glycosides were obtained from 3,4,6-tri-O-acetyl-d-glucal or 3,4-di-O-acetyl-l-rhamnal under mild reaction conditions in good yield and high anomeric selectivity. It was found that under certain conditions, reaction of 3,4-di-O-acetyl-l-rhamnal with thiol leads to temperature-dependent formation of C-1-S and C-3-S product. A temperature-dependent profile of the yield of these two products is given.