Direct 2,3-O-Isopropylidenation of α-D-Mannopyranosides and the Preparation of 3,6-Branched Mannose Trisaccharides

摘要

A highly efficient, regioselective method for the direct 2,3-O-isopropylidenation of α-D-mannopyranosides is reported. Treatment of various α-D-mannopyranosides with 0.12 equiv of the TsOH·H2O and 2-methoxypropene at 70 °C gave 2,3-O-isopropylidene- α-D-mannopyranosides directly in 80%～90% yields. Based on this method, a 3,6-branched α-D-mannosyl trisaccharide was prepared in 50.4% total yield using p-nitrophenyl 2,3-O- isopropylidene-α-D-mannopyranoside as the starting material.