HClO_4–silica-catalysed regioselective opening of benzylidene acetals and its application towards regioselective HO-4 glycosylation of benzylidene acetals in one-pot

摘要

Here we report a high-yielding method for the regioselective reductive ring opening of 4,6-O-benzylidene acetals of hexapyranosides using inexpensive and robust HClO_4–SiO_2 as the acidic catalyst and triethylsilane as the hydride donor. Under the optimized condition, gluco- and mannopyranosides give the respective 6-O-benzyl derivative in good to excellent yields while the corresponding galactopyranoside gives the corresponding 6-O-benzyl derivative in lower yield. As the optimized condition involves acidic catalyst, we also successfully developed further application of the present method for the tandem regioselective opening and glycosylation in one-pot.