Multigram-scale synthesis of L,D-heptoside using a Fleming-Tamao oxidation promoted by mercuric trifluoroacetate

An efficient multigram-scale synthesis of methyl 2,3,4,6-tetra-O-benzyl-L-glycero-α-D-manno-heptopyranoside from methyl 2,3,4-tri-O-benzyl-α-D-mannopyranoside is reported. It involves a sequence of Swern oxidation, Grignard addition and Fleming-Tamao reactions. The resulting scaffold was used as a precursor to design a small library of clickable L-heptosides. This study shows that the use of mercuric bistrifluoroacetate is required both to accelerate and to cleanly perform the Fleming-Tamao oxidation, without side-reactions.