Synthesis of thiosaccharides employing the Pummerer rearrangement of tetrahydrothiopyran oxides

The Pummerer rearrangement of 1-deoxy-5-thioglucopyranose derivatives carrying acetonides at the C3,4-positions proceeded regioselectively at the C1 position by treating with TFAA in the presence of pyridine. Studies employing deuterium-labelled derivatives revealed that the reaction was induced by E2 1,2-elimination of trifluoroacetic acid of the trifluoroacetoxy sulfonium intermediate. This methodology was applied to the synthesis of an isomaltotriose derivative consisting of 5-thioglucopyranoside units.