Alternative Routes to 4,6-O-Benzylidene β-Thioglycosides

The synthesis of glycosides generally requires the use of building blocks that need to be readily prepared, avoiding tricky reaction steps and boring purifications. Thioglycosides represent key donor intermediates for their activation in glycosylation reactions and for their great stability. Moreover, the presence of a benzylidene moiety confers to the molecule a double advantage: it can influence the stereochemistry of the glycosylation reaction and can be selectively opened to generate different species having a free secondary hydroxyl group. Here, the preparation of p-Tolyl 1-thio-4,6-O-benzylidene-2,3-di-O-benzyl-β-d-pyranoses of glucose, galactose, and mannose are described. The global procedure involved the exploitation of simple reactions and crystallization techniques, having a chromatographic purification for the last step only.