An improved synthesis of an umbelliferyl 5-thioxylopyranoside, precursor of the antithrombotic drug Iliparcil

4-Ethyl-2-oxo-2H-1-benzopyran-7-yl 2,3,4-tri-O-acetyl-5-thio-β-d-xylopyranoside, a synthetic intermediate of the orally active antithrombotic compound Iliparcil, has been prepared in 44–47% isolated yield. Different conditions were used for the glycosylation of 4-ethyl-2H-7-hydroxy-1-benzopyran-2-one 6 applying 2,3,4-tri-O-acetyl-5-thio-d-xylopyranosyl bromide (2), the analogous β-chloride 3 or the α-trichloroacetimidate 5 as donors. With halides 2 and 3, the reaction was carried out in the presence of ZnO–ZnCl2 or ZnO alone. Both promoters are cheap, safe and therefore compatible with large-scale industrial processes.