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-beta-D-xylopyr anoside, a synthetic intermediate of the orally active antithrombotic compo und Iliparcil, has been prepared in 44-47% isolated yield. Different condit ions 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 beta-chloride 3 or the alpha-trichloroacetimidate 5 as donors. Wi th halides 2 and 3, the reaction was carried out in the presence of ZnO-ZnC l2 or ZnO alone. Both promoters are cheap, safe and therefore compatible wi th large-scale industrial processes. (C) 1999 Elsevier Science Ltd. All rig hts reserved.