Sugar-derived 2-S-substituted-2H-pyran-3(6H)-ones: synthesis and reactivity Original Research Article

A practical procedure for the preparation of chiral 2-S-substituted-2H-pyran-3(6H)-ones is described. According to the reaction conditions, 1,5-anhydro-2,3,4-tri-O-acetyl-d-threo-pent-1-enitol (1) reacted with thiophenol under Lewis acid catalysis to afford the polysubstitution product 1,5-anhydro-2,3,4-tri-S-phenyl-2,3,4-trithio-d,l-threo-pent-1-enitol (2) or phenyl 2,4-di-O-acetyl-3-deoxy-1-thio-α- and β-d-glycero-pent-2-enopyranoside (3 and 4, respectively). The iodine-promoted addition of thiophenol or α-toluenethiol to 1 gave (2S)-2-phenylthio-2H-pyran-3(6H)-one (5) or its 2-benzylthio analogue 6, but these products showed low enantiomeric excesses (ee ∼40–60%). However, dihydropyranone 5 with high optical purity (ee >94%) was successfully obtained by treatment of 4 with iodine in acetonitrile. On the other hand, it was established that the benzylthio group of 5 exerts high stereocontrol in reduction and cycloaddition reactions performed on the α,β-unsaturated carbonyl system.