Studies on the synthesis and unusual behavior of vinyl sulfone-modified hexenopyranosylthymines

Although vinyl sulfone-modified- (VSM) pent-2′-enofuranosyl nucleosides 2 and hex-2-enopyranosyl glycoside 4 are easily synthesized from the corresponding mesylated sulfones 1c and 3c, respectively, via an oxidation-mesylation-elimination route, the 3′-C-sulfonyl-hex-2′-enopyranosylthymine 11 is not obtained from 10 and a glycal derivative 12 is formed instead. On the other hand, 3′-C-sulfonyl-hex-3′-enopyranosylthymine 20 is easily synthesized from the mesylated sulfone 19. Again unlike the reaction patterns of VSM-pent-2′-enofuranosyl nucleosides 2 and hex-2-enopyranosyl glycosides 4 as Michael acceptors, the reactions of nucleophiles with 3′-C-sulfonyl-hex-3′-enopyranosylthymine 20 yielded a rearranged product 21 instead of Michael adducts.