Reaction of the 4'-benzenesulfonyl derivatives of thymidine with organosilicon and organoaluminum reagents.

With an aim to develop a new approach to synthesize 4'-substituted nucleosides, reactions of thymidine derivatives having a benzenesulfonyl leaving group at the 4'-position with organosilicon and organoaluminum reagents were investigated. Two substrates 4alpha (alpha-L-isomer) and 4 beta (beta-D-isomer) were prepared for this purpose. Although reaction of 4alpha with organosilicon reagents gave preferentially the 4'-substituted (allyl and N(3)) beta-D-nucleoside, its reaction with AlMe(3) gave the 4'-methyl-alpha-L-thymidine as the major product. On the other hand, the substrate 4beta, upon reacting with AlMe(3), furnished the desired 4'-methylthymidine exclusively in high yield.