Treatment of the protected (E)-5′-deoxy-5′- [(p-toluenesulfonyl)methylene]uridine and adenosine derivatives with tributyl-or triphenylgermane hydride (AIBN/toluene/Δ) effected radical-mediated germyldesulfonylations to give 5′-(tributyl-or triphenylgermyl)methylene-5′-deoxyuridine and adenosine derivatives as single (E)-isomers. Analogous treatment of 2′-deoxy-2′-[(phenylsulfonyl) methylene]uridine with Ph 3 GeH afforded the corresponding vinyl triphenylgermane product. Stereoselective halodegermylation of the (E)-5′-(tributylgermyl)methylene-5′-deoxy nucleosides with N-iodosuccinimide or N-bromosuccinimide provided the Wittig-type (E)-5′-deoxy-5′-(halomethylene) nucleosides quantitatively, while no halodegermylations was observed with the 5′-deoxy-5′-(triphenylgermyl)methylene counterparts. Treatment of the vinyl trialkylgermanes with aqueous trifluoroacetic acid effected protiodegermylation, while vinyl triarylgermanes were stable under the acidic conditions.
Application of Germyldesulfonylation Reactions to the Synthesis of Germanium-Containing Nucleoside Analogues. -Both purine and pyrimidine nucleosides undergo desulfonylation by means of a radical-mediated procedure utilizing less toxic germane hydrides rather than the previously employed tin hydride reagents. Contrary to the stannyldesulfonylation reactions, the germyldesulfonylations of the vinyl sulfones (I) proceed stereoselectively. The yields are higher for the uridine substrates as it is in the case of stannyldesulfonylation reactions. Germyldesulfonylation reactions presumably occur via a radical-elimination mechanism in analogy to the silyl-and stannyldesulfonylation process. -(WNUK*, S. F.; SACASA, P. R.; RESTREPO, J.; Nucleosides, Nucleotides Nucleic Acids 28 (2009)
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