Hydrogermylation of 5-ethynyluracil nucleosides: formation of 5-(2-germylvinyl)uracil and 5-(2-germylacetyl)uracil nucleosides.

A stereoselective radical-mediated hydrogermylation of the protected 5-ethynyluracil nucleosides with trialkyl-, triaryl,- or tris(trimethylsilyl)germanes gave (Z)-5-(2-germylvinyl)uridine, 2'-deoxyuridine, or ara-uridine as major products. Reaction of the β-triphenylgermyl vinyl radical intermediate with oxygen and fragmentation of the resulting peroxyradical provided also 5-[2-(triphenylgermyl)acetyl]pyrimidine nucleosides in low to moderate yields. Thermal isomerization of the latter in MeOH occurred via a four-centered activated complex, and subsequent hydrolysis of the resulting O-germyl substituted enol yielded 5-acetyluracil nucleosides in quantitative yield.