Stereoselective Preparation of 3'-C-Allyluridines and 3'-Spiro-gamma-Lactone Uridine Analogues.

Grignard reactions of 3'-ketouridines 1a-c with allylmagnesium bromide and CeCl3 afforded novel 3'-C-allyluridines 2a-c and 3d-e. The diprotected 3'-keto nucleosides 1a-c afforded xylo-configurated compounds 2a-c and the 5'-unprotected 3'-keto nucleosides 1d-e afforded mixtures of xylo- and ribo-configurated compounds 2d/3d and 2e/3e. The allyluridine 2a was converted into the diol 4 by standard hydroboration and further oxidised to the 3'-spiro-gamma-lactone nucleoside 5. This compound and its deprotected analogue 6 are the first examples of a novel class of 3'-spiro nucleoside analogues.