Stereoselective synthesis of 3′-substituted 2′-deoxy C-nucleoside pyrazolo[1,5-a]-1,3,5-triazines and their 5′-phosphate nucleotides

3′-Substituted 2′-deoxynucleoside analogues in the pyrazolotriazine series were prepared from the corresponding 3′-ketonucleoside via the Wittig reaction or a stereoselective addition of alkynylcerium reagents.