Novel unsaturated purine nucleosides

The synthesis of a number of novel purine ribonucleosides bearing one degree of unsaturation at the 2-position is described. The two key reactions used in the synthesis of these compounds is a palladium-catalyzed cross-coupling reaction and an ozonolysis. These synthetic transformations have rarely been used in nucleoside chemistry. Isomerization of an allylpurine system to a vinylpurine system under the conditions of the cross-coupling reaction and also under fluoride ion catalysis is discussed. The novel 2-formylpurine nucleosides described appear to be easily hydrated.