Adenosine and guanosine analogs with 8-position vinyl and aryl groups, e.g. I [R = H, OAc, R1 = Ph, CH:CH2, C(OEt):CH2], were prepared by palladium catalyzed cross-coupling of organostannanes with 8-bromopurine nucleosides. The reaction conditions and catalyst composition were improved so that both vinyl and aryl modifications could be made by a general procedure.