Abstract The synthesis of 4-methoxy-, 4-amino-3-chloro-, and 4-amino-1-(2, 3-dideoxy-BD- glycero-pentofuranosyl) pyridazin-6-one nucleosides, 6, 19 and 20 is described. The synthesis of 3, 4-dichloropyridazin-6-one (10) was accomplished in 44% overall yield using bromomaleic anhydride (17) as the starting material. The condensation of the silylated base of 10 with the halogenose 12 in the presence of trimethylsilyl triflate as a catalyst afforded ...