Synthesis and chemistry of some pyridazine nucleosides related to certain 5‐substituted pyrimidine nucleosides

Condensation of 3,4‐dichloro‐6‐[(trimethylsilyl)oxy] pyridazine ( 3 ) with 1‐ O ‐acetyl‐2,3,5‐tri‐ O ‐benzoyl‐β‐ D ‐ribofuranose ( 4 ), by the stannic chloride catalyzed procedure, has furnished 3,4‐dichloro‐1‐(2,3,5‐tri‐ O ‐benzoyl‐β‐ D ‐ribofuranosyl) pyridazin‐6‐one ( 5 ). Nucleophilic displacement of the chloro groups and removal of the benzoyl blocking groups from 5 has furnished 3‐chloro‐4‐methoxy‐, 3,4‐dimethoxy‐, 4‐amino‐3‐chloro‐, 3‐chloro‐4‐methylamino‐, 3‐chloro‐4‐hydroxy‐, and 4‐hydroxy‐3‐methoxy‐1‐β‐ D ‐ribofuranosylpyridazin‐6‐one. An unusual reaction of 5 with dimethylamine is reported. Condensation of 4,5‐dichloro‐3‐nitro‐6‐[(trimethylsilyl)oxy]pyridazine with 4 yielded 4,5‐dichloro‐3‐nitro‐1‐(2,3,5‐tri‐ O ‐benzoyl‐β‐ D ‐ribofuranosyl)pyridazin‐6‐one ( 24 ). Nucleophilic displacement of the aromatic nitro groups from 24 is discussed. Condensation of 3 with 3,5‐di‐ O‐p ‐toluoyl 2‐deoxy‐ D ‐ erythro ‐pentofuranosyl chloride ( 28 ) afforded an α, β mixture of 2‐deoxy nucleosides. The synthesis of certain 3‐substituted pyridazine 2′‐deoxy necleosides are reported.