A large scale synthesis of 3‐chloro‐5‐methoxypyridazine

Abstract

Abstract A large scale synthesis of 3‐chloro‐5‐methoxypyridazine was developed (18 moles) that relies on the protection of the pyridazinone nitrogen of 4,5‐dichloro‐3(2 H )‐pyridazinone as the tetrahydropyranyl derivative 2 . The 5‐chloro position of the protected pyridazinone was selectively displaced with methoxide to give 3 followed by catalytic hydrogenation of the 4‐chloro group to give 4. Removal of the protecting group with acid followed by phosphorous oxychloride treatment gave the target compound 6 in good yield. This route is superior to the previously described synthesis of this compound.