Abstract
Improved syntheses of 1, 4-dihydroxypyrido [3, 4-d] pyridazine (II) and 1, 4-dichloropyrido [3, 4-d] pyridazine (I) were described. Reaction of I with alcohol and alkali gave 1, 4-dialkoxypyrido [3, 4-d] pyridazines (IIIa-c). Hydrolysis of I gave an isomeric mixture of 1-chloro-4-hydroxy- and 1-hydroxy-4-chloropyrido [3, 4-d] pyridazines (IV and V). Reaction of I with hydrazine hydrate afforded also an isomeric mixture of 1-chloro-4-hydrazino- and 1-hydrazino-4-chloropyrido [3, 4-d] pyridazines (VIII and IX). The structures of these compounds were determined by an alternative synthesis of V from known 1-hydroxy-4-aminopyrido [3, 4-d] pyridazine (VI) and by conversion of IX into V. Also described were the preparations of 1-hydroxypyrido [3, 4-d] pyridazine (VII) and isopropylidene derivatives (X and XI) of VIII and IX, and improved syntheses of 1, 4-dichlorophthalazine and ethyl 3-cyanoisonicotinate.
