Amination of 4‐nitropyridazine 1‐oxides by liquid ammonia/potassium permanganate

Abstract

Treatment of 4‐nitropyridazine 1‐oxide (1a) 3‐methoxy‐6‐chloro‐4‐nitropyridazine 1‐oxide (1b) or 3,6‐dimethoxy‐4‐nitropyridazine 1‐oxide (1c) with a solution of potassium permanganate in liquid ammonia gives in reasonable‐to‐good yields the corresponding 5‐amino‐4‐nitropyridazine 1‐oxides (75%, 54% and 62%, respectively). 3,6‐Dimethoxypyridazine (4a) and 3‐methoxypyridazine (4b) are converted into the corresponding 4‐aminopyridazines 6a,6b on treatment with potassium amide/liquid ammonia/potassium permanganate (yield 50 and 22% respectively). In the last‐mentioned reaction besides 6b 3,3′‐dimethoxy 4,4′‐bipyridazine (7, 23%) was obtained. It is suggested that the neutral 1:1 σ‐adducts formed between (1a–1c) and liquid ammonia and the anionic σ‐adducts, formed between (5a–5b) and potassium amide are intermediates in this amino‐oxidation reaction.

Nucleophilic substitution of the nitro group, fluorine and chlorine in aromatic compounds

“…2,63 Thus the reaction of 6-chloro-3-methoxy-4-nitropyridazine N-oxide (50) with potassium amide yields a s-complex at the unsubstituted position 5 of the ring; this complex is further oxidised to the aromatic amine 51. 64 Other examples of nucleophilic hydrogen substitution with retention of the nitro group and the chlorine atom in the azine ring have been described. 2,63 Intramolecular oxidation of a s-complex is also possible.…”

“…Although the nucleophilic substitution mechanism S N Ar (addition ± elimination) in arenes and heteroarenes has become classical in organic chemistry long ago, 1,7,10,11 some alternative mechanisms can also be used. These may be divided into several groups, viz., electron-transfer reactions (SET), 3 photochemical reactions, 6, 231 ± 233 , vicarious hydrogen substitution reactions (VNS), 2, 9 kine-and tele-substitutions, 6,234 ring opening ± closure reactions, mainly for heterocyclic compounds (ANRORC) 2,64 and reactions catalysed by transition metals. 235,236 It is known that the formation of s-complexes of the type 97 at nonsubstituted positions of activated aromatic rings proceeds much faster and the stabilities of these complexes strongly depend on the nature of the nucleophile, the substrate and some other factors.…”