NMR studies on σ‐adducts of heterocyclic systems with nucleophiles (Part VII). 1H‐NMR investigations on σ‐adduct formation of pyridazine, of pyridazine 1‐oxide and some of its derivatives with ammonia. A new substitution mechanism

In the reaction of 6‐chloro‐3‐methoxy‐4‐nitropyridazine 1‐oxide with methanolic ammonia and with liquid ammonia, amino‐demethoxylation occurs. By using 1H‐NMR spectroscopy we observed that with ammonia a σ‐adduct at C(5) is formed. The unusual substitution reaction at C(3) is proposed to take place in this σ‐adduct. This new substitution mechanism is discussed.