Pyridazines, hydroxylamino

The reactivity of halogens in pyridazine N- oxides towards nucleophilic substitution is in the order 5 > 3 > 6 > 4. This is supported by kinetic studies of the reaction between the corresponding chloropyridazine 1-oxides and piperidine. In general, the chlorine atoms in pyridazine A-oxides undergo replacement with alkoxy, aryloxy, piperidino, hydrazino, azido, hydroxylamino, mercapto, alkylmercapto, methylsulfonyl and other groups. 

Reaction of halopyridazines with hydroxylamine to give hydroxyla-minopyridazine has been achieved only with activated compounds [79H(12)1157, 79JHC861], This has been ascribed to the low nucleo-philicity of hydroxylamine when compared to that of amines or hydrazines. A 3-hydroxylamino group reacted with bromoacetaldehyde at room temperature to give the first example of an imidazo[l,2-ft]pyridazine 1-oxide (8IT1787). 

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