Pyridazine, 3-chloro-6-hydrazino-, reaction

Hydroxyphthalazin-l(2//)-one is obtained in a smooth reaction between phthalic anhydride and hydrazine hydrate and this is again the starting compound for many 1-substituted and/or 1,4-disubstituted phthalazines. The transformations of 1,4-dichloro-phthalazine, which is prepared in the usual manner, follow a similar pattern as shown for pyridazines in Scheme 110. On the other hand, phthalonitrile is the preferential starting compound for amino- and hydrazino-phthalazines. The most satisfactory synthesis of phthalazine is the reaction between a,a,a, a -tetrachloro-o-xylene and hydrazine sulfate in sulfuric acid (67FRP1438827), alt iough catalytic dehalogenation of 1-chloro- or 1,4-dichloro-phthalazine or oxidation of 1-hydrazinophthalazine also provides the parent compound in moderate yield. 

The unusual formation of N,N-dimethylaminophenyl substituted pyrimido[4,5-c]-pyridazines (74) by the reaction of the oxo compound (73) with phosphorus oxychloride and iV,AT-dimethylaniline has been reported (71CPB1849). The chlorination of other oxo substituted pyrimido[4,5-c]pyridazines with phosphorus oxychloride has been reported to be unsuccessful. Chloro derivatives of this heterocyclic ring undergo nucleophilic displacement with amines and hydrazine to give the corresponding amino and hydrazino substituted products. The catalytic dechlorination of these chloro substituted heterocycles has also been reported (68JHC523). 

The reaction of l-chloro-4-arylpyridazino[4,5-cyclic amines or hydrazine yields l-amino(or hydrazino)-4-arylpyridazino[4,5-d]pyridazines 10 in quantitative yield.29... 

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