Pyridazine, tetrachloro

Pyridazine, perfluoro-3,5-diisopropyl-photolysis, 7, 283 Pyridazine, tetrachloro-nucleophilic substitution, 3, 26 Pyridazine, tetrafluoro-nucleophilic substitution, 3, 26 Pyridazine, tetrahydro-, 3, 39-Uo Pyridazine, 3,4,5,6-tetrahydro-... 

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 base-catalyzed cyclization of ethyl 3-[alkyl(4-cyanopyridazin-3-yl)amino]propanoates gives ethyl 8-alkyl-5-amino-7,8-dihydropyridazine-6-carboxylates 1, which by acidic hydrolysis were converted to the corresponding ends 2. Due to their air sensitivity, ends 2 are partly converted into ethyl 8-alkyl-5-oxo-5,8-dihydiopyiido[2,3-c]pyridazine-6-carboxylates 3. To avoid mixtures, the oxidation is completed by treatment with tetrachloro-l,2-benzoquinone (o-chloranil).20... 

When chlorinated with an excess of phosphorus pentachloridc, 5,8-dichloropyrido[2,3-rf]pyridazine affords, dependent on the reaction temperature and time, the corresponding 3,5,8-trichloro, 2,3,5,8-tetrachloro or2,3,4,5,8-pentachloro derivatives 3, 4, and 5, respectively. The facility of introduction of a chloro substituent into the pyridine part decreases thus in the order position 3 > 2 > 4.8 7... 

In 2,3,5,8-tetrachloro- or 2,3,4,5,8-pentachloropyrido[2,3-t/]pyridazine all chloro substituents except that in position 3 can be exchanged for methoxy groups by refluxing in methanolic sodium methoxide to give the 3-chloro-2.5,8-trimethoxy and 3-chloro-2,4,5,8-te-tramethoxy compounds in low yield.87... 

Chlorine substituents are introduced into l,4-dichloropyrido[3,4-fi ]pyridazine by heating in a sealed tube with excess phosphorus pentachloride at increasing temperature to give the 1,4,8-trichloro 3 (150 °C, 3 h, 81 %), 1,4,7,8-tetrachloro 4 (250°C, 3 h, 59%) or 1,4,5,7,8-pentachloro 5 (270-280 °C, 3 h, 50%) derivatives thus revealing a position 8 then 7 then 5 sequence of substitution.87... 

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