2- Aryl-4.5-dichloro-3 -pyridazinones

Many (benzo)pyridazines are made from 1,4-diketo compounds, and the industrial supply of, for example, maleic and phthalic anhydrides and mucohalic acids make them attractive and widely used starting materials, which can be used in conjunction with substituted hydrazines to give a range of A-substituted derivatives. Some other 1,4-diketo compounds are commercially available on a smaller scale, including, for example, certain 3-benzoylpropionic acids from which 6-aryl-4,5-dihydro-3(2//)-pyridazinones can be prepared. When such precursors are not commercially available then ease and scope of synthetic approaches to the starting materials must be considered, but for established routes, such as 6-aryl-4,5-dihydro-3(2//)-pyridazinones from 3-aroylpropionic acids, a variety of synthetic methods have been developed so that a wide range of (substituted)aroyl derivatives can be prepared. Synthetically useful preformed (benzo)pyridazine derivatives that are commercially available include 4,5-dichloro-3(2F/)-pyridazinone, 3,6-dichloropyridazine, and 1,4-dichlorophthalazine. 

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