Formation of benzo rings

The annelation of benzo rings on pyridazines was covered in CHEC-II(1996) 1996CHEC-II(6)1 . Maes and Matyus reported new examples in their synthesis of the dibenzo[// ]phthalazin-l(27r)-one and dibenzo[//]cinnolin-3(27/)-one skeleton. Palladium-catalyzed intramolecular arylation of 2-benzyl-5-(2-bromophenyl)-4-phenylpyridazin-3(2//)-one yielded 2-benzyldibenzo[/,4]phthalazin-l(2//)-one. The synthesis of this new tetracyclic pyridazinone from 2-benzyl-5-(2-aminophenyl) -phenylpyridazin-3(2//)-one via a Pschorr-type reaction was also investigated. Similarly, the con-stmction of 2-methyldibenzo[/, ]cinnolin-3(2//)-one from 2-methyl-5-(2-bromophenyl)-6-phenylpyridazin-3(27T)-one and 2-methyl-5-(2-aminophenyl)-6-phenyl-pyridazin-3(2//)-one was performed 2003T5919 . 

Methodology used for the synthesis of polycyclic aromatic compounds can be applied to the annelation of benzene rings on to (benzo)pyridazines. For example 6,9-difluorobenzo[ ]phthalazine- 

10-dione has been prepared by an intramolecular acylation reaction under vigorous conditions in oleum (Equation (34)). The intermediate aroylpyridazinecarboxylic acid is made from 4,5-pyridazinecarboxylic anhydride and an aryllithium reagent 93JHC1597 . 

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