3-Methyl-5-aryl-4 -pyridazinones

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>. 

Pd-catalyzed coupling reactions at the 5-position of 6-phenyl-3(2W)-pyridazinones using a retro-ene transformation have been reported <02SL2062>, and the Pd-catalyzed arylation of 4-bromo-6-chloro-3-phenylpyridazine has been shown to be efficient and regioselective <02SL223>. The N-methylation of substituted 3(2//)-pyridazinones with Ai,iV-dimethylformamide dimethylacetal has been explored <02SC1675>, as have the preparation of 3-nitro-, -nitroso- and -chloro-derivatives of... 

Other 1,2-diazines synthesized included 4-amino-3-cinnolinecarboxylic acids <97PHA91 >, I -aryl-6-chloro-l,4-dihydro-4-oxothieno[2,3-c]pyridazine-3-carboxylic acids <97JPR284>, 2H-benzo[2,3-g]pyridazino[4,5-<7,e]quinolin-3-ones <97M681>, 3-chloro-4-carbamoyl-5-aryl-6-methylpyridazine N-oxides <97F67>, 2-aroyl-6-(hetero substituted)-3(2//)-pyridazinones <97HCM267>, and 5-(4-hydroxycinnolin-3-yl)tetrazoles 2-methyl-5-(4-acetoxycinnolin-3-yl)-... 

Ethyl l-aryl-4-methyl-6-oxo-5-cyanopyridazine-3-carboxylate 221 was synthesized from ethyl 2-arylhydrazono-3-oxobutanoate 220 and ethyl cyanoacetate in acetic acid in the presence of ammonium acetate (1986H(24)1219, 1989T3597, 1988LA1005). Gewald and Hain (1984S62) could prepare these same pyridazinones 221 by condensing ethyl acetoacetate and malononitrile and subsequently coupling 224. However,... 

Suzuki coupling reactions where also achieved on substrates that lead to 4-aryl-5-phenylethynyl- and 5-aryl-4-phenylethynyl-2-methyl-3(2H)-pyridazinones, in excellent yields (Equations 79 and 80, respectively) [112]. 

---