Pyridazine 4- methyl-3,6-diphenyl

IV-Methylation of polysubstituted pyridazinones is frequently accompanied by some side reactions, mainly substitutions. For example, methylation of 4-nitro-5,6-diphenyl-pyridazin-3(2//)-one with methyl iodide in the presence of sodium methoxide affords... 

Pyridazin-3(2H)-one, 4-amino-5,6-diphenyl-methylation, 3, 16 Pyridazin-3(2f/)-one, 2-aryl-Mannich reaction, 3, 20 Pyridazin-3(2H)-one, 6-aryl-4,5-dihydro-reaction... 

Reaction of 4 (R = H, Ar = C6H5) with i T-bromosuccinimide or, more cleanly, with. Y-chlorosuccinimide gave 4-methyl-3,6-diphenyl-pyridazine (24, R = CH3).26 Two possible mechanisms for the formation of 24 imply that carbon 5 is extruded in the ring contraction. 

Diaryl-l,2,4,5-tetrazines, when treated with bulky amides such as lithium di-isopropylamide, undergo two competing reactions. In the first, tetrazine is reduced with concomitant formation of an imine from the amide. The imine is then attacked further by amide to give a pyridazine. For example, 3,6-diphenyl-l,2,4,5-tetrazine is converted with lithium diethylamide into 3,6-diphenylpyridazine in low yield. With lithium di-isopropylamide, 4-methyl-3,6-diphenylpyridazine is obtained in moderate yield [83JCS(P1)1601]. 

Similar ring contractions in which the nitrogen-nitrogen bond is cleaved are found in the reductive ring contractions of pyridazines to pyrroles [148, 149], phthalazines to isoindoles [150], 5,6-diphenyl-1,2,4-triazinones to imidazolones [151], benzo-l,2,4-triazines to benzimidazoles [71], benzo-l,2,3-triazinone to indazolone [la, 152], benzo-l,2,3-triazin-3-oxide to indazole [la], benzo-2,3-diazepines to isoquinolines [153], benzo-l-pyrano-[4,3-e ]-as-triazin-3-one to benzopyranoimidazolone [154], and 2-methyl-4,5-dihydropyridazin-3-ones to pyrrolin-2-ones [155]. 

Diphenylcyclopropenone reacts smoothly with a variety of aromatic A-heterocycles and the reaction can be followed by disappearance of the 1850 cm band in the IR. The structures of the products have now been established and the method improved pyridazine and phthalazine give high yields of 2,3-diphenyl-l-hydroxypyrrolo[l,2- )]pyridazine and 2,3-diphenyl-l-hydroxypyrrolo[l,2-ajphthalazine, respectively (Equation (13)), and not the 1,2-diphenyl-3-hydroxy isomers as previously thought. These products can be derivatized as their acetates and methyl ethers without isolation <9lJOC5594>. 

The related substrate, 4-methyl-6-oxo-l-phenyl-l,6-dihydro-3,5-pyridazine-dicarbonitrile (154, R = Ph), and a-benzylidenemalononitrile (153) gave 8-amino-3-oxo-2,6-diphenyl-2,3-dihydro-4,7-cinnolinedicarbonitrile (155, R = Ph) [HN(CH2)s, pyridine, reflux, 4h 75%] analogs likewise. Ethyl 5-cyano-1 -o-methoxyphenyl-4-methyl-6-oxo-1,6-dihydro-3-pyridazinecar-boxylate (157) and diethyl 3-oxoglutarate (156) gave ethyl 4-cyano-6-ethoxycarbonylmethyl-8-hydroxy-2-o-methoxyphenyl-2,3-dihydro-7-cinnoU-necarboxylate (158) (AcOH, dioxane, reflux, 8h 79%) one analog... 

C2 9BrN20s, 5,6-Bis(methoxycarbonyl)-7-p-bromophenyl-3-methyl-4-phenylpyrrolo[ 1, 2-b]pyridazin-2-one, 39B, 207 C2 ftH21NO, 3-Methyl-a,a-diphenyl-1-isoquinolineethanol, 44B, 245 C2 H21N3O2, 1,3-Diphenyl-5-carbethoxymethylene-lH-4,5-dihydro-1,2,4-benzotriazepine, 45B, 286... 

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