2-Phenyl-6-hydroxy-3 -pyridazinone

Reaction of the 2-acetoxy-3(2//)-furanones (526) with monosubstituted hydrazines gives good yields of the pyridazinium-5-olates (527) together with varying amounts of isomeric products. Alkyl derivatives (527 R = alkyl) have also been prepared by base-catalyzed alkylation (Mel, Me2SO4, PhCH2Cl) of 3-methyl-6-phenyl-5-ethoxycarbonyl-4( 1 //)-pyridazinone. Reduction of the diphenyl compound 527 (R = Ar = Ph) by zinc and hydrochloric acid gives 3-ethoxycarbonyl-5-hydroxy-5-methyl-l,2-diphenyl-2-pyrrolin-4-one (528 R = Ar = Ph) (Scheme 21... 

SYNS AMERICAN CYANAMID 12,503 CL 12503 0,0-DIETHYL0-(2,3-DIHYDR0-3-0X0-2-PHENYL-6-PYRIDAZINYL)PHOSPHOROTHIOATE 0,0-DIETHYLPHOSPHOROTHIOATE, O-ESTER mth 6-HYDROXY-2-PHEN L-3(2H)-PYRIDAZINONE 0-(l,6)-PIHYDRO-6-OXO-1-PHENYLPYRIDAZIN-3-YL), 0,0-DIETHYLPHOSPHOROTHIOATE ENT 23,968 OFNACK OFUNACK PYRIDAFENTHION... 

O.O-DIETHYLPHOSPHOROTHIOATE, O-ESTER with 6-HYDROXY-2-PHENYL-3(2H)-PYRIDAZINONE see POPOOO... 

Direct chlorination of 2-phenyl-6-hydroxy-3(2//)-pyridazinone (50) in polar solvents (DMF, acetic acid) resulted in chlorination of the phenyl ring and rearrangement of the pyridazinone to give the trichlorophenylaminopyrrole-2,5-dione (51) as the major product the dichlorophenyl-aminopyrrole-2,5-dione (52, Scheme 7) was isolated as an intermediate. It is proposed that the pyridazinone is less stable after dichlorination of the phenyl ring and rearranges to the A -amino-maleimide (52), but the reasons for this are unclear <89JHC1649>. 

The synthesis of pyridazine derivatives from hydrazones includes the thermal cyclization of 2-arylhydrazono-3-oxo-5-phenyl-4-pentenenitriles (readily obtained from ethyl cinnamate by condensation with acetonitrile followed by Japp-Klingemann type reactions) to l-aryl-3-cyano-6-phenyl-5,6-dihydro-4(l//)-pyridazinones (Scheme 85) <86JHC93>, and base-induced cyclization of a hydrazone of a 4-chloro-l-arylbutan-l-one to prepare a 2,3,4,5-tetrahydropyridazine (Scheme 85) <88JHC1543>. An earlier route to 6-carboxy-5-hydroxy-2-phenyl-3(2//)-pyridazinone via condensation of benzenediazonium chloride and dimethyl acetonedicarboxylate has been adapted to give a series of aryl derivatives either as esters (by thermal cyclization) or as acids (by cyclization with hydroxide). Both cyclizations proceed in high overall yield (Scheme 86) and decarboxylation of the acids also proceeds in high yield <89JHC169>. 

A mixture of 4.0 g. 1-phenyl-4,5-dichloro-6(lH)-pyridazinone and 5%-NaOH heated 5 hrs. at 130° 2.2 g. l-phenyl-3-hydroxy-5-pyrazolecarboxylic acid. Y. Maki and K. Obata, Ghem. Pharm. Bull. 12, 176 (1964). 

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