2-Aryl-3-methyl-3-pyrazolin-5-ones

Lecher, Parker and Conn885 report that the cyclization of the hydrazone hydrazide, as in eq. 106, is the preferred synthesis for 2-aryl-3-methyl-3-pyrazolin-5-ones. 

Only half-a-dozen of these compounds are known (Table XLI) and at least this number of methods of preparing them have been reported. Borsche and Manteuffel125 have found that 2-pyrazolin-4,5-diones are formed as the by-products when oc-ketoesters are treated with aryl-diazonium salts. The principal products are 4-arylazo-2-pyrazolin-5-ones. Nitric acid oxidation of 3-methyl-l-phenyl-2-pyrazolin-5-one forms the corresponding 4,5-dione.809 Wislicenus and Gtiz1842 heated 4 -bromo - 4 - nitro -1 - (4 - bromophenyl) - 3 - methyl - 2 -pyrazolin - 5 - one in water and obtained the analogous 4-oxo compound. Acid hydrolysis of rubazonic acids, which are 4-imino-2-pyrazolin-5-ones, leads to 2-pyrazolin-4,5-diones.424 809 Oxidation of 4,4 -bis(2-pyrazolin-5-ones) or of rubazonic acids with nitric acid809 forms the 4,5-diones. 

Aminoethyl)-l,2,4-oxadiazoles (606 R = alkyl or aryl) readily isomerize to 3-acylamino-2-pyrazolines (607) on heating. Treatment of the salt (608) with triethylamine yields the transient ylide (609), which decomposes to methyl-phenylcarbodi-imide (610). 2,3-Diphenyl-l,2,4-oxadiazolin-5-one (611) rearranges photochemically to a mixture of the oxadiazolinones (612) and (613) pyrolysis gives 2-phenylbenzimidazole with extrusion of carbon dioxide. The oxadiazole (614) rearranges thermally to the indazole (615). ... 

Cyclocondensation of 3-methyl-l-(5-substituted-3-phenyl-lH-indol-2-ylcarbonyl)-5-(4fi)-pyrazolones with arylidene derivatives of malononitrile using a catalytic amount of triethylamine in refluxing ethanol affords heterocycle [ ]-fused 6-amino-4-aryl-5-cyano-4H-pyrans (14JHC303). Other fused 6-amino-4-aryl derivatives arise from the three-component reaction of benzaldehydes, active methylene compounds (malononitrile/ ethyl cyanoacetate) and 1,3-dicarbonyl compounds catalyzed by 1,8-diaz-abicyclo[5.4.0]undec-7-ene (DBU) in refluxing water (14JHC618). Similar pyrazole[f)]-fused derivatives are obtained from the reaction of benzaldehydes, malonitrile, and 3-substituted-2-pyrazolin-5-ones using sodium... 

M. N. Ehnson, A. S. Dorofeev, R. F. NasybuHin, S. K. Feducovich, G. I. Nikishin, ElectrochirtL Acta 2008, 53, 5033-5038. Electrocatalytic tandem Knoevenagel-Michael reaction of 3-methyl-2-pyrazolin-5-ones, aryl aldehydes and cyano-functionalized C-H acids facile and convenient multicomponent way to substituted 3-(5-hydroxy-3-methylpyrazol-4-yl)-3 - ary Ipropionitriles. 

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