Pyrazolin-4,5-diones

The synthesis of 4-azo-3-methyl-l-phenyl-2-pyrazolin-5-one is shown in eq. 176.1144 The 4-hydrazones of 2-pyrazolin-4,5-diones have... 

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. 

Some 1-carbonyl-3-methyl-2-pyrazoline-4,5-dione-4-arylhydrazones are active against Trichinella spiral is. 3 Against microfilarial infections, 2-ethyl-6-methyl-2,3,4,4a,5,6,7,8-octahydro-lH-pyrazino(l,2-c)pyrimidine-l-one seems to be very promising.0,0-Dimethyl-2,2,2-trichloro-l-hydroxyethylphosphonate, a choline esterase inhibitor, immobilizes the adult Onchocerca volvulus and consequently is useful in treating onchocerciasis. 1 8... 

Neither pyrazolidines (9), which have no double bonds, nor pyrazoline diones (10), with two double bonds, and pyrazoUdine triones (11), which have three double bonds, are covered in this article. 

The pyrazoline-dione NOA 407854 is prepared by refluxing aryl-malonamide 21 with oxadiazepane 25 and triethylamine in xylene [85]. 

Three double bonds. The most fully oxidized pyrazoles, the typical non-aromatic representatives of which are the pyrazoline-4,5-diones (1) and the pyrazolidine-3,4,5-triones (2), should be included here. 

Forbisen, 2,2, 3,3 -tetramethyl-l,l -diphenyl-4,4 -bi-3,3 -pyrazoline-5,5 -dione (706) (B-76MI40404), a by-product obtained in the manufacture of antipyrine, has been used in bovine anaplasmosis. 

Although A" -3-keto steroids are inert to diazomethane, Fieser ° observed pyrazoline formation (24) with the more reactive cholest-4-ene-3,6-dione (23). 

Acetoxypregna-5,16-dien-20-one, 211 3/3-Acetoxy-5a-pregnane-l 1,20-dione, 207 3 a-Acetoxy-5/3-pregnane-20-one, 178 3/3-Acetoxypregn-5-en-20-one, 71 3 /3-Acetoxypregn-5-en-20-one-[l 7 a, 16a-c]-A -pyrazoline, 106 3/3-Acetoxy-5a-pregn-9( 1 l)-en-20-one-[17a, 16a-c]-Ai-pyr azoline, 106, 107 17/3-Acetoxy-2,3-seco-5a-androstan-2,3-dioic acid, 409... 

Cycloadditions are in general an effective way of constructing cyclobutane rings. A wide variety of heterocyclic systems dimerize in this way. 1,3-Diacetylindole, for example, affords the head-to-tail dimer 242 on irradiation in ethanol.185 Ethyl 2-ethoxy-l,2-dihydroquinoline-l-carboxy-late is similarly converted in diethyl ether into the trans head-to-head dimer.186 Notable among many analogous photodimerizations are those reported in 1,4-dihydropyridines,187 in furo[3,2-b]pyridin-2(4//)-ones,188 in 8-methyl-s-triazolo[4,3-a]pyridine,189 and in 2H-2-benzazepine-1,3-diones.190 The [ 2 + 2] dimerization of amidopyrine is the first reported example of a photocycloaddition in a 4-pyrazolin-3-one.191... 

Only a limited number of derivatives of this ring system have been reported in literature. The only efficient synthesis utilized azoaroyl-1,2,4-triazines. Thus, condensation of 138 with hydrazines afforded the hydra-zones (139), which give 140 on reflux in acetic acid [85MI2,85PHA(39)504] (Scheme 20). It has been reported that derivatives of 74 were synthesized by cyclization of pyrazoline-4,5-dion-4-isothiosemicarbazones and 4-amidinohydrazones in phenol at 180-200°C (88JPR57). 

Pyrazoline-3,5-diones (68) are thermally or photochemically converted to ketenes [91TL1961],... 

The data in Tables XVI and XVIII reveal a general tendency for the 1,3,4-thiadiazoline tautomer 86B to predominate in the series of 1,3-diketone and 3-oxoaldehyde thiobenzoylhydrazones. The increased stability of the tautomer 86B is attributable to the greater nucleophilicity of the sulfur atom as compared with that of nitrogen, and to the lower strain of the ring containing the sulfur atom. As can be foreseen (see 84ZOR169), pentane-2,4-dione thiophenylacetylhydrazone exists as stable 5-hydroxy-2,4-dimethyl-l-thiophenylacetyl-2-pyrazoline (84ZOR180). 

Bromo-l-methylbenzo[c]pyrazolo[l,2-a]pyrazole-3,9-dione 4-(p-Chlorobenzal)-l,3-diphenyl-2-pyrazolin-5-one... 

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