4-Bromo-3-pyrazolin-5-ones

Extremely good yields have been reported in these halogenations.1605 4-Alkyl-2-pyrazohn-5-ones react with halogens readily, but even with an excess only monohalogenated products have been obtained.1605 Smith and co-workers1309 have found that l,3-dimethyl-2-pyrazolin-5-one reacts with bromine to give both the expected 4-bromo product and also l-bromo-3-methyl-2-pyrazolin-5-one. This same compound was obtained by bromination of 3-methyl-2-pyrazolin-5-one with A-bromo-succinimide.1309 4-Bromo-2-pyrazolin-5-ones have been prepared by bromination of 2-nitroso-3-pyrazolin-5-ones1209 (eq. 205) with... 

The reaction has proceeded satisfactorily with one or two benzoyl groups present,153,507 but a benzoyl group in position 1 has also been eliminated.153 The oxidation proceeds similarly when position 4 is substituted.608 Pyrazoline itself and monoalkyl- and monoaryl-pyrazolines give the corresponding pyrazoles only in small yield on oxidation with bromine.509,510 In the majority of cases bromination occurs together with oxidation, and often brominated products are the only ones isolated. Thus 1,3,5-triphenylpyrazoline yields a tribromide of unknown constitution.49 The hydro bromide of 4-bromopyrazole (43) was obtained almost quantitatively from 3-butoxy-J1-pyrazoline (42).611A mixture of 1,5-dimethylpyrazole and the 4-bromo compound... 

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

PyrazoUne-5-ones. Treatment of 2-bromo-l,3-diphenyl-l,3-propanedione (1) with methylhydrazine in ethanol at room temperature gives l-methyl-3,4-diphenyl-A -pyrazoline-5-one (2) in 56% yield. It is probably formed by a halohydrin rearrangement as indicated. 

Only two halogenated bis(2-pyrazolin-5-ones) have been reported (Table VI). One of these is prepared by bromination of 4,4 -methylidyne-bis(3-methyl-l-phenyl-2-pyrazolin-5-one) with bromine to give the 4-bromo analog.1682 In the second case1109 bromine is added to a diolefinic system connecting two 2-pyrazolin-5-one rings. 

As is the case with 2-pyrazolin-5-ones, direct bromination of 3-pyrazolin-5-ones can be used to prepare the 4-bromo derivatives. This bromination is not complicated by substitution of a second bromine at the same carbon atom, but further bromination occurs to give 3-pyrazolin-5-ones containing two or three atoms of bromine. In spite of considerable investigation of these polybrominated 3-pyrazolin-5-ones, their structures have not been conclusively established and several... 

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. 

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