589. The preparation of some trinitrophenylpyrazoles

Abstract

1-Phenylpyrazole and nitrophenylpyrazoles have been converted into trinitro-compounds by mixed acids a t loo", and the products orientated by synthesis. Some di-and the tri-nitrophenylpyrazoles give colours in the Janovsky reaction.l* NITRATION of l-phenylpyrazole with mixed acids at 100" gives 1-(2 : 4-dinitrophenyl)-4nitropyrazole ; the course of the reaction is indicated by nitration of l-phenylpyrazole at 12" and 22" which gives the intermediates l-p-nitrophenyl-and 4-nitro-l-p-nitrophenylpyrazole, respectively. Nitration of both these compounds a t 100" gives the trinitrocompound, which is also obtained by other nitrations (see Table ).1-(2 : 4-Dinitrophenyl)-4-nitropyrazole was characterised by its reaction with boiling methanolic sodium methoxide to give 4-nitropyrazole and 2 : 4-dinitroanisole. It was synthesised by condensation between 4-nitropyrazole [from pyrazole,* by nitration with mixed acids at 100" (cf. Buchner and F r i ~c h , ~ and Huttel et aZ.6)] and l-chloro-2 : 4-dinitrobenzene in ethanolic potassium hydroxide. Nitration of l-m-nitrophenyl-and 4-nitro-1-m-nitrophenyl-pyrazole with mixed acids at 100" gives 1 -(3 : 4-dinitrophenyl)-4-nitropyrazole, the orientation of which was established as follows. One nitro-group underwent nucleophilic replacement in ethanolic ammonia at loo", to give an amine which, on deamination, gave 4-nitro-l-~-nitrophenylpyrazole, the presence of a 9-nitro-group in the trinitro-compound being thus established. This trinitro-compound was synthesised as follows : Partial reduction of 4-nitro-l-p-nitrophenylpyrazole with ammonium hydrogen sulphide gave l-~-aminophenyl-4-nitropyrazole (the structure being shown by deamination

Pyrazolo[3,4-b]pyridines: Syntheses, reactions, and nuclear magnetic resonance spectra

“…1 b). 2,4-Dinitrophenyl moieties attached to N-1 or N-2 of an azole species are easily displaced by nucleophiles such as methoxide or ethoxide ions (40,41), and this strategy allows circumvention of the undesirable cyclizations of 5(3)-aminopyrazoles to pyrazolo[l,5-alpyrimidines. In this way the products 4 and 52 are obtained from the corresponding 1-(2,4-dinitrophenyl) precursors.…”

“…Exceptionally, cyclizations occur preferentially at C-4, not N-1, for reactions using sodium nitromalonaldehyde; these reactions may also be effected under basic conditions. We also applied the Gould-Jacobs method (34), in which 5-aminopyrazoles reacted with diethyl ethoxymethylenemalonate, ethyl ethoxymethylenecyanoacetate, or ethyl ethoxymethyleneacetoacetate, followed by thermal cyclization in phenyl ether or Dowtherm A to provide the pyrazolo[3,4-blpyrid-4-ones (4-hydroxy pyrazolo[3,4-blpyridines) [37][38][39][40][41][42][43][44] (see Scheme 2).…”

Reactions of Phenyl-Substituted Heterocyclic Compounds: Iii. Free-Radical Phenylation of 1-Phenylpyrazole

“…Khan et al (2))). The latter two biphenylylpyrazoles were also synthesized using the standard cyclization of the appropriate substituted hydrazine and 1,1,3,3-tetramethoxypropane (11). Attempted cyclization using o-hydrazinobiphenyl gave carbazole and biphenyb, with no evidence for the formation of 1-o-biphenylylpyrazole: this reaction, which is reminiscent of a Fischer indole cyclization, is under further study.…”

Synthesis of some 1-aryl-3,5-disubstituted-pyrazoles by N-arylation of 3,5-disubstituted-pyrazoles with 4-fluoro and 2-fluoronitrobenzene under microwave irradiation and classical heating

“…1 Moreover and according to some authors, this condensation leads to the formation of the undesired isomer as a major component. [2][3][4] Thereafter, direct substitution of N-nonsubstituted pyrazoles under previous reported conditions [5][6][7][8] such as K 2 CO 3 /DMF, K 2 CO 3 /DMSO, KOH/Bu 4 NBr, KOtBu and NaH/THF provide another powerful method for synthesis of N-arylpyrazoles. However, the reaction generally gives also a mixture of two regioisomers since pyrazole is an ambident nucleophile.…”