Recyclization with double heterocyclization on formylation of the hydrazone, 2-phenacyl-1H-benzimidazole

Dzvinchuk, I. B.; Vypirailenko, A. V.; Lozinskii, M. O.

doi:10.1007/bf02253177

Cited by 2 publications

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“…The 1 H NMR spectra of the compounds were recorded on a Varian VXR-300 instrument (300 MHz) using DMSO-d 6 and TMS as internal standard. For investigation of the pyrazole tautomerism a 0.1 M solution of the type 3 pyrazole in DMSO-d 6 was recorded twice at 3 and 24 h from the moment of preparation as a monitor of the achievement of equilibrium.…”

Section: Methodsmentioning

confidence: 99%

“…The IR spectra of compounds 6a,b were recorded on a UR-20 instrument for KBr tablets. The starting materials were prepared by known methods: 1 [10], 5 [6], 7a-i [5, 11[, and 9 [12]. Before determination of elemental composition and spectroscopic properties the synthesized compounds were dried for 7 h in a water pump vacuum desiccator at 115°C.…”

Section: Methodsmentioning

confidence: 99%

“…None the less the synthetic method we have developed for type 3 pyrazoles is quite efficient and likely to have a broader applicability. In particular it was found that 2-phenacylbenzimidazole methylhydrazone 9 also readily gives the 1-methyl-3-phenyl-substituted pyrazole 10 which has an obvious structural similarity to tautomer 3a and was used by us as a model compound for studying the tautomerism of type 3 compounds in DMSO-d 6 .…”

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confidence: 99%

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confidence: 97%

“…The result of the reaction is unexpected. However, the structure of the product is not in doubt because we had obtained it before by refluxing 2-phenacylbenzimidazole hydrazone 5 in DMF [6]. We have also investigated the report in [7] of a method of synthesis of pyrazoles based on the reaction of 2-phenacylazaheterocycle hydrazones with carboxylic anhydrides.…”

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Synthesis and tautomerism of 2-[3(5)-aryl(methyl)pyrazol-4-yl]-1-benzimidazoles

Dzvinchuk

Lozinskii

2006

Chem Heterocycl Compd

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An efficient method has been developed for the synthesis of 2-[3(5)-aryl(methyl)pyrazol-4-yl]-1H-benzimidazoles by cyclocondensation of 2-acylmethyl-1H-benzimidazoles benzoylhydrazones with DMFdimethylacetal. The tautomerism of the compounds obtained via migrations of a proton between the pyrazole nitrogen atoms has been studied by 1 H NMR. The more stable tautomers have electron acceptor aryl substituents placed at position 3 of the pyrazole ring and electron donor aryl substituents or a methyl at position 5.The tautomerism of pyrazole compounds due to the migrations of a proton between the nitrogen ring atoms has been systematically studied [1-3] since it depends unpredictable of the nature and position of the ring substituent. It influences the selectivity of a series of chemical reactions and has to be taken into account when determining the structure and chemical purity of the corresponding substrates by spectroscopic methods. The effect on it of the electronic effects of the two aryl substituents at positions 3 (or 5) and 4 of the heterocycle has not been studied up to this time. It is possible that such a situation is due to the absence of samples and methods suitable for carrying out a reliable investigation. Thus, starting from 2-phenacylbenzimidazole 1 via its formylation product 2 and subsequent reaction with hydrazine, we have obtained the pyrazole 3a which, according to 1 H NMR data exists in solution in equilibrium with its tautomeric form 3'a [4]. The signals of the pyrazole ring aromatic proton for both tautomers are seen separately and would seem suitable and unproblematic for qualitative and quantitative determination of the composition of the equilibrium. However, the hoped for assignment of signals to a specific tautomer is complicated by the lack of a sample for comparison. In addition, the method itself is limited for the preparation of a broad series of compounds for a number of reasons, in particular the poor selectivity in the final stage reaction. Hence we set ourselves the task of overcoming the problem by preparing a series of compounds of type 3 and studying their tautomeric behaviour.Routes for an efficient synthetic method were not obvious and we therefore chose a method of trial and error in the reactions of 2-phenacylbenzimidazole 1 and its hydrazones. Hence we tried a possible synthetic route analogous to the known method of preparing 2-(4-pyrazolyl)benzimidazoles [5] based on the cyclocondensation of compound 1 with aroylhydrazines. However, the corresponding reaction with formylhydrazine occurs to give a mixture of products, from which we isolated only 1-(3-pyrazolyl)-benzimidazole 4. The result of the reaction is unexpected. However, the structure of the product is not in doubt because we had obtained it before by refluxing 2-phenacylbenzimidazole hydrazone 5 in DMF [6].

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: ____________________________________________________________mentioning

confidence: 99%

mentioning

confidence: 97%

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confidence: 99%

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Synthesis and tautomerism of 2-[3(5)-aryl(methyl)pyrazol-4-yl]-1-benzimidazoles

Dzvinchuk

Lozinskii

2006

Chem Heterocycl Compd

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Synthesis and isomerism of 2-(3,5-diaryl-1H-pyrazol-4-yl)-1H-benzimidazoles

Dzvinchuk

Туров

Lozinskii

2009

Chem Heterocycl Comp

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mechanism and the isomerism of the obtained products are discussed. According to the data of 1 H NMR spectroscopy the stabilized isomer is that in which the electron-withdrawing aryl substituent is located in position 3 and the electron-donating substituent in position 5 of the pyrazole ring.It was found previously [1] that acylhydrazones of β-dicarbonyl compounds are cyclized into pyrazoles as a result of condensation of the carbonyl group of the acylhydrazone fragment and an activated methylene group, when a methyl or phenyl substituent is present on the nitrogen atom next to the carbonyl group of the hydrazone fragment. Later [2] we showed that aroylhydrazones of 2-phenacyl-1H-benzimidazole in the absence of such substituents also undergo an analogous cyclocondensation with the formation of 2-(3-aryl-5-phenyl-1H-pyrazol-4-yl)-1H-benzimidazoles on heating to 200 o C. In this case it is possible to combine the preparation of the hydrazones and their cyclocondensation in one process, however the reaction proceeds only with benzoylhydrazine and with its derivatives containing electron-withdrawing substituents in the benzene ring. Up to the present time we have produced new experimental data which indicate the broader possibilities of this reaction and enable elucidation of its mechanism.We have found that the interaction of a series of 2-phenacyl-1H-benzimidazoles 1a-e with 4-nitrobenzoylhydrazine 2a, proceeding through hydrazones 3a-e and their subsequent cyclocondensation, leads to 2-[5-aryl-3-(4-nitrophenyl)-1H-pyrazol-4-yl]-1H-benzimidazoles 4a-e. Derivatives 4a,c,d with various aryl substituents in positions 3 and 5 of the pyrazole ring therefore exist in DMSO-d 6 solution in equilibrium with the tautomeric forms 4'a,c,d.The reaction occurs smoothly on heating in DMSO at 150 o C for 1 h with triethylamine hydrochloride as catalyst.4-Methoxybenzoylhydrazine 2b, the electrophilicity of the carbonyl group of which is reduced due to the electron-donating effect of the MeO group, reacts under more rigid conditions. The interaction of reactants 1a and 2b occurs at 200 o C, in the presence of a small amount of diglyme preventing crystallization of

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Recyclization with double heterocyclization on formylation of the hydrazone, 2-phenacyl-1H-benzimidazole

Cited by 2 publications

References 1 publication

Synthesis and tautomerism of 2-[3(5)-aryl(methyl)pyrazol-4-yl]-1-benzimidazoles

Synthesis and tautomerism of 2-[3(5)-aryl(methyl)pyrazol-4-yl]-1-benzimidazoles

Synthesis and isomerism of 2-(3,5-diaryl-1H-pyrazol-4-yl)-1H-benzimidazoles

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