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Reactions with Heterocyclic Diazonium Salts, II Synthesis of Some New Pyrazolo[L,5-C]-As-Triazines and L,2,4-Triazolo[L,5-C] -As-Triazines

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Reactions with Heterocyclic Diazonium Salts, II Synthesis of Some New Pyrazolo[L,5-C]-As-Triazines and L,2,4-Triazolo[L,5-C] -As-Triazines Reactions with Heterocyclic Diazonium Salts, II Synthesis of Some New Pyrazolo[l,5-c]-as-triazines and l,2,4-Triazolo[l,5-c] -as-triazines Mohamed Hilmy Elnagdi, Mohamed Rifaat Hamza Elmoghayar, Shereif Mahmoud Fahmy, Mohamed Kamal Ahmed Ibraheim, and Hikmat Hussein Alnima Department of Chemistry, Faculty of Science, Cairo University, Giza, A. R. Egypt Z. Naturforsch. 88b, 216-219 (1978); received July 29/November 22, 1977 Heterocyclic Diazonium Salts, Pyrazolo[l,5-c]-as-triazines 3-Phenylpvrazole-5-diazonium chloride (2) couples with benzoylacetonitrile and with phenacylthiocyanate to yield the corresponding hydrazone derivatives 3 a, b. Whereas 3 a cyclised into the pyrazolo[l,5-c]-as-triazine derivative (4a) upon treatment with concen- trated sulphuric acid via elimination of water, treatment of 3 b with the same reagent under the same conditions has resulted in elimination of thiocyanic acid and the formation of the pyrazolo[l,5-c]-as-triazine derivative (4b). Treatment of 2 with aqueous sodium acetate has afforded the corresponding 3-phenyl- 5-diazopyrazole (6). The latter reacted readily with dipolarophiles to yield pyrazolo- [l,5-c]-as-triazine derivatives. Pyrazolo[l,5-c]-as-triazines has also been formed upon treatment of 6 with active methylene compounds. The mechanism of reaction of 2 and 6 with active methylene compounds is discussed. Diazotization of 5-amino-3-ethyl-l,2,4-triazole nitrate (7) has afforded the correspond- ing diazonium derivative which coupled with benzoylacetonitrile and with acetoacet- anilide to yield the corresponding hydrazones 9 a, b. The latter could be cyclised into l,2,4-triazolo[l,5-c]-as-triazines by the action of concentrated sulphuric acid. Diazotized 1 H-aminoazoles are versatile reagents cyclization of the coupling products of aryl- and their synthetic potentialities has received con- diazonium salts with phenacylthiocyanate [13]. siderable recent attention [1-5]. As a part of our Compound 3 a readily cyclised into the pyrazolo- program directed for development of new procedures [l,5-a]-as-triazine derivative (4a) upon treatment for the synthesis of bridge-head azoles [6-12] we with concentrated sulphuric acid. On the other have previously [6, 11] reported the synthesis of a hand, when 3 b was similarly treated, compound 4 b, variety of pyrazolo[l,5-c]-as-triazines and pyrazolo- the structure of which was inferred from analytical [l,5-c]-l,2,4-triazoles based on the coupling reaction and spectral data, was formed. The formation of 4b of 3-phenylpyrazole-5-diazonium chloride with from 3 b and concentrated sulphuric acid might be active methylene compounds. In continuation of assumed to proceed via initial elimination of thio- this work we report here the results of our further cyanic acid leading to the formation of a resonance investigation on the reaction of diazotized 1H- stablised nitrile imine intermediate which cyclises aminoazoles. The work has resulted, in addition to then to afford the final reaction products (c/. synthesis of several new pyrazolo[l,5-c]-as-triazines Chart 1). in clarification of the mechanistic pathways for Previously we have reported [11] that 2 reacts reaction of diazotized 5-aminopyrazoles with active with acrylonitrile, ethyl acrylate and with dimethyl methylene compounds. Thus, diazotization of acetylene-dicarboxylate to yield the pyrazolo[l,5-c]- 5-amino-3-phenylpyrazole (1) has afforded 3-phenyl - as-triazine derivatives 5a, b and 4c, respectively. pyrazole-5-diazonium chloride (2) which coupled Intermediacy of 3-phenyl-5-diazopyrazole (6) has with benzoylacetonitrile and with phenacylthio- been suggested to account for the formation of cyanate to yield the corresponding hydrazon these products. Now, we would like to report the derivatives 3 a, b, respectively. The isolation of 3 b isolation of 6 as well as its reactions with dipolaro- from reaction of 2 and phenacylthiocyanate is philes [13]. Thus, when 2 was treated with aqueous incontrast to the recently reported spontaneous sodium acetate solution it was converted almost quantitatively into the diazobetaien 6. The latter Requests for reprints should be sent to Dr. M. H. was stable at room temperature but exploded when Elnagdi, Department of Chemistry Faculty of Science, Cairo University, Giza, A. R. Egypt. heated at 145 °C. Compound 6 decomposed on Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung This work has been digitalized and published in 2013 by Verlag Zeitschrift in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der für Naturforschung in cooperation with the Max Planck Society for the Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Advancement of Science under a Creative Commons Attribution Creative Commons Namensnennung 4.0 Lizenz. 4.0 International License. M. H. Elnagdi et al. • Reactions with Heterocyclic Diazonium Salts 217 boiling in ethanol or in benzene. The nature of the direct formation of 4f. This result clearly indicate decomposition products will be a subject for a that the accepted assumption [15] that the acid separate comunication. When compound 6 was eliminated during the coupling reaction is respon- treated with acrylonitrile ethyl acrylate or with sible, by catalysing cyclisation of a hypothetically dimethyl acetylenedicarboxylate, products identical formed hydrazones, for the inability of several in all aspects with those previously formed on authors to isolate acyclic intermediates for the treatment of 2 with the same reagents were formed coupling reaction of diazotized 1 H-aminoazoles in excellent yields. Compound 6 readily added less with certain active methylene compounds. It seems reactive dipolarophiles namely chalcone and methyl to us most probable that the formation of cyclic or cinnamate to yield the pyrazolo[l,5-c]-as-triazine acyclic products from the coupling reaction with derivatives 5 c, d, respectively. active methylene compounds with diazotized Compound 6 reacted with benzoylacetonitrile, aminoazoles is determined by the mechanistic ethyl acetoacetate, 3-iminobutyronitrile, ethyl pathway for the reaction. Thus, reagents affording cyanoacetate and with malononitrile to yield the directly cyclic products react, most likely, with the pyrazolo[l,5-c]-as-triazine derivatives 4a, d-g. Un- diazonium compound, which under the coupling der similar conditions compound 6 failed to react condition is expected to exist in equilibrium with with phenacylthiocyanate. the diazobetaiene, via a 1,3-dipolarcyclo addition. On the other hand, the formation of hydrazones * results from a usual coupling reaction. NH2 N=N NH.N=C ^ NaN02 Cl" PhC0CH2X In order to gain further information of the ,NH VNH CO RF HCl PTV Ph Ph mechanism of coupling of diazotized 5-amino- 3a : X = CN pyrazoles with active methylene compounds a re- 3b: X = SCN | NaN02 investigation of the behavior of 2 toward a variety of active methylene compounds was undertaken. It has been found that 2 reacts with ethyl acetoacetate RCH=CHX sQt- and with 3-iminobutyronitrile under a variety of Ph' basic, neutral and acidic conditions to yield 4a,d-g pyrazolo[l,5-c]-as-triazine derivatives (4d, e). The R = H , X = CN N=N R =H , X = C02C2H5 same products were obtained on treatment of 6 R = Ph, X = COPh Ph with the same reagents in ethanolic solutions. On R=Ph, X = C02CH3 the other hand, benzoylacetonitrile, ethyl cyano- C-C02C2H5 acetate and malononitrile afforded the respective C-CO2C2H5 Ph hydrazones when the coupling reaction was per- 4c formed in faintly acidic medium. In neutral and in basic media the cyclic pyrazolo[l,5-c]-as-triazines 4a: R=Ph , X=CN (4 a, f, g) were the only isolable reaction products. 4b R= Ph , X= H Compounds 4 a, f, g were also formed from the 4c R = X = C02CH3 4d R = CH3,X= CO2C2H5 reaction of 6 with the same reagents in ethanolic 4e R= CH3, X= CN solutions. Phenacylthiocyanate did not react with 2 R = NH2, x = C02C2H5 4f; in basic or in neutral media. However in acidic 4 g • R = NH2,X = CN solutions the acyclic hydrazones 3 b was the only In an attempt to prepare authentic speciment of obtainable product. These results are in good 4f via cyclization of the hydrazone 7, recently agreement with the suggested mechanism of reac- synthesised via coupling of 2 with ethyl cyano- tion of 2 with active methylene compounds. acetate, it has been found that the latter (7) is only As an extention of our work an investigation of formed when the coupling is performed in presence the behavior of 5-amino-3-ethyl-l,2,4-triazole (8) on of an excess of acetic acid as has been described for diazotization was undertaken. Similar to literature its synthesis. Coupling of 2 and ethyl cyanoacetate attempted diazotization of 8 in the presence of in less acidic media using the experimental procedure hydrochloric acid resulted in the formation of the recently reported by us [11] has resulted in the corresponding chloro derivative 9. On the other 218 M. H. Elnagdi et al. • Reactions with Heterocyclic Diazonium Salts 218 hand, diazotization of 8 in the presence of nitric stirring to this solution. The reaction mixture was acid has generated the corresponding diazonium kept at room temperature for two hours and the salt in solution. Although attempted isolation of the solid product, so formed, was collected by filtration. Recrystallisazion from ethanol afforded analytically latter has resulted in its decomposition, evidence pure sample of 3a as brown crystals, m.p. 235 °C, for the formation of the diazonium salt was obtained yield 80%. IR: 1640 cm-1 (conjugated CO), via coupling with benzoylacetonitrile and with 2220 cm-1 (conjugated CN) and3300-3380 cm-1 (NH). acetoacetanilide to yield the corresponding hydra- Ci8H13ON3 zones 10 a, b. Attempted coupling of ethylaceto- Found C 68.69 H4.ll N 22.29, acetate, ethyl cyanoacetate or with 3-iminobutyro- Calcd C 68.56 H 4.16 N 22.21.
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