Pyrazolium Salts Research Articles

Stereoselective synthesis of N-unsubstituted pyrazolidines from 3-nitro-2-trichloromethyl-2 H-chromenes and hydrazine hydrate

The reaction of 3-nitro-2-trichloromethyl-2H-chromenes with hydrazine hydrate in ethanol at room temperature results in 3,4-trans, 4,5-trans-3-(2-hydroxyaryl)-4-nitro-5-trichloromethylpyrazolidines in 56–73% yields; the structures of these compounds were established by 1 H NMR, 2D COSY and 2D NOESY spectra. Unlike pyrazoles and pyrazolines whose synthetic methods are well developed, 1 pyrazolidines are not so readily accessible. They were previously obtained by reduction of pyrazolines 2 or pyrazolium salts 3,4 and by the reactions of hydrazine with 1,3-dibromides 2,5 or phenylhydrazones with electron-deficient alkenes. 6 In a study of the reactivity of 3-nitro-2-trihalomethyl-2Hchromenes 1 synthesised by tandem condensation of salicylic aldehydes with 1-nitro-3,3,3-trihalopropenes, 7 we found that the reaction of these compounds with hydrazine hydrate did not end at the stage of nucleophilic addition to C(4), as was the case with a number of S-, N- and C-mononucleophiles, 8,9 but involved recyclisation of the pyrane ring to the pyrazolidine ring. The reaction of 3-nitro-2-trichloromethyl-2H-chromenes 1a–c with an equimolar amount of 60% hydrazine hydrate in ethanol at room temperature resulted in pyrazolidines 2a–c each as a single, most thermodynamically stable 3,4-trans, 4,5-trans-diastereomer in 56–73% yields. † As far as we know, no functionalised N-unsubstituted pyrazolidines have been reported before. Phenylhydrazine does not react with chromenes 1a,c under these conditions. Products 2a–c are white high-melting powders stable in storage. Note that pyrazolidine 2b is not oxidised in air when kept in a chloroform solution for five days, and its configuration does not change on refluxing in methanol in the presence of K2CO3. A possible reaction mecha

The calculated enthalpies of the nine pyrazole anions, cations, and radicals: a comparison with experiment

Enthalpies of 12 pyrazole species including neutral, anions, cations, and radicals have been calculated at the G3B3 level. The main conclusions are: (i) there are ten equilibria between species of which six have been measured experimentally and the agreement is excellent; (ii) two structures, cyclic and chain, have been found for the pyrazolium-radical 8 that are able to explain the electrochemistry of pyrazolium salts; (iii) the aromaticity, calculated as the NICS indexes, is related to the unexpected stability of the pyrazole anion 3.

Regioselective Synthesis of Silylated Pyrazolines and Indazolines by Reaction of Pyrazolium and Indazolium Salts with Silyllithium Reagents.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and Catalytic Application of Palladium Pyrazolin-3-ylidene Complexes

Oxidative addition of a 3-halo 1,2-disubstituted pyrazolium salt to a palladium(0) complex leads to the formation of the first reported palladium pyrazolin-3-ylidene complex. Comparison of the new system with the analogous imidazolin-2-ylidene complex in Heck catalysis shows higher yields for the new system by a factor of 2.

Morphology and nanomechanics of conducting plastic crystals.

We present a temperature-controlled scanning probe microscopy characterisation of morphology and mechanical behaviour of conducting N,N'-cyclized pyrazolium salts. These salts are plastic crystals belonging to the pyrazolium trifluoromethanesulfonimide family. Going from a five-membered to a seven-membered ring, and adding a methyl group in alpha to either the five-membered or six-membered rings, allows modulation of the temperature of the phase transitions. Before and after the transitions, the materials' Young moduli, hardnesses and surface roughnesses change. We attribute these macroscopic modifications to specific states: brittle, elastoplastic and viscoplastic, corresponding to variations in the extent of the dislocations present in the crystal lattice planes of the compounds.

Lithium conducting pyrazolium imides plastic crystals: a new solid state electrolyte matrix

In this paper, we present the results of our current research in plastic-crystal-based lithium batteries. The N, N′-ringed pyrazolium salts of trifluoromethanesulfonimide (TFSI) are a new family of organic plastic crystals. Their exceptional properties have underlined their potential as new electrolyte materials for application in electrochemical devices such as lithium batteries. Both single-phase and multi-phase plastic crystals of the pyrazolium series were investigated. Battery results confirmed pyrazolium plastic crystals to be superior solid-state electrolyte materials. The rate capability and attainable capacity of the reported battery investigation demonstrate that plastic crystal pyrazoliums are excellent contenders as new solid-state electrolytes.

Regioselective Synthesis of Substituted Triazolium Salts via 1,3‐Dipolar Cycloaddition Reactions.

The regioselectivity of 1,3-dipolar cycloaddition reactions of 1-aza-2-azoniaallene salts with α,β-unsaturated nitriles such as acrylonitrile or cyclohexylidene acetonitrile afforded only 1,2,4-triazolium salts via addition to the nitrile group, while the other expected pyrazolium salts were not observed. Moreover, 1-aza-2-azonia-allene salts reacted with other competitive systems such as α-iminonitrile derivatives yielding only triazolium salts via addition to the nitrile and not to the imino group. Treatment of cumulene with 3-pyridylnitrile afforded the pyridinium salt. However, 2,3-dimethyl-5-(2,6-dimethoxyphenyl)-[1,2,4]triazole could be prepared from cumulene and 2,6-dimethoxybenzonitrile. Some reactions of nitriles with 1-aza-2-azonia-allene salts prepared from 1,2,3-indantrione and 9-acetylphenanthrene are discussed.

Regioselective Synthesis of Substituted Triazolium Salts via 1,3-Dipolar Cycloaddition Reactions

The regioselectivity of 1,3-dipolar cycloaddition reactions of 1-aza-2-azoniaallene salts with α,β-unsaturated nitriles such as acrylonitrile or cyclohexylidene acetonitrile afforded only 1,2,4-triazolium salts via addition to the nitrile group, while the other expected pyrazolium salts were not observed. Moreover, 1-aza-2-azonia-allene salts reacted with other competitive systems such as α-iminonitrile derivatives yielding only triazolium salts via addition to the nitrile and not to the imino group. Treatment of cumulene with 3-pyridylnitrile afforded the pyridinium salt. However, 2,3-dimethyl-5-(2,6-dimethoxyphenyl)-[1,2,4]triazole could be prepared from cumulene and 2,6-dimethoxybenzonitrile. Some reactions of nitriles with 1-aza-2-azonia-allene salts prepared from 1,2,3-indantrione and 9-acetylphenanthrene are discussed.

Quaternization and dequaternization of pyrazoles in solvent‐free conditions: Conventional heating versus microwave irradiation

AbstractWe report a study on the quaternization and dequaternization of pyrazoles by conventional heating and microwave irradiation in solvent‐free conditions. Microwave irradiation produces an acceleration in the quaternization rate and a rapid equilibration between quaternized and non quaternized products. Dequaternization is also more rapid and a change on the selectivity is observed using symmetric pyrazolium salts.

Anderson-Evans type molybdotellurates with diazolium cations: preparation, structure and properties of (H 2imz) 6 [TeMo 6O 24]·4H 2O and (H 2pyz) 6 [TeMo 6O 24]·Te(OH) 6

Two new Anderson-Evans molybdotellurates with imidazolium and pyrazolium cations have been prepared. X-ray crystallographic studies have been made from crystals of both compounds. The imidazolium salt (C 3H 5N 2) 6 [TeMo 6O 24]·4H 2O ( 1) crystallizes in the monoclinic space group P2 1/n with a = 14.372(3), b = 11.275(2), c = 13.019(3) A ̊ , β = 91.17(3)°, V = 2109.2(2) A ̊ 3 at 20°C and Z = 2; structural analysis is based on 6172 independent reflections ( l ≥ 2 σ( l)) with least-squares refinement of 297 parameters converged to R = 0.049. The crystal structure consists of a [TeMo 6O 24] 6− with the TeO 6 octahedron at the centre surrounded by six MoO 6 sharing edges. The protonated organic bases bond with the anion in the crystal by hydrogen bonds. The pyrazolium salt (C 3H 5N 2) 6 [TeMo 6O 24]·Te(OH) 6 ( 2) crystallizes in the triclinic space group P-1 with a = 10.920(2), b = 11.518(2), c = 10.056(2) A ̊ , α = 93.92(3), β = 103.97(3), γ = 109.80(3)°, V = 1139.1(4) A ̊ 3 at 20° C and Z = 2 . Structure analysis with least-squares refinement of 311 parameters for 6599 independent reflections ( l ≥ 2 σ( l)) converged to R = 0.0526. The crystal structure of this compound consists in discrete [TeMo 6O 24] 6− anions and Te(OH) 6 units bonded to pyrazolium cations by hydrogen bonds. The IR spectra of both compounds are discussed on the D 3 d symmetry of the [TeMo 6O 24] 6 anion. The compounds have been studied by 1H, 95Mo and 125Te NMR spectroscopy, indicating in DMF the presence of octahedral species for both compounds, and a dissimilar behavior in H 2O solution. While compound 1 undergoes a clear hydrolitic process forming tetrahedral MoO 4 2− species, compound 2 is more stable in aqueous media. Thermogravimetry and differential scanning calorimetry of 1 show that this compound loses the four water molecules through an endothermic process ΔH = 137 kJ mol −1. The residual products were characterized by chemical analysis, IR and XPS spectroscopy. The best kinetic parameter values, corresponding to a solid state process involving the loss of the water molecules, were found on the basis of dynamic and isothermal methods. The best representation of a reaction mechanism is the random nucleation-one nucleus on each particle: −ln(1 − α) = kt. The values of activation energy ( E a = 93.3 kJmol −1), entropy of activation ( ΔS ≠ = −42.2 J K −1 mol −1), enthalpy of activation ( ΔH ≠ = 76.7 kJ mol −1) and free energy of activation ( ΔG 340.15 K ≠ = 91.1 kJ mol −1) have been determined.

Reactions of pyrazolium salts with silyllithium reagents. Regioselective synthesis of 5-silylated 3-pyrazolines

1,3,5-trisubstituted-2-methylpyrazolium iodides react with dimethylphenylsilyl- and tert-butyldiphenylsilyllithium leading, in general, to one of the corresponding 5-silyl-3-pyrazolines. The silyl group is easily substituted by electrophiles to give 5-functionalized 3-pyrazolines.Moreover, 5-silyl-3-pyrazolines undergo thermic ring opening with silicon-rearrangement affording α-silylated β-diimines.

Cycloadditions of 1-Aza-2-azoniaallene Salts derived from coumarin and camphor

The 1-aza-2-azoniaallene salt 8 prepared from 3-acetyl coumarin via the hydrazone 6 and the (chloroalkyl)azo derivative 7 reacts with nitriles to afford the 3-(3-chromenyl)-1,2,4-triazolium salts 11a–d. With diisopropylcarbodiimide the triazolium salt 13 and with norborene a tricyclic pyrazolium salt 14 are obtained. Concurrent to these cycloadditions the by-product 12 is formed by intramolecular cyclization of the cumulene 8. Similarly, the intramolecular cyclization product 18 is isolated as the sole product when the 1-aza-2-azoniaallene salt 17a (prepared from the ethyl carbazone of camphor by chlorination and treatment of the product 16a with SbCl5) was treated with nitriles, carbodiimides or alkenes. In contrast, 1,2,4-triazolium salts 20a–c, 23c, respectively pyrazolium salts 20d–f, and 1,3,4-thiadiazolium salts 23a,b are obtained by reaction of the 1-aza-2-azoniaallene salt 17b with nitriles, respectively alkenes, alkynes, diisopropylcarbodiimide, and isothiocyanates. The constitutions of two of these products (20e, 23a) were secured by X-ray structural analysis.

LINK Synthesis with 3-Hydroxy-1H-pyrazoles: 3-Carboxyisoalkyloxy-1H-pyrazoles - bicyclic acylpyrazolium salts and ?-Lactams - 3-Carboxyisoalkyloxy-4,5-dihydro-1H-pyrazol-5-ones

1-Substituted 3-hydroxy-1H-pyrazoles 1 react with chloroform, NaOH, and aceton resp. butan-2-one O-regiospecifically to yield 2-methyl-2-[(1H-pyrazol-3-yl)oxy]-propanoic resp. -butanoic acids 14via a dichlorocarbene (12)–dichlorooxirane (9) pathway. Chlorides 17 of 14 easily cyclize to N-acylpyrazolium salts 18/19, which quantitatively afford esters 22–26 and amides 27–29 of 14. Enantiomers of the butanoic acid 14th, obtained via their diastereomeric cholesterol esters, differ in their stimulus to peroxisome proliferation. At 140 °C pyrazolium salts 18 undergo thermolysis to bicyclic β-oxa-γ-lactams 30–32. 3-Carboxyisoalkylamino-pyrazoles similarly give 1H-β-aza-γ-lactams 34. Reactions of 14 with surplus SOCl2 result in 6-chloro- 37 resp. 7-chloro-β-oxa-γ-lactams 38via chlorosulfinylation and extrusion of SO, and in 4,4-bispyrazolyl-sulfoxide 39. A mild introduction of additional O-functions into pyrazoles affording 4,5-dihydro-3-hydroxy-5-oxo-1H-pyrazoles 52–57 is presented. Biological effects of the new pyrazoles are protection against shock and ADP-induced thromboembolism, reduction of serum lipids and improvement of blood flow.

ChemInform Abstract: Reactions of Pyrazoles and Pyrazolium Salts with Complex Metal Hydrides and Organometallic Reagents. Synthesis of Pyrazolines and Pyrazolidines.

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Reactions of pyrazoles and pyrazolium salts with complex metal hydrides and organometallic reagents. Synthesis of pyrazolines and pyrazolidines

Abstract 2-Pyrazolin-4-oximes have been synthesized by reaction of 4-nitroso- and 4-nitropyrazoles with complex metal hydrides and organometallic reagents. Furthermore, 4-nitropyrazolium tetrafluoroborates are reactive substrates towards organolithium and Grignard compounds leading to new and highly substituted 4-nitro-3-pyrazolines and 4-nitropyrazolidines. The formation of 3-pyrazolines is regioselective and, when diastereoisomer pyrazolidines are possible, only the most stable 3,4-trans and/or 4,5-trans isomers were obtained.

Catalytic silylotropy inN-trimethylsilylpyrazole derivatives

Silylotropy in 4-substitutedN-trimethylsilypyrazoles is studied by dynamic1H,13C, and29Si NMR spectroscopy. The catalytic 1,2-migration of a trimethylsilyl group in 4-halo-N-trimethylsilylpyrazoles was detected. Silylotropy inN-trimethylsilylpyrazoles in the presence of halogens of trimethylhalosilanes is believed to proceed through formation ofN,N′-bis(trimethylsilyl)pyrazolium salts, the barrier of silylotropy in pyrazoles being markedly reduced.

ChemInform Abstract: The Reduction of Functionalized Pyrazolium Salts as a Stereoselective Route to Functionalized Pyrazolidines.

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The reduction of functionalized pyrazolium salts as a stereoselective route to functionalized pyrazolidines

Functionalized pyrazolium salts 1 react with metal complex hydrides (LiAlH 4 and NaBH 4) to give pyrazolidines 2 with good-to-excellent levels of diastereoselectivity. The stereochemical course of the reduction is essentially anti, leading to trans,trans-pyrazolidines. The relative configuration of the crystalline pyrazolidine 2c has been determined by X-ray crystallographic analysis.

On the Reaction of 1‐Aza‐2‐azoniaallene Salts with Isocyanates

Abstract1‐Aza‐2‐azoniaallene salts 3, prepared in situ from geminal chloroalkylazo compounds 2 with Lewis acids, react with isocyanates 4 to give 4,5‐dihydro‐5‐oxo‐3H‐1,2,4‐triazolium salts 6 and 4,5‐dihydro‐5‐oxo‐1H‐1,2,4‐triazolium salts 7, respectively. The intramolecular cyclization of 3u opens a new route to cinnolinium salts 11. Allenes 3 react with isobutene to give pyrazolium salts 8. According to AM1 calculations the cycloadditions of 3 to isocyanates proceed in two steps via acylium salts 5 as intermediates. Mechanistically, the rearrangements 6 → 7 resemble Wagner‐Meerwein rearrangements rather than pericyclic [1,5]‐sigmatropic shifts.

Heterocyclic betaines. Aza analogs of sesquifulvalene. 2. Azolium azolate inner salts: synthesis, reactivity, and structure of a 1:1 adduct with dimethyl acetylenedicarboxylate

Reaction of an activated 2-chloroazole with several N-alkylazoles afforded the N-azolylazolium salts, deprotonation of which results in a series of the title mesomeric betaines 7 and 8. Their reactivity toward electrophiles and dipolarophiles under mild conditions reflects the highly dipolar structures of 7 and 8. The thermal stability and dequaternization reactions of some of their corresponding N-azolylimidazolium and -pyrazolium salts have also been studied