Pyrazolyl Ring Research Articles

N‐Pyrazolylpropanamide – a Versatile Ligand for the Construction of Supramolecular Hydrogen‐Bonded Frameworks

AbstractThe syntheses and single‐crystal X‐ray structures of several first‐row transition metal complexes containing the multifunctional acrylamide‐derived ligand N‐pyrazolylpropanamide (1 = L) are reported. The general synthesis involves treatment of appropriate transition metal salts with an excess of 1 in ethanolic solution in the presence of triethylorthoformate as dehydrating agent. This way the perchlorates of iron(II) and cobalt(II) afforded the complexes [L2M(EtOH)2](ClO4)2[M = Fe (2), Co (3), in good yields (82 and 85 %)]. Light green L2NiCl2 (4) was obtained analogously from NiCl2·6H2O. Hydration of 4 afforded the dark green cationic nickel(II) complex [L2Ni(H2O)4]Cl2 (4a). In compounds 2–4 the N‐pyrazolylpropanamide acts as N, O‐chelating ligand. In contrast, monodentate nitrogen coordination via the pyrazolyl ring was found for the dicoordinate silver(I) complex [L2Ag]NO3·H2O (5). The molecular and crystal structures of 2, 3, 4a, and 5 were determined by X‐ray diffraction.

Structural Variations in Copper(II) Complexes of a Bitopic Bis(pyrazolyl)methane Ligand

AbstractThe equal molar reaction of Cu(BF4)2·3H2O with the ditopic, bis(pyrazolyl)methane ligand p‐[CH(pz)2]2C6H4 (Lp) where pz is a pyrazolyl ring, in methanol produces [Cu(μ‐Lp)(CH3OH)](BF4)2·(CH3OH)0.62 (1) and a similar reaction in water/methanol yields [Cu(μ‐Lp)(CH3OH)]2(SiF6)(BF4)2·(CH3OH)2 (2). The water/ethanol solvent system yields both [Cu2(μ‐Lp)(H2O)6](SiF6)2·(H2O)4 (3) and [Cu(μ‐Lp)(H2O)](BF4)2·(CH3CH2OH)2 (4), and if the ratio of Cu(BF4)2·3H2O and Lp is changed to 2:1, only 3 forms. Recrystallization of the solid formed from the reaction of THF solutions of Cu(BF4)2·3H2O with Lp from DMSO yields [Cu2(μ‐Lp)(DMSO)6](BF4)4·(DMSO)2·C6H6·(H2O)0.5 (5) and a recrystallization of compound 1 from DMSO yields [Cu2(μ‐Lp)(DMSO)6](BF4)4·(DMSO)2·C6H6 (6). Complexes 1, 2, and 4 are coordination polymers in which the N4O‐coordinated, square‐pyramidal copper(II) ions are oriented in an anti conformation withrespect to the phenylene spacer of Lp. Complexes 3, 5 and 6 are dinuclear with N2O3‐coordinated, square‐pyramidal copper(II) ions again oriented in an anti configuration with respect to the bridging Lp. The square pyramidal geometries show axial elongation, a result of pseudo Jahn–Teller electronic effects. In the cases of the coordination polymers, the axially coordinated solvent molecule is lost at low temperatures upon heating of the crystals. The three compounds in each structural type have nearly the same overall configurations. Cooperative effects of O–H···F, O–H···O and C–H···F hydrogen bonding interactions organize the supramolecular structures and influence the crystal packing of complexes 1–4. The C–H···F interactions have metrics that indicate they are unusually strong, due to the enhanced polarization of the C–H bond and charge assistance from the anionic fluorine atom.

99mTc(I) Scorpionate Complexes for Brain Imaging: Synthesis, Characterization and Biological Evaluation

The new dihydrobis(azolyl)borate ligand Na[H2B(tim(Me))(3,5-Me2pz)] (L1) was synthesized and used to prepare the complexes fac-[M(κ(3)-H(μ-H)B(tim(Me))(3,5-Me2-pz))(CO)3] (M = Re (4), 99mTc (4a)). L1 and 4 were characterized by common analytical techniques, including X-ray diffraction analysis for 4. The successful synthesis of complex 4a, obtained with high radiochemical purity, has shown for the first time that dihydrobis(azolyl)borate ligands combining 2- mercaptoimidazolyl and pyrazolyl rings are capable of stabilizing the fac-[99mTc(CO)3]+ unit. Complex 4a displays a high in vitro stability, in PBS (pH 7.4), indicating that the B-H...99mTc bond is retained even under physiological conditions. Biodistribution studies in mice have shown that 4a can cross the blood-brain barrier, emerging as a good alternative for the design of radiopharmaceuticals for brain imaging.

Tris(pyrazolyl)phosphine Oxides. Synthesis and Coordination Chemistry with Copper(I)

A set of substituted tris(pyrazolyl)phosphine oxides (OP(pzx)3) has been prepared in high yield and applied as neutral scorpion-type ligands. The P apex provides a convenient spectroscopic handle. Substitution at the 3-position of the pyrazolyl ring influences the steric demands of the ligand, while substitution at the 5-position enhances the stability. Copper(I) acetonitrile complexes of the OP(pzx)3 ligands were prepared and tested in ligand exchange reactions with PPh3 and CO. The ν(CO) values of the carbonyl complexes demonstrate the electron-withdrawing properties of the ligands. These observations show that OP(pzx)3 ligands are an interesting extension of the widely used scorpion-type ligands.

Synthesis, structural characterisation and cytotoxicity of new iron(III) complexes with pyrazolyl thiosemicabazones

New iron(III) complexes of 5-methyl-3-formylpyrazole-N(4)-dimethylthiosemicarbazone (HMPZNMe2) (I) and 5-methyl-3-formylpyrazole-N(4)-diethylthiosemicarbazone (HMPZNEt2) (III), [Fe(MPZNMe2)2]NO3·H2O (II) and [Fe(MPZNEt2)2]NO3·H2O (IV), respectively, have been synthesised for the first time and physico-chemically characterised by magnetic measurements (polycrystalline state), electronic and IR spectra. Both are cationic complexes containing two monodeprotonated tridentate ligands with NNS donor sites and an anionic counterpart; the complex species behave as 1:1 electrolytes in MeOH. IR spectra (4000–200cm−1) indicate coordination to iron(III) centre via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulfur atom. X-ray crystallographic data of (II) (monoclinic, C2/c) and (IV) (P1¯, triclinic) have authenticated the FeN4S2 octahedral coordination in both complex ions, as envisaged from the spectral data. In both species, the two azomethine nitrogen atoms are trans to each other, while the pyrazolyl ring nitrogen and the thiolato sulfurs atoms are in cis positions. We further observed that both the ligands and their corresponding complexes were capable of killing HeLa cells in culture, but the cytotoxicity of the complexes was found to be greater than their corresponding ligands. Complex (II) does not have any role in cell-cycle progression, but complex (IV) arrests the M-phase to prevent cell-cycle progression.

Synthesis, Antimicrobial and Antiproliferative Activity of Novel Silver(I) Tris(pyrazolyl)methanesulfonate and 1,3,5-Triaza-7-phosphadamantane Complexes

Five new silver(I) complexes of formulas [Ag(Tpms)] (1), [Ag(Tpms)(PPh(3))] (2), [Ag(Tpms)(PCy(3))] (3), [Ag(PTA)][BF(4)] (4), and [Ag(Tpms)(PTA)] (5) {Tpms = tris(pyrazol-1-yl)methanesulfonate, PPh(3) = triphenylphosphane, PCy(3) = tricyclohexylphosphane, PTA = 1,3,5-triaza-7-phosphaadamantane} have been synthesized and fully characterized by elemental analyses, (1)H, (13)C, and (31)P NMR, electrospray ionization mass spectrometry (ESI-MS), and IR spectroscopic techniques. The single crystal X-ray diffraction study of 3 shows the Tpms ligand acting in the N(3)-facially coordinating mode, while in 2 and 5 a N(2)O-coordination is found, with the SO(3) group bonded to silver and a pendant free pyrazolyl ring. Features of the tilting in the coordinated pyrazolyl rings in these cases suggest that this inequivalence is related with the cone angles of the phosphanes. A detailed study of antimycobacterial and antiproliferative properties of all compounds has been carried out. They were screened for their in vitro antimicrobial activities against the standard strains Enterococcus faecalis (ATCC 29922), Staphylococcus aureus (ATCC 25923), Streptococcus pneumoniae (ATCC 49619), Streptococcus pyogenes (SF37), Streptococcus sanguinis (SK36), Streptococcus mutans (UA159), Escherichia coli (ATCC 25922), and the fungus Candida albicans (ATCC 24443). Complexes 1-5 have been found to display effective antimicrobial activity against the series of bacteria and fungi, and some of them are potential candidates for antiseptic or disinfectant drugs. Interaction of Ag complexes with deoxyribonucleic acid (DNA) has been studied by fluorescence spectroscopic techniques, using ethidium bromide (EB) as a fluorescence probe of DNA. The decrease in the fluorescence of DNA-EB system on addition of Ag complexes shows that the fluorescence quenching of DNA-EB complex occurs and compound 3 is particularly active. Complexes 1-5 exhibit pronounced antiproliferative activity against human malignant melanoma (A375) with an activity often higher than that of AgNO(3), which has been used as a control, following the same order of activity inhibition on DNA, i.e., 3 > 2 > 1 > 5 > AgNO(3)≫ 4.

ChemInform Abstract: Simple and Efficient Synthesis of 2,6‐Dialkyl‐3,5‐dialkoxycarbonyl‐4‐ (3‐aryl‐1‐phenyl‐pyrazol‐4‐yl)pyridines Using TPAP/NMO as a Catalyst under Mild Conditions.

AbstractThe reaction is not sensitive to the electronic and sterical effects of the substituents on the pyrazolyl rings and affords the products with excellent yields.Substrate (V) with the substituent bearing a methylthio‐group is oxidized to yield the methylsulfonyl pyridine derivative (IVb).

3-[(E)-3-(4-Methoxyphenyl)prop-2-enoyl]-1-(4-methylphenyl)-5-phenyl-1H-pyrazole-4-carbonitrile

In the title compound, C27H21N3O2, the non-H atoms of the meth­oxy­phenyl­acryloyl substitutent of the pyrazolyl ring are almost co-planar (r.m.s. deviation = 0.070 Å), and the mean plane is twisted by 18.7 (1)° with respect to the pyrazolyl ring. The phenyl and tolyl substituents are aligned at 48.9 (1) and 44.5 (1)° with respect to the pyrazolyl ring. Weak inter­molecular C—H⋯O and C—H⋯N hydrogen bonding is present in the crystal structure.

Synthesis and structural characterization of iron complexes with 2,2,2-tris(1-pyrazolyl)ethanol ligands: Application in the peroxidative oxidation of cyclohexane under mild conditions

The reactions of FeCl 2.2H 2O and 2,2,2-tris(1-pyrazolyl)ethanol HOCH 2C(pz) 3 ( 1) (pz = pyrazolyl) afford [Fe{HOCH 2C(pz) 3} 2][FeCl 4]Cl ( 2), [Fe{HOCH 2C(pz) 3} 2] 2[Fe 2OCl 6](Cl) 2·4H 2O ( 3·4H 2O), [Fe{HOCH 2C(pz) 3} 2][FeCl{HOCH 2C(pz) 3}(H 2O) 2] 2(Cl) 4 ( 4) or [Fe{HOCH 2C(pz) 3} 2]Cl 2 ( 5), depending on the experimental conditions. Compounds 1– 5 were isolated as air-stable crystalline solids and fully characterized, including ( 1– 4) by single-crystal X-ray diffraction analyses. The latter technique revealed strong intermolecular H-bonds involving the OH group of the scorpionate 2 and 3 giving rise to 1D chains which, in 3, are further expanded to a 2D network with intercalated infinite and almost plane chains of H-interacting water molecules. In 4, intermolecular π⋯π interactions involving the pyrazolyl rings are relevant. Complexes 2– 5 display a high solubility in water (S 25 °C ca. 10–12 mg mL −1), a favourable feature towards their application as catalysts (or catalyst precursors) for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone, with aqueous H 2O 2/MeCN, at room temperature (TON values up to ca. 385).

Spin crossover in di-, tri- and tetranuclear, mixed-ligand tris(pyrazolyl)methane iron(ii) complexes

A series of polynuclear mixed-ligand tris(pyrazolyl)methane iron(II) complexes displaying high temperature spin crossover behaviour has been synthesised. These complexes are of the type [(Fe((3,5-Me(2)pz)(3)CH))(n)(μ-L)](BF(4))(2n), where μ-L is one of five bridging ligands X(CH(2)OCH(2)C(pz)(3))(n), (X = the central linking moiety, pz = pyrazolyl ring and n = 2 (ditopic), 3 (tritopic) or 4 (tetratopic)). Throughout the series the terminal tris(3,5-dimethylpyrazolyl)methane co-ligand (3,5-Me(2)pz)(3)CH and the BF(4)(-) counter anion were kept constant while variations in the central linking moiety have produced three dinuclear complexes and a trinuclear and tetranuclear complex, all isolated as solvates. The three dinuclear complexes are a 1,4-xylene-bridged complex 1·2DME, a 2,6-naphthalene-bridged complex 2·2.5MeCN.2DME and a 1,4-butene-bridged complex 3·2DME. The trinuclear complex 4·solvent (solvent undefined) has a 1,3,5-mesitylene core and the tetranuclear complex, 5·8MeCN.2(t)BuOMe, has a 1,2,4,5-tetramethylbenzene core (DME = dimethoxyethane, (t)BuOMe = tertiarybutyl-methylether). The trinuclear cluster has a "3-up" cup shape with the cups arranging themselves in pairs to form capsules that contain anion guests. All the solvated compounds have been structurally characterised and both the solvated and desolvated versions have had their magnetic and thermal properties thoroughly investigated by variable temperature magnetic susceptibility, differential scanning calorimetric and Mössbauer spectral methods. They all display typical low spin iron(II) magnetic behaviour at room temperature and all undergo a spin state transition to high spin iron(II) above room temperature. In particular, complex 1·2DME shows an abrupt spin transition which shifts, upon desolvation, to a lower value of T(1/2) and in addition displays a small thermal hysteresis.

Pyrazolyl methyls prescribe the electronic properties of iron(ii) tetra(pyrazolyl)lutidine chloride complexes

A series of iron(II) chloride complexes of pentadentate ligands related to α,α,α',α'-tetra(pyrazolyl)-2,6-lutidine, pz(4)lut, has been prepared to evaluate whether pyrazolyl substitution has any systematic impact on the electronic properties of the complexes. For this purpose, the new tetrakis(3,4,5-trimethylpyrazolyl)lutidine ligand, pz**(4)lut, was prepared via a CoCl(2)-catalyzed rearrangement reaction. The equimolar combination of ligand and FeCl(2) in methanol gives the appropriate 1:1 complexes [FeCl(pz(R)(4)lut)]Cl that are each isolated in the solid state as a hygroscopic solvate. In solution, the iron(II) complexes have been fully characterized by several spectroscopic methods and cyclic voltammetry. In the solid state, the complexes have been characterized by X-ray diffraction, and, in some cases, by Mössbauer spectroscopy. The Mössbauer studies show that the complexes remain high spin to 4 K and exclude spin-state changes as the cause of the surprising solid-state thermochromic properties of the complexes. Non-intuitive results of spectroscopic and structural studies showed that methyl substitution at the 3- and 5- positions of the pyrazolyl rings reduces the ligand field strength through steric effects whereas methyl substitution at the 4-position of the pyrazolyl rings increases the ligand field strength through inductive effects.

Potassium S2N-heteroscorpionates: structure and iridaboratrane formation

The potassium salts of the new S(2)N-heteroscorpionate ligand hydrobis(methimazolyl)(3,5-dimethylpyrazolyl)borate [HB(mt)(2)(pz(3,5-Me))](-) and its known analogue hydrobis(methimazolyl)(pyrazolyl)borate [HB(mt)(2)(pz)](-) (prepared from KTp' or KTp and methimazole, Hmt), and the adduct KTp·Hmt have polymeric structures in the solid state (the first a ladder and the other two chains). The iridaboratranes [IrHLL'{B(mt)(2)X}] (X = pz(3,5-Me) or pz), prepared from the heteroscorpionate anion and [{Ir(cod)(μ-Cl)}(2)] (LL' = cod), subsequent carbonylation [LL' = (CO)(2)] and then reaction with phosphine [LL' = (CO)(PR(3)), R = Ph or Cy], have a pendant pyrazolyl ring and a bicyclo-[3.3.0] cage formed by an S(2)-bound B(mt)(2) fragment. The binuclear species [(cod)HIr{μ-B(mt)(3)}IrCl(cod)], the only isolated product of the reaction of KTm with [{Ir(cod)(μ-Cl)}(2)], also has an S(2)-bound iridaboratrane unit but with the third mt ring linked to square planar iridium(I).

π–π Stacking and magnetic coupling mechanism on a mono-nuclear Mn(II) complex

A novel magnetic coupling is observed in a unpublished crystal that consists of a mono-nuclear manganese(II) complex, namely, [Mn(DPP)(NCS) 2] (DPP = 2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline), in which neutral DPP molecule functions as tridentate chelated ligand. In the complex Mn(II) ion assumes a distorted trigonal bipyramidal geometry and in the crystal there is a π–π stacking interaction between the adjacent complexes, which involves pyridyl ring and the symmetry-related pyrazolyl ring and pyridyl ring. The fitting for the data of the variable-temperature magnetic susceptibilities with infinite uniform Mn(II) chain formula gave the magnetic coupling constant J = −0.11 cm −1, and theoretical calculations reveal that there exists a very weak anti-ferromagnetic coupling between the adjacent Mn(II) ions with J = −0.02 cm −1. The magnetic coupling sign is explained based on McConnell I spin-polarization mechanism with the analysis of the spin density population and the factors that dominate the magnetic coupling magnitude.

Synthesis and antimicrobial activity of novel 5-amino-4-cyano-1H-pyrazole and quinazolin-4(3H)-one derivatives

New substituted aroylhydrazones (4a-f) were synthesized from the acid hydrazide (3) and the corresponding aldehyde or aldose. 5-Amino-4-cyano-1H-pyrazole derivatives (6a-f) were prepared by the reaction of the aroylhydrazones (4a-f) with malononitrile. The synthesized compounds were tested for antimicrobial activity against various bacteria and fungi and showed moderate to high inhibition activities. Compounds incorporating a sugar moiety as well as a pyrazolyl ring in their structure displayed the highest antimicrobial activity.

Probing the Antioxidant Action of Selenium and Sulfur Using Cu(I)-Chalcogenone Tris(pyrazolyl)methane and -borate Complexes

Hydroxyl radical generated from the reaction of Cu(+) with hydrogen peroxide results in oxidative DNA damage, and this damage is implicated in aging, cancer, and many other diseases. Selenium- and sulfur-containing compounds can act as antioxidants, and coordination of selenium and sulfur to copper is one explanation for this antioxidant activity. To determine how copper coordination results in antioxidant activity, biologically relevant tris(pyrazolyl)methane and borate Cu(+) complexes of the formulas Tp*Cu(L) and [Tpm(R)Cu(L)](+), where (L = N, N'-dimethylimidazole selone, dmise; N, N'-dimethylimidazole thione, dmit; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate; Tpm(R) = tris(pyrazolyl)methane, R = H; Tpm, R = Me; Tpm*, R = iPr; Tpm(iPr)), have been synthesized and characterized. The structures of complexes Tp*Cu(Dmit), Tp*Cu(dmise), [Tpm(R)Cu(dmise)][BF(4)], and [Tpm(R)Cu(Dmit)][BF(4)] (where R = H; Tpm, R = Me; Tpm*, R = iPr; Tpm(iPr)) were determined by X-ray crystallography. All the Cu(+) centers adopt distorted tetrahedral coordination geometry, and Cu-Se and Cu-S distances for all the complexes are approximately 2.30 Å, and 2.20 Å, respectively. The effects of counterion and steric bulk at the 3 and 5 positions of the pyrazolyl ring on the structural and spectroscopic properties are discussed. Selone or thione coordination to copper significantly alters the Cu(+/2+) redox potential: Cu-selone complexes have Cu(2+/+) potentials from -283 to -390 mV, whereas those of Cu-thione complexes range from 70 to -232 mV versus NHE. The Cu-selone complexes have Cu(2+/+) potentials near or below that of the cellular reductant NADH (-324 mV). Thus, selenium and sulfur coordination to copper in biological systems may prevent the Cu(2+) reduction by NADH required for the catalytic formation of damaging hydroxyl radical.

Para-Quinone-Containing Bis(pyrazol-1-yl)methane Ligands: Coordination Behavior Toward CoII and a C−H Activation Reaction with CeIV

Two series of sterically demanding para-dimethoxyphenyl-substituted bis(pyrazol-1-yl)methane ligands have been synthesized, i.e., L2(R,R') = ((MeO)(2)C(6)H(3))C(H)(pz(R,R'))(2) and L3(R,R') = ((MeO)(2)C(6)H(3))C(Me)(pz(R,R'))(2) (R,R' = 3-Me,5-Me; 3-Ph,5-H; 3-tBu,5-H). In the solid state, already the sterically least encumbered derivative L2(Me2) is able to stabilize Co(II) complexes of the form [X(2)Co(L2(Me2))] (X = Cl, NO(3)); in solution, these complexes are at an equilibrium with the 1:2 species [Co(L2(Me2))(2)](2+). Oxidative demethylation of L3(Ph) and L3((t)Bu) with [Ce(NH(4))(2)(NO(3))(6)] leads to the corresponding para-benzoquinonyl-substituted bis(pyrazol-1-yl)methane ligands L4(Ph) and L4((t)Bu). Contrary to that, the methyl derivative L3(Me2) is transformed into the ortho-benzoquinone species L5(Me2), which still contains one methoxy substituent while one oxygen atom has been newly introduced. The formation of L5(Me2) requires (i) the admission of air, (ii) the presence of both methoxy substituents of L3(Me2), and (iii) the presence of (methyl) substituents both at the exocyclic carbon atom and at the 5- positions of the pyrazolyl rings. The parent ortho-hydroquinonyl-substituted bis(pyrazol-1-yl)methane ligand ((HO)(2)C(6)H(3))C(H)(pz(H,H))(2) is readily available from 3,4-dihydroxybenzaldehyde and (pz(H,H))(2)SO/pyridine.

4-{[4-(Dimethylamino)benzylidene]amino}-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one

The azomethine double-bond in the title Schiff base, C20H22N4O, has an E-configuration. The aromatic ring of the benzyl­idene portion (r.m.s. deviation 0.011 Å) and the five-membered pyrazolyl ring (r.m.s. deviation 0.033 Å) form a dihedral angle of 19.0 (1)°. The phenyl substituent is twisted by 55.0 (1)° with respect to the five-membered ring.

Pyrazolate-bridged group 11 metal(I) complexes: Substituent effects on the supramolecular structures and physicochemical properties

Polynuclear homoleptic pyrazolate-bridged group 11 metal(I) complexes with three different alkyl substituted pyrazolate anions, 3,5-diisopropylpyrazolate (3,5- iPr 2pz − = L1 −), 3- tert-butyl-5-isopropylpyrazolate (3- tBu-5- iPrpz − = L3 −), and 3,5-di- tert-butylpyrazolate (3,5- tBu 2pz − = L4 −), i.e. [Cu( μ-3,5- iPr 2pz)] 3 ( CuL1), [Ag( μ-3,5- iPr 2pz)] 3 ( AgL1), [Au( μ-3,5- iPr 2pz)] 3 ( AuL1), [Cu( μ-3- tBu-5- iPrpz)] 4 ( CuL3), [Ag( μ-3- tBu-5- iPrpz)] 3 ( AgL3), [Au( μ-3- tBu-5- iPrpz)] 4 ( AuL3), [Cu( μ-3,5- tBu 2pz)] 4 ( CuL4), [Ag( μ-3,5- tBu 2pz)] 4 ( AgL4), and [Cu( μ-3,5- tBu 2pz)] 4 ( AuL4), were systematically synthesized in order to investigate the influence of pyrazole bulkiness on their structures and physicochemical properties. The structural characterization indicates that the geometries are greatly influenced by the steric hindrance exerted by the substituent groups of the pyrazolyl rings and the differences of the central metal (I) ionic radius (Cu + < Au + < Ag +). These complexes were also characterized by spectroscopic techniques, namely, UV–Vis, IR/far-IR, Raman, and luminescence spectroscopy.

ChemInform Abstract: Cyclocondensation of 2-Phenacyl-1H-benzimidazole with Acylhydrazines: Synthesis and Tautomerism of 2-(Pyrazol-4-yl)-1H-benzimidazoles.

The previously unknown 2-(pyrazol-4-yl)benzimidazoles containing aryl groups in the pyrazolyl ring have been obtained by the reaction of 2-phenacyl-1H-benzimidazole with aroylhydrazines. The compounds with nitrophenyl and pyridyl substituents in the pyrazole ring show pyrazolyl tautomerism with differences in the1H NMR spectra. A semi-empirical method is proposed to determine the tautomeric composition of the synthesized pyrazoles.

ChemInform Abstract: Synthesis of Optically Active α-Amino Acids Containing Pyrazolyl Ring as Substituent.

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