Chemistry of naphthazarin derivatives. 12. Synthesis and investigation of prototropic tautomerism of 3-(alk-1-enyl)-2-hydroxynaphthazarins

Substituted 3-(alk-1-enyl)-2-hydroxynaphthazarins were synthesized. According to data from IR spectroscopy, these compounds exist in organic aprotic solvents as mixtures of tautomeric 1,4-naphthoquinonoid forms. The compositions of tautomeric mixtures were quantitatively determined. The effects of the structure of the alkenyl substituent and the polarity of the solvent on the tautomeric equilibrium were qualitatively estimated.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2519–2525, November, 2004.     

Tautomerism of dihydro-1,2,4-triazolo[1,5-α]pyrimidines containing 2-hydroxy- and 4-dimethylaminoaryl substituents

We have studied the effect of structural factors and the nature of the solvent on the tautomeric composition of aromatic substituted dihydro-1,2,4-triazolo[1,5-a]pyrimidines. The kinetics of the tautomeric exchange of 5-(2-hydroxyphenyl)-7-phenyldihydro-1,2,4-triazolo[1,5-a]pyrimidines has also been investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 245–249, February, 1991.     

Keto-enol tautomerism of 4-hydroxy-3-phenyl-2-(2-chloroacetamidophenyl)-1-isoquinolone

Three crystalline modifications of the N-chloroacetyl derivative were obtained in the chloroacetylation of 2-(2-aminophenyl)-4-hydroxy-3-phenyl-1-isoquinolone. It was established by IR spectroscopy that they differ with respect to isomeric composition and the character of the intermolecular hydrogen bonds. For the first time, both keto-enol tautomeric forms were isolated in individual form in the 4-hydroxy-1-isoquinolone series.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 542–543, April, 1985.     

Reaction of 2-(2-oxoethylidene)furan-3(2H)-ones with isopropylidenehydrazides of aromatic carboxylic acids: Synthesis of 3-hydroxy-3-(2-oxoethyl)-2,3-dihydropyridazin-4(1H)-ones

3-Hydroxy-3-(2-oxoethyl)-6-phenyl-2,3-dihydropyridazin-4(1H)-ones were obtained by the reaction of methyl 3-oxo-5-phenylfuran-2(3H)-ylideneacetate or 2-[2-(4-chlorophenyl)-2-oxoethylidene]-5-phenylfuran-3(2H)-one with benzoic or p-nitrobenzoic isopropylidenehydrazides. Equilibrium C₍₅₎H and C₍₅₎H₂ tautomeric forms were detected in solutions of the 4-chlorophenyl derivatives in DMSO-d₆. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1156–1158, August, 2007.     

Synthesis, spectral studies of salicylidine-pyridines: crystal and molecular structure of 2-[(1E)-2-aza-2-(5-methyl(2-pyridyl)ethenyl)]-4-bromobenzen-1-ol

Schiff bases derived from different meta-substituted salicylaldehyde and 5-methylaminopyridine have been synthesized and characterized by elemental analysis, FT-IR, NMR and UV-vis techniques. NMR assignments were made using (1)H, (13)C NMR and aided by 2D HETCOR and HMBC heteronuclear correlation techniques. The UV-vis spectra of the compounds were found useful in understanding the existence of tautomeric equilibria [phenol-imine (O-H...N) and keto-amine (O...H-N) forms] in polar and non-polar solvents. In order to rationalize the stabilization of tautomer in solid state, X-ray structure of 2-[(1E)-2-aza-2-(5-methyl(2-pyridyl)ethenyl)]-4-bromobenzen-1-ol (6) was determined. According to our crystallographic result, it has enol-imine tautomeric form.     

Synthesis of 6-Methyl-4-(1-methyl-2-buten-1-yl)-2-(2-cyclohexen-1-yl)- and 6-Methyl-4-(1-methyl-2-buten-1-yl)-2-(1-cyclohexen-1-yl)anilines

Alkenylation of 6-methyl-2-(2-cyclohexen-1-yl)- and 2-(1-cyclohexen-1-yl)anilines with piperylene in the presence of AlCl₃ and transformation of the resulting cyclohexenylanilines into carbazole structures were studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 441–443.Original Russian Text Copyright © 2005 by Gataullin, Ishberdina, Sotnikov, Abdrakhmanov.     

Nitration of Some 3-(2-Furyl)-2-propenones with Dinitrogen Tetraoxide

Nitration of 3-(2-furyl)-2-propenones with dinitrogen tetraoxide leads to the corresponding 3-(4-nitro-2-furyl)-2-propenones. If the furyl group contains a substituent in position 5, the nitration occurs at the side chain to afford 3-(5-R-2-furyl)-2-nitro-2-propenones.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005, pp. 431–436.Original Russian Text Copyright © 2005 by Sitkin, Klimenko.     

Synthesis of 2-Chloromethyl-5-aryl-, 2-Chloromethyl-5-(5-methyl-2-furyl)-, and 2-Chloromethyl-5-(1,5-dimethyl-2-pyrrolyl)-1,3,4-oxadiazoles from Tetrazole Derivatives

Acetylation of 5-aryltetrazoles, 5-(5-methyl-2-furyl)tetrazole, and 5-(1,5-dimethyl-2-pyrrolyl)tetrazole with chloroacetyl chloride was studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5, 2005, pp. 787–789.Original Russian Text Copyright © 2005 by Baranov, Tsypin, Malin, Laskin.     

3-Alkyl-2-[3(4)-pyridyl]-5-(2-vinyloxyethoxymethyl)-oxazolidines

1-Alkylamino-3-(2-vinyloxyethoxy)-2-propanols react with 3-and 4-pyridinecarbaldehydes to give equimolar mixtures of cis- and trans-3-alkyl-5-(2-vinyloxyethoxymethyl)-2-[3(4)-pyridyl]oxazolidines.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 1, 2005, pp. 104–108.Original Russian Text Copyright © 2005 by Kukharev, Stankevich, Lobanova, Klimenko, Kukhareva.     

Synthesis and molecular structure of 1-(pyrimidin-2-yl)-2-(4-aryl-1,3-thiazol-2-yl)hydrazines

Reactions of some 2-hydrazinopyrimidine hydrochlorides with potassium thiocyanate gave 1-(pyrimidin-2-yl)thiosemicarbazides which underwent Hantzsch condensation with aryl chloromethyl ketones to produce 1-(pyrimidin-2-yl)-2-(4-aryl-1,3-thiazol-2-yl)hydrazine hydrochlorides. The protonation was accompanied by mutually dependent tautomeric rearrangements of heterocyclic fragments.     

Pyridine-substituted hydroxythiophenes. V. Preparation of 5-(2-, 3-and 4-pyridyl)-2-hydroxythiophenes

5-(2-, 3- and 4-Pyridyl)-2-t-butoxythiophenes have been prepared in very good yields by Pd(0) catalyzed cross-coupling of the three isomeric bromopyridines with 5-trimethylstannyl-2-t-butoxythiophene derived from 2-bromothiophene via 2-t-butoxythiophene. Dealkylation of 5-(2-, 3- and 4-pyridyl)-2-t-but-oxythiophenes with boron trifluoride etherate in dichloromethane at room temperature led to predominant formation of rearranged products, 5-(2- and 3-pyridyl)-3-t-butyl-3-thiolene-2-ones, together with a small amount of 5-(2- and 3-pyridyl)-2-hydroxythiophenes as a mixture of two tautomeric keto forms in the case of the 2-pyridyl and the 3-pyridyl isomers, and exclusive formation of rearranged product in the case of the 4-pyridyl isomer. However, dealkylation of 2-methoxy-5-(2-, 3- and 4-pyridyl)thiophenes, prepared similarly to the 5-(2-, 3- and 4-pyridyl)-2-t-butoxythiophenes, with boron tribromide under the same reaction conditions as above resulted exclusively in the tautomeric mixture of 5-(2- and 3-pyridyl)-3-thiolene-2-ones and 5-(2- and 3-pyridyl)-4-thiolene-2-ones in the case of the 2-pyridyl and 3-pyridyl isomers. In the case of the 4-pyridyl isomer polymerization took place.     

Dimer Mechanism for the Tautomeric Conversion of 4-Amino-2-oxopyrimidine

Values of the enthalpy (ΔH), atomic charges (q_i), and bond orders (P_ij) for six tautomeric forms of 4-amino-2-oxopyrimidine have been calculated by the semiempirical AM1 quantum-chemical method. It was found that the most stable of these is 4-amino-2-oxo-1H-pyrimidine (cytosine). By analogy with complementary pairs of nucleotide bases, the tautomeric conversion of cytosine and other oxo forms can come about via a dimeric intermolecular mechanism. A novel interpretation is proposed for the conversion of cytosine to 4-amino-2-oxo-3H-pyrimidine as a result of a 1H-3H two stage proton transfer.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 564–568, April, 2005.     

Synthesis of 5-Amino-4-(4-aryl-2-thiazolyl)-2,3-Dihydro-2-Pyrrolones

A method was developed for preparation of 5-amino-4-(4-aryl-2-thiazolyl)-2,3-dihydro-2-pyrrolones by alkylation of 4-aryl-2-thiazolylacetonitriles by N-substituted chloroacetamides in the presence of K₂CO₃. In 1-(1-naphthyl)-substituted pyrrolones atropoisomerism was observed.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 2, 2005, pp. 266–269.Original Russian Text Copyright © 2005 by Resnyanskaya, Tverdokhlebov, Tolmachev, Volovenko.     

Crystal and Molecular Structure of 2H- and 2-(p-Tolylamino)-5,6-dimethylthieno[2,3-d]pyrimidin-4-ones

The crystal and molecular structure of 2H- and 2-(p-tolylamino)-5,6-dimethylthieno[2,3-d]pyrimidin-4-ones was investigated by X-ray diffraction. In crystals, the tautomeric form with a localized N(1)=C(2) bond is realized. A comparative analysis of the two structures using the literature data is given to examine the conjugation effect on the geometrical parameters of a pseudoaromatic pyrimidine system.     

Synthesis of 2-(1-Alkoxyvinyl)oxazolidines by Condensation of 2-Alkoxypropenals with 2-Aminoalkanols and Ring-Chain Tautomerism of the Products

Reactions of 2-alkoxypropenals with 2-aminoalkanols afforded tautomeric mixtures of previously unknown 2-(1-alkoxyvinyl)oxazolidines and imino alcohols. The condensation takes 2 h at room temperature (89-100%) or 1-5 min under microwave irradiation. The tautomeric equilibrium shifts toward the open-chain structure with increase in the solvent polarity (CDCl₃, CD₂OD, DMSO-d ₆, D₂O) and temperature. The presence of substituents in the oxazolidine ring raises the stability of the cyclic tautomer.     

Synthesis and Transformations of 4-(4-Ethoxycarbonylphenylamino)- and 4-(2-Carboxyphenylamino)quinolines

Synthesis was performed of 4-(4-ethoxycarbonylphenylamino)- and 4-(2-carboxyphenylamino)-2-methylquinolines by reaction of 2-methyl-4-chloroquinoline with anesthesin and anthranilic acid. In concentrated sulfuric acid 4-(2-carboxyphenylamino)-2-methylquinoline underwent cyclization into 6-hydroxy-7-methylquinolino[3,2-c]quinoline, and the alkaline hydrolysis of 4-(4-ethoxycarbonylphenyl-amino)quinoline afforded 2-methyl-4-(4-carboxyphenylamino)quinoline.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 786–787.Original Russian Text Copyright © 2005 by Avetisyan, Aleksanyan, Ambartsumyan.     

2-(2-pyridyl)-3-thioindan-1-one: Synthesis,tautomerism, and complexing properties

Chelate and molecular complexes of 2-(2-pyridyl)-3-thioindan-1-one were prepared. The structure of the ligand (prevalent tautomeric form), including the coordination mode, was proved by ¹H NMR, IR, and EXAFS spectroscopy and by quantum-chemical calculations. The soft-hard properties of the ligand were demonstrated.     

Experimental and computational studies on zwitterionic (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate

The Schiff base compound (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate has been synthesised and characterized by IR, UV–Vis, and X-ray single-crystal determination. Ab initio calculations have been carried out for the title compound using the density functional theory (DFT) and Hartree–Fock (HF) methods at 6-31G(d) basis set. The calculated results show that the DFT/B3LYP and HF can well reproduce the structure of the title compound. Using the TD-DFT and TD-HF methods, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental ones is determined. Molecular orbital coefficient analyses reveal that the electronic transitions are mainly assigned to n → π* and π → π* electronic transitions. To investigate the tautomeric stability, optimization calculations at B3LYP/6-31G(d) level were performed for the NH and OH forms of the title compound. Calculated results reveal that the OH form is more stable than NH form. In addition, molecular electrostatic potential and NBO analysis of the title compound were performed at B3LYP/6-31G(d) level of theory.     

Tautomers of azine derivatives. 21. Tautomerism in 2-(2-hydroxyaryl)azines

Tautomerism in 2-(2-hyroxyaryl)azines has been studied using ¹⁷O NMR and UV spectroscopy. Consideration has been given to the influence of solvent and structural factors which facilitate the establishment of a tautomeric equilibrium in these compounds.Communication 20, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 75–80, January, 1990.     

Synthesis and properties of 5-(5-nitro-2-furyl)thiazolines

The reactions of 2-amino-4-methyl-5-(5-nitro-2-furyl)thiazole with excess methyl iodide leads to 3,4-dimethyl-2-methylamino-5-(5-nitro-2-furyl)thiazolium iodide, which is converted to 2-imino-3,4-dimethyl-5-(5-nitro-2-furyl)thiazoline under the influence of bases. The iminothiazoline structure was proved by comparison of the spectral characteristics of its acetyl derivative and the isomeric 2-(N-acetyl-N-methyl) amino-4-methyl-5-(5-nitro-2-furyl)thiazole. The pKa values of 2-amino-4-methyl-5-(5-nitro-2-furyl)thiazole and 3,4-dimethyl-2-imino-5-(5-nitro-2-furyl)-thiazoline were determined, and the constant of the aminothiazole-iminothiazoline tautomeric equilibrium was calculated.Translated from Khimiya Geterosiklicheskikh Soedinenii, No. 10, pp. 1337–1340, October, 1985.