Nitropyrazoles

A number of substitutedN-nitropyrazoles were prepared by direct nitration of substituted pyrazoles. The dependence of the direction of nitration on the reaction conditions was studied. For Part 9, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1198–1201, June, 1997.     

Nitropyrazoles

A preparative method ofN-amination of pyrazoles bearing nitro groups and other electron withdrawing substituents in the pyrazole ring with hydroxylamine-O-sulfonic acid involving control of the pH of the medium has been elaborated. A series of previously unknown pyrazoles has been prepared. Basicities of 1-aminopyrazole and 1-amino-4-nitropyrazole have been measured and differences between the basicities of theC- andN-amino groups for the pyrazole series have been revealed.For part 3, see ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1434–1436, August, 1993.     

Multinuclear magnetic resonance study of some mesoionic oxatriazoles containing nitrogenous exocyclic groups

¹H,¹³C,¹⁴N and¹⁵N NMR measurements are reported for four mesoionic 1-oxa-2, 3, 4-triazoles containing exocyclic nitrogenous groups. The NMR signal assignments are discussed and compared with those previously published for some corresponding oxatriazoles. The results obtained support the proposed cyclic mesoionic structures for the compounds studied. The questions of possible charge delocalization and valence tautomerism are addressed. Compound with N^– H as a exocyclic group (Fig. 1) is found to be relatively unstable, this is attributed to proton migration in the corresponding non-cyclic form of this molecule.Published in Khimiya Geterotsikiicheskikh Soedinenii, No. 9, pp. 1260–1263, September, 1995.     

Computational 1H NMR: Part 1. Theoretical background

This is the first one of the three closely interrelated reviews to be published in Magnetic Resonance in Chemistry dealing with accordingly theoretical background, chemical applications, and biochemical studies of and by means of computational ¹H NMR. Presented in the first part of the review is a general outline of the modern theoretical methods and accuracy factors of computational ¹H NMR involving locally dense basis set schemes, solvent effects, vibrational corrections, and relativistic effects performed at the density functional theory and/or nonempirical levels. This review is dedicated to Prof. Stephan Sauer in view of his invaluable contribution to the field of computational nuclear magnetic resonance.     

A review with comprehensive data on experimental indirect scalar NMR spin-spin coupling constants across hydrogen bonds

Scalar NMR spin-spin coupling constants across hydrogen bonds are fundamental in structural studies and as test grounds for theoretical calculations. Since they are scattered among many articles of different kinds, it seems useful to collect them in the most comprehensive way.     

Stereochemicai study of 7-aryl-1,7,8,8a-tetrahydro-3(2H)indolizinones by1H and13C NMR

Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by¹H and¹³C NMR. Complete assignment of¹H NMR signals and analysis of¹H-¹H coupling constants were performed using the iterative PANIC program. Values of³ J _6,7,³ J _7,8endo, and⁴ J _5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of¹³C NMR signals was performed on the basis of analysis of the¹³C-¹H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996.     

High-resolution NMR spectroscopic trends and assignment rules of metal-free, metallated and substituted corroles

Major advances over the last few years have facilitated the synthesis of a large variety of meso-only substituted corroles that display interesting catalytic, therapeutic and photophysical properties. This work is the first to study extensively the NMR spectral characteristics of both metallated and non-metallated triarylcorroles in various organic solvents and provide guidelines for easy and reliable assignments of 1D 1H spectra from trends of J coupling constants and chemical shifts. An excellent correlation is found between C=C bond lengths derived from 3J(H,H) values and experimental lengths determined by x-ray crystallography of the same molecules. The nuclear Overhauser effect provides a robust 1D 1H NMR tool for determining the selectivity of electrophilic substitutions. Variable-temperature NMR and isotopic labelling reveal a single preferred tautomerization state and unsymmetric ring orientations at -70 degrees C. The beta-pyrrole protons demonstrate long-range heteronuclear couplings with the coordination core (15N) and with the ortho-19F nuclei of the meso-carbon aryl rings. In sum, application of multinuclear magnetic resonance to corroles and their metal complexes, through the compilation of chemical shifts and J couplings and the recognition of trends therein, provides basic information essential to reliable spectral assignments. Additionally, the conclusions drawn about the structures of corroles and the electron densities at various positions of the corrole macrocycle resulting from the application of high-resolution NMR techniques are of importance to an in-depth understanding of the molecular interactions and processes of this relatively new and rapidly expanding class of compounds.     

A theoretical study of multinuclear coupling constants in pyrazoles

The 243 coupling constants of eight N-R-pyrazoles [R=H, CH3, C6H5, COCH3, NH2, NO2, SO2CF3, Si(CH3)3] have been calculated and compared with 131 experimental values. The agreement is good and can be used to estimate new couplings. The whole collection has been statistically analyzed.     

1H, 13C and 15N NMR chemical shifts of substituted pyrazolo[1,5‐a]pyrimidines

¹H, ¹³C and ¹⁵N NMR chemical shifts of 10 substituted pyrazolo[1,5‐a]pyrimidines were assigned based on DQF ¹H, ¹H COSY, PFG ¹H, ¹³C HMQC and PFG ¹H,X (X = ¹³C and ¹⁵N) HMBC experiments and on literature data. Copyright © 2002 John Wiley & Sons, Ltd.     

N-Oxides of polychloropyridines.13C NMR study

The effect ofN-oxidation of a series of polychloropyridines on¹³C NMR parameters has been studied. It has been established that inN-oxides of polychloropyridines an electric field through-space effect of theN-oxide group predominates in the shielding of the -carbon atom compared to the other carbon atoms. A linear correlation between¹³C NMR chemical shifts and total charge densities calculated by the MNDO method for the carbon atoms ofN-oxides of polychloropyridines has been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2425–2428, December, 1995.The authors are grateful to V. V. Kolchanov for help in the synthesis of compounds under study.     

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.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 3011–3013, December, 1996.     

Ascorbigen A—NMR identification

The connectivities of all atoms in ascorbigen A, an important metabolite, were determined unambiguously for the first time. The connectivity between carbon atoms was established by 2D INADEQUATE, and one-bond ¹³C–¹³C coupling constants were determined for all pairs of directly connected carbon atoms except for two strongly coupled carbon pairs. The ¹³C–¹³C coupling in one of the pairs was proved by a modification of standard INADEQUATE; however, the signals from the other pair were too weak to be observed. The connectivity within the two strongly coupled C–C pairs was confirmed by a combination of COSY and gHSQC; the latter experiment also identified all C–H bonds. The proton nuclear magnetic resonance (¹H NMR) spectra in dry dimethyl sulfoxide allowed identification and assignment of the signals due to NH and OH protons. The derived structure, 3-((1H-indol-3-yl)methyl)-3,3a,6-trihydroxytetrahydrofuro[3,2-b]furan-2(5H)-one, agrees with the structure suggested for ascorbigen A in 1966. The density functional theory (DFT) calculations showed that among 16 possible stereoisomers, only two complied with the almost zero value of the measured ³J(H6–H6a). Of the two stereoisomers, 3S,3aS,6S,6aR and 3R,3aR,6R,6aS, the latter was excluded on synthetic grounds. The nuclear Overhauser effect measurements unveiled close proximity between H2′ proton of the indole and the H6a proton of the tetrahydrofuro[3,2-b]furan part. Detailed structural interpretation of the measured NMR parameters by means of DFT NMR was hampered by rotational flexibility of the indole and tetrahydrofuro[3,2-b]furan parts and inadequacy of Polarizable Continuum Model (PCM) solvent model.     

1H–13C HMBC NMR experiments as a structural and analytical tool for the characterization of elusive trans/cis hydroperoxide isomers from oxidized unsaturated fatty acids in solution

The radical-dependent oxidation of unsaturated fatty acids is a fundamental reaction in lipid chemistry, biochemistry, and technology. We report herein the first successful application of ¹H–¹³C HMBC NMR experiment for the identification and quantification of complex and minor (3.9% to 0.85%) components of cis and trans primary hydroperoxide isomers of oxidized oleate and linoleate methyl esters in solution, without the need of laborious isolation of the individual components.     

Structure-NMR chemical shift relationships for novel functionalized derivatives of quinoxalines

(1)H, (13)C and (15)N NMR chemical shifts for a variety of novel quinoxalines were determined by different 2D methods and were calculated using the GIAO DFT approach. Comparison with experimental data shows good correlations in the case of (1)H, (13)C and (15)N chemical shifts. Different combinations of basis sets were tested. In non-polar solvents quinoxalines exist as dimers owing to strong hydrogen bonding. Calculations for dimers improve the correlation between experiment and theory. Additive empirical methods for estimating chemical shifts have drawbacks and have to be used with a great care for this type of compound.     

2-Polyfluoroalkylchromones. 12. Nitration of 5,7-dimethyl-2-polyhaloalkylchromones and complete assignment of signals in the 1H and 13C NMR spectra of 5,7-dimethyl-2-trifluoromethylchromone and its mono- and dinitro derivatives

The nitration of 5,7-dimethyl-2-polyhaloalkylchromones affords either 5,7-dimethyl-6-nitro- or 5,7-dimethyl-6,8-dinitro-2-polyhaloalkylchromones, depending on the reaction conditions. Signals in the ¹H and ¹³C NMR spectra of the sterically hindered chromones were completely assigned using the 2D NOESY, HETCOR, and COLOC spectra. The influence of nonplanar nitro groups on chemical shifts of carbon atoms was studied. Some spectral peculiarities of the peri-methyl group were revealed. The ¹H-¹H and ¹³C-¹H spin-spin coupling constants, including the extreme six-bond long-range coupling between the protons of the Me(5) group and H(8), were determined.     

NMR study of E/Z isomerism in N‐alkoxybenzoimidic acid derivatives

Well defined E/Z isomers of N‐methoxy‐p‐nitrobenzimidoyl chloride, N‐methoxybenzimidoyl chloride, methyl N‐methylbenzohydroximate and ethyl N‐hydroxybenzimidate were prepared in order to provide model data for studies of benzhydroximic acid derivatives and related compounds. NMR parameters [¹H, ¹³C and ¹⁵N chemical shifts and ¹J(¹³C, ¹³C) coupling constants] were determined. The results show that stereochemically most significant are the values of ¹J(¹³C, ¹³C) couplings between aromatic C_ipso and C?N carbons and that the relationship, |J_cis| > |J_trans|, known for this coupling from oximes, is not affected by electronegative substituents at the C?N carbon atom, but the values are. Copyright © 2002 John Wiley & Sons, Ltd.     

Flavonoid glycosides fromThalictrum squarrosum St. ex Willd. andThalictrum minus L.

Two flavonoid allose diglycosides were found in the terrestrial part ofThalictrum squarrosum St. ex Willd. andT. minus L. (Ranunculaceae). 7,4′-Di-O-β-allopyranosylapigenin was isolated fromT. minus. InT. squarrosum, its monoacetate was also found and characterized as 7-O-(6-O-acetyl-β-allopyranosyl)-4′-O-(β-allopyranosyl)apigenin. The sites of attachment of the carbohydrate residues were determined by HMBC; the location of the acetate group was identified by ROESY. Both substances were isolated from these plants for the first time. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 392–394, February, 1999.     

Multinuclear magnetic resonance study of the structure and tautomerism of azide and iminophosphorane derivatives of chloropyridazines

Some azido‐ and iminophosphorane derivatives of 3,6‐dichloro‐ and 3,4,5,6‐tetrachloropyridazine were synthesized and studied by means of NMR measurements. Based on multinuclear data (chemical shifts, coupling constants) for compounds containing the azide group, no potentially possible tetrazole–azide equilibrium can be observed, even under acidic conditions. An unusual substitution of a chlorine atom (in position 4) of tetrachloropyridazine in the reaction with hydrazine was demonstrated by NMR measurements of two newly synthesized compounds containing azido‐ and iminophosphorane groups. Using multinuclear magnetic resonance data, the sites of ethylation and protonation of azido‐ and iminophosphorane derivatives of chloropyridazines were established. In the case of the tetrazolopyridazines, ethylation occurs at the N1′ and N2′ atoms, whereas for monocyclic compounds it takes place at the N1 and/or N2 atoms of the pyridazine ring. Preferred sites of protonation are the N1′ atom of the tetrazole ring and the N1 atom of the pyridazine ring. Moreover, the structures of potassium salts of 6‐(3‐cyano‐1‐triazeno)tetrazolo[1,5‐b] pyridazine and its amido derivative were established using NMR data, especially ¹⁵N NMR chemical shifts. Copyright © 2002 John Wiley & Sons, Ltd.     

13C and1H NMR study of 3-R-substitutedtrans-2-oxadecalins and 1-R-substitutedcis- andtrans-2-oxahydrindans

Previously synthesized 3-substitutedcis- andtrans-2-oxadecalins and 1-substitutedcis- andtrans-2-oxahydrindans were studied by ¹³ C and ¹ H NMR. The structure and configuration of these compounds were established.A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 117912 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 861–865, April, 1992.     

Synthesis and structures of pyridoannelated 1,2,3,4-tetrazine 1,3-dioxides

Treatment of 2- and 4-amino-3-(tert-butyl-NNO-azoxy)pyridines with nitrating agents (N₂O₅or NO₂BF₄) afforded the first representatives of pyridoannelated 1,2,3,4-tetrazine di-N-oxides, viz., pyrido[2,3-e][1,2,3,4]tetrazine 1,3-dioxide (9), 7-nitropyrido[2,3-e][1,2,3,4]tetrazine 1,3-dioxide (10), and pyrido[3,4-e][1,2,3,4]tetrazine 2,4-dioxide (11). These compounds were studied by ¹H, ¹³C, and ¹⁴N NMR spectroscopy. The 1:1 complex of compound 10 with benzene was studied by X-ray diffraction analysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2471–2477, November, 2004.