The stereochemical investigation of 3-Aryl-4-methyl-1,2,3-oxathiazolidine 2-oxides using NMR

The title compounds were prepared by the reaction of the corresponding N-2-hydroxyisopropylanilines with thionyl chloride in the presence of triethylamine, and their pmr and cmr spectra were examined. On the basis of the chemical shifts due to the γ- and δ-effects, the stereochemical structures are discussed.     

Reactions of 2,4-disubstituted 5-nitro-1,2,3-triazole 1-oxides. 2. Oxidation of 2-substituted 4-amino(alkylamino)-5-nitro-1,2,3-triazole 1-oxides

The oxidation of substituted aminonitrotriazole oxides to the corresponding dinitro derivatives of triazole and azotriazole oxides has been studied. Communication 1, see ref. [1]. N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russia; e-mail: cheminst@mail.psu.ru. Institute of Chemical Physics at Chernogolovka, Russian Academy of Sciences, 124432 Chernogolovka, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1356–1362, October, 1999.     

A semiempirical conformational analysis of the 3-phenyl-1,2,3-oxathiazolidine 2-oxide

An extensive conformational search for the heterocyclic compound 3-phenyl-1,2,3-oxathiazolidine 2-oxide has been carried out using the semiempirical quantum-mechanical method PM3. All torsion angles were varied in the geometry optimization procedure which led to the prediction of four distinct conformers. Barriers to internal rotation leading to conformational interconversions were also calculated. The results of the present study indicate that this five-member ring substituted heterocyclic system may be expected to exist as a mixture of stable conformers rather than a unique molecular entity.     

Carbon-13 NMR studies of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. Conformational isomerism and substituent effects

Characteristic ^13C chemical shift ranges and substituent shifts of heterocyclic ring carbon atoms have been identified for a number of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. ¹³CNMR spectra may be used to detect slow internal rotation about the aryl C? N-1 bond in compounds with diastereomeric rotational isomers; many corresponding carbon atoms in the rotamers have distinctly different chemical shifts. The δ-effects originating from aryl ortho substituents are both electronic and steric in origin.     

Carbon-13 NMR studies on 3-phenyl-as-triazine 4-oxides

The substituent chemical shifts of a series of para substituted-3-phenyl-as-triazine 4-oxides were studied using the Swain-Lupton F and R values. This data was compared to that obtained for parasubstituted biphenyls, phenyl pyrroles and phenyl furans. It was found that the substituent chemical shifts in the triazines behaved in a similar manner to that in the biphenyl system.     

Solvent-Free Synthesis of 2-Amino-3-aryl-5-substituted Thiophenes as Anti-inflammatory Agents using KF-Al2O3 under Microwave Irradiation

The synthesis of 2-amino-3-aryl-5-substituted thiophenes as anti-inflammatory agents catalyzed by KF-Al₂O₃ under microwave irradiation is reported.     

Acylation of 2-aryl-5-imino-2,5-dihydro-1,2,3-thiadiazoles

A large series of new 5-acyl-and 5-sulfonylthiadiazolimines was prepared by acylation of 2-aryl-5-imino-2,5-dihydro-1,2,3-thiadiazoles. Compounds obtained are more stable than the initial substances and do not transform into 1,2,4-thiadiazoles.     

Conformational analysis of 2-methyl-5-alkyl- and 5-aryl-1,3,2-dioxaborinanes

Quantum chemical study of conformational isomerization of 2-methyl-5-alkyl- and 5-aryl-1,3,2-dioxaborinanes using RHF/6-31G(d) method led to the conclusion that the equilibrium between equatorial and axial sofa conformers is shifted to the latter form. Based on the experimental and theoretically calculated vicinal coupling constants J _HH the quantitative conformational composition and the values of ΔG ⁰ for substituents at the C⁵ ring atom were established.     

Synthesis of 3-substituted 4-imino-4,5-dihydro-1,2,3-triazole 1-oxides and 4-amino-1,2,3-triazole 1-oxides. Crystal and molecular structure of 4-imino-5,5-dimethyl-3-phenyl-4,5-dihydro-1,2,3-triazole 1-oxide

A new procedure for the synthesis of triazole N-oxides, based on base-induced intramolecular cyclization of 1-(-cyanoalkyl)-3-aryl(hetaryl)triazen-1-oxides, is proposed. An X-ray study of 4-imino-5,5-dimethyl-3-phenyl-4,5-dihydro-1,2,3-triazole 1-oxide was carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 746–751, April, 1993.     

Synthesis of 1-aryl-2-alkenyldiazene 1-oxides

1-Aryl-2-alkenyldiazene 1-oxides were prepared by the reactions of 1-aryl-2-bromodiazene 1-oxides with olefins followed by dehydrobromination of the intermediate 1-aryl-2-(-bromoalkyl)diazene 1-oxides by triethylamine.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 924–927, May, 1995.This work was carried out at the Scientific Educational Center of the Institute of Organic Chemistry of the RAS with financial support of the Russian Foundation for Basic Research (Project No. 93-03-18461).     

Conformational studies of N(3)-substituted [1,3,4]-oxadiazinan-2-ones

Pseudoephedrine-based [1,3,4]-oxadiazinan-2-ones acylated at the N(3)-position with either acetyl (2a), propionyl (2b), or phenylacetyl (2c) substituents are known to undergo conformational changes that are observable by (13)C NMR spectroscopy. The conformational properties of new [1,3,4]-oxadiazinan-2-one derivatives 2d-k are examined by X-ray crystallography and variable-temperature (13)C NMR spectroscopy and further evaluated by semiempirical AM1 calculations. The collected data reveal that the conformational changes of the overall ring system are dependent upon the stereoelectronic factors of the N(3)-substituent.     

Carbon-13 NMR studies on some 5-substituted quinoxalines

Eleven 5-substituted quinoxalines (NO₂, NH₂, COOH, OCH₃, CH₃, OH, F, Cl, Br, I, CN, the latter five not reported previously) have been synthesized by standard methods. Their ¹³C NMR spectra have been measured in DMSO-d₆ and assigned on the basis of substituent parameters, by line widths and by intensities. The chemical shifts compare favorably with those calculated using benzene substituent parameters, and are very close to those of corresponding carbons in 1-substituted phenazines. The correlation with the chemical shifts of the corresponding positions in 1-substituted naphthalenes is also close except for those of carbons 4a and 8a in the quinoxalines which, due to their proximity to nitrogen, are downfield (in some cases 12 ppm) of the signals of the corresponding carbons in naphthalene. 5-Fluoroquinoxaline was also measured in CDCl₃, CD₃COCD₃, CD₃CN, CD₃OD, C₆D₆ and CD₃COOD. In all solvents an abnormally low ²J(CF) (～ 12 Hz) was found for C-4a and no C? F spin-spin splitting could be detected for the three-bond coupling of C-8a. Similar abnormalities were found in 2-fluoroaniline and 2-fluoroacetanilide. There are linear relationships between the Q parameter of the substituent and the chemical shift of carbons 4a, 5 and 6. A linear relationship also exists between the chemical shift of C-8 (‘para’ position) and the Hammett σ_p parameter of the substituent.     

13C NMR spectra of cyclic nitrones. 2. 1- and 4-substituted 2,2,5,5-tetramethyl-3-imidazoline 3-oxides

The chemical shift of the carbon atom of the nitrone group in the ¹³C NMR spectra of 3-imidazoline 3-oxides lies in the region of 117–152 ppm and depends on the electronic effect of the substituants at positions 1, 4, and 5 of the heterocycle. Increase in the electron-withdrawing character of the substituent at these positions leads to an upfield shift of the signal for the nitrone carbon atom, and this corresponds to the increase in electron density on it.Communication 1 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, dp. 252–259, February, 1985.     

Carbon-13 NMR spectra of 3-aryl-2-thioxo-4-imidazolidinones. Conformational isomerism and substituent effects

A ¹³C NMR study of a series of 3-aryl-2-thioxo-4-imidazolidinones, which are capable of existing as enantiomeric or diastereomeric rotational isomers about the aryl C? N bond, shows that rates of internal rotation are slow at the probe temperature. The effects of hetero- and aryl-ring substituents on hetero-ring carbon atoms have been established.     

Carbon-13 chemical shifts of 3-substituted thietanes,thietane 1-oxides and thietane 1,1-dioxides

Carbon-13 chemical shifts of the α- and β-carbon atoms for 12 thietane 1,1-dixides, 9 thietane 1-oxides and 7 thietanes with a variety of 3-substituents [H, CH(CO₂Et)₂, SEt, Br, SPh, Ph, Cl, NMe₂, OH, OSiMe₃, OAc, OEt] are correlated according to the nature of the sulfur atom (Y=sulfone, sulfoxide, sulfide) and the nature of the 3-substituent (X) by the equations δ_α= a_Y+b_X and δ_β=a_X+b_Y, where a and b are parameters characteristic of X and Y. One-bond coupling constants [J(CH)] are reported for 21 compounds. The chemical shifts for the α- and the β-carbon atoms of the sulfones show the ‘fore-membered ring sulfone effect’ (α-carbon unusually deshielded, β-carbon unusually shielded), but the α-carbon-hydrogen coupling constants are similar to those of the sulfoxides and sulfides; the β-carbon-hydrogen coupling constants are sensitive to the nature of the substituent (X) but no special β-effect is observed. Comparison of the chemical shifts of the α-methylene carbon atoms of 3-phenyl-, 3-(β-naphthyl)- and 3-(α-thienyl)-thietes with those of the coresponding sulfones also reveals the ‘four-membered ring sulfone effect’ cis- and trans-3-Substituted thietane 1-oxides may be distinguished by the greater downfield shift for the β-carbon atom in the trans-isomer.     

Conformational analysis of 5-substituted 1,3-dioxanes

Quantum-chemical study on the potential energy surface of 5-alkyl- and 5-phenyl-1,3-dioxanes at the RHF/6-31G(d) level of theory revealed two pathways for conformational isomerizations of the equatorial and axial chair conformers. Potential barriers to this process were estimated. The Gibbs conformational energies ΔG° of substituents at C⁵ in the 1,3-dioxane ring were determined on the basis of experimental (¹H NMR) and theoretical vicinal coupling constants, which turned out to be consistent with published data.