- Two new methods for 2,3-pyridyne formation
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The compounds 2-chloro-4-methoxypyridine and 4-methoxy-2-trifluoromethylsulfonyloxy-3-trimethylsilylpyridine were shown to be relatively efficient precursors for 4-methoxy-2,3-pyridyne as was evidenced by its trapping with furan, 2-methylfuran and 2-methoxyfuran. These findings constitute the first published report of the use of either directed-deprotonation or fluoride-induced elimination to prepare the reactive 2,3-pyridyne intermediate.
- Walters, Michael A.,Shay, John J.
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Read Online
- Revealing the Macromolecular Targets of Fragment-Like Natural Products
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Fragment-like natural products were identified as ligand-efficient chemical matter for hit-to-lead development and chemical-probe discovery. Relying on a computational method using a topological pharmacophore descriptor and a drug database, several macromolecular targets from distinct protein families were expeditiously retrieved for structurally unrelated chemotypes. The selected fragments feature structural dissimilarity to the reference compounds and suitable target affinity, and they offer opportunities for chemical optimization. Experimental confirmation of hitherto unknown macromolecular targets for the selected molecules corroborate the usefulness of the computational approach and suggests broad applicability to chemical biology and molecular medicine. Target acquired: Hitherto unknown macromolecular targets of the fragment-like natural products goitrin, isomacroin, and graveolinine were discovered through the use of a computational target-prediction tool tailored for natural products. The results suggest that such methods will find application in target discovery for natural products and could inspire the design of new chemical entities for chemical biology and molecular medicine.
- Rodrigues, Tiago,Reker, Daniel,Kunze, Jens,Schneider, Petra,Schneider, Gisbert
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- THE MOLECULAR COMPLEX OF 4-(N-PYRIDINIUM)PYRIDINE-N-OXIDE CHLORIDE WITH TETRACYANOETHYLENE IN THE SYNTHESIS OF SUBSTITUTED PYRIDINE N-OXIDES
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The structure of the complex of 4-(N-pyridinium)pyridine-N-oxide chloride with tetracyanoethylene was studied by 13C NMR spectroscopy.The results of the investigation, suggesting the use of this complex in the synthesis of substituted pyridine derivatives, were confirmed experimentally by its reaction with oxygen and with nitrogen-containing nucleophiles.
- Rodina, L. L.,Ryzhakov, A. V.,Alekseeva, O. O.
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Read Online
- Method for preparing sulfone and N-oxygen compound by using green and efficient oxidation system
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The invention discloses a method for preparing sulfone and N-oxygen compound by using a green and efficient oxidation system. The method comprises the following steps of: by using a tertiary amine compound or aromatic thioether or fatty thioether compound as a raw material, H2O2 as an oxidant, methanol as a reaction solvent and potassium carbonate as an alkali, introducing sulfuryl fluoride 5O2F2gas as an accelerator; performing stirring at room temperature under a sealed condition for oxidation reaction; and after finishing the reaction, filtering to remove solid potassium carbonate, dryingto remove water, filtering to obtain a crude product, and finally carrying out column chromatography separation to obtain a pure product. Tertiary amine is oxidized into an N-oxygen compound, and thethioether is oxidized into sulfone. According to the method, the sulfuryl fluoride (SO2F2) which is very cheap and easy to obtain is used as the reaction promoter, green and environment-friendly hydrogen peroxide (H2O2) is used as an oxidizing agent, and so that the yield of the reaction is generally high; after the reaction, byproducts are only water and inorganic salts (SO4 and F) whichare easy to remove and free of pollution, and the green and efficient oxidation system can be realized, and therefore, the method is suitable for large-scale industrial production.
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Paragraph 0048-0050
(2021/01/29)
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- SO2F2-mediated oxidation of primary and tertiary amines with 30% aqueous H2O2 solution
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A highly efficient and selective oxidation of primary and tertiary amines employing SO2F2/H2O2/base system was described. Anilines were converted to the corresponding azoxybenzenes, while primary benzylamines were transformed into nitriles and secondary benzylamines were rearranged to amides. For tertiary amine substrates quinolines, isoquinolines and pyridines, their oxidation products were the corresponding N-oxides. The reaction conditions are very mild and just involve SO2F2, amines, 30% aqueous H2O2 solution, and inorganic base at room temperature. One unique advantage is that this oxidation system is just composed of inexpensive inorganic compounds without the use of any metal and organic compounds.
- Liao, Xudong,Zhou, Yi,Ai, Chengmei,Ye, Cuijiao,Chen, Guanghui,Yan, Zhaohua,Lin, Sen
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supporting information
(2021/11/01)
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- From Pyridine- N-oxides to 2-Functionalized Pyridines through Pyridyl Phosphonium Salts: An Umpolung Strategy
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The reactions of pyridine-N-oxides with Ph3P under the developed conditions provide an unprecedented route to (pyridine-2-yl)phosphonium salts. Upon activation with DABCO, these salts readily serve as functionalized 2-pyridyl nucleophile equivalents. This umpolung strategy allows for the selective C2 functionalization of the pyridine ring with electrophiles, avoiding the generation and use of unstable organometallic reagents. The protocol operates at ambient temperature and tolerates sensitive functional groups, enabling the synthesis of otherwise challenging compounds.
- Bugaenko, Dmitry I.,Yurovskaya, Marina A.,Karchava, Alexander V.
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supporting information
p. 6099 - 6104
(2021/08/03)
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- Visible-Light-Mediated C-H Alkylation of Pyridine Derivatives
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We report herein a visible-light-mediated C-H alkylation of pyridine derivatives that proceeds by simple combination of a large variety of N-alkoxypyridinium ions with alkanes in the presence of 2 mol % of fac-Ir(ppy)3 under blue illumination. The mild reaction conditions together with the high group functional tolerance make of this process a useful synthetic platform for the construction of structurally strained heterocycles. Detailed mechanistic investigations, including density functional theory calculations and quantum yield measurement, allowed us to understand factors controlling the reactivity and the selectivity of the reaction.
- Rammal, Fatima,Gao, Di,Boujnah, Sondes,Gaumont, Annie-Claude,Hussein, Aqeel A.,Lakhdar, Sami
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supporting information
p. 7671 - 7675
(2020/10/09)
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- Reaction of Pyridine-N-Oxides with Tertiary sp2-N-Nucleophiles: An Efficient Synthesis of Precursors for N-(Pyrid-2-yl)-Substituted N-Heterocyclic Carbenes
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N-(Pyrid-2-yl)-substituted azolium and pyridinium salts, precursors for hybrid NHC-containing ligands, were obtained with excellent regioselectivity, employing a deoxygenative CH-functionalization of pyridine-N-oxides with substituted imidazoles, thiazoles, and pyridine. Unlike the traditional SNAr-based methods, this approach provides high yields for substrates bearing substituents of different electronic nature. The utility of azolium and pyridinium salts thus prepared was also highlighted by the synthesis of pyridyl-substituted imidazolyl-2-thione, benzodiazepine as well as 2-aminopyridines.
- Bugaenko, Dmitry I.,Karchava, Alexander V.,Yurovskaya, Marina A.
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supporting information
p. 5777 - 5782
(2020/12/01)
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- Electrochemical Deoxygenation of N-Heteroaromatic N -Oxides
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An electrochemical method for the deoxygenation of N-heteroaromatic N -oxide to give the corresponding N-heteroaromatics has been developed. Several classes of N-heterocycles such as pyridine, quinoline, isoquinoline, and phenanthridine are tolerated. The electrochemical reactions proceed efficiently in aqueous solution without the need for transition-metal catalysts and waste-generating reducing reagents.
- Xu, H.-C.,Xu, P.
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supporting information
p. 1219 - 1221
(2019/06/08)
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- FUSED MORPHOLINOPYRIMIDINES AND METHODS OF USE THEREOF
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The present disclosure relates to Fused Morpholinopyrimidines, pharmaceutical compositions comprising an effective amount of a Fused Morpholinopyrimidine and methods for using a Fused Morpholinopyrimidine in the treatment of a neurodegenerative disease, comprising administering to a subject in need thereof an effective amount of a Fused Morpholinopyrimidine.
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Paragraph 1005
(2017/05/14)
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- Solvent- and halide-free synthesis of pyridine-2-yl substituted ureas through facile C-H functionalization of pyridine: N -oxides
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A novel solvent- and halide-free atom-economical synthesis of practically useful pyridine-2-yl substituted ureas utilizes easily accessible or commercially available pyridine N-oxides (PyO) and dialkylcyanamides. The observed C-H functionalization of PyO is suitable for the good-to-high yielding synthesis of a wide range of pyridine-2-yl substituted ureas featuring electron donating and electron withdrawing, sensitive, or even fugitive functional groups at any position of the pyridine ring (63-92%; 19 examples). In the cases of 3-substituted PyO, the C-H functionalization occurs regioselectively providing a route for facile generation of ureas bearing a 5-substituted pyridine-2-yl moiety.
- Rassadin, Valentin A.,Zimin, Dmitry P.,Raskil'dina, Gulnara Z.,Ivanov, Alexander Yu.,Boyarskiy, Vadim P.,Zlotskii, Semen S.,Kukushkin, Vadim Yu.
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p. 6630 - 6636
(2018/03/01)
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- FUSED MORPHOLINOPYRIMIDINES AND METHODS OF USE THEREOF
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The present invention relates to Fused Morpholinopyrimidines, pharmaceutical compositions comprising an effective amount of a Fused Morpholinopyrimidine and methods for using a Fused Morpholinopyrimidine in the treatment of a neurodegenerative disease, comprising administering to a subject in need thereof an effective amount of a Fused Morpholinopyrimidine.
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Paragraph 0320
(2015/05/19)
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- FUSED MORPHOLINOPYRIMIDINES AND METHODS OF USE THEREOF
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The present disclosure relates to Fused Morpholinopyrimidines, pharmaceutical compositions comprising an effective amount of a Fused Morpholinopyrimidine and methods for using a Fused Morpholinopyrimidine in the treatment of a neurodegenerative disease, comprising administering to a subject in need thereof an effective amount of a Fused Morpholinopyrimidine.
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Paragraph 0726
(2015/08/03)
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- Metal-free methylation of a pyridine N-oxide C-H bond by using peroxides
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Metal-free methylation of a pyridine N-oxide C-H bond was developed using peroxide as a methyl reagent under neat conditions. Pyridine N-oxide derivatives with various groups (e.g., Cl, NO2, and OCH3) were all suitable substrates, and the desired products were obtained in moderate to excellent yields under standard conditions. Moreover, the methylation can be performed with a good yield on the gram-scale experiment. Tentative mechanistic studies show that the methylation is a classical radical process.
- Li, Gang,Yang, Suling,Lv, Bingjie,Han, Qingqing,Ma, Xingxing,Sun, Kai,Wang, Zhiyong,Zhao, Feng,Lv, Yunhe,Wu, Hankui
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supporting information
p. 11184 - 11188
(2015/11/27)
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- PYRIDINYL-SUBSTITUTED PYRAZOLYL CARBOXAMIDES
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The invention relates to pyrazolyl-based carboxamide compounds useful as ICRAC inhibitors, to pharmaceutical compositions containing these compounds and to methods of using these compounds for the treatment and/or prophylaxis of diseases and/or disorders, in particular inflammatory diseases and/or inflammatory disorders.
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Paragraph 0438; 0439; 0440
(2015/06/24)
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- Rational design, synthesis, and characterization of deep blue phosphorescent Ir(III) complexes containing (4′-Substituted-2′- pyridyl)-1,2,4-triazole ancillary ligands
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On the basis of the results of frontier orbital considerations, 4-substituted-2′-pyridyltriazoles were designed to serve as ancillary ligands in 2-phenylpyridine main ligand containing heteroleptic iridium(III) complexes that display deep blue phosphorescence emission. The iridium(III) complexes, Ir1-Ir7, prepared using the new ancillary ligands, were found to display structured, highly quantum efficient (Φp = 0.20-0.42) phosphorescence with emission maxima in the blue to deep blue 448-456 nm at room temperature. In accord with predictions based on frontier orbital considerations, the complexes were observed to have emission properties that are dependent on the electronic nature of substituents at the C-4 position of the pyridine moiety of the ancillary ligand. Importantly, placement of an electron-donating methyl group at C-4′ of the pyridine ring of the 5-(pyridine-2′-yl)-3-trifluoromethyl-1,2,4-triazole ancillary ligand leads to an iridium(III) complex that displays a deep blue phosphorescence emission maximum at 448 nm in both the liquid and film states at room temperature. Finally, an OLED device, constructed using an Ir-complex containing the optimized ancillary ligand as the dopant, was found to emit deep blue color with a CIE of 0.15, 0.18, which is close to the perfect goal of 0.15, 0.15.
- Park, Hea Jung,Kim, Ji Na,Yoo, Hyun-Ji,Wee, Kyung-Ryang,Kang, Sang Ook,Cho, Dae Won,Yoon, Ung Chan
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p. 8054 - 8064
(2013/09/12)
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- Phosphorescent light-emitting iridium complex containing pyridyltriazole ligand
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An Ir complex having a pyridyl triazole ligand substituted with at least one substituent on its pyridyl ring, and a light emitting material comprising such Ir complex. Such light emitting material was found to have a significantly enhanced photophosphorescence quantum yield and hypsochromic blue shifted photophosphorescent emission over other Ir complexes with a pyridyl triazole ligand having no substituent in its pyridine ring. Use of such light emitting material and an organic light emitting device including the same.
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- Equilibrium of acyl transfer between pyridine N-oxides and their acylonium salts
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Transfer of acyl groups from N-acyloxypyridinium salts to pyridine N-oxides in acetonitrile was studied. The equilibrium constants of acyl exchange were determined. These quantities vary in the range covering eight orders of magnitude, depending on the st
- Rubachenko,Schroeder,Chotii,Kovalenko,Red'ko,Lenska
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p. 1241 - 1246
(2008/12/22)
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- Identical acyl transfer reactions between pyridine N-oxides and their N-acylonium salts
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28 identical acyl exchange reactions R-CO-Nu+, X- + Nu between pyridine N-oxides in acetonitrile were studied. Here, X- = BPh 4 - and R = methyl, N,N-dimethylamino, N,N-diethylamino, 4-morpholino, 1-piperidino, N-methyl, N-phenylamino, or N,N-diphenylamino group. The IR and NMR spectroscopic characteristics of acyloxypyridinium salts were determined, and the quantum-chemical parameters of all reagents calculated. The results were subjected to correlation analysis. It was found that the rate of identical acyl transfer reactions was controlled by the interaction of frontier orbitals in the transition state.
- Rybachenko,Shroeder,Chotii,Kovalenko,Red'Ko,Gierzyk
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p. 1608 - 1612
(2008/03/14)
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- Preparation, characterization, and aquation kinetics of pyridine N-oxide complexes of chromium(III)
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A series of (H2O)5Cr(X-pyO)3+ ions (pyO = pyridine N-oxide, X = H, 3-CH3, 4-CH3, 4-OCH3, 4-NO2) were prepared by the reduction of the corresponding pyridine N-oxide adducts of diperoxochromium(VI) species with acidic ferrous perchlorate. The (H2O)5Cr(X-pyO)3+ complexes undergo aquation to yield Cr(H2O)63+ and X-pyO according to the rate law kobs = ko + k -1[H+]-1. The values of the rate constants extrapolated to 298 K at 1.0 M ionic strength are: k0 = 2.80 × 10-6 s-1, k-1 = 1.86 × 10-8 M s-1 (X = 4-NO2); 7.80 × 10-8, 6.27 × 10-10 (H); 4.80 × 10-8, 3.20 × 10 -10 (3-CH3); 3.05 × 10-8, 1.60 × 10-10 (4-CH3); and 2.37 × 10-9, 4.76 × 10-11 (4-OCH3). The reaction of the 4-OCH 3 complex exhibits two additional terms in the rate law, k 1[H+] + k-2[H+]-2. The binding of 4-OCH3-pyO to chromium is suggested to take place through the methoxy group. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Kotowski, Mirjana,Marcec, Radovan,Butkovic, Vjera,Bakac, Andreja,Orhanovic, Matko
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p. 2894 - 2899
(2007/10/03)
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- Concise total syntheses of variolin B and deoxyvariolin B
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The total synthesis of the marine alkaloid variolin B has been achieved in 8 steps and 17% overall yield, starting from commercially available 4-chloro-2-methylthiopyrimidine. The key reaction involves the tandem deoxygenation and cyclization of a triarylmethanol using a combination of triethylsilane and trifluoroacetic acid. In addition, the deoxygenated analogue was prepared in 6 steps and 23% overall yield, starting from the same starting material.
- Anderson, Regan J.,Hill, Jonathan B.,Morris, Jonathan C.
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p. 6204 - 6212
(2007/10/03)
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- Rate and equilibrium constants of benzoyl group transfer between pyridine N-oxides
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Kinetic characteristics of 19 transfer reactions of benzoyl group from N-benzoyloxypyridinium salts to pyridine N-oxides and 4-dimethylaminopyridine were studied in acetonitrile by the stopped-flow method. The rate of an identical reaction for 4-methoxypyridine was measured by dynamic NMR spectroscopy. For 5 other identical reactions the rates were estimated from Bronsted correlations. Equilibrium constants were estimated with the use of UV spectrophotometry (6), IR spectroscopy (2), from kinetic data (K ij = k ij /k ji ) (2), and in one case as logK i-j = logK i-x - logK j-x . The second order rate constants (k ij ) varied in the range 102-105 l mol -1 s-1, the equilibrium constants (K ij ) in the range 102-10-2; the activation parameters (ΔH ≠) were within 15-50 kJ mol-1, (-ΔS ≠) -20-110 J mol-1 K-1. The reactions under study occur in a single stage following the concerted SN2 mechanism through an early associative transition state. The benzoyl groups exchange rate and equilibrium are well described by simplified Marcus equation (omitting the quadratic term). 2005 Pleiades Publishing, Inc.
- Rybachenko,Schroeder,Chotii,Lenska,Red'Ko,Kovalenko
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p. 774 - 778
(2007/10/03)
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- Stabilised 2,3-pyridyne reactive intermediates of exceptional dienophilicity
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The enhanced dienophilicity of 4-methoxy, 4-aryloxy and 4-thiophenoxy analogues 6-9 of 2,3-pyridyne (2) relative to 2 itself is reported. The regioselective lithiation of 4-alkoxy-(22, 23 and 25) and 4-thiophenoxy-2- chloropyridme (24) at low temperatures, followed by elimination of lithium chloride affords 4-alkoxy- and 4-thiophenoxypyridynes, which can be trapped in situ in a [4+2] cycloaddition reaction with furan to give endoxides 28-31 in moderate to good yields (25-58%). In contrast, precursors with a hydrogen (18) or methyl (12) substituent at C-4 give no evidence for pyridyne formation under these conditions. Attempts to generate 6-isopropoxy-2,3-pyridyne (10) from the low-temperature lithiation of 2-chloro-6-isopropoxypyridine were unsuccessful due to the instability of the 2-chloro-6-isopropoxy-5-lithiopyridine. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Connon, Stephen J.,Hegarty, Anthony F.
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p. 3477 - 3483
(2007/10/03)
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- Oxidation of substituted pyridines by dimethyldioxirane: Kinetics and solvent effects
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The second order rate constants for the oxidation of substituted pyridines by dimethyldioxirane at 23°C in dried acetone were found to correlate with sigma values (ρ = -2.91). The reaction was shown to be very sensitive to protic, polar solvents. The oxidation of a series of substituted pyridines by dimethyldioxirane (1) produced the expected N-oxides in quantitative yields. The second order rate constants (k2) for the oxidation of a series of substituted pyridines (2a-g) by dimethyldioxirane were determined in dried acetone at 23°C. An excellent correlation with Hammett sigma values was found (ρ = -2.91, r = 0.995). Kinetic studies for the oxidation of 4-trifluoromethylpyridine by 1 were carried out in the following dried solvent systems: acetone (k2 = 0.017 M-1 s-1), carbon tetrachloride/acetone (7:3; k2 = 0.014 M-1 s -1), acetonitrile/acetone (7:3; k2 = 0.047 M-1 s-1), and methanol/acetone (7:3; k2 = 0.68 M-1 s-1). Kinetic studies of the oxidation of pyridine by 1 versus mole fraction of water in acetone [k2 = 0.78 M-1 s-1 (χ = 0) to k2 = 11.1 M-1 s-1 (χ = 0.52)] were carried out. The results showed the reaction to be very sensitive to protic, polar solvents.
- Winkeljohn, W. Rucks,Vasquez, Pedro C.,Strekowski, Lucjan,Baumstark, Alfons L.
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p. 8295 - 8297
(2007/10/03)
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- The Rate and Equilibrium Constants for N-, O-Acyl Transfer
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Reactions with dimethylcarbamoyl group transfer from N-acylpyridinium salts to pyridine N-oxides and from N-acyloxypyridinium salts to pyridines in acetonirile solutions were studied. Their rate and equilibrium constants and activation parameters were determined. The reactions were shown to be one-step and to follow the SN2 mechanism. Equations relating the rate and equilibrium parameters of the N-O and O-N acyl transfer reactions to the basicity of the nucleophile and outgoing group were obtained.
- Rybachenko,Chotii,Kovalenko,Shreder
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p. 1695 - 1698
(2007/10/03)
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- Rate and Equilibrium Constants of Dimethylcarbamoyl Transfer between Pyridine N-Oxides
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Dimethylcarbamoyl transfer from N-acyloxypyridinium salts to pyridine N-oxides in acetonitrile occurs in one stage by the forced concerted SN2 mechanism. The rate and equilibrium of the reaction are fairly described by the Bronsted equation. The Marcus equation provides a much higher quality of reactivity predictions.
- Schroeder,Rybachenko,Chotii,Kovalenko,Grebenyuk,Lenska,Eitner
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p. 455 - 462
(2007/10/03)
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- Acetyl exchange between pyridine N-oxides in acetonitrile solutions: An attempt to apply the Marcus equation to acetyl transfer
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Forty-three (including eight identical) reactions of acetyl transfer from N-acetyloxypyridinium salts to pyridine N-oxides in acetonitrile solutions were studied. The rate constants k2 vary in the range 107-10-1 1 mol-1 s-1; the equilibrium constants K, in the range 107-10-7; the activation enthalpy ΔH≠, in the range 17-30 kJ mol-1; the activation entropy -ΔS≠, in the range 60-85 J mol-1 K-1; and the heat of reaction -ΔH0, within ±50 kJ mol-1. All reactions occur in a single stage by the concerted SN2 mechanism with a low degree of bond cleavage in the transition state. The rate and equilibrium of the acetyl exchange are satisfactorily described by the Bronsted equation. The quality of predicting the reactivity is substantially improved by introducing into the correlation equation a second parameter, the rates of identical reactions.
- Rybachenko,Schroeder,Chotii,Titov,Kovalenko,Leska,Grebenyuk
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p. 1608 - 1615
(2007/10/03)
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- Equilibrium of acetyl transfer between pyridine N-Oxides and their acetylonium salts
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The equilibrium constants of acetyl transfer between O-acetylonium salts of a series of pyridine N-oxides and 4-(4-dimethylaminostyryl)pyridine N-oxide in acetonitrile and methylene chloride were determined. The equilibrium constants correlate with the ac
- Rybachenko,Chotii,Kovalenko,Schroeder
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p. 786 - 788
(2007/10/03)
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- The Kinetics and Mechanism of the Reaction of Pyridine-N-Oxides with Alkyl Halides
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The kinetics of formation of N-alkoxypyridinium salts and their decomposition to the starting reagents in acetonitrile at 25°C is studied. The decomposition of the salts takes place only in the ion pair. Similar mechanism of proton and methyl group transfer in reactions with participation of pyridines and pyridine-N-oxides was demonstrated noted.
- Matveev,Koblik,Popov,Savelova,Matvienko
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p. 271 - 275
(2007/10/03)
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- Heats of acyl transfer from N-, O-acyl salts of organic bases to 4-dimethylaminopyridine N-oxide
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The heats of acyl exchange reactions between a number of N-, O-acyl salts and 4-dimethylaminopyridine N-oxide and 4-dimethylaminopyridine were measured in solutions of aprotic solvents. The spectroscopic characteristics and the electrolytic dissociation constants of the salts were obtained and the thermochemical and structural data compared. Changes in the heats under structural actions are satisfactorily described by a two-parameter correlation equation including the ionization potentials of bases and the integrated intensities of salt C=O stretching vibrations as variables.
- Rybachenko,Titov,Gol'dshtein,Grebenyuk,Chotii,Semenova
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p. 192 - 196
(2007/10/03)
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- Acyl transfer in the series of N-acyl(N-acyloxy)pyridinium salts
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The kinetics of acyl group transfer from N-acyl(N-acyloxy)pyridinium salts to 4-(p-dimethyl-aminostyryl)pyridine N-oxide in acetonitrile were studied, and the rate constants and activation parameters determined. Correlation equations were obtained connecting the reactivity and structural characteristics. The influence of the structure of the electrophile on the rate constants, activation parameters, and thermodynamic characteristics of the transition state were discussed.
- Rybachenko,Shreder,Titov,Chotiy,Semenova,Makarova
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p. 980 - 984
(2007/10/03)
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- An Improved Synthesis of Homoproline and Derivatives
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An improved, general synthesis of substituted homoprolines has been developed by using readily available substituted pyridines (1).A key step in this synthetic procedure involves the known conversion of pyridine-N-oxides to 2-cyanopyridines (3) in nearly quantitative yields.The resulting nitriles are hydrolyzed to the corresponding pyridine-2-carboxylic acids (4).Subsequent reduction of the aromatic ring with PtO2/H2 gives the homoprolines (5) in good yields as racemic cis isomers.This procedure also can be utilized for the preparation of 5,6-benzohomoprolines fromthe appropriate quinoline precursors.The N-tert-butyloxycarbonyl (Boc) derivatives of these amino acids (useful intermediates for peptide synthesis) were also prepared in good yields.
- Shuman, Robert T.,Ornstein, Paul L.,Paschal, Jonathan W.,Gesellchen, Paul D.
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p. 738 - 741
(2007/10/02)
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- UV-Spectroscopic Study of the Influence of Traces of Water on the Protolytic Equilibria of Substituted Pyridine N-Oxides in Aprotic Solvents
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Using a UV-spectrophotometric method, an attempt has been made to estimate quantitatively the influence of traces of water in aprotic solvents on the acidic-basic equilibria involving heterocyclic N-oxides.The N-oxides under study were pyridine N-oxide, (PyO), 4-methoxy-pyridine N-oxide (4-MeOPyO), and 2-, 3-, and 4-picoline N-oxide (2-, 3-, and 4-PicO).For particular N-oxide the UV-spectra of acetonitrile solutions containing the free base and/or its simple or semiperchlorate have been recorded.To carry out the calculations various equilibrium models which include the protolytic equilibrium with water and basic species present in the solvent have been tested using the program STOICHO which is based on nonlinear regression analysis.It turned out that apart from the acidic-basic dissociation of a protonated N-oxide and cationic homoconjugation (the equilibria which are usually considered in such systems) it is absolutely necessary to take into account the protolytic equilibria between the cationic acid and water present as impurity.Implications concerning investigations of other equilibrium systems in aprotic solvents and, in particular, the quality of the acidity constants for the calibration agents used in potentiometry are discussed.
- Liwo, Adam,Sokoloswki, Krzysztof,Wawrzynow, Alicja,Chmurzynski, Lech
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p. 1113 - 1124
(2007/10/02)
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- New description of substituent effect on electronic spectra by means of substituent constants-VI. Ultraviolet spectra of 4-substituted pyridine N-oxides and blue shifted iodine bands of their EDA complexes with iodine
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Electronic spectra of 4-substituted pyridine N-oxides and their EDA complexes with iodine were studied.The substituent effect on the near u.v. 1A1 intramolecular CT bands of the N-oxides and on the blue shifted iodine bands caused by CT complex formation are discussed in terms of a general equation, theoretically derived in order to describe the substituent effect on electronic spectra by means of substituent constants.The results are quite successful and supported by semi-empirical SCFMO-Cl calculations.Based on the results mentioned above, the character of n-? type N-oxide-iodine CT complexes is also examined.The complex formation constants(log K) and pKa values of the N-oxides correlate especially well, indicating that the CT interaction mechanism cannot be neglected in proton addition reactions such as hydrogen bonding and pKa values.
- Uno, Bunji,Kano, Kenji,Kaida, Naoki,Kubota, Tanekazu
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p. 937 - 944
(2007/10/02)
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- THERMODYNAMICS OF THE ASSOCIATION OF SUBSTITUTED PYRIDINE 1-OXIDES WITH 1-NAPTHOL IN METHYLENE CHLORIDE
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The effect of the structure of pyridine 1-oxides on their electron-donating power in the formation of a hydrogen bond with 1-napthol in methylene chloride was investigated.A relation was found between the thermodynamic and spectroscopic characteristics of the associate and the constants of the substituents in the pyridine 1-oxide in terms of the Yukawa-Tsuno equation.In contrast to the low basicity in water, the pyridine 1-oxides are some of the strongest organic bases in proton-inert media.
- Chimishkyan, A. L.,Grabarnik, M. S.,Orlov, S. I.,Kurkovskaya, L. N.,Perlov, A. V.
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p. 988 - 993
(2007/10/02)
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- The Equilibrium in the Formation of N-acetoxypyridinium Salts
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The interaction of pyridine N-oxides with acetyl chloride and acetyl bromide has been investigated in chloroform, methylene chloride, and acetonitrile.The equilibrium constants and the thermodynamic characteristics of the formation of N-acetoxypyridinium salts have been obtained.
- Rybachenko, V. I.,Chotii, K. Yu.,Kozhevina, L. I.,Titov, E. V.
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p. 813 - 816
(2007/10/02)
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- THERMAL AND PHOTOCHEMICAL DECOMPOSITION OF 3- AND 4-AZIDOPYRIDINE 1-OXIDES IN NUCLEOPHILIC SOLVENTS
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The thermolysis and photolysis of the title compounds in aniline, N-methylaniline, N,N-dimethylaniline, morpholine and dioxane containing methoxide ion in methanol afforded complex mixtures from which only major products were isolated.No ring-expansion products were detected.In aniline, many of its known oxidation products were found, the N-oxide acting as an oxidizing agent.Hydrogen-abstraction products were the main ones formed from pyridine 1-oxides.
- Abramovitch, Rudolph A.,Bachowska, Barbara,Tomasik, Piotr
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p. 805 - 815
(2007/10/02)
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