- Chemistry of ketoacetals: II. β,β′-Ketodiacetal and β,β′-hydroxydiacetals in reactions with amminia and amines
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β,β′-Ketodiacetal and β,β′-hydroxydiacetals react with ammonium acetate in acetic acid to afford substituted pyridine, and with aromatic amines in the presence of hydrochloric acid form substituted pentamethine salts. 2005 Pleiades Publishing, Inc.
- Kharitonova,Panin,Belova
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- 3-Hydroxypyrroles and 1H-pyrrol-3(2H)-ones. Part 14. Pyrolysis of oxazolidinylmethylene derivatives of Meldrum's acid - Synthesis of N-alkenyl-3-hydroxypyrroles and related reactions
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Flash vacuum pyrolysis (FVP) of the title compounds 14 and 17 at 600-625°C (0.005 Torr) gives the N-alkenyl-pyrrolones 22 and 23 respectively. The mechanism is shown to involve hydrogen transfer and cyclisation of the methyleneketene intermediate (e.g. 25) to a fused pyrrolone (e.g. 28). This species fragments to create an azomethine ylide which provides the alkenyl substituent by a further hydrogen transfer. Similar reactions are shown by the thiazolidine derivatives 20 and 21, though in the latter case the initial bicycles 35 and 37 can be observed by NMR spectroscopy. When the normal sites for hydrogen transfer are blocked by substituents (as in compound 16) an alternative hydrogen transfer-cycloaddition sequence leads to the fused pyridin-4-one 43.
- Gaber, Abd El-Aal M.,Hunter, Gordon A.,McNab, Hamish
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p. 548 - 554
(2007/10/03)
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- Equilibration of N-(2-cyanoethyl)pyridinium cations with substituted pyridines and acrylonitrile. A change in rate-determining step in an E1cb reaction
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The rates of equilibration of N-(2-cyanoethyl)pyridinium cations (1) with the corresponding pyridines and acrylonitrile have been measured in aqueous solutions of ionic strength 0.1 at 25 °C. Second-order rate constants (kOH) have been obtained for the hydroxide ion catalyzed elimination reactions of 16 ring-substituted 1 having pyridine leaving groups of pKBH in the range 1.5-9.7. Bronsted plots of log kOH vs pKBH are "concave down" with two distinct linear regions having β1g = -0.30 (for pKBH 1g = -0.93 (for pKBH > 5.8). This observation is consistent with a change in rate-determining step within an E1cb reaction mechanism from rate-determining deprotonation of 1 (i.e., (E1cb)irrev) for pKBH rev) for pKBH > 5.8. This interpretation is supported by 1H NMR spectral observations in basic D2O, which show no incorporation of deuterium into the acrylonitrile product for pKBH BH > 5.8. Rates of nucleophilic attack of pyridines and pyridinone anions (pKBH > 6) upon acrylonitrile have also been measured. These display a linear Br?nsted plot of βnuc = 0.20. Combination of β1g and βnuc gives βeq = 0.13 for the Michael-type addition of pyridinium cations to acrylonitrile to produce 1. Although the rates of the addition of pyridines of pKBH nuc = 0.20 for pyridines of pKBH > 5.8 to rate-determining protonation of the carbanionic intermediate with βnuc = 0.83 for pyridine nucleophiles of pKBH irrev region but is extremely weak under the current experimental conditions.
- Bunting, John W.,Toth, Andrea,Heo, Christina K. M.,Moors, Rodney G.
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p. 8878 - 8885
(2007/10/02)
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- The Photo-initiated Substitution Reaction of 4-Chloropyridine and the Related 1-(4'-Pyridyl)-4-pyridone with Benzophenone in Aqueous 2-Propanol
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4-Chloropyridine (1) converts to 1-(4'-pyridyl)-4-pyridone (4) in aqueous 2-propanol.The photo-initiated reaction of both of these compounds in acidic and non-acidic 4:1 2-propanol/water with and without benzophenone is reported.
- Cosgrove, John P.,Vittimberga, Bruno M.
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p. 1277 - 1280
(2007/10/02)
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- EFFECT OF THE POSITION OF THE NITROGEN ATOM IN HETERO- AND HOMOAROMATIC HYDROXY COMPOUNDS ON THE CONTENT OF THE HIGHLY POLAR TAUTOMER OF AN ORGANIC AMPHOLYTE IN WATER
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In the transition from 3-hydroxypyridine to 3-aminophenol the content of the highly polar tautomer is reduced by 1E4 times, while in the transition from 4-hydroxypyridine to 4-aminophenol it is reduced by 1E5 times.In the series of aminophenols the transition from the 3- to the 4-isomer leads to an increase of an order of magnitude in the content of the highly polar tautomer.The results from calculations of the content of the highly polar tautomer in the 3- and 4-aminophenol systems by a method where the acid-base constants of the systems and model compounds were used show that it is large enough at the isoelectric point (1E-3 and 1E-4 mole percent respectively) to be taken into account during discussion of the characteristics of these systems.The content of the highly polar tautomer is determined not only by the acidity of the hydroxy group in the molecule of the low-polarity tautomer and by the basicity of the endo- or exocyclic nitrogen atom in it but also by the stability of the molecule of highly polar tautomer.The latter, in turn, depends on the possibility of conjugation in its molecule.
- Zaionts, V. I.,Korovitskaya, L. A.,Agrest, F. B.,Gutshabach, E. Sh.,Yachkula, S. S.
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p. 1153 - 1158
(2007/10/02)
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- Theoretical Description of Solvent Effects. V. The Medium Influence on the Lactim-Lactam Tautomerism of Hydroxyazines
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Der Loesungsmitteleffekt auf die Tautomeriegleichgewichte der Titelverbindungen wird mit Hilfe klassischer und quantenchemischer Versionen der Solvatonen- und der Reaktionsfeldtheorie berechnet.In Uebereinstimmung mit dem Experiment ergeben alle getesteten Verfahren eine Gleichgewichtsverschiebung zugunsten der Lactamform.Zur quantitativen Beschreibung dieses Effektes ist jedoch das Reaktionsfeldmodell besser geeignet.
- Krebs, C.,Foerster, W.,Weiss, C.,Hofmann, H.-J.
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p. 369 - 378
(2007/10/02)
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- Synthetic Applications of N-N Linked Heterocycles. Part 12. The Preparation of 4-Alkylthio- and 4-Arylthio-pyridines by Regiospecific Attack of Thioalkoxide Ions on N-(4-Oxopyridin-1-yl)pyridinium Salts
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Thiolate ions add regiospecifically to N-(4-oxopyridin-1-yl)pyridinium salts (2)-(7) to give in good to excellent yields only the 1,4-dihydropyridine adducts (8)-(13), regardless of whether or not the pyridone moiety carries substituents for sterically shielding the 2- and 6-positions of the pyridinium ring.The addition is believed to be thermodynamically controlled.Decomposition of the dihydro-adducts under free-radical conditions, or by pyrolysis, gives good yields of pyridin-4-yl thioethers (14) and (16) though the reaction failed with the 2-methyl adducts (9).An improved synthesis of 6-methyl-4-oxopyran-2-carboxylic acid is also described.
- Sammes, Michael P.,Leung, Christopher W. F.,Mak, Chi Keung,Katritzky, Alan R.
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p. 1585 - 1590
(2007/10/02)
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- Transacylations with Acyl Derivatives of 4-Pyridones
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Aliphatic and aromatic amines as well as thiols react with N-acyl-4-pyridones (2a, b) and with 4-(benzoyloxy)pyridine (3a) in methylene chloride or chloroform to give the N-substituted amides 4-6 and the thiol esters 7 and 8, respectively, with very good yields.Primary and secondary alcohols react more slowly, tert-butyl alcohol only with 3a to the tert-butyl esters 12 under basic catalysis or with the much more reactive N-(trihaloacetyl)-4-pyridones 3b, c.N-Acetyl-4-pyridone (2a) possesses a much higher acylation potential than N-acetylimidazole (13a).
- Effenberger, Franz,Bessey, Eberhard
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p. 2100 - 2109
(2007/10/02)
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- Displacement of Protomeric Equilibria by Self-Association: Hydroxypyridine-Pyridone and Mercaptopyridine-Thiopyridone Isomer Pairs
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Values of both self-association and protomeric equilibrium constants are reported for 2-hydroxypyridine-2-pyridone, 4-hydroxypyridine-4-pyridone, and 2-mercaptopyridine-2-thiopyridone isomer pairs in different solvents.These results provide quantitative evidence for significant differences in the positions of protomeric equilibria for self-associated and monomeric species.The 2-substituted isomers are associated as well-known dimers while the 4-substituted systems form oligomers.In polar and hydrogen-bonding solvents self-association is substantially reduced.Sterically hindered 2- and 4-pyridones are less associated than unhindered systems.The implication of these results, that determinations and interpretations of protomeric equilibrium should take into account the possible dominance of self-association, is discussed.
- Beak, Peter,Covington, Johnny B.,Smith, Stanley G.,White, J. Matthew,Zeigler, John M.
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p. 1354 - 1362
(2007/10/02)
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