- A novel method for the synthesis of 2-ketomethylquinolines under solvent-free conditions using microwave irradiation
-
Several 2-ketomethylquinolines are synthesized by heating 2-methylquinolines with acyl chlorides, in a conventional microwave oven.
- Loghmani-Khouzani, Hossein,Sadeghi, Majid M.,Safari, Javad,Minaeifar, Alireza
-
p. 4363 - 4364
(2007/10/03)
-
- Substituent and temperature controlled tautomerism: Multinuclear magnetic resonance, X-ray, and theoretical studies on 2-phenacylquinolines
-
Proton-transfer equilibria in chloroform solution of twelve 2-phenacylquinolines were studied by 1H, 13C and 15N NMR spectroscopies. The (Z)-enaminone form stabilized by an intramolecular hydrogen bond was found to prevail in all cases. Electron-donating substituents in the phenacyl part of the molecule lead to an increase of the ketimine form (to 33% for p-NMe2). Variable temperature 1H NMR measurements show that higher temperatures have the same effect. The negative logarithm values of the equilibrium constant, pKT, were found to be linearly dependent on Hammett σ substituent constants. The pKT vs. temperature correlation also has a linear character. In general, strong electron-withdrawing substituents cause transformation of the ketimine to the enaminone form to become more exothermic but values of the heat of reaction for 2-phenacylquinolines studied are not linearly dependent on σ. X-Ray data show that the strength of the internal hydrogen bond in the enaminone form increases for strong electron-withdrawing substituents. Rough estimation shows this bond to be stronger in chloroform solution than in the crystalline state. π-Electron delocalization in the six-membered quasi-ring involving the H...O bond is very strong. This effect is responsible for the predominance of the tautomeric enaminone form in 2-phenacylquinolines. On the other hand, semiempirical AM1 and PM3 calculations show that in the gas phase the ketimine tautomer is energetically favored in most cases.
- Kolehmainen, Erkki,Osmialowski, Borys,Krygowski, Tadeusz M.,Kauppinen, Reijo,Nissinen, Maija,Gawinecki, Ryszard
-
p. 1259 - 1266
(2007/10/03)
-
- The Use of 1H-15N Coupling Constants for the Investigation of Tautomeric Equilibria of Azines
-
15N-1H coupling constants can be measured over a large range by means of the Broadband-INEPT NMR-technique.These coupling constants are used to determine the positions of tautomeric equilibria of 2-(acetylmethyl)-azines with high accuracy. - Keywords: Azine tautomerism; Broadband-INEPT, 15N NMR
- Mueller, Norbert,Lapachev, Vjacheslav V.
-
p. 1201 - 1204
(2007/10/02)
-
- The Mechanism of Imine-Enamine Tautomerism of 2- and 4-Phenacylquinolines
-
Isomerisations of 2- and 4-phenacylquinolines to their enaminone tautomers via 1,3 or 1,5 carbon-nitrogen hydrogen shifts occur by stepwise acid- or base-catalysed pathways simolar to those for the enolisation of ketones.The reactions are observed as relaxations of the unstable to stable tautomers by stopped-flow spectrophotometry or, where the aromatic imine is the stable form, by trapping the enaminone with iodine in the reverse reaction.Evidence of mechanism comes from observations of general acid and general base catalysis, agreement between kinetically determined pKa values and independently measured values, and comparisons between rate and equilibrium constants for protonation of the enaminone tautomers and their N-methyl derivatives.The reactions show a primary isotope effect and yield normal Broensted plots with α ca. 0.5.The kinetically determined pKa values indicate N- rather than O-protonation of phenacylquinolines but for the enaminones O-protonation competes kinetically with the thermodynamically preferred C-protonation.Combination of pKa values for C-, N-, and O-protonation leads to equilibrium constants Kτ for enamine-imine and (protonated) keto-enol tautomerisation.The effect of 2- and 4-N-protonation (proton activating factors) upon rates and equilibria for ionisation of hydrogen from the methylene carbons is discussed and evidence of 'imbalance' in charge development on the carbon base in the transition state is noted.A concerted intramolecular 1,3-proton transfer is predicted but not observed.
- Carey, A. R. Edwin,Fukata, Gouki,O'Ferrall, Rory A. More,Murphy, Michael G.
-
p. 1711 - 1722
(2007/10/02)
-