Electron ionisation induced fragmentation of ethyl 5(1H)‐oxo‐ and 7(1H)‐oxo‐1‐aryl‐2,3‐dihydroimidazo[1,2‐a]‐pyrimidine‐6‐carboxylates: evidence for an unusually regioselective rearrangement of M+• ions

Ovcharenko, Vladimir V.; Pihlaja, Kalevi; Matosiuk, Dariusz

doi:10.1002/rcm.535

Cited by 6 publications

(3 citation statements)

References 7 publications

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“…As a continuation of our electron ionization mass spectrometric studies of compounds being able to exhibit tautomeric forms, [1][2][3][4][5][6][7][8][9] we decided to study the behavior of 2phenacylpyridine (1a) and its derivatives (1b-n) substituted in the benzene ring ( Figure 1). It is known that in chloroform these compounds exist in equilibrium with (Z)-2-(2hydroxy-2-phenylvinyl)pyridines.…”

Section: Introductionmentioning

confidence: 99%

Electron Ionization Mass Spectra and Tautomerism of 2-Phenacylpyridines

Martiskainen

Gawinecki²,

Ośmiałowski³

et al. 2006

Eur J Mass Spectrom (Chichester)

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The electron ionization mass spectra of 2-phenacylpyridine (ketimine form) and its 13 derivatives substituted in the benzene ring (1an: a R = H, b 3-Me, c 4-Me, d 4-NH(2), e 3-F, f 4-F, g 4-OMe, h 4-Cl,i 4-N(CH(3))(2),j 4-NO(2), k 4-CF(3), l 4-N(CH(2))(4), m 4- Br, n 3-Br) were recorded at 70 eV to determine the fragmentation routes and to screen the presence of their enolimine tautomers, (Z-)-2-(2-hydroxy-2-phenylvinyl)pyridines in the gas phase. The total ion currents (TIC) of the ions [MH](+), [MHCO](+), 2-PyCH(2)O(+), and RC(6)H(4)CO(+) (= ArCO(+) ) showed a fair or good correlation with the Hammett s constants (R = 0.859, 0.876, 0.912, and 0.926, respectively). The relative abundances (RA) of both the [MCO](+.) and the [MHCO](+) ion increased with the decreasing electron donating ability of the substituents and also correlated relatively well with the Hammett constants (R = 0.834 and 0.907, respectively). These observations, in comparison to the NMR results, show that the relative contribution of the ketimine tautomer also increases in the gas phase with the increasing electron donating ability of the phenyl substituent, i.e. the TIC of the ArCO(+) ion decreases whereas that of [MH](+) ion increases.

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Section: Introductionmentioning

confidence: 99%

Electron Ionization Mass Spectra and Tautomerism of 2-Phenacylpyridines

Martiskainen

Gawinecki²,

Ośmiałowski³

et al. 2006

Eur J Mass Spectrom (Chichester)

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“…ions to the total ion current in the spectra of compounds 5 is greater by an order of magnitude than in compounds 4. The mass spectra are described in more details elsewhere [10].…”

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The psuedo‐michael reaction of 2‐aminoimidazolines 2. Part 1. Synthesis and structure assignment of isomeric 5(1H)‐Oxo and 7(1H)‐Oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates

Matosiuk

Pihlaja

Ovcharenko

et al. 2003

Journal of Heterocyclic Chem

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The pseudo-Michael reaction of 1-aryl-2-aminoimidazolines-2 with diethyl ethoxymethylenemalonate (DEEM) was investigated. Extensive structural studies were performed to confirm the reaction course. For derivatives with N1 aromatic substituents, it was found that the reaction course was temperature dependent. When the reaction temperature was held at -10 °C only the formation of 1-aryl-7(1H)-oxo-2,3-dihydroimidazo[1,2-a]pyrimidine-6-carboxylates (4) was observed in contrast to earlier suggestions. Under the room temperature conditions, the same reaction yielded mixtures, with varying ratio, of isomeric 1-aryl-7(1H)-oxo-(4a-4f) and 1-aryl-5(1H)-oxo-2,3-dihydroimidazo[1,2-a]pyrimidine-6-carboxylates (5a-5f). The molecular structure of selected isomers, 4b and 5c, was confirmed by X-ray crystallography. Frontal chromatography with delivery from the edge was applied for the separation of the isomeric esters. The isomer ratio of the reaction products depended on the character of the substituents on the phenyl ring. The 1-aryl-7(1H)-oxo-carboxylates (4a-4f) were preferably when the phenyl ring contained H, 4-CH 3 , 4-OCH 3 and 3,4-Cl 2 substituents. Chloro substitution at either position 3 or 4 in the phenyl ring favored the formation of isomers 5a-5f. The isomer ratios were confirmed both by 1 H NMR and chromatography. The reaction of the respective hydrobromides of 1-aryl-2-aminoimidazoline-2 with DEEM, in the presence of triethylamine, gave selectively 5(1H)-oxo-esters (5a-5f). J. Heterocyclic Chem., 40, 93 (2003).Diethyl ethoxymethylenemalonate (DEEM) is a wellknown reagent for heterocyclic annelation. Its reaction with 2-aminoazaheterocycles has been widely used to obtain fused pyrimidines bearing the β-oxo-acid moiety. To date, the formation of 4-oxo-pyrimidine-3-carboxylates has been reported [1]. Only Agata [2] and Koekoesi et al [3,4] suggested that the NH-C=NH system (e.g. present in cyclic amidines) can yield mixtures of isomeric products (2-or 4-oxo esters) when reacted with Michael reagents such as DEEM. Their results indicated that the isomer ratio depended only on the ring size. The main product was always a 4-oxo isomer, which suggested that reaction starts at the exo N6 nitrogen atom.At present the molecular geometry of three 5(1H)-oxo-2,3-dihydroimidazo[1,2-a]pyrimidine derivatives are known; two with N8-phenyl [5,6] and one with N1-methyl [7] substitution. The 7(1H)-oxo-2,3-dihydroimidazo[1,2-a]pyrimidine system has not been reported earlier.Differences in the structures of 1-aryl-2,3-dihydroimidazo[1,2-a]pyrimidine result from the location of the carbonyl group; in the 5-oxo compound, one of the guanidine N-atoms is part of the lactam group whereas in the case of the 7-oxo compound the carbonyl and the C5-C6 double bond give the pyrimidine ring a pseudo-quinoid character.Pharmacological activity of isomeric esters on the CNS of laboratory animals (mice, rats) was reported [8] and

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“…We have previously made use of electron ionization mass spectrometry (EI‐MS) to study compounds with possible tautomeric forms 1–13. In the present work we set out to study a set of 2‐phenacylquinoline derivatives 1a – h (Fig.…”

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Electron ionization mass spectra and tautomerism of substituted 2‐phenacylquinolines

Martiskainen

Gawinecki

Ośmiałowski

et al. 2009

Rapid Comm Mass Spectrometry

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Tautomerism has been studied conventionally in solutions or in the solid state. However, the importance of mass spectrometry in the gas phase was realized relatively late. 2-Phenacylquinolines are known to undergo ketimine-enaminone tautomerism. The ratio of tautomers is dependent on the nature of the phenyl ring substituent and the Hammett substituent constants sigma. Theoretical calculations indicate the presence of ketimine and enaminone tautomers in the gas phase. The electron ionization mass spectra of eight 2-phenacylquinolines (ketimine form) were recorded at 70 eV in order to determine the fragmentation routes and to screen for the presence of their enaminone tautomers, (Z)-2-benzoylmethylene-1,2-dihydroquinolines, in the gas phase. The relative abundances or total ion currents of some ions correlated with the Hammett substituent constants and Hammett-Brown constants. The product ions [M-CO](+.) and [M-HCO](+) were observed. A reaction mechanism is suggested for the formation of these ions, requiring skeletal rearrangements. The results furnish information relating to tautomerism in the gas phase.

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Electron ionisation induced fragmentation of ethyl 5(1H)‐oxo‐ and 7(1H)‐oxo‐1‐aryl‐2,3‐dihydroimidazo[1,2‐a]‐pyrimidine‐6‐carboxylates: evidence for an unusually regioselective rearrangement of M^+• ions

Cited by 6 publications

References 7 publications

Electron Ionization Mass Spectra and Tautomerism of 2-Phenacylpyridines

Electron Ionization Mass Spectra and Tautomerism of 2-Phenacylpyridines

The psuedo‐michael reaction of 2‐aminoimidazolines 2. Part 1. Synthesis and structure assignment of isomeric 5(1H)‐Oxo and 7(1H)‐Oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates

Electron ionization mass spectra and tautomerism of substituted 2‐phenacylquinolines

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