Intermolecular N-H...O Hydrogen Bonding Assisted by Resonance. II. Self Assembly of Hydrogen-Bonded Secondary Enaminones in Supramolecular Catemers

Bertolasi, Valerio; Gilli, Paola; Ferretti, Valeria; Gilli, Gastone

doi:10.1107/s0108768197008677

Cited by 60 publications

(32 citation statements)

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“…Although electron donation from N to O atoms always shortens the C-N bond and lengthens C=O, this effect is exaggerated by resonance-assisted hydrogen bonding [14]. Sometimes a cyclohexene ring is found in an almost ideal sofa conformation [15], but other reported structures differ greatly from it.…”

Section: Theoretical Calculationsmentioning

confidence: 90%

“…The heteroconjugated enaminone system HN-C=C-C=O in E139 would form resonance-assisted hydrogen bonds [14], and intermolecular bonds can give rise to infinite molecular chains called catemers. The cyclohexene ring holds the enaminone system in a fixed conforma- Hydrogen bonding area C tion, and theoretical ab initio calculations confirmed that the C11(S), C12(R) enantiomer with both substituents equatorial had the lowest energy.…”

Section: Structural Requirements For Anticonvulsant Activity Of E139mentioning

confidence: 99%

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X-Ray Crystallographic and Theoretical Studies of an Anticonvulsant Enaminone: Methyl 4-(4’-Bromophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate

et al. 2003

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Objective: The aims of this study were to establish the structure of the potent anticonvulsant enaminone methyl 4-(4′-bromophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (E139), and to determine the energetically preferred conformation of the molecule, which is responsible for the biological activity. Materials and Methods: The structure of the molecule was determined by X-ray crystallography. Theoretical ab initio calculations with different basis sets were used to compare the energies of the different enantiomers and to other structurally related compounds. Results: The X-ray crystal structure revealed two independent molecules of E139, both with absolute configuration C11(S), C12(R), and their inverse. Ab initio calculations with the 6-31G, 3-21G and STO-3G basis sets confirmed that the C11(S), C12(R) enantiomer with both substituents equatorial had the lowest energy. Compared to relevant crystal structures, the geometry of the theoretical structures shows a longer C–N and shorter C=O distance with more cyclohexene ring puckering in the isolated molecule. Conclusion: Based on a pharmacophoric model it is suggested that the enaminone system HN–C=C–C=O and the 4-bromophenyl group in E139 are necessary to confer anticonvulsant property that could lead to the design of new and improved anticonvulsant agents.

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Section: Theoretical Calculationsmentioning

confidence: 90%

Section: Structural Requirements For Anticonvulsant Activity Of E139mentioning

confidence: 99%

X-Ray Crystallographic and Theoretical Studies of an Anticonvulsant Enaminone: Methyl 4-(4’-Bromophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate

et al. 2003

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“…The dihedral angle between the leastsquares planes is 77.72(8)°,which is slightly larger than its relative structures because of the more bulky naphthyl group, but much bigger than its acyclic b-enaminone [4,5]. Unlike the acyclic b-enaminones [4,5], the formation of the intramolecular hydrogen bond is forbidden [6] because of the torsional strain in the cyclic compounds. Thus, the secondary amine can only give rise to intermolecular H-bonds with oxygen atom of carbonyl group.…”

Section: Experimnetal Detailsmentioning

confidence: 97%

Crystal structure of 5,5-dimethyl-3-(naphthalen-1- ylamino)cyclohex-2-enone, C18H19NO

Tang¹,

Li-Tao²,

Zhang³

et al. 2009

Zeitschrift Für Kristallographie - New Crystal Structures

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Source of materialAm ixture of the 5,5-dimethylcyclohexane-1,3-dione (2.86 g, 20.mmol), naphthalen-1-amine (2.75 g, 19.6 mmol) and sulfamic acid (0.2 g, 0.2 mmol) in methanol (5 mL) was stirred under reflux for 2hours. After completion of the reaction, it was evaporated to dryness, followed by chromatography to the pure enaminone 4.25.g(82 %). Experimnetal detailsHatoms bonded to Natoms were located in adifference Fourier map and refined isotropically without restraints. Hatoms bonded to Catoms were positioned geometrically and allowed to ride on their parent atoms with d(C-H) =0 .93 Å and U iso (H) =1 .2 U eq (C). The ketone-enaminone structure is manifested by the C13-O1 and C11-C12 bond lengths of 1.2480 Å and 1.3656 Å,respectively. The fragment (N1−C11−C12−C13−O1) is nearly planar (the maximum deviation being −0.009(2) Å for C11). The shortening of N1-C11 and C12-C13 bond length and coplanarity of the fragment indicates the significant conjugation. The other bond lengths and angles are quite typical, thus they don't call for further discussion. In the title compound, cyclohexanone ring adopts ah alf-chair conformation with the maximum deviation being 0.304(2) Å for C15. The naphthyl and cyclohexenone moieties are not coplanar. The dihedral angle between the leastsquares planes is 77.72(8)°,which is slightly larger than its relative structures because of the more bulky naphthyl group, but much bigger than its acyclic b-enaminone [4,5]. Unlike the acyclic b-enaminones [4,5], the formation of the intramolecular hydrogen bond is forbidden [6] because of the torsional strain in the cyclic compounds. Thus, the secondary amine can only give rise to intermolecular H-bonds with oxygen atom of carbonyl group. One-dimensional helical infinite chain via intramolecular Hbond is observed in the crystal. It is worthy of note, that the Hbond is nearly linear (N1−H1···O1 =174°).

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“…O tipo e o volume de substituintes em enaminonas acíclicas podem favorecer uma determinada forma isomérica, em razão de uma menor tensão estrutural ou de uma maior planaridade para conjugação de elétrons π 6,7 . O tautomerismo imino-enamina também pode favorecer o equilíbrio conformacional 8 , e o isômero cis-s-cis pode ser estabilizado por ponte de hidrogênio intramolecular (R 1 = H) [9][10][11] . A isomeria conformacional também é observada para o grupo amino (R 1 ≠ R 2 ), cuja restrição rotacional se intensifica proporcionalmente ao grau de conjugação no sistema enaminona 12 (neste caso a nomenclatura pode ser do tipo…”

Section: Introductionunclassified

Síntese de enaminonas

Ferraz¹,

Pereira²

2004

Quím. Nova

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Recebido em 18/9/02; aceito em 13/6/03 SYNTHESIS OF ENAMINONES. The general term "enaminone" is applied to any compound bearing the conjugated system N-C=C-C=O. Enaminones are typical capto-dative ethylenes, showing particular properties due to π-electron delocalization. Their reactivity can be predicted by structural patterns of substitution, conformation and configuration, making them versatile synthetic building blocks. In this review, a variety of methods for the synthesis of enaminones is described. The methods were divided into condensation of amines to β-dicarbonyl compounds, addition of amines to α,β-unsaturated carbonyl compounds, condensation between carbonyl compounds and N-unsaturated functions and other methods, covering the period from 1993 to 2001.Keywords: β-enamino ketones; β-enamino esters; methods of preparation. INTRODUÇÃOO termo geral "enaminona" refere-se a qualquer composto que apresente o sistema conjugado N-C=C-C=O. Enaminonas são compostos β-enamino carbonílicos, derivados de β-dicetonas, β-ceto ésteres e outros compostos β-dicarbonílicos. Os representantes mais comuns desta classe são β-enamino cetonas e β-enamino ésteres, também chamados de amidas vinílogas e carbamatos ou uretanas vinílogas, respectivamente; denominações como "β-aminoenona", "acilvinilamina" e "acilenamina" também são encontradas na literatura.Compostos deste tipo são considerados etilenos capto-dativos típicos, devido ao efeito mesomérico dos substituintes acil e amino sobre a ligação dupla (o que também é denominado efeito "pushpull" de elétrons) 1 . A deslocalização de elétrons π, decorrente deste efeito, tem como conseqüência uma notável polarização destes carbonos olefínicos (como se pode constatar pelos seus deslocamentos químicos de 13 C não usuais) 2 , conferindo a estes compostos uma natureza reativa distinta de seus correlatos estruturais enamina e enona (pela estabilização de seus estados de transição polares) 3 . O efeito mesomérico em enaminonas também é responsável pela coexistência de isômeros conformacionais e configuracionais, devido à restrição rotacional de ligações σ (aumento do caráter π das ligações N-C e C-CO) e à atenuação da barreira de isomerização da dupla ligação olefínica (caráter π diminuído) 4 , esta última podendo ocorrer até mesmo à temperatura ambiente 5 . Quatro formas isoméricas (Esquema 1) são possíveis, e a predominância e a interconversão entre elas dependem de diversos fatores estruturais. O tipo e o volume de substituintes em enaminonas acíclicas podem favorecer uma determinada forma isomérica, em razão de uma menor tensão estrutural ou de uma maior planaridade para conjugação de elétrons π 6,7 . O tautomerismo imino-enamina também pode favorecer o equilíbrio conformacional 8 , e o isômero cis-s-cis pode ser estabilizado por ponte de hidrogênio intramolecular (R 1 = H) [9][10][11] . A isomeria conformacional também é observada para o grupo amino (R 1 ≠ R 2 ), cuja restrição rotacional se intensifica proporcionalmente ao grau de conjugação no sistema enaminona 12 (neste caso a ...

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Intermolecular N-H...O Hydrogen Bonding Assisted by Resonance. II. Self Assembly of Hydrogen-Bonded Secondary Enaminones in Supramolecular Catemers

Abstract: The crystal structures of 15 compounds containing the 2-en-3-amino-l-one heterodienic system and forming intermolecular N--H...O hydrogen bonds assisted by resonance (RAHB) are reported: (1) 3-phenylamino-

Cited by 60 publications

References 31 publications

X-Ray Crystallographic and Theoretical Studies of an Anticonvulsant Enaminone: Methyl 4-(4’-Bromophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate

X-Ray Crystallographic and Theoretical Studies of an Anticonvulsant Enaminone: Methyl 4-(4’-Bromophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate

Crystal structure of 5,5-dimethyl-3-(naphthalen-1- ylamino)cyclohex-2-enone, C18H19NO

Síntese de enaminonas

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