Mechanism of rearrangement reactions of ketenimine–4-acylfuran-2,3-dione cycloadducts—a semiempirical molecular orbital study

Fabian, Walter M. F.; Kollenz, G.

doi:10.1039/p29950000515

Cited by 9 publications

(5 citation statements)

References 17 publications

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“…Paths A2 and B are, however, both consistent with the 17 O isotope distribution in 8 obtained from differently labeled 1 . Activation energies calculated by AM1 for path A2 are significantly higher than those obtained for path B …”

Section: Introductionsupporting

confidence: 71%

“…At least three pathways leading to 8 are conceivable (Scheme ): (i) [4 + 2] cycloaddition of the CC double bond of the ketene imine across the oxa 1,3-dienic subunit of 1 to yield the primary cycloadduct 3 , followed by direct rearrangement to 8 (path A1 in Scheme ); (ii) stepwise rearrangement 3 → 5 → 7 → 8 (path A2 in Scheme ); and (iii) addition of the ketene imine CN double bond across the oxa 1,3-diene to give the primary cycloadduct 4 , followed by a sequence of ring opening/recyclizations ( 4 → 6 → 8 , path B in Scheme ). Isotopic labeling studies as well as semiempirical molecular orbital calculations are inconsistent with path A1. Paths A2 and B are, however, both consistent with the 17 O isotope distribution in 8 obtained from differently labeled 1 .…”

Section: Introductionmentioning

confidence: 99%

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Substituent Effects on Site Selectivity (CC vs CN) in Heterocumulene−Heterodiene [4 + 2] Cycloadditions: Density Functional and Semiempirical AM1 Molecular Orbital Calculations

Fabian

Kollenz

1997

J. Org. Chem.

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The effect of substituents on the site selectivity (C=C vs C=N) in the [4 + 2] cycloaddition between heterocumulenes (ketene imines) 2a-g with heterodienes (acroleines 9a-n and 4-acylfuran-2,3-diones 1a-d) is treated by semiempirical AM1 molecular orbital and density functional calculations using Becke's three-parameter hybrid method (B3LYP/6-31G). For some reactions calculations were also done at the B3LYP/6-31+G level of theory. For reaction of the oxa 1,3-dienes with ketene imines unsubstituted at the terminal carbon invariably addition across the C=C heterocumulene double bond has a lower activation energy than addition across the C=N double bond. Substitution of methyl or especially phenyl groups at the ketene imine C-terminus leads to a reversal of the respective activation energies. Incorporation of the oxa 1,3-diene system into the heterocyclic dione 1 substantially enhances the reactivity ( approximately 10 kcal mol(-1) lower activation energies) as compared to similarly substituted acroleins. At the DFT level of theory all reactions are found to proceed via a concerted asynchronous mechanism.

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Section: Introductionsupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Substituent Effects on Site Selectivity (CC vs CN) in Heterocumulene−Heterodiene [4 + 2] Cycloadditions: Density Functional and Semiempirical AM1 Molecular Orbital Calculations

Fabian

Kollenz

1997

J. Org. Chem.

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“…The formation of similar tropylium cation radicals for azulene and its derivatives have been identified by electron spin resonance spectroscopy in the literatures. 43,44 The energy levels of the HOMO and LUMO of the polymers were estimated from the oxidation onset (E onset ) and the onset absorption wavelength of the UV-vis spectra, and the results are given in Table 3.…”

Section: Resultsmentioning

confidence: 99%

“…The electron removal for polymer P3 or P5 occurs at the electron-rich cyclopentadiene part of the azulene ring to form a cationic radical, which probably further rearranges to form a closed shell structure (Scheme ). The formation of similar tropylium cation radicals for azulene and its derivatives have been identified by electron spin resonance spectroscopy in the literatures. , The energy levels of the HOMO and LUMO of the polymers were estimated from the oxidation onset ( E onset ) and the onset absorption wavelength of the UV−vis spectra, and the results are given in Table . The introduction of azulene in conjugated polymers leads to a substantial reduction in oxidation of potentials.…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Electronic, and Emission Spectroscopy, and Electrochromic Characterization of Azulene−Fluorene Conjugated Oligomers and Polymers

Wang¹,

Ng²,

Jia³

et al. 2009

Macromolecules

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Two model compounds, 1,3-bis(9,9-dihexylfluoren-2-yl)azulene (M1), and 1,3-bis[7-(9,9,9′,9′-tetrahexyl-2,2′-bifluoren-7-yl)azulene (M2), and polymers, poly[2,7-(9,9-dialkylfluorenyl)-alt-(1′,3′-azulenyl)] (P1−P4) and poly{[1,3-bis(9′,9′-dihexylfluoren-2′-yl)azulenyl]-alt-[2′′,7′′-(9′′,9′′-dialkylfluorenyl]} (P5, P6) were synthesized by reacting 1,3-dibromoazulene or 1,3-bis(7-bromo-9,9-dihexylfluoren-2-yl)azulene with a suitable 9,9-dialkylflourenyl-2-borate or 2,7-diborate via Suzuki cross-coupling reactions. The thermal and optical properties of the polymers were characterized by thermogravimetric analysis, differential scanning calorimetry, and UV−vis and fluorescence spectroscopy. M1, M2, and P1−P6 are nonfluorescent in the neutral state in different organic solvents. However, M1, M2, P5, and P6 become fluorescent upon the addition of trifluoroacetic acid in THF, with relative quantum efficiencies of 0.004−0.06. The “switching on” of the fluorescence for the azulene−fluorene copolymers and model compounds is due to the formation of a 6π electron aromatic azulenium cation, which alters the overall electronic character, particularly, the HOMO and LUMO, and subsequently the band gap. Cyclic voltammograms of polymer films prepared by spin-coating polymer solution onto an indium−tin oxide-coated glass substrate showed that all of the polymers films exhibited the relatively low half-wave oxidation potentials in the range 0.84−0.93 V vs Ag/AgCl. Electrochromic devices of P3 and P5 with a sandwich structure of PET-ITO/polymer/PMMA-PC-LiClO4/PET-ITO were fabricated, and color changes from light yellow to brown and from yellow to green for polymers P3 and P5 films, respectively, are observed.

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“…The proposed mechanism for these reactions was corroborated by isotopic labeling studies and theoretical calculations . 4- N- Aryliminobenzylfuran-2,3-diones 3 , obtainable from 1 (X = O) by reaction with aryl carbodiimides 3b (Scheme ), easily rearrange via a so-called long-range Dimroth rearrangement at elevated temperatures to 4-acylpyrrole-2,3-diones 1 (X = N−Ar). 3b, …”

Section: Introductionmentioning

confidence: 79%

Site of Nucleophilic Attack and Ring Opening of Five-Membered Heterocyclic 2,3-Diones: A Density Functional Theory Study

Fabian

2002

J. Org. Chem.

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The site of nucleophilic addition to five-membered heterocyclic 2,3-diones (4-iminomethylfuran-2,3-dione A1 and 4-formyl-pyrrole-2,3-dione B1) is studied by density functional theory calculations (B3LYP/6-31G) with water as the nucleophile. Both uncatalyzed and water-assisted 1,2-addition to the lactone (lactam) and the keto carbonyl group, and conjugate addition to C5 of the heterocycle and the heteroatom of the 4-iminomethyl (formyl) moiety are considered. In addition, concerted and stepwise ring fission of the lactone (lactam) ring is also treated. The effect of solvation (aqueous solution) is taken into account by the polarizable continuum model (PCM) and the Poisson-Boltzmann SCRF method (PB-SCRF), as well as explicit water molecules. Only this latter approach yields meaningful activation free energies. Barriers for addition of H2O increase in the order 1,4-addition to C5 < addition to the lactone (lactam) carbonyl < hydration of the 3-keto group. No reaction path for concerted water-assisted ring opening could be found.

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Mechanism of rearrangement reactions of ketenimine–4-acylfuran-2,3-dione cycloadducts—a semiempirical molecular orbital study

Cited by 9 publications

References 17 publications

Substituent Effects on Site Selectivity (CC vs CN) in Heterocumulene−Heterodiene [4 + 2] Cycloadditions: Density Functional and Semiempirical AM1 Molecular Orbital Calculations

Substituent Effects on Site Selectivity (CC vs CN) in Heterocumulene−Heterodiene [4 + 2] Cycloadditions: Density Functional and Semiempirical AM1 Molecular Orbital Calculations

Synthesis, Electronic, and Emission Spectroscopy, and Electrochromic Characterization of Azulene−Fluorene Conjugated Oligomers and Polymers

Site of Nucleophilic Attack and Ring Opening of Five-Membered Heterocyclic 2,3-Diones: A Density Functional Theory Study

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