- The Mystery of the Benzene-Oxide/Oxepin Equilibrium—Heavy-Atom Tunneling Reversed by Solvent Interactions
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The equilibrium between benzene oxide (1) and oxepin (2) is of large importance for understanding the degradation of benzene in biological systems and in the troposphere. Our studies reveal that at cryogenic temperatures, this equilibration is governed by rare heavy-atom tunneling. In solid argon at 3 K, 1 rearranges to 2 via tunneling with a rate constant of approximately 5.3×10?5 s?1. Thus, in a nonpolar environment, 2 is slightly more stable than 1, in agreement with calculations at the CCSD(T) level of theory. However, if the argon is doped with 1 % of H2O or CF3I as typical hydrogen or halogen bond donors, respectively, weak complexes of 1 and 2 are formed, and now 2 is tunneling back to form 1. Thus, by forming non-covalent complexes, 1 becomes slightly more stable than 2 and the direction of the heavy-atom tunneling is reversed.
- Prado Merini, Melania,Sander, Wolfram,Schleif, Tim
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supporting information
p. 20318 - 20322
(2020/10/02)
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- Chemical Equivalent of Arene Monooxygenases: Dearomative Synthesis of Arene Oxides and Oxepines
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Direct epoxidation of aromatic nuclei by cytochrome P450 monooxygenases is one of the major metabolic pathways of arenes in eukaryotes. The resulting arene oxides serve as versatile precursors to phenols, oxepines, or trans-dihydrodiol-based metabolites.
- Siddiqi, Zohaib,Wertjes, William C.,Sarlah, David
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p. 10125 - 10131
(2020/06/27)
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- Synthesis and Desymmetrization of meso Tricyclic Systems Derived from Benzene Oxide
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Ozonolysis of the Diels-Alder adducts derived from benzene oxides and N-alkylmaleimides resulted in fully substituted, meso bicyclic systems bearing six contiguous stereocenters, isolated as diols upon reductive workup with NaBH4. Variation in the workup allowed for isolation of two different diastereoisomers, through double epimerization of the imide stereocenters. Desymmetrization of the resulting meso diols via asymmetric nucleophilic epoxide opening and acylation reactions provided access to highly substituted, enantioenriched fused rings.
- Matías, Desirée M.,Johnson, Jeffrey S.
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p. 4859 - 4866
(2018/04/26)
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- Reaction of O(3P) atoms with benzene
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The gas-phase reaction of O(3P) atoms with benzene was investigated in a flow system in the pressure range of 50-100 mbar and a temperature of 295 ± 2 K with a focus on the product formation. O2 concentrations in the carrier gas were in the range of (7.7-84) × 1014 molecule cm-3. The primary stable products detected were phenol, benzene oxide/oxepin and a not identified compound with the probable composition C5H6O. The yields of phenol and benzene oxide/oxepin were 0.12 ± 0.02 and 0.26 ± 0.06, respectively, being not affected by the experimental conditions. For benzene oxide/oxepin, a rapid consecutive reaction with O(3P) atoms was observed with a rate coefficient of k(295 K) = (1.1 ± 0.1) × 10-10 cm3 molecule-1 s-1 measured at a pressure of 100 mbar. A substance with the formula C6H6O2 (likely oxepin 4,5-epoxide or oxepin 2,3-epoxide), the isomers of muconaldehyde, as well as formic acid, acrolein and trans-butenedial were identified as products of the reaction of O(3P) atoms with benzene oxide/oxepin.
- Berndt, Torsten,Boege, Olaf
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p. 391 - 403
(2007/10/03)
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- Is benzene oxide homoaromatic? A microcalorimetric study
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Rate constants and heats of reaction for the aromatization of benzene oxide (1) and the acid-catalyzed aromatization of benzene hydrate (2) in highly aqueous solution giving phenol and benzene, respectively, have been measured by heat-flow microcalorimetry. The measured heat of reaction of benzene oxide, ΔH = -57.0 kcal mol-1, is much larger than that of benzene hydrate, ΔH = -38.7 kcal mol-1, despite an unusually low reactivity of benzene oxide, rate ratio 0.08. The measured enthalpies agree with those calculated using the B3LYP hybrid functional corrected with solvation energies derived from semiempirical AM1/SM2 calculations. Comparison with the measured enthalpies of the corresponding reactions of the structurally related 1,3-cyclohexadiene oxide (3) and 2-cyclohexenol (4) of ΔH = -24.9 kcal mol-1 (includes a small calculated correction of - 1.2 kcal mol-1) and ΔH ~ 0 kcal mol-1, respectively, gives a smaller aromatization energy for the benzene oxide than for the benzene hydrate reaction (ΔΔΔH = 6.6 kcal mol-l). This suggests that benzene oxide is unusually stabilized by a significant amount of homoaromatization as has been proposed previously (J. Am. Chem. Soc. 1993, 115, 5458). This unusual stability accounts for more than half of the ~107 times lower than expected reactivity of benzene oxide toward acid-catalyzed isomerization. The rest is suggested to originate from an unusually high energy of the carbocation-forming transition state.
- Jia,Brandt,Thibblin
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p. 10147 - 10152
(2007/10/03)
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- Photochemical reaction of ozone and benzene: An infrared matrix isolation study
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The photolysis of benzene/ozone mixtures in an argon matrix at 12 K with UV light of λ ≥ 280 nm leads to the following products: phenol, 2,4-cyclohexadienone, benzene oxide, and butadienylketene (hexa-1,3,5-trien-1-one). The identification of butadienylketene as a product is based on deuterium isotopic shifts and agreement with density functional vibrational frequency calculations. We find an average phenol/ butadienylketene branching ratio of 4.3 during the course of photolysis. This is the first report in the literature of the observation of a ketene product from the reaction of oxygen atoms with benzene.
- Parker, James K.,Davis, Steven R.
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p. 4271 - 4277
(2007/10/03)
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- ?-Facial stereoselectivity in the Diels-Alder reactions of benzene oxides
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The Diels-Alder reactions of N-phenylmaleimide and dimethyl acetylenedicarboxylate with benzene oxide (1,3,5-cyclohexatriene 1,2-oxide, 3) and its more substituted derivatives 1,2-dimethyl-1,3,5-cyclohexatriene 1,2-oxide (7) and 10-oxatricyclodeca-2,4-diene (11) in a kinetic manner gave exclusively products of addition anti to the plane-nonsymmetrical oxygen.The structures of the adducts were determined unequivocally by nuclear Overhauser enhancements in their 1H nuclear magnetic resonance spectra and by X-ray crystallographic methods.The ?-facial stereoselectivity was rationalized in terms of unfavorable orbital interactions, steric hindrance between the dienophile and the syn face of benzene oxide, and ?-donation by the oxygen. Key words: cycloaddition, Diels-Alder, syn-anti, ?-facial stereoselectivity, benzene oxide.
- Gillard, James R.,Newlands, Michael J.,Bridson, John N.,Burnell, D. Jean
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p. 1337 - 1343
(2007/10/02)
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- Photochemical Transformations, 64. The 3? -> 3?-Route to Oxepines/Benzene Oxides
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The 7-oxanorbornadiene skeleton (8a), its 2,3-bis(trifluoromethyl)derivative (8b), and several 2,3-dicarboxylic esters with potential dipolarophilic groups at C-1 (16a-d, 17a-c) were synthesized and selectively transformed into the 3-oxaquadricyclanes (18a,b, 19a-d, and20a-c) through sensitized (8a,b) or direct (16a-d, 17a-c) photoexcitation.In the thermolysis of these oxaquadricyclanes a(C6D6) = 32.6 +/- 0.3 kcal/mol (32.2 +/- 1.4 kcal/mol); lg A = 15.8 (14.5)> CF3(CH3CO2) substituents at C-2(3) favor the scission of the opposite (neighbouring) cyclopropane bonds.Competition experiments with dimethyl acetylenedicarboxylate as external dipolarophile support the stepwise mechanism of the oxaquadricyclane -> oxepine conversion.The intramolecular carbonyl ylide-interception cannot compete with oxepine formation in 19a-d but is efficient in 20 a-c.The unusually low activation barrier (Ea(C6D6) = 23.5 +/- 1 kcal/mol; lg A = 11.6) and singular specifity in case of 20a is interpreted in terms of a concerted ?2 + ?2 + ?2>-cycloaddition to the bishomofuran unit of the oxaquadricyclane skeleton.
- Prinzbach, Horst,Bringmann, Horst,Markert, Juergen,Fischer, Gerhard,Knothe, Lothar,et al.
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p. 589 - 615
(2007/10/02)
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