- Examination of Selectivity in the Oxidation of ortho- and meta-Disubstituted Benzenes by CYP102A1 (P450 Bm3) Variants
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Cytochrome P450 CYP102A1 (P450 Bm3) variants were used to investigate the products arising from the P450 catalysed oxidation of a range of disubstituted benzenes. The variants used all generated increased levels of metabolites compared to the wild-type enzyme. With ortho-halotoluenes up to six different metabolites could be identified whereas the oxidation of 2-methoxytoluene generated only two aromatic oxidation products. Addition of an ethyl group markedly shifted the selectivity for oxidation to the more reactive benzylic position. Epoxidation of an alkene was also preferred to aromatic oxidation in 2-methylstyrene. Significant minor products arising from the migration of one substituent to a different position on the benzene ring were formed during certain P450-catalysed substrate turnovers. For example, 2-bromo-6-methylphenol was formed from the turnover of 2-bromotoluene and the dearomatisation product 6-ethyl-6-methylcyclohex-2,4-dienone was generated from the oxidation of 2-ethyltoluene. The RLYF/A330P variant altered the product distribution enabling the generation of certain metabolites in higher quantities. Using this variant produced 4-methyl-2-ethylphenol from 3-ethyltoluene with ≥90 % selectivity and with a biocatalytic activity suitable for scale-up of the reaction.
- Munday, Samuel D.,Dezvarei, Shaghayegh,Lau, Ian C.-K.,Bell, Stephen G.
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p. 2512 - 2522
(2017/07/12)
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- Copper-catalyzed C-N bond cross-coupling of aryl halides and amines in water in the presence of ligand derived from oxalyl dihydrazide: Scope and limitation
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An efficient and convenient method has been developed for the copper-catalyzed C-N bond cross-coupling of aryl bromides with electron-donor substituents and aliphatic amines in water. The new ligand system N-phenyloxalyl bishydrazide/hexane-2,5-dione has been shown to be considerably more efficient in the copper-catalyzed C-N bond cross-coupling reaction as compared to the ligands described in the literature and allowed decreasing of the catalyst amount (up to 2 mol %) to achieve acceptable yields of isolated products (46-84%). Acceptor substituted aryl bromides, aryl bromides with substituents in the ortho-position, and some aryl dichlorides can undergo the C-N cross-coupling under the developed conditions, but their reactivity is lower.
- Kurandina,Eliseenkov,Khaibulova,Petrov,Boyarskiy
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p. 7931 - 7937
(2015/09/15)
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- Reactions of OH and SO4.- with Some Halobenzenes and Halotoluenes: A Radiation Chemical Study
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The optical absorption and kinetic characteristics of the transients formed in the reactions of OH and SO4.- with bromobenzene, ortho and meta-isomers of chloro- and bromobenzenes, and monobromotoluenes have been studied by pulse radiolysis technique.The rates for OH reaction are generally higher (k = (1.7-4.4)X109 M-1s-1) than those found for the SO4.- reaction (k = (0.4-2.3)x109 M-1s-1). ρ+ values of -0.4 for OH and -1.2 for SO4.- reactions were obtained from the Hammett analysis.The formation of substituted hydroxycyclohexadienyl radicals (λmax = 315-330 nm) is the major reaction channel, and the phenoxyl type radical (λ >/=400 nm) formation is an additional minor process in the SO4.- reaction.Abstraction of H by SO4.- from the -CH3 group is only significant with the para-isomers of bromo- and chlorotoluenes.This result is in accord with the observed yields (70 percent of SO4.-) of the products resulting from the oxidation of the 4-chlorobenzyl radical in the presence of K3Fe(CN)6 under steady-state conditions.The total yields of the phenolic products accounting for >90 percent of OH and SO4.- suggest that the attack at the ipso positions is considerably small.The rate constants for OH reactions relative to benzene at positions 3 and 6 of 2-chlorotoluene and positions 2 and 3 of 4-chlorotoluene are between 1.18 and 1.39, indicating that the directing effects of -CH3 and -Cl groups are comparable.This is also reflected in the additive effects of activation of the ortho and para-positions and deactivation of meta-positions by these substituents in 3-chlorotoluene.
- Merga, Getahun,Rao, B. S. M.,Mohan, H.,Mittal, J. P.
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p. 9158 - 9164
(2007/10/02)
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- ipso NITRATION. XXIX. NITRATION OF SUBSTITUTED 4-METHYLANISOLES AND PHENOLS
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Nitration of 2-chloro-4-methylanisole (1a) in acetic anhydride gives (Z)-4-chloro-3-methoxy-6-methyl-6-nitrocyclohexa-2,4-dienyl acetate (2a), 2-chloro-4-methyl-4-nitrocyclohexa-2,5-dienone (3a), and 2-chloro-4-methyl-6-nitroanisole (4a).Similarly 2-bromo-4-methylanisole (1b) gives (Z)-4-bromo-3-methoxy-6-methyl-6-nitrocyclohexa-2,4-dienyl acetate (2b), 2-bromo-4-methyl-4-nitrocyclohexa-2,5-dienone (3b), and 2-bromo-4-methyl-6-nitroanisole (4b), whereas 4-methyl-2-nitro-anisole (1c) gives (Z)-3-methoxy-6-methyl-4,6-dinitrocyclohexa-2,4-dienyl acetate (2c), (Z)-3-methoxy-6-methyl-2,6-dinitrocyclohexa-2,4-dienyl acetate (7), and 4-methyl-2,6-dinitroanisole (4c).Nitration of 3-chloro-4-methylanisole (9a) gives 3-chloro-4-methyl-4-nitrocyclohexa-2,5-dienone (10a), 3-chloro-4-methyl-2-nitro anisole (11a), and 5-chloro-4-methyl-2-nitroanisole (12a), and 4-methyl-3-nitroanisole (9c) gives (Z)-3-methoxy-6-methyl-5,6-dinitrocyclohexa-2,4-dienyl acetate (13), 4-methyl-2,3-dinitroanisole (11c), and 4-methyl-2,5-dinitroanisole (12c).Nitration of 2-chloro-4-methylphenol (14) in chloroform gives 3a and 2-chloro-4-methyl-6-nitrophenol (5a), and 3-chloro-4-methylphenol (15) gives dienone 10a, 3-chloro-4-methyl-2-nitrophenol (16), and 5-chloro-4-methyl-2-nitrophenol (17).
- Fischer, Alfred,Henderson, George N.,RayMahasay, Sumit
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p. 1233 - 1240
(2007/10/02)
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- Miticidal 2-(2-alkyl-2,3-dihydrobenzofuran-7-yl)-N-alkoxy-N-alkyl-diazenecarboxamides
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Miticidal 2-(2-alkyl-4-(or 5)-bromo (or chloro)-2,3-dihydrobenzofuran-7-yl)-N-alkoxy-N-alkyldiazenecarboxamides.
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- Miticidal (2-alkyl-3,4-dihydro-2H-1-benzopyran-8-yl)-diazenecarboxylic acid esters
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Certain miticidal (2-alkyl-3,4-dihydro-2H-1-benzopyran-8-yl)diazenecarboxylic acid esters.
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- THE REACTIONS OF UNACTIVATED ARYL HALIDES WITH SODIUM METHOXIDE IN HMPA; SYNTHESIS OF PHENOLS, ANISOLES, AND METHOXYPHENOLS
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Sodium methoxide reacts with dichlorobenzenes in HMPA to give the chloroanisoles as a result of a SNAr process.Excess MeONa then effects the demethylation of the ethers to give the chlorophenols via an SN2 reaction.With tri- and tetrachlorobenzenes the initially formed chloroanisoles can be dealkylated to chlorophenols or can suffer further substitution to give the chlorodimethoxybenzenes; these react with excess MeONa to give the chloromethoxyphenols.The results obtained with the various isomers of the di-, tri-, and tetrachlorobenzenes are presented and discussed on the basis of the electronic effects of the substituents.
- Testaferri, L.,Tiecco, M.,Tingoli, M.,Chianelli, D.,Montanucci, M.
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p. 193 - 198
(2007/10/02)
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