- A bioinspired heterogeneous catalyst based on the model of the manganese-dependent dioxygenase for selective oxidation using dioxygen
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A hybrid bioinspired material with manganese(ii) complexes grafted on the surface of a mesostructured porous silica is investigated. The Mn sites mimic the manganese-dependent dioxygenase (MndD), which is an enzyme that catalyses the oxidation of catechol derivatives. The metal complexes were introduced in the silica using a dinuclear complex [Mn2L2(Cl)2(μ-Cl)2] as a precursor with a clickable ligand N,N′-bis[(pyridin-2-yl)methyl]prop-2-yn-1-amine (L). Azide moieties covalently grafted on MCM-41 type mesoporous silica were utilised to anchor the manganese complex through Huisgen cycloaddition using CuBr(PPh3)3 as a catalyst. A second functional group-trimethylsilyl or pyridine—was grafted on the silica to bring, together with nanopore size confinement, a similar metal environment as in MndD. The mesostructure of the materials was maintained after incorporation of the Mn complex. Catalytic oxidation of 3,5-di-t-butyl-catechol (3,5-DTBC) into quinone occurred without the need of an additional base when the metal complex was confined in the porous solid. In comparision, the oxidation of 4-t-butyl-catechol (4-TBC) that always required a basic media led to a total oxidation into the ortho-quinone, contrary to the molecular analogue.
- Chaignon, Jérémy,Gourgues, Marie,Khrouz, Lhoussain,Moliner, Nicolás,Bonneviot, Laurent,Fache, Fabienne,Castro, Isabel,Albela, Belén
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- Mechanistic Studies on Bioinspired Aerobic C-H Oxidation of Amines with an ortho-Quinone Catalyst
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We report herein our mechanistic studies of the ortho-quinone-catalyzed aerobic oxidation of primary, secondary, and tertiary amines. Two different catalytic pathways were discovered for the reductive half reactions: for primary amines, the reaction was found to proceed via a transamination pathway, while the reactions with secondary amines and tertiary amines proceeded via hydride transfer. We also found that the amine substrates could significantly promote the regeneration of the ortho-quinone catalyst in the oxidative half reaction, in which a proton transfer occurs between the amine substrates and catechol derivatives (the reduced form of the ortho-quinone catalyst).
- Zhang, Ruipu,Qin, Yan,Zhang, Long,Luo, Sanzhong
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p. 2542 - 2555
(2019/03/08)
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- A divergent and selective synthesis of ortho- and para-quinones from phenols
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Abstract We describe a divergent synthesis of substituted ortho- and para-quinones by catalytic aerobic oxygenation of phenols. Substituted quinones are omnipresent in chemistry and biology, but their synthesis frequently suffers from low efficiency and poor scope. Our methodology employs a catalytic aerobic di-functionalization of phenols to aryloxy-ortho-quinones. Regioselective substitution with an alcohol provides the alkoxy substituted ortho- or para-quinone, while hydrolysis affords the para-hydroxyquinone. These are mild and selective conditions for the synthesis of diversely substituted quinones from readily available phenol starting materials.
- Huang, Zheng,Kwon, Ohhyeon,Esguerra, Kenneth Virgel N.,Lumb, Jean-Philip
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p. 5871 - 5885
(2015/08/04)
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- Bioinspired organocatalytic aerobic C-H oxidation of amines with an ortho -quinone catalyst
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A simple bioinspired ortho-quinone catalyst for the aerobic oxidative dehydrogenation of amines to imines is reported. Without any metal cocatalysts, the identified optimal ortho-quinone catalyst enables the oxidations of α-branched primary amines and cyclic secondary amines. Mechanistic studies have disclosed the origins of different performances of ortho-quinone vs para-quinone in biomimetic amine oxidations.
- Qin, Yan,Zhang, Long,Lv, Jian,Luo, Sanzhong,Cheng, Jin-Pei
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supporting information
p. 1469 - 1472
(2015/03/30)
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- Photochemical nitration by tetranitromethane. Part XXXV. A possible addition/elimination pathway in the photochemical reaction of 2,5-di-tert-butyl-1,4-dimethoxybenzene and tetranitromethane
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The photolysis of the charge transfer complex of 2,5-di-tert-butyl-1,4-dimethoxybenzene (1) and tetranitromethane gives exclusively 4-tert-butyl-2,5-dimethoxynitrobenzene (2) in both dichloromethane and acetonitrile at room temperature. Photolysis in dichloromethane in the presence of trifluoroacetic acid (0.10-1.0 mol dm-3), gives 2,5-di-tert-butyl-1,4-benzoquinone (3) (6-25%), 5-tert-butyl-4-methoxy-1,2-benzoquinone (4) (9-25%) and 5-tert-butyl-4-methoxy-1,2-dihydroxybenzene (5) (13-25%) together with 2 (25-71%). Nitration of 1 with HNO3/acetic anhydride or a solution of nitrogen dioxide in dichloromethane gives 2 as the main product, together with products 3-5. It is suggested that 2 is formed in the photolysis by the decomposition of transient adducts, in which trinitromethyl and NO2 have been added across the aromatic ring. The protonation of trinitromethanide by trifluoroacetic acid eliminates the nucleophile and thus inhibits the formation of adducts, and the products are then formed mainly by coupling of nitrogen dioxide with the radical cation 1?+ or 1. Acta Chemica Scandinavica 1997.
- Svensson, Jan Olof
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- Evaluation of the cytotoxic potential of catechols and quinones structurally related to butylated hydroxyanisole
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The cytotoxicity of 2- and 3-butylated hydroxyanisole (BHA) and 18 related aromatic compounds has been determined employing cultured P388 and KB cells. The phenolic compounds, 3-BHA and 2-BHA, had moderately low cytotoxic activity. Their corresponding catechols had ED50 values that were much lower than those of the parent compounds. This substantial increase in the cytotoxic activity is attributed to the presence of the catechol group, which is known to undergo one-electron oxidation readily to give the corresponding semiquinone radical. Other related catechols had similar cytotoxic activity. In general, derivatization of the catechol functionality resulted in a decrease of the cytotoxic potential of the compounds. Monoacetylation or monomethylation of the catechols gave products that were less potent cytotoxic agents than the parent compounds. Further loss of activity was observed when both hydroxy groups of the catechol function were blocked. Substitution of a methoxy group in place of a hydrogen atom in these compounds resulted in a significant increase of cytotoxicity, whereas the replacement of a methoxy group with a methyl group reduced the cytotoxicity. The catechols and quinones derived from 2-BHA were more active when compared with those derived from 3-BHA. The t-butyl group adjacent to the catechol or quinone moiety in the 3-BHA derivatives appeared to exert a significant steric effect toward the cytotoxic potential of these compounds. These results suggest the potential use of o-quinones and catechols as cytotoxic and antitumor agents.
- Lam,Garg,Swanson,Pezzuto
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p. 393 - 395
(2007/10/02)
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- Photolysis of the Ozonide Derived from 1,4-Benzodioxins. Synthesis of Labile o-Benzoquinones
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By the photolysis of the ozonide derived from 1,4-benzodioxins, o-benzoquinones were obtained in moderate yields independent of the stability of o-benzoquinones and of the substituent groups, except the nitro group.Through the mechanistic studies, it was indicated that o-benzoquinones were formed through a radical decomposition pathway, while catechols were formed through an ionic decomposition pathway induced by acidic impurities.
- Kashima, Choji,Tomotake, Atsushi,Omote, Yoshimori
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p. 5616 - 5621
(2007/10/02)
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- Synthesis and Reactions of o-Benzoquinone Monosulfonimides
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4-Alkoxy(R2O)-5-alkyl(R1)-N-sulfonyl>-o-benzoquinone imines (10a-d: R1, R2; a, Me, Me; b, Me, n-C16H33; c, t-Bu, Me; d, t-Bu, n-C16H33) are synthesized by the oxidation of o-s
- Fujita, Shinsaku
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p. 177 - 183
(2007/10/02)
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- Reaction of 4-tert-Butylcatechol and Its Derivatives with Methoxy(pyridine)copper(II) Chloride in the Absence of Oxygen. A New Structure Reminiscent of Those Resulting from "Extradiol" Oxidations of Catechols in the Presence of Oxygen
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Reaction of methoxy(pyridine)copper(II) chloride with 4-tert-butylcatechol, 4-tert-butyl-1,2-benzoquinone 4-tert-butyl-3-methoxycatechol, 4-tert-butyl-3-chlorocatechol, or 3,5-di-tert-butylcatechol in pyridine in the absence of oxygen provides 2,2-dimetho
- Demmin, Timothy R.,Rogic, Milorad M.
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p. 4210 - 4214
(2007/10/02)
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