- 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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- Model studies of topaquinone-dependent amine oxidases. 1. Oxidation of benzylamine by topaquinone analogs
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The aerobic oxidation of benzylamine by model compounds of topaquinone, the active site organic cofactor in copper-containing amine oxidases, was studied in order to elucidate the chemical function of the cofactor in substrate oxidation. In this study, topaquinone hydantoin (1(ox)) and a series of 2-hydroxy-5-alkyl-1,4-benzoquinones which differ in the bulk of their alkyl substituent (5, 6, 7, and 8) were employed as model compounds of the cofactor. The p-quinones (9, 10, 11, and 12) and the o-quinone (13 and 14) were prepared in order to compare them to the topaquinone analogs. Benzylamine was oxidized by the topaquinone analogs (1(ox), 5, 6, 7, and 8) to yield N-benzylidenebenzylamine (PhCH = NCH2Ph) as a sole product in acetonitrile at room temperature. The quinones bearing a bulky substituent (1(ox), 5, and 6) were found to be more efficient catalysts than those bearing a small primary alkyl group (7 and 8). In the latter case, the dimers (16 and 17) of the substrate Schiff base intermediates (15, R = methyl, ethyl) were isolated. The p-quinones (9, 10, 11, and 12) were catalytically inactive. The o-quinones (13 and 14) had detectable catalytic activity at room temperature. In anaerobic reactions of the o-quinones (13 and 14) with benzylamine, quantitative formation of the product (PhCH = NCH2Ph) was observed. For both o-quinones, products and intermediates which support a transamination mechanism were identified by 1H NMR spectroscopy. The order of reactivity of quinones (5 > 14 > 13) reflects their redox potentials, such that regeneration of quinone may be rate-determining with o-quinones. These results demonstrate a substantial role of the 2-hydroxyl group of the topaquinone in preventing the formation of Michael adducts with substrate amine and in facilitating the reoxidation of aminoresorcinol intermediates.
- Mure, Minae,Klinman, Judith P.
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p. 8698 - 8706
(2007/10/02)
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- Iron Porphyrin-Catalyzed Oxidation of 1,2-Dimethoxyarenes: A Discussion of the Different Reactions Involved and the Competition between the Formation of Methoxyquinones or Muconic Dimethyl Esters
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This paper describes the oxidation of an α,β-diarylpropane lignin dimer model and other dimethoxyarenes by several iron porphyrin-based biomimetic systems.From 1-(3,4-dimethoxyphenyl)-2-phenylpropanol (1), three types of products are identified: the 3,4-dimethoxybenzaldehyde derived from the Cα-Cβ cleavage of the propyl side chain and either quinones or muconic dimethyl esters resulting from oxidations at level of the dimethoxyaryl group.The selectivity of the reaction is discussed with respect to the nature and reactivity of the high-valent iron-oxo species formed upon reaction of the oxidants, H2O2 or magnesium monoperoxyphthalate (MMP), with the iron porphyrins.Fe(TF5PP)Cl-catalyzed oxidation of 1 by H2O2 in an aprotic medium (CH3CN/CH2Cl2), yields a clean "lignin peroxidase-like" reaction with selective formation of the aldehyde.In an aqueous buffered solution, MMP oxidation of para-substituted 1,2-dimethoxyarenes catalyzed by an iron tetrakis(pentafluorophenyl)-β-tetrasulfonatoporphyrin, Fe(TF5PS4P), clearly depends on the electronic properties of the para-substituent.The reaction is selective for para-quinone formation in the case of an electron-releasing group and for muconic dimethyl ester formation in the case of an electron-withdrawing group.
- Artaud, Isabelle,Ben-Aziza, Khaled,Mansuy, Daniel
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p. 3373 - 3380
(2007/10/02)
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