- Overcoming naphthoquinone deactivation: Rhodium-catalyzed C-5 selective C-H iodination as a gateway to functionalized derivatives
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We report a Rh-catalyzed method for the C-5 selective C-H iodination of naphthoquinones and show that complementary C-2 selective processes can be achieved under related conditions. C-C bond forming derivatizations of the C-5 iodinated products provide a gateway to previously inaccessible A-ring analogues. The present study encompasses the first catalytic directed ortho-functionalizations of simple (non-bias) naphthoquinones. The strategic considerations outlined here are likely to be applicable to C-H functionalizations of other weakly coordinating and/or redox sensitive substrates.
- Jardim, Guilherme A. M.,Da Silva, Eufranio N.,Bower, John F.
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- Oxidative Dearomatization of Phenols and Polycyclic Aromatics with Hydrogen Peroxide Triggered by Heterogeneous Sulfonic Acids
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We report herein a method for the oxidative dearomatization of phenols and bare polycyclic arenes into the corresponding quinoid derivatives using hydrogen peroxide. The reaction is catalyzed by sulfonic acids and best results were achieved using heterogenized species. The best results using phenols were achieved using a hybrid material, namely a perfluorinated polymer functionalized with sulfonic acid groups supported on silica. The dearomatization of polycyclic aromatic hydrocarbons performed better using the polymeric acid catalyst. These methods operate under mild conditions, using mild and benign oxidants and thus minimizing the formation of waste.
- Pancrazzi, Francesco,Maestri, Giovanni,Maggi, Raimondo,Viscardi, Rosanna
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supporting information
p. 5407 - 5414
(2021/10/25)
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- Rhodium-catalyzed C-H bond activation for the synthesis of quinonoid compounds: Significant Anti-Trypanosoma cruzi activities and electrochemical studies of functionalized quinones
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Thirty four halogen and selenium-containing quinones, synthesized by rhodium-catalyzed C-H bond activation and palladium-catalyzed cross-coupling reactions, were evaluated against bloodstream trypomastigotes of T.?cruzi. We have identified fifteen compounds with IC50/24?h values of less than 2?μM. Electrochemical studies on A-ring functionalized naphthoquinones were also performed aiming to correlate redox properties with trypanocidal activity. For instance, (E)-5-styryl-1,4-naphthoquinone 59 and 5,8-diiodo-1,4-naphthoquinone 3, which are around fifty fold more active than the standard drug benznidazole, are potential derivatives for further investigation. These compounds represent powerful new agents useful in Chagas disease therapy.
- Jardim, Guilherme A.M.,Silva, Thaissa L.,Goulart, Marilia O.F.,de Simone, Carlos A.,Barbosa, Juliana M.C.,Salom?o, Kelly,de Castro, Solange L.,Bower, John F.,da Silva Júnior, Eufranio N.
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p. 406 - 419
(2017/05/19)
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- Rearrangements in the Cerium(IV) and Manganese(III) Oxidations of Substituted Naphthalenes and the NIH Shift Mechanism
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Ceric ammonium sulphate oxidation of 1- and 1,4-disubstituted naphthalenes gives 2- and/or 2,3-disubstituted 1,4-naphthoquinones through migration of substituents (D, Br, Ph).Similar rearrangements are also observed in the manganese(III) oxidation and also in the anodic oxidation of these substrates.The results are consistent with the proposal that these oxidations go through the formation of radical cation followed by reaction with H2O and further oxidation of the radical to the carbocationic intermediate on the way to the corresponding 1,4-naphthoquinone.Oxidation of 1,4-diphenylnaphthalene gives 2,3-diphenyl-1,4-naphthoquinone or 4-hydroxy-2,4-diphenyl-1(4)H-naphthalenone.The results are in accordance with the conclusion that such rearrangements do not require prior formation of arene oxide intermediates, originally proposed for the NIH shift mechanism.
- Bhatt, M. Vivekananda,Periasamy, Mariappan
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p. 3575 - 3586
(2007/10/02)
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