- 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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- 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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