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Catechin derivatives were oxidized in air in the presence of the Trametes villosa laccase/1-hydroxybenzotriazole (HBT) system in buffered water/1,4-dioxane as reaction medium. The oxidation products, flavan-3,4-diols and the corresponding C-4 ketones, are bioactive compounds and useful intermediates for the hemisynthesis of proanthocyanidins, plant polyphenols which provide beneficial health properties for humans. Determinations of oxidation potentials excluded that catechin derivatives could be directly oxidized by laccase Cu(II), while it resulted in the H-abstraction from benzylic positions being promptly promoted by the enzyme in the presence of the mediator HBT, the parent species producing in situ the reactive intermediate benzotriazole-N-oxyl (BTNO) radical. A remarkable and unexpected result for the laccase/HBT oxidative system has been the chemoselective insertion of the oxygen atom into the C-4-H bond of catechin derivatives. Mechanistic aspects of the oxidation reaction have been investigated in detail for the first time in order to corroborate these results. Since the collected experimental findings could not alone provide information useful to clarify the origin of the observed chemoselectivity, these data were expressly supplemented with information derived by suitable molecular modeling investigations. The integrated evaluation of the dissociation energies of the C-H bonds calculated both by semiempirical and DFT methods and the differential activation energies of the process estimated by a molecular modeling approach suggested that the observed selective oxidation at the C-4 carbon has a kinetic origin. [ABSTRACT FROM AUTHOR]

Catecholamines, sympathomimetic drugs and adrenergic receptor antagonists, have been prepared by a regioselective oxidation of the corresponding 4-hydroxyphenethylamine derivatives by 2-iodoxybenzoic acid (IBX) in homogeneous as well as in heterogeneous conditions and followed by cleavage of the amino protective group. By using polymer-supported IBX, after the first oxidation, the oxidant can be recovered, regenerated, and efficiently reused for several additional times. An efficient, easy and green procedure for the synthesis of N-(methoxycarbonyl)dopamine, key component of many pharmaceuticals, has also been reported. [ABSTRACT FROM AUTHOR]

Abstract: Highly oxidized lignans produced during the cytochrome P-450 metabolism in the cells show biological activities significantly different from those of their parent natural compounds. Lignans precursors of mammalian enterolignans were treated with a methyltrioxorhenium/hydrogen peroxide catalytic system to afford new compounds oxidized at benzylic as well as in arylic positions. The evaluation of the antioxidant and apoptogenic activity by in vivo protocols of these compounds showed some interesting structure–activity relationships related to the oxidation degree of the molecules. [Copyright &y& Elsevier]

Abstract: A convenient and efficient synthesis of monoterpene epoxides by application of methyltrioxorhenium and heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium and microencapsulated polystyrene/methyltrioxorhenium catalytic systems in ionic liquids is described here. It was found that even highly sensitive terpenic epoxides were obtained in excellent yields. Environmentally friendly, easily available and low cost (UHP) urea hydrogen peroxide adduct was used as the primary oxidant. Catalysts were stable systems for at least four recycling oxidations. Experimental results showed that the reactions performed in ionic liquids were more selective and efficient than the ones performed in molecular solvents. [Copyright &y& Elsevier]

Abstract: A useful and novel application of polymer-supported IBX for the chemoselective and regioselective oxidation of phenolic compounds has been described. Hydroxytyrosol and carboxymethylated hydroxytyrosol have been prepared in good conversions and yields under green chemistry conditions in the presence of dimethyl carbonate as the solvent. Polymer-supported reagent has been recovered by simple filtration, regenerated and reused for more cycles of oxidation reactions without loss of efficiency. [Copyright &y& Elsevier]

Abstract: Environmentally friendly oxidations of various organic compounds with the hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic system have been described in dimethyl carbonate (DMC), a cheap commercially available and benign chemical having interesting solvating properties, low toxicity and high biodegradability. Oxidations proceeded with good conversions and in good yields. Spectrophotometric analysis demonstrated that the [CH3ReO(O–O)2] complex was formed in DMC and that it was stable for several days at room temperature. [Copyright &y& Elsevier]

Abstract: New p-benzoquinones were obtained by oxidation of catechin and epicatechin derivatives with the hydrogen peroxide/methyltrioxorhenium catalytic system. Reactions were carried out both in homogeneous and heterogeneous conditions and proceeded with high conversion and moderate yields. Polymer-supported methyltrioxorhenium systems were used as heterogeneous catalysts. After the first oxidation, the catalytic systems can be recovered and reused for five consecutive times without loss of stability and efficiency. [Copyright &y& Elsevier]

Abstract: A convenient and efficient application of hydrogen peroxide/methyltrioxorhenium in ionic liquids [bmim]BF4 and [bmim]PF6 for the oxidation of hydroxylated and methoxylated benzaldehydes and acetophenones to the corresponding phenols is described. Good yields of products were obtained in short reaction times. [Copyright &y& Elsevier]

The Baeyer–Villiger oxidation of cyclic ketones can be effected by methyltrioxorhenium/hydrogen peroxide in the ionic liquid [bmim]BF4. After simple extraction of the lactone with diethyl ether, the catalyst can be repeatedly recycled and efficiently reused for the lactonisation process in the same reaction medium. [Copyright &y& Elsevier]

The oxidation of halogen anions by dimethyldioxirane (DMD) produced reactive species which led, in acidic media, to the halogenation of activated aromatic rings. The reaction can be efficiently controlled to obtain selective and mixed halogenated species. [ABSTRACT FROM AUTHOR]

Abstract: An efficient route to 3,4-dihydroxylphenylalanine (DOPA) and DOPA peptides was described by oxidation of l-tyrosine and l-tyrosine derivatives with 2-iodoxybenzoic acid (IBX). DOPA was obtained after an situ reduction of the corresponding ortho-quinone with sodium dithionite. Oxidation reactions proceeded in good yields and high chemo- and regio-selectivity. The chirality of the DOPA residue was retained under the reaction conditions. The efficiency and the selectivity of the reaction were successfully tested using recyclable polymer-supported IBX. [Copyright &y& Elsevier]

affording hydroxyethylbenzophenone derivatives under green chemistry conditions [ABSTRACT FROM AUTHOR]