Catalytic oxidation of catechins to p-benzoquinones with hydrogen peroxide/methyltrioxorhenium

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.     

Dimethyl carbonate: an environmentally friendly solvent for hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic oxidations

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.     

Synthetic Aspects of Metal-Catalyzed Oxidations of Amines and Related Reactions

The metabolism of amines is governed by a variety of enzymes such as amine oxidase, flavoenzyme, and cytochrome P-450. A wide variety of compounds are produced such as ammonia and alkaloids in selective and clean oxidation reactions that proceed under mild reaction conditions. Simulation of the functions of these enzymes with simple transition metal complex catalysts may lead to the discovery of biomimetic, catalytic oxidations of amines and related compounds. Indeed, metal complex catalyzed oxidations have been found to proceed with high efficiency. The first section of this review discusses the dehydrogenative oxidations of amines with transition metal catalysts by transition metal catalysts that simulate amine oxidase. The second section highlights the catalytic oxidation of secondary amines to nitrones by simulation of flavoenzymes. The third section describes the simulation of the function of cytochrome P-450 with lowvalent ruthenium complexes and peroxides. Biomimetic ruthenium-catalyzed oxidations of tertiary amines, secondary amines, and other substrates such as amides, β-lactams, nitriles, alcohols, alkenes, ketones, and even nonactivated hydrocarbons can be performed selectively under mild conditions. These three general approaches provide highly useful strategies for synthesis of fine chemicals and biologically active compounds such as alkaloids, amino acids, and β-lactams.     

CO_2选择氧化低碳烷烃的研究进展

本文以低碳烷烃的选择催化氧化反应为对象 ,对几种 CO2 选择氧化低碳烷烃的反应工艺进行了归纳总结 ,重点分析讨论了催化氧化反应中 CO2 作为氧化剂的作用机制 ,并提出了研究展望。     

Simple Copper Catalysts for the Aerobic Oxidation of Amines: Selectivity Control by the Counterion

We describe the use of simple copper‐salt catalysts in the selective aerobic oxidation of amines to nitriles or imines. These catalysts are marked by their exceptional efficiency, operate at ambient temperature and pressure, and allow the oxidation of amines without expensive ligands or additives. This study highlights the significant role counterions can play in controlling selectivity in catalytic aerobic oxidations.     

Efficiently Aerobic Dehydrogenation of N-Heterocycles and Hydrocarbons over MnAl Oxides

Dehydrogenation of saturated N-heterocycles and hydrocarbons provides an important route to corresponding aromatic compounds. Herein, an efficient and selective MnAlO-catalyzed aerobic oxidative dehydrogenation of five- and six-membered N-heterocycles, imines and hydrocarbons is presented. The reaction features excellent yields of the products, mild reaction conditions, readily available and reusable catalyst. Various N-heterocycles and hydrocarbons can be tolerated by the reaction system and transformed to the corresponding aromatic counterparts. Mechanistic studies revealed that the reaction proceeds mainly through an electron transfer mechanism.     

Transition Metal Catalysts Bearing Multidentate Ligands for Efficient and Environmental Benign Oxidations by H2O2

In this perspective, two different classes of multidentate ligands (aminotriphenolate and dipyridinimine) and the corresponding metal (Ti, V, Mo, W, Fe) complexes are described. These catalysts can activate efficiently the environmental benign H₂O₂ oxidant, promoting a wide variety of oxidative processes (sulfoxidations, N-oxidations, epoxidations, haloperoxidation, alcohol oxidation, hydroxylation).     

Hydrogen abstraction and electron transfer with aminoxyl radicals: synthetic and mechanistic issues

Aminoxyl radicals (R(2)NO(*)) are a valuable class of reactive intermediates with interesting synthetic and reactivity properties. This Minireview summarizes salient synthetic results obtained in radical oxidations using aminoxyl radicals, and then focuses on reactivity issues arising from recent literature surveys. The structural and reactivity features of the aminoxyl radical and substrate provides a possible explanation of the double reactivity of the aminoxyl radicals. This mechanistic dichotomy between H-atom abstraction and electron-abstraction routes is highlighted in this Minireview.