Methyltrioxorhenium catalyzed oxidation of 1,2-diols to 1,2-diketones using hydrogen peroxide as oxidant

A variety of 1,2-diols were oxidized selectively to the corresponding 1,2-diketones by the dropwise addition of 30% aqueous hydrogen peroxide using methyltrioxorhenium as catalyst.     

Aerobic cascade oxidation of substituted cyclopentane-1,2-diones using metalloporphyrin catalysts

A method for the aerobic cascade oxidation of cyclopentane-1,2-diones using metal porphyrins as catalysts, yielding hydroxydiacids 2, ketoacid 3 and diketoacids 4 which are the intermediates of important biologically active compounds is reported. This method is operationally simple and can be employed under ambient conditions.     

Catalytic monosilylation of 1,2-diols

The selective monosilylation of 1,2-diols catalyzed by dimethyltin dichloride was successfully developed. This procedure was applied to various 1,2-diols, giving monosilylated products in good to excellent yields with high chemoselectivity.     

氧化铜修饰羟基磷灰石负载金对醇类需氧氧化的双金属协同催化

采用均匀沉积-沉淀法制备了氧化铜修饰羟基磷灰石负载金催化剂(Au/CuO-HAP),并用原子吸收光谱、N2吸附脱附、X射线粉末衍射、透射电镜和X射线光电子能谱等方法对催化剂结构和形貌进行了表征.考察了催化剂对醇类液相需氧氧化的催化性能.与单金属Au/HAP或CuO-HAP相比较,双金属Au/CuO-HAP对苯甲醇氧化的催化活性和苯甲醛的选择性有显著提高,120 oC反应1.5 h,苯甲醇的转化率和苯甲醛的选择性分别达到99.7%和98.4%.在Au/CuO-HAP的催化下,其它类型的芳香醇均可高选择性转化为相应的醛或酮. Au/CuO-HAP催化剂有很好的稳定性和可回收性,4次回收后,其催化活性没有明显变化.     

Oxidation of cyclopentane-1,2-dione: a study with O labeled reagents

The asymmetric oxidation of 3-alkyl-cyclopentane-1,2-diones with the Ti(OⁱPr)₄/tartaric ester/t-BuOOH complex, which gives, in a cascade process, highly enantiomerically enriched γ-lactone acids, was studied by ¹⁸O isotopic labeling in the substrate and in the oxidant. The path of the labeled atoms was followed by ¹³C NMR spectroscopy. It was found that the oxidative ring cleavage of 1,2-dione proceeds via a Baeyer-Villiger-type oxidation mechanism.     

Zinc-catalyzed aerobic oxidation of benzoins and its extension to enantioselective oxidation

Zn(II)-DABCO complex is used as an efficient catalyst for the aerobic oxidation of benzoins to benzils in the presence of molecular oxygen. Usage of chiral zinc complex as catalyst resulted in enantioselective oxidative kinetic resolution of racemic benzoin to yield enantiomerically enriched benzoins.     

Solid-supported Pd(0): an efficient heterogeneous catalyst for aerobic oxidation of benzyl alcohols into aldehydes and ketones

Solid-supported nano- and microparticles of Pd(0) (SS-Pd) were used as heterogeneous catalysts for aerobic oxidation of benzyl alcohols. Primary and secondary benzyl alcohols gave the corresponding products in good yields. In addition, the catalysts could be reused up to five runs without significant loss of activities.     

Selective aerobic oxidation of hydroxy compounds catalyzed by photoactivated ruthenium-salen complexes (selective catalytic aerobic oxidation)

Selective oxidation of alcohols to the corresponding carbonyl compounds is one of the most fundamental reactions in organic synthesis. Traditional methods for this transformation generally rely on stoichiometric amount of oxidants represented by Cr(VI) or DMSO reagents, though their synthetic utility is encumbered by unpleasant waste materials. From ecological and atom-economic viewpoints, catalytic aerobic oxidation is much more advantageous because molecular oxygen is ubiquitous and the byproduct is basically non-toxic water or hydrogen peroxide. On the other hand, phenol derivatives undergo oxidative coupling, forming C-C or C-O bond, through radical intermediates coupled with an electron-transfer process. Molecular oxygen is also well known to serve as electron acceptor in this reaction. Thus, a variety of transition metal complexes have so far been examined for aerobic oxidations of alcohols and phenols, and high catalytic activities have been achieved in some cases. However, stereo- and chemo-selective aerobic oxidations are still limited in number and are of current interest. Presented in this paper is our recent studies on catalytic aerobic oxidations with photoactivated nitrosyl ruthenium-salen complexes, including asymmetric oxidation of secondary alcohols to ketones (kinetic resolution), enantioselective oxidative coupling of 2-naphthols to binaphthols and oxygen-radical bicyclization of 2,2'-dihydroxystilbene, chemoselective oxidation of primary alcohols to aldehydes and diols to lactols, and asymmetric desymmetrization of meso-diols to lactols.     

Preparation of polymer incarcerated gold nanocluster catalysts (PI-Au) and their application to aerobic oxidation reactions of boronic acids,alcohols, and silyl enol ethers

Heterogeneous gold nanocluster catalysts immobilized by the method known as polymer incarceration were prepared. Polystyrene-derived polymers with epoxide and alcohol moieties, which could be cross-linked under heating conditions, were employed as supports for their preparation. Cationic gold salts were reduced in a solution of NaBH₄ and the polymers. Poor solvents for the polymers were added, and the polymers were precipitated and encapsulated gold nanoclusters with weak but multiple interactions between a gold nanocluster surface and the π electrons of benzene rings. The polymer capsules were heated under neat conditions to afford heterogeneous gold nanocluster catalysts; namely, polymer-incarcerated gold nanoclusters. The catalysts thus prepared could be applied to the aerobic oxidation of phenyl boronic acids, alcohols, and silyl enol ethers. We found that the choice of polymers, good and poor solvents for the polymers, metal loadings, heating conditions for cross-linking, and final activation were all crucial for obtaining high-activity catalysts.     

B2pin2-mediated copper-catalyzed oxidation of alkynes into 1,2-diketones using molecular oxygen

An intriguing aerobic oxidation of alkynes through copper catalysis is described, in which bis(pinacolato)diboron (B₂pin₂) played a dominant intermediary role in the formation 1,2-diketones. This novel protocol, which can be performed at room temperature, is versatile for various substituted alkynes, including diarylalkynes and arylalkylalkynes. The mechanism of this reaction was preliminarily investigated by control experiments.     

Highly selective oxidation of amines to imines by Mn2O3 catalyst under eco-friendly conditions

Enhancing the selectivity of imines for the oxidative self-coupling of primary amines was found to be challenging in the heterogeneous catalysis. Three different manganese oxides (M-3, M-4, M-5) were synthesized by controlling the calcination temperature using a simple template-free oxalate route. The prepared manganese oxides were systematically characterized using XRD, N₂ sorption, SEM, TEM, XPS, H₂-TPR techniques. M-4 gave 96.2% selectivity of imine at 100% conversion of benzylamine, which was far more superior than other existing protocols. Mn³⁺/Mn⁴⁺ ratio was found to affect the selectivity of the imines. The probable reaction pathway for amines oxidation catalyzed by manganese oxides was proposed for the first time.     

Nitrite-containing resin as an efficient and recyclable catalyst for aerobic oxidation of oximes to carbonyl compounds

Using novel nitrite-containing resin as an NO source and Amberlyst-15 as cocatalyst, we developed aerobic oxidation of oximes to corresponding carbonyl compounds with molecular oxygen as a clean oxidant reagent. It was distinguished from the previous related reports, and the experimental results indicated that additional water obviously decreased the yield. This process provides a better choice for oxidative deoximation with many advantages, such as high yield, simple procedure, high catalytic performance, and recyclable catalyst.     

Recyclable gold nanoparticle catalyst for the aerobic alcohol oxidation and C-C bond forming reaction between primary alcohols and ketones under ambient conditions

A recyclable gold catalyst is synthesized from readily available reagents by immobilizing gold nanoparticles in aluminum oxyhydroxide support through a simple sol-gel method. The catalyst showed the high activity even at room temperature in the aerobic oxidation of various alcohols and in the coupling reaction between primary alcohols and ketones.     

Efficient ruthenium-catalyzed aerobic oxidation of amines by using a biomimetic coupled catalytic system

Efficient aerobic oxidation of amines was developed by the use of a biomimetic coupled catalytic system involving a ruthenium-induced dehydrogenation. The principle for this aerobic oxidation is that the electron transfer from the amine to molecular oxygen occurs stepwise via coupled redox systems and this leads to a low-energy electron transfer. A substrate-selective ruthenium catalyst dehydrogenates the amine and the hydrogen atoms abstracted are transported to an electron-rich quinone (2a). The hydroquinone thus formed is subsequently reoxidized by air with the aid of an oxygen-activating [Co(salen)]-type complex (27). The reaction can be used for the preparation of ketimines and aldimines in good to high yields from the appropriate corresponding amines. The reaction proceeds with high selectivity, and the catalytic system tolerates air without being deactivated. The rate of the dehydrogenation was studied by using quinone 2a as the terminal oxidant. A catalytic cycle in which the amine promotes the dissociation of the dimeric catalyst 1 is presented.     

Comparative study of the catalytic hydroconversion of cyclopentane over iridium and platinum single-crystal surfaces

In the context of fuel upgrading by selective ring opening of naphthenes, we have investigated the catalytic conversion of cyclopentane in large hydrogen excess over iridium and platinum single-crystal surfaces. Both (111) and (112) orientations have been considered. The catalytic tests have been performed at 1 kPa and 25–600 °C using a recently developed surface reactor equipped with laser heating and online gas chromatography. Only cyclopentene and C₁–C₄ cracking products are formed on iridium, while platinum additionally catalyzes the formation of pentane around 200 °C, which dehydrogenates to pentene at 250 °C. Noticeably, on both metals, the surface steps prevent hydrocarbon cracking (up to 400 °C) at the benefit of dehydrogenation. In all cases, a carbon overlayer is formed on the surfaces in the course of the reaction.     

A novel method of synthesis of 1,2-diketones from 1,2-diols using N-bromosuccinimide

A simple and convenient procedure is reported for the synthesis of benzils and aliphatic 1,2-diketones of cyclic and open chain compounds from corresponding hydrobenzoins and 1,2-diols by refluxing with N-bromosuccinimide in carbon tetrachloride in presence or absence of pyridine.     

Hydrosilylation of alkynes catalysed by platinum on titania

The heterogeneous hydrosilylation of alkynes catalysed by platinum on titania is reported. A variety of hydrosilanes react with both terminal and internal alkynes to furnish the corresponding vinyl silanes in high yields and short reaction times as well as in a regio- and stereoselective manner. The catalyst can be easily recovered and reused in several consecutive cycles.     

硝酸铁催化氧化二芳基乙醇酮制备二芳基乙二酮

用AcOH作溶剂,PEG400做相转移催化剂,硝酸铁能将二芳基乙醇酮催化氧化为二芳基乙二酮。产物结构用IR,MS和1H NMR光谱对其进行了表征。该方法有反应时间短,产率较高,操作简便等优点,是一种有效的由二芳基乙醇酮氧化制备二芳基乙二酮的方法。     

Aerobic oxidative transformation of primary alcohols and amines to amides promoted by a hydroxyapatite-supported gold catalyst in water

In the presence of an easily prepared hydroxyapatite-supported gold catalyst, namely Au/HAP, various kinds of structurally diverse primary alcohols including benzylic and aliphatic ones, and amines involving aromatic and secondary ones could be converted into the corresponding amides in water with up to 99% yield. Meanwhile, on the basis of experimental observations and literatures, a plausible reaction pathway was described to elucidate the reaction mechanism.