Efficient aerobic oxidative dehydrogenation of dihydropyrimidinones and dihydropyrimidines

4-Substituted dihydropyrimidinones and dihydropyrimidines were first efficient aerobic oxidized to the corresponding pyrimidinones and pyrimidines, respectively, in high yields by molecular oxygen in the presence of catalytic amount of N-hydroxyphthalimide (NHPI) and Co(OAc)₂ in a mild and environmental benign condition.     

Copper-catalyzed aerobic oxidative cyclization protocol for the synthesis of quinazolines via amination of C(sp3)-H bonds of methylazaarenes

A new aerobic copper-catalyzed three-component synthesis of azaaryl-substituted quinazolines has been developed, which featured inexpensive methylazaarenes as C1 sources, easily available copper salts as the catalysts and O₂ as a sole oxidant. The transformation had very good substrate applicability towards methylazaarenes, and various azaaryl-substituted quinazolines were obtained in moderate to good yields.     

The catalytic activity of a cyclometalated ruthenium(III) complex for aerobic oxidative dehydrogenation of benzylamines

The ruthenium(III) complex bearing benzo[h]quinoline as a cyclometalated ligand was synthesized and characterized by ESI-MS, elemental analysis, cyclic voltammetry and crystallography. The complex serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzylamines to the corresponding benzonitriles under mild conditions.     

Copper-catalyzed aerobic oxidative cross-coupling of arylamines and dialkylphosphites leading to N-arylphosphoramidates

An efficient method to generate N–P bonds directly from N–H and P–H bonds is described. Various arylamines and dialkylphosphites were directly oxidized to the corresponding N-arylphosphoramidates at room temperature in moderate to good yields by using an inexpensive catalyst–oxidant (CuBr/air) system.     

Copper-catalyzed addition of water affording highly substituted furan and unusual formation of naphthofuran ring from 3-(1-alkenyl)-2-alkene-1-al

We have developed a novel one-pot reaction to generate highly substituted furan through the addition of water followed by oxidation and unusual cyclization to naphthofuran ring under the same reaction condition.     

Cu-catalyzed aerobic oxidative synthesis of sulfonamides from sulfonyl hydrazides and amines

An environmentally friendly route for sulfonamides has been developed. The oxidative coupling of sulfonyl hydrazides and amines was catalyzed by CuBr₂ to produce various sulfonamides with the water and nitrogen gas as byproducts. Preliminary experiments revealed that the sulfonyl radical is likely to be involved in the reaction mechanism.     

Selective copper(II)-catalyzed aerobic oxidative cleavage of aromatic gem-disubstituted alkenes to carbonyl compounds under neutral and mild conditions

Three copper(II) catalytic systems, CuCl₂·2H₂O, CuCl₂·2H₂O+phenanthroline, and [Cu(μ-Cl)Cl(phen)]₂ were used to cleave alkenes to their corresponding carbonyl compounds under aerobic and neutral conditions. [Cu(μ-Cl)Cl(phen)]₂ shows enhanced selectivity over the other two catalytic systems. The oxidative cleavage reactions were carried out in mixed H₂O/THF solvent system under oxygen (4 atm) at 60°C. The real oxidant is 2-hydroperoxytetrahydrofuran, which is generated in situ in the process through the reaction between THF and oxygen catalyzed by copper(II). The cleavage reactions are selective for aromatic gem-disubstituted alkenes. Aromatic internal alkenes are slow to be oxidized, and both aliphatic terminal and internal alkenes are inert to oxidative cleavage. Free radical scavenger 2,2,6,6, tetramethylpiperidinyl-1-oxyl (TEMPO) deactivates the reaction indicating the involvement of free radical path in the reaction mechanism.     

New efficient catalysts for the aerobic oxidation of ethers

Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported.     

A highly efficient reusable homogeneous copper catalyst for the selective aerobic oxygenation sulfides to sulfoxides

Readily available copper showed efficient activity and great selectivity for the homogeneous catalysis of oxidation of sulfides to sulfoxides using molecular oxygen as the oxidant. The reaction proceeds under mild conditions in the presence of a catalytic amount of TEMPO. Importantly, the catalysts could be conveniently recovered and reused. And this methodology was proved to be applicable for the transformation of various aromatic and aliphatic sulfides into the corresponding sulfoxides with high conversion and high selectivity.     

Gold- and gold-palladium/poly(1-vinylpyrrolidin-2-one) nanoclusters as quasi-homogeneous catalyst for aerobic oxidation of glycerol

Glycerol was oxidized catalytically under aerobic conditions in the presence of monometallic nanoclusters of gold on poly(1-vinylpyrrolidin-2-one) (PVP) to give hydroxymalonic acid (tartronic acid) as the major product, together with 2,3-dihydroxypropanoic acid (glyceric acid) and hydroxyacetic acid (glycolic acid) as minor products. In contrast, oxalic acid was selectively obtained when bimetallic Au-Pd:PVP nanoclusters were used as the catalyst.     

Copper(I) iodide dimethyl sulfide catalyzed 1,4-addition of alkenyl groups from alkenyl-alkylzincate reagents

The presence of catalytic quantities of the copper(I) iodide dimethyl sulfide complex {(CuI)₄(SMe₂)₃} with alkenyl-alkylzincate reagents allows for the complete chemoselective 1,4-addition of various alkenyl groups to a number of α,β-unsaturated carbonyl compounds in CH₂Cl₂ at +35 °C. The 1,4-addition of the mixed vinylzincate reagent is more efficient than the corresponding vinylzirconocene reagent in CH₂Cl₂ or THF. By employing CH₂Cl₂ as a medium, the asymmetric copper-catalyzed addition of the vinyl groups to α,β-unsaturated imides is facilitated by the presence of TMSOTf to give excellent yields and up to 95:5 diastereomeric ratios (dr).     

Selective aerobic oxidation of benzylic amines to aryl nitriles catalyzed by CuBr2/N-methyl imidazole

A convenient and efficient copper-catalyzed aerobic oxidation of primary amines to aryl nitriles was described. Various benzylic and allylic amines were selectively oxidized to the corresponding nitriles in high yields using CuBr₂/NMI as the catalyst and O₂ as the oxidant. The oxidation reaction profiles monitored by ¹H NMR disclosed the scenario of the reaction path as well as the role of the additives. The addition of NMI increased the rate of reaction and suppressed the hydrolysis and the deamination.     

Cobalt-catalyzed aerobic oxidation of (E)- and (Z)-bishomoallylic alcohols

Stereoselectivity for (5-phenyltetrahydrofur-2-yl)alkan-1-ol formation (cis:trans < 1:99) from 5-methyl- and 5-phenyl-substituted 1-phenylpent-4-en-1-ols via cobalt-catalyzed aerobic oxidation was independent of the olefinic π-bond configuration of the substrates.     

Copper-catalyzed Csp-chalcogen bond formation: Versatile approach to N-(3-(organochalcogenyl)prop-2-yn-1-yl)amides

This work describes the copper-catalyzed Csp-chalcogen bond formation through cross-coupling reactions of propynylbenzamides and diorganyl dichalcogenides at room temperature, under open atmosphere. Generally, the reactions have proceeded very smoothly, affording the new class of organochalcogen-containing propynylbenzamides in good yields. Notably, this protocol showed to be tolerant to neutral, electron-donating and electron-withdrawing substituents present in both reaction substrates. In addition, the applicability of the carbon-chalcogen bond as a reactive site has been proved by successfully employment of the N-methyl-N-(3-(butylselanyl)prop-2-yn-1-yl)benzamide as a precursor in palladium-catalyzed Suzuki and Sonogashira type reactions.     

Synthesis and hydrolytic cleavage of 1-aryl-5-cyano-6-(2-dimethylaminovinyl)-4-oxo(thioxo)-1,4-dihydropyrimidines

1-Aryl-5-cyano-6-(2-dimethylaminovinyl)-4-oxo-1,4-dihydropyrimidines and their 4-thioxo analogs, which were prepared in three steps from cyanoacetamide and cyanothioacetamide, respectively, were subjected to hydrolysis. In aqueous AcOH, hydrolysis of N-(dimethylaminomethylene)-2-cyano-5-dimethylamino-2,4-pentadieneamide derivatives containing amino groups at position 3 afforded formylpyridones. The reaction of 2-cyano-3-dimethylaminothiocrotonamide with DMF dimethyl acetal gave rise to 3-cyano-4-dimethylamino-2-methylthiopyridine.     

Effective cleavage of ditertiary glycols via vanadium(V)-catalyzed aerobic oxidation

The aerobic oxidation of ditertiary glycols catalyzed by oxytrichlorovanadium resulted in carbon-carbon bonds cleavage producing the ketones efficiently.     

Facile synthesis of highly active Co(II) and Fe(II) phthalocyanine catalysts for aerobic oxidation of phenolic compounds

In this work, 2,3-dichlorophenoxy substituted cobalt and iron phthalocyanines have been synthesized and used as efficient catalysts for aerobic oxidation of nitrophenols. Co(II) and Fe(II) phthalocyanines have been characterized by IR, ¹H NMR, ¹³C NMR, UV–vis, and mass spectroscopies. tert-butyl hydroperoxide (TBHP), m-chloroperoxybenzoic acid, hydrogen peroxide, and air oxygen have been used as oxygen source. These catalysts offered the highest activity on 4-nitrophenol oxidation in 3 h. In order to achieve the best reaction conditions, oxidant ratio, temperature, and oxidant type have been investigated with different nitrophenols in 3 h.     

V2O5纳米片固载Pt纳米粒子催化剂的构建及其增强催化空气氧化脱硫性能

以铂系金属为代表的贵金属催化剂在工业反应中通常表现出优异的催化性能,这是因为其具有独特的d带电子结构和较高的价电子比.近年来,由于大气排放法规愈发严苛,铂系贵金属催化剂在催化空气氧化燃油脱硫方面的研究引起了广泛关注.在该催化反应中,铂系金属纳米粒子可以有效活化空气中的氧气,产生的活性氧物种可以将油品中的噻吩类硫化物氧化为其对应的强极性砜类物质,从而可以将其从非极性的油品中分离出来,有效实现油品中硫化物的深度氧化脱除.然而,在反应过程中铂系贵金属纳米粒子易发生流失和烧结,从而导致催化剂的失活.因此,急需寻找一类可以有效固载铂系贵金属纳米粒子的载体.在目前已报道的众多载体中,以ZrO₂、TiO₂、CeO₂、ZnO等为代表的过渡金属氧化物引起了广泛的关注.通常认为,铂系贵金属纳米粒子的d轨道电子和过渡金属氧化物之间可形成金属-载体强相互作用.然而,目前所使用的过渡金属氧化物载体的比表面积较小,从而导致铂系贵金属纳米粒子难以有效且均匀地分散于其表面.本文采用热膨胀气相剥离法制备了超薄V2O5纳米片,并通过超声辅助沉积法将Pt纳米粒子固载于其表面,从而得到一系列可高效活化空气氧化脱硫的催化剂(Pt NPs-n/V₂O₅纳米片).通过电感耦合等离子体光谱、高倍透射电镜、原子力显微镜、X射线光电子能谱、X射线衍射、拉曼光谱和氮气吸附脱附等方法对催化剂的结构和形貌进行了表征.结果表明,尺寸为4-5 nm的Pt纳米粒子可有效均匀分散于层数约为6层的V2O5纳米片表面;在空气氧化脱硫反应中,当催化剂中Pt理论负载量为2 wt%时,反应5 h后,油品的脱硫率可达99.1%,实现了硫化物的深度氧化脱除.该反应体系对不同硫浓度、不同含硫底物的油品均有较好的脱除效果,但对含有烯烃、芳烃的油品脱除效果较差.此外,催化剂循环使用7次后,其脱硫活性仍无明显下降,表现出优异的重复使用性能.对反应后的催化剂进行表征,发现Pt几乎不发生流失,这可能是由于Pt纳米粒子和V₂O₅纳米片之间形成了金属-载体强相互作用.该结果为其他空气氧化反应的有效进行提供了新思路.     

Selective reductive cleavage of 2-(phenylthio)pyrimidines for efficient synthesis of 2-(H)pyrimidines

A reaction method is described for selective reductive cleavage of 2-(phenylthio)pyrimidines using Pd(OAc)₂ and Et₃SiH to produce 2-(H)pyrimidines. The reaction proceeds efficiently with a wide range of 2-(phenylthio)pyrimidines. Considering the ready availability of 2-(arylthio)pyrimidines derived from oxidative CS cross coupling of 3,4-dihydropyrimidin-1H-2-thiones (DHPMs), this method unambiguously provides a shortcut to the preparation of 2-(H)pyrimidines with unprecedented diversity.