Transition-metal-free: a highly efficient catalytic aerobic alcohol oxidation process

A highly efficient catalytic system without transition metals has been developed for aerobic alcohol oxidations. Under the optimal reaction conditions, various alcohol substrates were converted into their corresponding carbonyl compounds by air with TEMPO/Br2/NaNO2 as catalyst, especially the oxidation of benzylic alcohols to benzaldehydes in high yields.     

A multipolymer system for organocatalytic alcohol oxidation

A system involving two polymer-supported reagents for the selective and organocatalytic oxidation of alcohols to aldehydes or ketones has been developed in which both polymeric reagents can be recovered and reused.     

Polyoxometalate compound: a highly efficient heterogeneous catalyst for aerobic alcohol oxidation

Oxidation of alcohols to aldehydes and ketones has been studied using atmospheric oxygen and a catalytic amount of Na_6.3Fe_0.9[AlMo₁₁O₃₉]·2H₂O in toluene under heating (80 or 110 °C) in high yields. Secondary alcohols can be chemoselectively converted into ketones in the presence of primary hydroxyl groups.     

Chemoselective organocatalytic aerobic oxidation of primary amines to secondary imines

Biomimetic aerobic oxidation of primary benzylic amines has been achieved by using a quinone catalyst. Excellent selectivity is observed for primary, unbranched benzylic amines relative to secondary/tertiary amines, branched benzylic amines, and aliphatic amines. The exquisite selectivity for benzylic amines enables oxidative self-sorting within dynamic mixtures of amines and imines to afford high yields of cross-coupled imine products.     

Zeolite-confined Nano-RuO(2): A green,selective, and efficient catalyst for aerobic alcohol oxidation

The development of green, selective, and efficient catalysts, which can aerobically oxidize a variety of alcohols to their corresponding aldehydes and ketones, is of both economic and environmental significance. We report here the synthesis of a novel aerobic oxidation catalyst, a zeolite-confined nanometer-sized RuO(2) (RuO(2)-FAU), by a one-step hydrothermal method. Using the spatial constraints of the rigid zeolitic framework, we sucessfully incorporated RuO(2) nanoparticles (1.3 +/- 0.2 nm) into the supercages of faujasite zeolite. Ru K-edge X-ray absorption fine structure results indicate that the RuO(2) nanoclusters anchored in the zeolite are structurally similar to highly hydrous RuO(2); that is, there is a two-dimensional structure of independent chains, in which RuO(6) octahedra are connected together by two shared oxygen atoms. In our preliminary catalytic studies, we find that the RuO(2) nanoclusters exhibit extraordinarily high activity and selectivity in the aerobic oxidation of alcohols under mild conditions, for example, air and ambient pressure. The physically trapped RuO(2) nanoclusters cannot diffuse out of the relatively narrow channels/pores of the zeolite during the catalytic process, making the catalyst both stable and reusable.     

泡沫铜无溶剂催化氧化苄醇的应用研究

本文报道了在模拟的鼓泡床反应器中,以1-甲基咪唑(NMI)和2,2,6,6-四甲基-1-哌啶基氧基(TEMPO)作为助催化剂,空气泵鼓入空气作为氧源,泡沫铜作为催化剂,室温、无溶剂条件下催化氧化苄醇的应用研究.具体优化条件为:以50 mmol苯甲醇为反应底物,2.5 mmol泡沫铜,0.625 mmol NMI,2.5...     

Highly efficient aerobic oxidation of oximes to carbonyl compounds catalyzed by metalloporphyrins in the presence of benzaldehyde

Highly efficient oxidation of oximes to carbonyl compounds by molecular oxygen with benzaldehyde as an oxygen acceptor in the presence of metalloporphyrins has been reported. The simple structural manganese porphyrin showed an excellent activity for the oxidative deoximation reactions of various oximes. Moreover, different factors influencing oximes oxidation, that is, catalyst, solvent, and temperature, have been investigated. A possible mechanism for the deoximation reaction has been proposed.     

Highly enantioselective organocatalytic Biginelli reaction

A series of binol- and H8-binol-based phosphoric acids have for the first time been evaluated for their ability to catalyze Biginelli reactions of aldehydes, thiourea or urea, and beta-keto esters. A new chiral phosphoric acid, derived from 3,3'-diphenyl-H8-binol, exhibited superior catalytic activity and enantioselectivity compared to its structural analogues, affording high enantioselectivities ranging from 85 to 97% ee with a wide scope of substrates. A metal-free preparation of optically active monastrol was achieved on the basis of the current process.     

New efficient organocatalytic oxidation of benzylic compounds by molecular oxygen under mild conditions

Efficient aerobic oxidation of benzylic compounds has been achieved under no irradiation using a new organocatalytic system in the presence of acridine yellow and N-hydroxyphthalimide with assistance of a catalytic amount of molecular bromine. Various substrates, especially alkylaromatics, were effectively oxygenated to the corresponding carbonyl compounds with molecular oxygen as oxidant under mild conditions. For instance, indan was oxidized with 92% conversion and 79% selectivity for 1-indanone under 0.3 MPa of O₂ at 75 °C.     

Highly efficient organocatalytic kinetic resolution of activated nitroallylic acetates with aldehydes via conjugate addition-elimination

A novel, efficient, and unprecedented organocatalytic kinetic resolution has been developed. For the first time, a variety of nitroallylic acetates 1a-i have been resolved with aldehydes in the presence of 2 (2.5 mol %) via conjugate addition-elimination. The densely functionalized products 3a-o were obtained with excellent enantioselectivities (up to >99% ee), and unreacted substrates 1a-i were recovered with good to excellent optical purity (up to 98% ee).     

Highly selective aerobic oxidation of alcohol catalyzed by a gold(I) complex with an anionic ligand

Highly selective aerobic oxidation of alcohols to carbonyl compounds was catalyzed by a gold(I) complex with an anionic ligand in solution.     

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.     

高效多羟胺有机催化剂选择性催化分子氧氧化研究进展

基于氧气(空气)为氧源的选择性催化分子氧氧化技术在制备含氧精细化学品或食品添加剂与医药等的重要中间体方面一直受到科学界的广泛关注.由于碳氢化合物中碳氢键的反应惰性和分子氧的自旋禁阻作用,设计与开发高效催化剂或催化体系以实现碳氢化合物的选择性氧化是当前催化氧化领域的研究热点.在已发展的过渡金属盐、仿生催化剂、有机催化剂、酶、碳材料和卤化物等众多催化剂中,以N-羟基邻苯二甲酰亚胺(NHPI)为代表的羟胺有机催化剂由于在温和条件下的卓越催化性能而备受瞩目.尽管基于羟胺有机催化剂的催化体系具有良好的工业应用前景,但仍存在催化剂高温易分解、使用量较大和可回收性较差等缺点.近年来,许多实验与理论工作围绕改进这些缺点展开,设计了一系列羟胺有机催化剂及其协同催化体系,如在NHPI结构中修饰疏水链基团、吸电子基团、N-烷氧基团和离子液体,或固载金属-有机框架材料、无机物和聚合物,或组合光催化剂.尽管已有大量综述总结了相关研究进展,但尚未见到有关近年来发展的多羟胺有机催化剂及其高效催化氧化性能的综述报道.本文综述了近15年来多羟胺有机催化剂选择性催化分子氧氧化碳氢化合物的研究进展.首先,简要概述了N,N-二羟基邻苯二甲酰亚胺(NDHPI)和N,N',N"-三羟基异氰基尿酸(THICA)两种多羟胺有机催化剂的合成方法,系统介绍了它们在各类碳氢化合物氧化中的高效催化性能,并与普遍应用的NHPI的催化性能进行对比.由于NDHPI与THICA具有多羟胺的独特结构,它们只需要比NHPI更少的用量便可获得比NHPI更高的催化氧化效率,可以直接利用高压空气实现对碳氢化合物的选择性催化氧化,并且在较高温度下依然具有较好的催化效果.在此基础上,介绍了联系实验与理论之间的重要工作,总结了多羟胺有机催化剂的合理设计策略.理论计算研究揭示了NDHPI与THICA的催化性能优于NHPI的主要原因是具有类似于吸电子效应的多羟胺与多氮氧自由基结构能显著增强催化剂的夺氢活性.通过对NDHPI结构的进一步修饰和夺氢活性研究,提出了该类催化剂的合理设计策略:在芳环体系中增加共轭的羟胺基团数量,或在NDHPI苯环中掺杂N原子或引入离子对基团都能提高催化剂的夺氢活性;增大芳环共轭体系对催化剂的夺氢活性影响较小,但该活性仍高于NHPI.这也为基于碳材料的非均相共轭多羟胺有机催化剂的开发提供了理论依据.最后,结合羟胺有机催化剂的发展现状和上述设计策略,设计了基于金属卟啉/席夫碱等仿生催化剂、(含离子对结构)聚合物、非均相碳材料和多N-烷氧基团等几种具有潜在发展前景的模型多羟胺有机催化剂,分别讨论了这些催化剂的优点和局限性,并展望了多羟胺有机催化剂的可能应用及其在催化氧化过程中仍需系统研究的方向.     

The facile and efficient organocatalytic platform for accessing 1,2,4-selenadiazoles and thiadiazoles under aerobic conditions

The first organocatalytic approach towards synthesis of rarely explored 1,2,4-selenadiazole and thiadiazole scaffolds have been devised using corresponding carboxamides as substrates. The transformations were realized using two distinct conditions in the presence of catalytic vitamin B₃ or thiourea under aerobic conditions. Developed methods overcome the associated limitations of previous reported approaches and the desired products were obtained in high yields and selectivity without the formation of toxic side-products.     

Highly efficient iridium-catalyzed oxidation of organosilanes to silanols

Hydrolytic oxidation of organosilanes to the corresponding silanols can be performed highly efficiently with a catalyst system of [IrCl(C(8)H(12))](2) under essentially neutral and mild conditions, and various types of silanols are produced in good to excellent yields.     

Highly efficient catalytic aerobic oxidations of benzylic alcohols in water

A highly efficient catalytic system without transition metals in water has been developed for aerobic oxidations of benzylic alcohols. The newly developed catalyst system could oxidize benzylic alcohols and heteroaromatic analogues with 1 mol % TEMPO as a catalyst and with a catalytic amount of 1,3-dibromo-5,5-dimethylhydantoin and NaNO2 as cocatalysts. Under the optimal conditions, various alcohols could be converted into their corresponding aldehydes or ketones in high yields.     

Highly dispersed palladium nanoparticles on mesocellular foam: an efficient and recyclable heterogeneous catalyst for alcohol oxidation

Palladium nanoparticles immobilized on amino-functionalized mesocellular foam constitute an efficient catalyst for the aerobic oxidation of primary and secondary alcohols to their corresponding carbonyl compounds in high to excellent yields. An exceptionally high TON of 365?000 was reached for the oxidation of 1-phenylethanol under solvent-free reaction conditions. The catalyst can be recycled many times with retained activity as shown by the identical rate curves of the first and fifth runs.     

Highly efficient organocatalytic asymmetric Michael addition of homoserine lactone derived cyclic imino esters to nitroolefins

An efficient stereoselective Michael addition reaction of homoserine lactone derived cyclic imino esters to nitroolefins promoted by a bis(cinchona alkaloid) (DHQD)₂AQN was achieved. This catalytic system features a wide substrate scope, furnishing the corresponding products with excellent diastereoselectivity (>95:5 dr) and good enantioselectivity (up to 87% ee) under mild conditions, and the Michael adducts could be easily transformed into highly functionalized spirocyclic γ-butyrolactone-pyrrolidines through a sequential nitro-Mannich reaction.     

Unexpected roles of molecular sieves in palladium-catalyzed aerobic alcohol oxidation

Methods for palladium-catalyzed aerobic oxidation of alcohols often benefit from the presence of molecular sieves. This report explores the effect of molecular sieves on the Pd(OAc)2/pyridine and Pd(OAc)2/DMSO (DMSO = dimethyl sulfoxide) catalyst systems by performing kinetic studies of alcohol oxidation in the presence and absence of molecular sieves. Molecular sieves enhance the rate of the Pd(OAc)2/pyridine-catalyzed oxidation of alcohols, and the effect is attributed to the ability of molecular sieves to serve as a Br?nsted base. In contrast, no rate enhancement is observed for the Pd(OAc)2/DMSO-catalyzed reaction. Both catalyst systems exhibit improved catalyst stability in the presence of molecular sieves, manifested by higher catalytic turnover numbers. Control experiments indicate that neither of these beneficial effects is associated with the ability of molecular sieves to absorb water, a stoichiometric byproduct of these reactions. Finally, the use of simultaneous gas-uptake and in-situ IR spectroscopic studies reveal that molecular sieves inhibit the disproportionation of H2O2, an observation that contradicts a previous suggestion that the beneficial effect of molecular sieves may arise from their ability to promote H2O2 disproportionation.