Metal-mediate reactions based formal synthesis of triptonide and triptolide

A formal synthesis of triptolide and triptonide has been achieved based on metal-mediate reactions. Specially, Noyori’s ruthenium catalyzed enantioselective transfer hydrogenation, indium(III) catalyzed cationic polyene cyclization, palladium catalyzed carbonylation, rhodium catalyzed double bond migration, and palladium catalyzed ortho sp² C–H bond oxygenation reactions served as convenient entry points for the preparation of the tetracyclic building blocks and the C14 hydroxyl group.     

镍催化偶联反应机理研究进展(英文)

近期发展了很多镍催化的偶联反应作为在有机合成中高效构建C–C键的方法,同时开展了很多关于控制镍催化反应活性和选择性的机理研究.这些研究发现,镍催化反应机理往往和相应的钯催化反应机理不同,因为镍催化偶联经常包括自由基和双金属机理.本文总结了镍催化偶联反应机理的最新进展.对于这些反应机理的理解为发展具有更高效率和选择性的镍催化偶联反应提供了帮助.     

Pd-catalyzed cross-coupling reactions of alkyl halides

Cross-coupling reactions have become indispensable tools for creating carbon-carbon (or heteroatom) bonds in organic synthesis. Like in other important transition metal catalyzed reactions, such as metathesis, addition, and polymerization, unsaturated compounds are usually employed as substrates for cross-coupling reactions. However during the past decade, a great deal of effort has been devoted to the use of alkyl halides as saturated compounds in cross-coupling reactions, which has resulted in significant progress in this undeveloped area by introducing new effective ligands. Many useful catalytic systems are now available for synthetic transformations based on C(sp(3))-C(sp(3)), C(sp(3))-C(sp(2)) and C(sp(3))-C(sp) bond formation as complementary methods to conventional C(sp(2))-C(sp(2)), C(sp(2))-C(sp) and C(sp)-C(sp) coupling. This tutorial review summarizes recent advances in cross-coupling reactions of alkyl halides and pseudohalides catalyzed by a palladium complex.     

Recent trends in synthetic strategies using magnetic nanostructures as green catalysts in synthesis of pyran analogues

In recent years, magnetic nanoparticles and nanocomposites play an important role as a nanocatalyst in the creation of a wide range of bioactive heterocycles with extraordinarily high activity and selectivity, low energy consumption, and extended life. Among all heterocycles, many natural products, pharmaceuticals, and bioactive compounds contain pyran scaffolds which have a wide range of uses in biomedical research, industry, and medicine. Additionally, these are also widely used in the synthesis of novel heterocyclic systems as precursors. This study focused on recent advances in the last 5 years in using various magnetic recoverable and recycled nanoparticles and nanocomposites to synthesize pyran derivatives and their pharmacological activity. This article has been classified into three subsections: (i) MNPs-metal nanocomposite catalyzed reactions, (ii) MNPs-organic based nanocomposite catalyzed reactions, and (iii) MNPs-ionic liquid nanocomposite catalyzed reactions and (iv) MNPs-acid based nanocomposite to describe catalytic efficiency of magnetic nanocomposites for the synthesis of pyran derivatives. A comparative study of nanocomposites and different approaches for green synthesis of pyrans by highlighting the advantages and disadvantages along with catalyst recovery and recyclability has been mentioned, which will help scientists to probe and stimulate the study of these scaffolds.     

Recent progress and current applications of Sonogashira coupling reaction in water

The use of aqueous media in palladium‐catalyzed reactions has become popular because water‐based synthetic processes are inherently safer as well as being inexpensive. Moreover, it does not require dry solvents, and the products may easily be isolated by extraction, which greatly facilitates the operation. Thus the use of water in palladium‐catalyzed reactions represents one of the most economically and environmentally viable options for many organic transformations. In this review, recent developments of Sonogashira reaction in water or aqueous media will be disclosed. Copyright © 2013 John Wiley & Sons, Ltd.     

Asymmetric Catalytic Reactions Catalyzed by Chiral Titanium Complexes

Chiral titanium complexes is very importance catalyst to asymmetric catalytic reactions. A series of catalytic systems based on titanium-chiral ligands complexes has been reported. This presentation will discuss some of our recent progress on asymmetric catalytic reactions catalyzed by chiral titanium complexes.     

Expanding the catalytic activity of nucleophilic N-heterocyclic carbenes for transesterification reactions

[reaction: see text] Currently, there is a renewed interest in reactions that are catalyzed by organic compounds. Typical organic catalysts for acylation or transesterification reactions are based on either nucleophilic tertiary amines or phosphines. This communication discusses the use of nucleophilic N-heterocyclic carbenes as efficient transesterification catalysts. These relatively unexplored and highly versatile organic catalysts were found to be mild, selective, and more active than traditional organic nucleophiles.     

非钯催化剂催化Heck反应研究进展

非钯催化剂用于催化Heck反应有较多的报道.与钯催化剂相比,一些非钯催化剂(如镍、铜、钴等)显示了更优越的性能.近年来,铂、铑、钌、铁等催化体系也被用于Heck反应.对近年来非钯催化剂用于催化Heck反应的研究进行了归纳总结.     

A new catalytic method for the determination of vanadium

A new catalytic method for the determination of 0–0.6 ppm of vanadium is described. The method is based on the catalytic action of vanadium on the reaction of bromate with bromide at pH = 1.80 ± 0.05. In this hitherto unreported reaction no bromine is formed, but in a two-step process hypobromite is produced. The rate is monitored by potentiometry, and results are evaluated from the recorded potential vs time curves. The optimal conditions for the determination have been investigated, and interferences as well as their elimination studied.The stoichiometry, mechanism, and kinetics of both the uncatalyzed and the catalyzed reactions were investigated, and the rate constants (for 20 °C) and the entropies and enthalpies of activation of both the uncatalyzed and the catalyzed reactions were determined.     

Pd0‐Catalyzed Intramolecular α‐Arylation of Sulfones: Domino Reactions in the Synthesis of Functionalized Tetrahydroisoquinolines

A new strategy for the synthesis of tetrahydroisoquinolines based on the Pd⁰‐catalyzed intramolecular α‐arylation of sulfones is reported. The combination of this Pd‐catalyzed reaction with intermolecular Michael and aza‐Michael reactions allows the development of two‐ and three‐step domino processes to synthesize diversely functionalized scaffolds from readily available starting materials.     

Chemo‐ and Enzyme‐Catalyzed Reactions Revealing a Common Temperature‐Dependent Dynamic Solvent Effect on Enantioselectivity

The enantiomeric ratio E of enzyme‐catalyzed (Candida antarctica lipase and lipase PS) and chemo‐catalyzed (L ‐proline‐based diamines) acylation reactions of 1‐(naphthalen‐2‐yl)ethanol, 2‐phenylpropanol, and 2‐benzylpropane‐1,3‐diol is dependent on solvent and temperature. Plots of ln E vs. 1/T showed the presence of inversion temperatures (T_inv). The T_inv values for the bio‐catalyzed and the chemo‐catalyzed reactions are fairly in agreement, and correspond as well to the T_NMR values obtained by variable‐temperature ¹³C‐NMR experiments on the substrates in the same solvent of the resolution. This result demonstrates that clustering effects in the substrate solvation manage the chemical and the enzymatic enantioselectivity, and, moreover, that the solute? solvent cluster is always the real reacting species in solution for chemical as well as for enzymatic reactions.     

DESs: Green solvents for transition metal catalyzed organic reactions

The recent development about using DESs as green solvents in transition metal catalyzed organic reactions was highlighted, and Au, Metal impregnated on magnetite, Pd, Ru catalyzed organic reactions proceeded smoothly in DESs and gave corresponding products in reasonable yields. And in some cases, the catalytic systems could be recycled up to several times.     

DESs: Green solvents for transition metal catalyzed organic reactions

In this review, the recent development about using DESs as green solvents in transition metal catalyzed organic reactions was highlighted. Firstly, the development of DESs was simply introduced. After presenting the advantages of DESs, transition metals catalyzed organic reactions using DESs as green solvents were classified and introduced in detail. Different transition metals such as Au, metal impregnated on magnetite, Pd and Ru catalyzed organic reactions proceeded smoothly in DESs and gave corresponding products in good yields. And in some cases, the catalytic systems could be recycled up to several times without any decrease in activity.     

Enantioselective Synthesis of 3‐Substituted Cyclobutenes by Catalytic Conjugate Addition/Trapping Strategies

A copper‐catalyzed tandem process to generate chiral cyclobutene derivatives has been developed. It is based on an enantioselective conjugate addition or reduction of a cyclobutenone and sequential trapping with a chlorophosphate in a one‐pot process. These phosphates are stable under mildly acidic conditions and serve as good electrophiles in Negishi coupling reactions.     

Cu‐Catalyzed Formal Methylative and Hydrogenative Carboxylation of Alkynes with Carbon Dioxide: Efficient Synthesis of α,β‐Unsaturated Carboxylic Acids

The sequential hydroalumination or methylalumination of various alkynes catalyzed by different catalyst systems, such those based on Sc, Zr, and Ni complexes, and the subsequent carboxylation of the resulting alkenylaluminum species with CO₂ catalyzed by an N‐heterocyclic carbene (NHC)–copper catalyst have been examined in detail. The regio‐ and stereoselectivity of the overall reaction relied largely on the hydroalumination or methylalumination reactions, which significantly depended on the catalyst and alkyne substrates. The subsequent Cu‐catalyzed carboxylation proceeded with retention of the stereoconfiguration of the alkenylaluminum species. All the reactions could be carried out in one‐pot to afford efficiently a variety of α,β‐unsaturated carboxylic acids with well‐controlled configurations, which are difficult to construct by previously reported methods. This protocol could be practically useful and attractive because of its high regio‐ and stereoselectivity, simple one‐pot reaction operation, and the use of CO₂ as a starting material.     

Acid‐Acid‐Catalyzed Tandem Reactions Driven by an Additive‐Like Component

Acid‐catalyzed tandem reactions with auto‐tandem catalysis are effective for simplifying organic synthesis. However, some of the reported reactions were established based on the use of well‐designed substrate with complex structure. In some cases, owing to the existence of a big gap between each catalytic cycle, it is hard to bind all the individual reaction steps to be a peaceful sequence. To enrich the diversity and also to strengthen the practical usefulness of the methodology developed by auto‐tandem catalysis, an additive‐like component was added to induce acid‐acid‐catalyzed tandem reaction. During the reaction, the additive‐like component acted either as an activator to increase the reactivity of the starting material or a hided reagent to enable successful transformation of the intermediate. Many novel tandem reactions were established in a one‐pot manner with the aid of this strategy. Importantly, this strategy not only allows the use of simple and commercially available chemicals as substrates, but also possesses multiple merits, such as simplifying operation, lowering waste generation and enhancing synthetic efficiency and atom‐economy. A summarization of the additive‐like component‐induced auto‐tandem catalysis with an acid catalyst was given in this review, in which many acid‐acid‐catalyzed tandem reactions were discussed. The reported additive‐like components were classified as three types: oxidative type, reductive type and neutral type depending on their mechanisms in assisting the establishment of acid‐acid‐catalyzed tandem reactions. Many examples were collected and analyzed from the viewpoints of simplifying the synthesis and manifesting their superior and distinct functionalities of the additives. A perspective of this concept was also given at the end of this review.     

A Single‐Molecule‐Level Mechanistic Study of Pd‐Catalyzed and Cu‐Catalyzed Homocoupling of Aryl Bromide on an Au(111) Surface

On‐surface Pd‐ and Cu‐catalyzed C?C coupling reactions between phenyl bromide functionalized porphyrin derivatives on an Au(111) surface have been investigated under ultra‐high vacuum conditions by using scanning tunneling microscopy and kinetic Monte Carlo simulations. We monitored the isothermal reaction kinetics by allowing the reaction to proceed at different temperatures. We discovered that the reactions catalyzed by Pd or Cu can be described as a two‐phase process that involves an initial activation followed by C?C bond formation. However, the distinctive reaction kinetics and the C?C bond‐formation yield associated with the two catalysts account for the different reaction mechanisms: the initial activation phase is the rate‐limiting step for the Cu‐catalyzed reaction at all temperatures tested, whereas the later phase of C?C formation is the rate‐limiting step for the Pd‐catalyzed reaction at high temperature. Analysis of rate constants of the Pd‐catalyzed reactions allowed us to determine its activation energy as (0.41±0.03) eV.     

离子液体在有机反应中的应用

室温离子液体，由含氮的有机阳离子和无机阴离子组成，可溶解各种有机、无 机、金属有机化合物。它们没有蒸气压、不易燃、容易循环使用。近年已发现，离 子液体可广泛地用于许多过渡金属化合物和酶催化的反应。着重讨论这方面的发展 状况。     

硫酸盐水合物催化下的酯化反应 II: 催化线性自由能方程

A new relationship based on the Hammett equation is derived for the esterification reaction of substituted carboxylic acid in the presence of hydrated sulphate salts and is called a catalyzing linear free energy equation. The equation can be expressed as log(KR(M)/K0Mn))=\s\*\T\^M + Ym where KR(M) is the rate constant of the esterification reaction of substituted acetic acid catalyzed by hydrated sulphate salts of M matal, K0(Mn) is the rate constant of that of acetic acid catalyzed by MnSO4.H2O, Ym is active index of catalyst. For reactions catalyzed by certain catalysts the rate constant of substituted acetic acid can be estimated from the equation.     

Ligand‐Promoted Rhodium(III)‐Catalyzed ortho‐C−H Amination with Free Amines

Ligand development for rhodium(III)‐catalyzed C−H activation reactions has largely been limited to cyclopentadienyl (Cp) based scaffolds. 2‐Methylquinoline has now been identified as a feasible ligand that can coordinate to the metal center of Cp*RhCl to accelerate the cleavage of the C−H bond of N ‐pentafluorophenylbenzamides, providing a new structural lead for ligand design. The compatibility of this reaction with secondary free amines and anilines also overcomes the limitations of palladium(II)‐catalyzed C−H amination reactions.