Transition Metal‐Catalyzed C?H Activation of Indoles

The last decades have seen a tremendous expanse in the application of C H activation of many different substrate classes, including the invaluable indole scaffold. Following the exciting emergence of C H activation as a multi‐faceted platform for functionalization, a versatile tool box has been developed for the preparation of structurally diverse indoles. This review article discusses recent advances and strategies for transition metal‐catalyzed C H activation of indoles.

     

An Efficient Synthesis of Polysubstituted Pyridines via C?H Oxidation and C?S Cleavage of Dimethyl Sulfoxide

An expedient cleavage of the C S bond of dimethyl sulfoxide (DMSO) has been developed for the preparation of substituted pyridines from ketones. In this transformation, the co‐product formic acid was formed from ammonium formate, which acted as an important catalyst for the reaction. Notably, this transformation exhibited a broad substrate scope towards a wide variety of different ketones to give the corresponding substituted pyridines in high yields. Mechanistic studies suggested that dimethyl sulfoxide delivered a methylene fragment, which was subsequently captured in situ to give a pyridine.

     

Synthesis of Biaryls through Aromatic C?H Bond Activation: A Review of Recent Developments

This review describes recent progress made in the rapidly developing field of C H bond activation, in particular for syntheses of biaryls. The catalysts presented here provide convenient strategies for the direct arylation of arenes, via single or double C H bond activation, leading to inter‐, and intramolecular carbon‐carbon bond formation. The literature from mid‐2009 to December 2013 has been discussed.

     

Zinc‐Catalyzed Organic Synthesis: C?C,C?N,C?O Bond Formation Reactions

Zinc is the 24^th most abundant element in the Earth’s crust. Since the discovery of pure zinc metal in the 18^th century, the main application of zinc metal is as materials. Because zinc salts are abundant, cheap, non‐toxic, and exhibit environmentally benign properties, organic chemists have been interested in using zinc salts as catalysts in organic synthesis during the last three decades. Within this review, we have summarized the progress on applications of zinc salts in organic reactions. Our the target is to emphasize the special properties of zinc catalysts, and further promote the interest of organic chemists.     

Synthesis of [60]Fullerene‐Fused Tetralones via Palladium‐ Catalyzed Ketone‐Directed sp2 C?H Activation and sp3 C?H Functionalization

The palladium‐catalyzed ketone‐directed dual sp² C H activation and sp³ C H functionalization has been applied for fullerene functionalization for the first time. The sec‐alkyl aryl ketones have been exploited to react with [60]fullerene (C₆₀) to provide the novel and scarce C₆₀‐fused tetralones. The combined use of a highly active cationic palladium(II) catalyst and trifluoromethanesulfonic acid is crucial for the improvement of the reaction yield. A plausible reaction mechanism leading to the observed products has been proposed, and the electrochemistry of the fullerene products has also been investigated.

     

Tandem Catalysis: Alcohol Oxidation and C?C Bond Formation via C?H Bond Activation

A tandem process involving oxidation of a benzylic alcohol functionality followed by hydroarylation is described. These two atom‐economic sequences are very convenient to access functionalized aromatic ketones, using simple ruthenium trichloride as catalyst precursor. Moreover they appear to be highly compatible, tolerant, and selective toward various functional groups, and the ease of the protocol should make it very convenient for synthetic purposes.     

Copper(II) Acetate/Oxygen‐Mediated Nucleophilic Addition and Intramolecular C?H Activation/C?N or C?C Bond Formation: One‐Pot Synthesis of Benzimidazoles or Quinazolines

Diarylcarbodiimides or benzylphenylcarbodiimides are converted to 1,2‐disubstituted benzimidazoles or 1,2‐disustituted quinazolines via addition/intramolecular C H bond activation/C‐N or C C bond forming reaction using copper(II) acetate/oxygen [Cu(OAc)₂/O₂] as the oxidant at 100 °C in one‐pot cascade procedure.     

Iron‐Catalyzed C?H Fuctionalization of Indoles

An easily available iron catalyst was developed to accomplish the C H functionalization of indoles with α‐aryl‐α‐diazoesters in high yields under mild conditions. The asymmetric C H functionalization of indoles was also realized by using iron complexes of chiral spiro bisoxazolines with up to 78% ee.     

Magnetically Retrievable Nano Crystalline Nickel Ferrite‐ Catalyzed Aerobic,Ligand‐Free C?N,C?O and C?C Cross‐ Coupling Reactions for the Synthesis of a Diversified Library of Heterocyclic Molecules

A new nickel ferrite nano‐crystal‐catalyzed, ligand‐free strategy for the construction of C N, C O, and C C bonds is presented, in which easily available nitrogen and oxygen nucleophiles, aryl/heteroaryl halides and arylboronic acids are used for the cross‐coupling reactions. The reactions can be performed at low catalyst loadings with excellent functional group tolerance and chemoselectivity. A variety of functional groups are compatible with the reaction conditions, including nitro, methoxy, as well as acid‐ and base‐sensitive heteroaromatic groups. This unprecedented chemistry nicely complements classical methods for the N‐arylation of amines/heteroamines, the O‐arylation of phenols/hydroxycoumarins and biaryl/heteroaryl synthesis. The low cost, easy to handle nature and the simplicity of this catalytic system render the method competitive with comparable copper‐ and palladium‐based protocols which require the presence of sophisticated ligands. Nickel ferrite magnetic nanoparticles were prepared by a simple hydrothermal method and characterized by using XRD, TEM image, energy dispersive X‐ray analysis, XPS and FT‐IR. The easy recovery of the catalyst and high yield of the products make the protocol attractive, sustainable and economic. The catalyst was reused for five cycles with almost unaltered catalytic activity.

     

Direct Trifluoromethylation of the C?H Bond

Trifluoromethylation meets C H activation: after transition metal‐catalyzed trifluoromethylation became more and more popular, trifluoromethylation via C H activation is now emerging as the latest attraction. Several pioneering examples and their mechanisms are discussed in this review.     

Expedient Synthesis of Functionalized Triarylmethanols through Tandem Formation of Geminal C?C and C?O Bonds

The rearrangement/oxidation of N,N‐disubstituted anilines and the formal dehydrogenative cross‐coupling of diarylmethanols with aniline derivatives have been developed for the preparation of symmetric and unsymmetric functionalized triarylmethanols. Both reactions proceed smoothly in trifluoroacetic acid in the presence of an inexpensive oxidant (manganese dioxide or potassium persulfate) and a catalytic amount of palladium diacetate to give a range of functionalized triarylmethanols in moderate to good yields and with extremely high regioselectivity. The two unprecedented reactions involve tandem formation of geminal C C and C O bonds, and they are synthetically useful, atom‐efficient, and operationally simple.     

Grignard‐Type Arylation of Aldehydes via a Rhodium‐Catalyzed C?H Activation under Mild Conditions

An efficient Grignard‐type arylation of aldehydes via aryl C H activation was achieved under mild conditions catalyzed by rhodium. The reaction provides an easy access to a wide variety of benzyl alcohols and can tolerate various functional groups as well as air and water.     

Synthesis and thermal behavior of polymeric precursors for Si?B?C?N ceramic

Polyborosilazanes (PBSZs) were synthesized by co‐ammonolysis of 2,4,6‐trichloroborazine and dichloromethylsilane and used as precursors for Si? B? C? N ceramics. The pyrolyzed products were characterized with Fourier transform infrared, X‐ray photoeletron spectroscopy, thermogravimetric analysis (TGA), X‐ray diffraction, and scanning electron microscopy (SEM). The results indicated the content of B or Si plays an important role in controlling the high temperature behavior of the precursors. The resistance of the ceramics, which were obtained from pyrolysis of PBSZs at 1500°C, toward oxidative attack up to 1000°C was also investigated by TGA and SEM/EDX. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Lewis Acid‐Catalyzed C?H Functionalization for Synthesis of Isoindolinones and Isoindolines

The Lewis acid‐catalyzed C H functionalization of 2‐substituted azaarenes with N‐sulfonylaldimines has been developed, which provides a rapid and efficient approach for synthesis of heterocycle‐containing isoindolinones and isoindolines.     

Continuous‐Flow C?H Borylation of Arene Derivatives

A new continuous‐flow system for C H borylation has been developed. An insoluble catalyst prepared from chloro(1,5‐cyclooctadien)iridium(I) dimer and 2,2′‐bipyridine‐4,4′‐dicarboxylic acid in the presence of bis(pinacolato)diboron exhibited high reactivity under continuous‐flow processing without the loss of expensive iridium metal.     

Ruthenium‐Catalyzed Remote Electronic Activation of Aromatic C?F Bonds

The tandem isomerization and nucleophilic aromatic substitution of allylic fluoro‐substituted benzylic alcohols is described for the first time. In the presence of the ruthenium complex Ru(PPh₃)₃(CO)(H)₂, 1‐(4‐fluorophenyl)prop‐2‐en‐1‐ol is converted into the corresponding para‐amino ketone or para‐phenolic substituted ketone.     

C?C Bond Formation via C?H Activation and C?N Bond Formation via Oxidative Amination Catalyzed by Palladium‐ Polyoxometalate Nanomaterials Using Dioxygen as the Terminal Oxidant

An efficient heterogeneous palladium‐polyoxometalate catalyst with the formula Pd‐H₆PV₃Mo₉O₄₀/C has been successfully developed for carbon‐carbon (C C) bond formation via carbon‐hydrogen (C H) activation and carbon‐nitrogen (C N) bond formation via oxidative amination using oxygen as the terminal oxidant. The coupling processes are simple, and use relatively mild conditions to form the desired products. In addition, less waste is generated as no additional reagents such as organic/inorganic oxidants are required, and water is the only by‐product generated.     

Chemische Synthese des Dodecanucleotids dC?A?C?A?A?G?C?T?T?G?T?G

Chemical Synthesis of the Dodeecanuceleotide. dC A C A A G C T T G T G For studies of some sequence dependent structural factors the self-complementary dodecanucleotide dC A C A A G C T T G T G was required. Its chemical synthesis is reported according to the diester approach starting with the monomers dC, dpA, dpG, dpC and dpT.     

Chemische Synthese des Dodecanucleotids dpT?T?T?T?T?T?C?A?T?C?A?T

Chemical Synthesis of the Dodecanucle otide dpT T T T T T C A T C A T For studies on the specifity of enzymes, the dodecanucleotide dpT T T T T T C A T C A T was required. Its chemical synthesis is reported starting with the mononucleotides dpT, dpC and dpA.     

Design and Synthesis of Polycyclic Imidazole‐Containing N‐ Heterocycles based on C?H Activation/Cyclization Reactions

A new strategy for the synthesis of polycyclic imidazole‐containing N‐heterocycles, based on the two general synthetic ways, namely the Pd(II)‐catalyzed intramolecular arylation via CH/C Hal and CH/CH coupling reactions, was developed. The method proposed here enables the synthesis of many fused N‐heterocycles containing purine, 1‐deazapurines and benzimidazole structural units.