Transition Metal‐Mediated Direct C?H Arylation of Heteroarenes Involving Aryl Radicals

This review gives an overview of the generation of aryl radicals, mediated by transition metals, and their use for the C H arylation of heteroarenes. The different sources of aromatic derivatives able to generate aryl radicals via a metal‐assisted reduction or oxidation are discussed, with a critical view of the developed systems. The radical arylations of nitrogen‐, oxygen‐ or sulfur‐containing heterocycles are then described and mechanistic considerations are discussed as well.

     

Polyheterocycles by Palladium(II)‐Catalyzed Oxidative Domino Reactions Involving Direct C?H Functionalization

A novel palladium(II)‐catalyzed oxidative domino reaction sequence of diyne‐enones and substituted indoles to afford polyheterocycles involving direct C H functionalization using air as oxidant has been developed.     

Recent Advances in Asymmetric C?C and C‐Heteroatom Bond Forming Reactions using Polymer‐Bound Catalysts

The synthesis of enantiomerically pure compounds is one of the major challenges in organic synthesis. In this review, we present the state of the art in asymmetric catalysis using immobilized chiral ligands and complexes for asymmetric C C and C‐heteroatom bond forming reactions. Chiral catalysts based on dendrimers and soluble polymeric supports are considered. In particular, addition reactions to carbon‐carbon double bonds, asymmetric 1,2‐addition reactions using, e.g., dialkylzinc reagents, metal‐catalyzed substitution reactions and cycloaddition reactions are covered. Specific emphasis is placed on enantioselective epoxidation and aldol reactions. A further aspect is the (hetero) Diels–Alder reaction catalyzed by immobilized ligands.     

N‐Imide Ylide‐Based Reactions: C?H Functionalization,Nucleophilic Addition and Cycloaddition

As valuable building blocks for introducing nitrogen, N‐imide ylides represent an important class of reactive species and are synthons for the synthesis of nitrogen‐containing heterocycles that potentially have biological activities. During the past decades, tremendous efforts have been devoted to the tandem processes involving N‐imide ylides as well as their asymmetric applications. In particular, several types of N‐imide ylide‐based reactions have been established, such as C H functionalization, nucleophilic addition, and cycloaddition, etc. In this review, recent advances in N‐imide ylides chemistry are presented ordered according to the sequence of various reaction types.

     

Copper‐Catalyzed Direct Arylselenation of Anilines by C?H Bond Cleavage

We describe here an efficient and regioselective synthesis of arylselanyl anilines by copper‐catalyzed direct arylselenation of arylamines. Using a catalytic amount of copper iodide in dimethyl sulfoxide at 110 °C under an air atmosphere, a range of arylselanyl anilines was obtained directly from substituted diaryl diselenides in moderate to good yields via C H bond cleavage of aryl amines.

     

Highly Efficient Metal‐Free Cross‐Coupling by C?H Activation between Allylic and Active Methylenic Compounds Promoted by DDQ

A metal‐free very highly efficient and concise oxidative‐coupling reaction promoted by 2,3‐dichloro‐5,6‐dicyanoquinone (DDQ) between diarylallylic sp³ C H and active methylenic sp³ C H bonds is reported. The corresponding products are obtained in good to excellent yields.     

Copper‐Catalyzed Cross‐Dehydrogenative Coupling (CDC) of Alkynes and Benzylic C?H Bonds

The activation of benzylic C H bonds and subsequent coupling with terminal alkynes in the presence of 2,3‐dichloro‐5,6‐dicyanoquinone (DDQ) and a catalytic amount of copper(I) triflate is presented. Good to moderate yields of disubstituted alkynes are obtained for this cross‐dehydrogenative coupling (CDC) reaction between a variety of aromatic alkynes and diphenylmethane derivatives.     

Stable Nickel(0) Phosphites as Catalysts for C?N Cross‐Coupling Reactions

Herein we describe the design and preparation of inexpensive, air‐stable nickel phosphite‐based catalysts for use in the C N cross‐coupling reaction. The combination of nickel tetrakis(triphenyl phosphite) {Ni[P(OPh)₃]₄} and 1,1′‐bis(diphenylphosphino)ferrocene (dppf), and in particular a newly developed catalyst (dppf)Ni[P(OPh)₃]₂, were found to be extremely effective in catalyzing a range of amination reactions of anilines and amines with aryl chlorides. This new catalyst system offers an alternative to the bis(cyclooctadienyl)nickel [Ni(COD)₂] and palladium(0) catalysts commonly used for C N bond formation.

     

Development of Efficient and Reusable Diarylphosphinopolystyrene‐Supported Palladium Catalysts for C?C Bond Forming Cross‐Coupling Reactions

Short and versatile syntheses of reusable diarylphosphinopolystyrene‐supported palladium catalysts 3a – j are described. The bis(o‐tolyl)phosphino catalyst 3b is particularly efficient for the Suzuki and Sonogashira cross‐couplings, whereas the bis(m‐tolyl)phosphino catalyst 3c is the most active catalyst for Heck reactions. The couplings are performed under non‐anhydrous reaction conditions and require only low amounts of supported palladium (0.5 mequivs. for Suzuki–Miyaura, 1.0 mequiv. for Sonogashira and 0.5 mequivs. for Heck reactions could be sufficient). Catalysts 3a–j are recovered by filtration and can be reused more than four times with no loss of efficiency.     

One‐Pot Tandem Palladium‐Catalyzed Decarboxylative Cross‐Coupling and C?H Activation Route to Thienoisoquinolines

Two experimental approaches to the synthesis of a scarcely reported biologically active thienoisoquinoline system are demonstrated. A 5‐step linear synthesis employing a palladium‐catalyzed decarboxylative cross‐coupling and functionalization sequence allowed for the preparation of a diverse range of substituted thienoisoquinoline systems. Alternatively the palladium‐catalyzed decarboxylative cross‐coupling and C H activation steps can be telescoped to produce a one‐pot reaction sequence that provides efficient access to aryl‐substituted thienoisoquinolines.

     

Arene C?H Bond Functionalization Coupling with Cyclization of Allenes

Under the catalysis of a rhodium(III) complex, the cyclization of 2,3‐allenols was most probably initiated with the C H bond functionalization of N‐methoxybenzamides using the tetramethylcyclopentadiene anion (C₅Me₄⁻) as ligand, affording differently substituted 2,5‐dihydrofuran derivatives. Highly efficient axial‐to‐central chirality transfer has been observed.     

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.     

Iron‐Catalyzed C?N Cross‐Coupling of Sulfoximines with Aryl Iodides

An inexpensive and experimentally simple, iron‐catalyzed N‐arylation reaction of NH‐sulfoximines with aryl iodides is reported. This complementary method to the known palladium‐ and copper‐catalyzed ones features the use of a combination of environmentally friendly FeCl₃ and N,N′‐dimethylethylenediamine (DMEDA) as catalytic system and allows the efficient preparation of various N‐arylsulfoximines in high yields.     

Direct Synthesis of 4‐Organylselanylpyrazoles by Copper‐ Catalyzed One‐Pot Cyclocondensation and C?H Bond Selenylation Reactions

We describe herein an efficient protocol to synthesize selanyl‐substituted pyrazoles by cyclocondensation and copper‐catalyzed direct C H bond selenation reactions. The products were obtained in moderate to excellent yields by the one‐pot multicomponent reactions of hydrazines, 1,3‐diketones and diorganyl diselenides, using catalytic amounts of copper bromide and bipyridine. These reactions tolerated a range of substituents in the starting materials and proved to be an efficient methodology for combinatorial synthesis of new selenium‐containing pyrazoles with potential applications in biological studies.

     

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 Arylation of Thiophenes via Palladium‐Catalysed C?H Functionalisation at Low Catalyst Loadings

Palladium associated with cis,cis,cis‐1,2,3,4‐tetrakis(diphenylphosphinomethyl)cyclopentane (Tedicyp) was found to promote the direct 2‐arylation of a variety of thiophene derivatives via C H functionalisation in good yields using very low catalyst loadings. Electron‐deficient, electron‐excessive or sterically‐congested aryl bromides are tolerated. Moreover, several substituents on the aryl bromide or thiophene derivatives such as acetyl, formyl, nitrile, nitro, ester, methoxy, fluoro or trifluoromethyl are tolerated. The most reactive aryl bromides were coupled with thiophenes derivatives using as little as 0.1–0.01 mol % catalyst.     

Palladium‐Catalyzed/Lewis Acid‐Promoted Alkene Dimerization and Cross‐Coupling with Alcohols via C?H Bond Activation

The cross‐couplings of alcohols to alkenes with the palladium/Lewis acid system are reported. This reaction occurs in a successive alkene dimerization, direct C H activation of alcohol and sp³ sp³ bond forming sequence via an interesting domino process.     

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.