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.

     

Copper‐Mediated ortho‐Nitration of Arene and Heteroarene C?H Bonds Assisted by an 8‐Aminoquinoline Directing Group

A copper‐mediated, chelation‐assisted ortho C H bond nitration of benzoic acid derivatives using sodium nitrite as the source of the nitro group has been achieved with the aid of an 8‐aminoquinoline directing group. Selective mono‐ or dinitration can be achieved by simply changing the reaction conditions. The method shows excellent functional group tolerance and provides a novel and straightforward route for the preparation of ortho‐nitrated benzoic acids.

     

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.

     

Iron‐Catalyzed C?C Bond Cleavage and C?N Bond Formation

A novel approach for C N bond formation was developed by iron‐catalyzed C C bond cleavage. Anilines and sulfonamides reacted smoothly with 2‐substituted 1,3‐diphenylpropane‐1,3‐diones to afford N‐alkylation products, in which the 1,3‐dicarbonyl group acts as a leaving group in the presence of an iron catalyst. The reversible C C bond cleavage plays a driving force to give the thermodynamically stable products. The method is complementary to the previous methods for C N bond formation.     

Copper‐Catalyzed Highly Regioselective Oxidative C?H Bond Amidation of 2‐Arylpyridine Derivatives and 1‐Methylindoles

Copper(I) bromide‐catalyzed amidation of 2‐arylpyridine derivatives and 1‐methylindoles with a variety of amides was achieved by employing tert‐butyl peroxide (TBP) as oxidant. Aryl halides could be tolerated under the reaction conditions. Neither a special ligand nor a base was required for this amidation process.     

Copper‐Catalyzed Synthesis of α‐Thioaryl Carbonyl Compounds Through S?S and C?C Bond Cleavage

A method to access α‐thioaryl ketones and α‐thioaryl esters employing copper acetate (hydrate) as catalyst and readily accessible diaryl disulfides and β‐diketones (or β‐keto esters) has been developed. Both alkyl‐ and aryl‐substituted carbonyl compounds can be prepared.

     

Rhodium(III)‐Catalyzed in situ Oxidizing Directing Group‐ Assisted C?H Bond Activation and Olefination: A Route to 2‐Vinylanilines

A new and efficient method for the synthesis of 2‐vinylanilines from the reaction of arylhydrazine hydrochlorides with alkenes and diethyl ketone via a rhodium‐catalyzed C H activation is described. The oxidant‐free olefination reaction involves the in situ generation of an  N NCR¹R² moiety as the oxidizing directing group thus providing an easy access to 2‐vinylanilines.

     

Palladium‐Catalyzed C?H Functionalization of Ferrocenecarboxylic Acid by using 8‐Aminoquinoline as a Removable Directing Group

A mild and efficient palladium‐catalyzed synthetic method for the C H functionalization of N‐(quinolin‐8‐yl)ferrocenecarboxamide has been developed. Various aryl iodides containing I, NO₂, CN, COMe, CO₂Et, and NH functionalities and also alkyl iodides underwent the Pd‐catalyzed intermolecular carbon‐carbon bond forming reaction with ferrocenecarboxamide successfully which led to a diverse array of bis(aryl/alkyl)ferrocenecarboxamides in 34–92% yields. Cross‐coupling of the ferrocenyl C H bond with aryl iodides can also be achieved utilizing an economical Ni catalyst. Additionally, selective monoalkylation of ferrocenecarboxamide was studied using sodium bicarbonate as base and dibenzylphosphoric acid as additive under Pd‐catalyzed reaction conditions. Subsequently, removal of the directing group, 8‐aminoquinoline, from bis(aryl)ferrocenecarboxamides led to bis(aryl)ferrocenes bearing versatile methyl ester and carboxaldehyde functional groups.

     

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.     

Palladium‐Catalyzed Oxidative sp2 C?H Bond Acylation with Aldehydes

An efficient method was developed for the direct acylation of arene sp² C H bonds with aldehydes using palladium acetate as catalyst and peroxide as oxidant. The solvent‐free oxidative acylation reaction assisted by a pyridine directing group provides an easy access to aromatic, aliphatic, and optical active ketones.     

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.     

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.     

Copper‐Catalyzed Aerobic Oxidative Synthesis of 5‐Substituted Imidazo/Benzimidazoquinazolinones through Intramolecular C?H Amination

A simple and efficient copper‐catalyzed aerobic oxidative method for the synthesis of imidazo/benzimidazoquinazolinones has been developed through direct intramolecular C H amination of (1H‐imidazol‐1‐yl)[2‐(alkylamino)phenyl]methanones, and the corresponding target products were obtained in moderate to good yields.     

Palladium‐Catalyzed Oxidative C?H Bond Acylation of Acetanilides with Benzylic Alcohols

An efficient and clean method to construct C C bonds has been developed via the acylation reaction of acetanilides with benzylic alcohols using tert‐butyl hydroperoxide (TBHP) as oxidant catalyzed by palladium acetate in the presence of triflic acid (TfOH). The acylation reactions exhibit excellent reactivities, and up to 95% yield of the corresponding aryl ketone could be obtained under the optimal conditions.     

Rhodium‐Catalyzed N‐tert‐Butoxycarbonyl (Boc) Amination by Directed C?H Bond Activation

N‐tert‐Butoxycarbonyl azide (BocN₃) was shown to be an efficient and economic source for the directed introduction of N‐Boc protected amino groups into the thiophene and benzene nucleus. Yields for the amination of 2‐pyridin‐2‐ylthiophenes (10 examples) were 52–88%. For the amination of the respective benzenes (10 examples) yields between 54% and 99% were recorded with an improved reactivity observed for substrates that bear an electron‐withdrawing group. The reaction was applied to short total syntheses of the indoloquinoline alkaloids quindoline and cryptolepine. The facile removal of the Boc protecting group was the key to the success of the syntheses. The scope of the reaction was extended to a C(sp³) H bond amination and to the amination of 2‐phenyloxazoline. For the amination of 2‐pyridin‐2‐ylbenzene a kinetic deuterium isotope effect of 2.0 was determined.

     

Easy Access to 1‐Amino and 1‐Carbon Substituted Isoquinolines via Cobalt‐Catalyzed C?H/N?O Bond Activation

A green atom‐economical method for the synthesis of highly functionalized 1‐amino and 1‐carbon substituted isoquinolines from the reaction of N′‐hydroxybenzimidamides and aryl ketoximes, respectively, with alkynes via pentamethylcyclopentadienylcobalt(III)‐catalyzed C H/N O bond activation is described. The external oxidant‐free annulation reaction uses the =NOH moiety in N′‐hydroxybenzimidamides or N‐aromatic ketone oximes as the directing group and internal oxidant. This first row transition metal‐catalyzed annulation serves as an efficient alternative for the synthesis of isoquinolines, as water is the only by‐product and expensive noble metals such as rhodium(III), iridium(III), palladium(II), and ruthenium(II) are not required. The reaction proceeds via C H activation, alkyne insertion, reductive elimination, and N O activation.

     

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.

     

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.     

The Copper‐Catalyzed C‐3‐Formylation of Indole C?H Bonds using Tertiary Amines and Molecular Oxygen

A copper‐catalyzed formylation reaction has been developed by employing oxygen (O₂) as the clean oxidant. The C H bonds of indoles were C‐3‐formylated by tetramethylethylenediamine (TMEDA) and water (H₂O; in situ formed and external added water) as the carbonyl source in moderate to good yields with good functional group tolerance. Thus, it represents a facile procedure leading to 3‐formylindoles.     

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.