Amination Of Arenes Research Articles

Continuous Flow for the Photochemical C‐H Amination of Arenes

AbstractThe direct C−H amination of arenes by aminium radicals generated by photolysis of N‐chloroamines is demonstrated under continuous flow conditions. The reactions proceed with comparable efficiency to small scale batch processes but are superior to larger scale batch operations. The continuous generation of the N‐chloroamine from the amine precursor can be integrated into the process, facilitating the continuous direct conversion of secondary amines to their arylated derivatives.

Cobalt(II)-Catalyzed Electrooxidative C-H Amination of Arenes with Alkylamines.

An environmentally friendly electrochemical protocol about cobalt-catalyzed C-H amination of arenes has been developed, which offers a simple way to access synthetically useful arylamines. In divided cells, a wide variety of arenes and alkylamines are examined to afford C-N formation products without using external oxidants, which avoids the formation of undesired byproducts and exhibits high atom economy. Importantly, the reaction can also be extended to gram level with moderate efficiency. KIE experiments indicate that C-H bond cleavage might not be involved during the rate-limiting step.

Radical-mediated direct C-H amination of arenes with secondary amines.

Aryl dialkyl amines, valuable subunits of a wide range of effect chemicals, are accessed by intramolecular amination of aromatic C-H bonds employing UV photolysis of N-chloroamines. The reactions show good functional group tolerance and allow access to a range of fused and bridged polycyclic structures. The homogeneous reaction conditions allow for the one-pot conversion of secondary amines to their arylated derivatives. Experimental and theoretical evidence supports the involvement of electrophilic aminium radicals which react via direct ortho-attack on the arene.

Copper‐Mediated Tandem C(sp2)‐H Amination and Annulation of Arenes with 2‐Aminopyridines: Synthesis of Pyrido‐fused Quinazolinone Derivatives

AbstractAn efficient and convenient copper‐mediated tandem C(sp2)‐H amination and annulation of arenes with 2‐aminopyridines to provide 11H‐pyrido[2,1‐b]quinazolin‐11‐ones has been developed. A variety of benzamides and 2‐aminopyridines bearing different substituents are compatible with this transformationmagnified image

Teaching Old Compounds New Tricks: DDQ-Photocatalyzed C-H Amination of Arenes with Carbamates, Urea, and N-Heterocycles.

The C−H amination of benzene derivatives was achieved using DDQ as photocatalyst and BocNH2 as the amine source under aerobic conditions and visible light irradiation. Electron‐deficient and electron‐rich benzenes react as substrates with moderate to good product yields. The amine scope of the reaction comprises Boc‐amine, carbamates, pyrazoles, sulfonimides and urea. Preliminary mechanistic investigations indicate arene oxidation by the triplet of DDQ to radical cations with different electrophilicity and a charge transfer complex between the amine and DDQ as intermediate of the reaction.

Direct Aryl C−H Amination with Primary Amines Using Organic Photoredox Catalysis

AbstractThe direct catalytic C−H amination of arenes is a powerful synthetic strategy with useful applications in pharmaceuticals, agrochemicals, and materials chemistry. Despite the advances in catalytic C−H functionalization, the use of aliphatic amine coupling partners is limited. Described herein is the construction of C−N bonds, using primary amines, by direct C−H functionalization with an acridinium photoredox catalyst under an aerobic atmosphere. A wide variety of primary amines, including amino acids and more complex amines are competent coupling partners. Various electron‐rich aromatics and heteroaromatics are useful scaffolds in this reaction, as are complex, biologically active arenes. We also describe the ability to functionalize arenes that are not oxidized by an acridinium catalyst, such as benzene and toluene, thus supporting a reactive amine cation radical intermediate.

Rhodium‐Catalyzed Amination and Annulation of Arenes with Anthranils: C‐H Activation Assisted by Weakly Coordinating Amides

AbstractA rhodium(III)‐catalyzed C−H amination of benzamides and isoquinolones with anthranils has been realized under assistance of weakly coordinating amide, leading to a bifunctionalized amination product which can further cyclize to acridine under in situ or ex situ conditions.magnified image

Nucleophilic Amination of Methoxy Arenes Promoted by a Sodium Hydride/Iodide Composite.

A method for the nucleophilic amination of methoxy arenes was established by using sodium hydride (NaH) in the presence of lithium iodide (LiI). This method offers an efficient route to benzannulated nitrogen heterocycles. Mechanistic studies showed that the reaction proceeds through an unusual concerted nucleophilic aromatic substitution.

Nucleophilic Amination of Methoxy Arenes Promoted by a Sodium Hydride/Iodide Composite

AbstractA method for the nucleophilic amination of methoxy arenes was established by using sodium hydride (NaH) in the presence of lithium iodide (LiI). This method offers an efficient route to benzannulated nitrogen heterocycles. Mechanistic studies showed that the reaction proceeds through an unusual concerted nucleophilic aromatic substitution.

Site-Selective Copper-Catalyzed Amination and Azidation of Arenes and Heteroarenes via Deprotonative Zincation.

Arene amination is achieved by site-selective C-H zincation followed by copper-catalyzed coupling with O-benzoylhydroxylamines under mild conditions. Key to this success is ortho-zincation mediated by lithium amidodiethylzincate base that is effective for a wide range of arenes, including nonactivated arenes bearing simple functionalities such as fluoride, chloride, ester, amide, ether, nitrile, and trifluoromethyl groups as well as heteroarenes including indole, thiophene, pyridine, and isoquinoline. An analogous C-H azidation is also accomplished using azidoiodinane for direct introduction of a useful azide group onto a broad scope of arenes and heteroarenes. These new transformations offer rapid access to valuable and diverse chemical space of aminoarenes. Their broad applications in organic synthesis and drug discovery are demonstrated in the synthesis of novel analogues of natural product (-)-nicotine and antidepressant sertraline by late-stage amination and azidation reactions.

Nature Inspires an Aerobic Coupling of Phenol and Amine

In this issue of Chem , Lumb and colleagues report on an effective and simple catalytic system of copper and diamine ligands for the bio-inspired and unified synthesis of 1,2-aminophenols through direct aerobic phenol-amine coupling. Using this method, they prepared a structurally diverse family of 1,2-aminophenols and their derived heterocycles, including immunosuppressive benzoxazoles and the indole alkaloid cephalandole A.

Photo-induced oxidant-free oxidative C\u2013H/N\u2013H cross-coupling between arenes and azoles

Direct cross-coupling between simple arenes and heterocyclic amines under mild conditions is undoubtedly important for C–N bonds construction. Selective C(sp2)-H amination is more valuable. Herein we show a selective C(sp2)-H amination of arenes (alkyl-substituted benzenes, biphenyl and anisole derivatives) accompanied by hydrogen evolution by using heterocyclic azoles as nitrogen sources. The reaction is selective for C(sp2)-H bonds, providing a mild route to N-arylazoles. The KIE (kinetic isotope effect) experiment reveals the cleavage of C–H bond is not involved in the rate-determining step. Kinetic studies indicate the first-order behaviour with respect to the arene component. It is interesting that this system works without the need for any sacrificial oxidant and is highly selective for C(sp2)-H activation, whereas C(sp3)-H bonds are unaffected. This study may have significant implications for the functionalization of methylarenes which are sensitive to oxidative conditions.

Fe-Catalyzed Amination of (Hetero)Arenes with a Redox-Active Aminating Reagent under Mild Conditions.

A novel and efficient Fe-catalyzed direct C-H amination (NH2 ) of arenes is reported using a new redox-active aminating reagent. The reaction is simple, and can be performed under air, mild, and redox-neutral conditions. This protocol has a broad substrate scope and could be used in the late-stage modification of bioactive compounds. Mechanistic studies demonstrate that a radical pathway could be involved in this transformation.

ChemInform Abstract: Cobalt‐Catalyzed Direct Amination of Arenes with Alkylamines via Bidentate‐Chelation Assistance.

AbstractThe title reaction features low catalyst loading and readily available reagents, but it only applies to cyclic amines.

Aza-Annulation by C–H Arene Amination with O-Sulfonylhydroxyamines

Aza-Annulation by C–H Arene Amination with O-Sulfonylhydroxyamines

Direct and Practical Synthesis of Primary Anilines through Iron-Catalyzed C–H Bond Amination

The direct C–H amination of arenes is an important strategy to streamline the discovery and preparation of functional molecules. Herein, we report an operationally simple arene C–H amination reaction that, in contrast to most literature precedent, affords directly the synthetically versatile primary aniline products without relying on protecting group manipulations. Inexpensive Fe(II)-sulfate serves as a convenient catalyst for the transformation. The reaction tolerates a wide scope of arenes, including structurally complex drugs. Importantly, the arene substrates are used as limiting reagents in the transformation. This operationally simple transformation should considerably accelerate the discovery of medicines and functional molecules.

ChemInform Abstract: Towards Uniform Iodine Catalysis: Intramolecular C—H Amination of Arenes under Visible Light.

AbstractA mild protocol is developed for the intramolecular aryl amination reaction using visible light and iodine as catalysts in the presence of a mild hypervalent iodine oxidant.

Continuous-Flow Electrophilic Amination of Arenes and Schmidt Reaction of Carboxylic Acids Utilizing the Superacidic Trimethylsilyl Azide/Triflic Acid Reagent System.

A continuous flow protocol for the direct stoichiometric electrophilic amination of aromatic hydrocarbons and the Schmidt reaction of aromatic carboxylic acids using the superacidic trimethylsilyl azide/triflic acid system is described. Optimization of reagent stoichiometry, solvent, reaction time, and temperature led to an intensified protocol at elevated temperatures that allows the direct amination of arenes to be completed within 3 min at 90 °C. In order to improve the selectivity and scope of this direct amination protocol, aromatic carboxylic acids were additionally chosen as substrates. Selected carboxylic acids could be converted to their corresponding amine counterparts in good to excellent yields (11 examples, 55-83%) via a Schmidt reaction employing similar flow reaction conditions (<5 min at 90 °C) and a similar reactor setup as for the amination. The safety issues derived from the explosive, toxic, and volatile hydrazoic acid intermediate, the corrosive nature of triflic acid, and the exothermic quenching were addressed by designing a suitable continuous flow reaction setup for both types of transformations.

A Bis(silylene)-Substituted ortho-Carborane as a Superior Ligand in the Nickel-Catalyzed Amination of Arenes.

The synthesis and structure of the first 1,2-bis(NHSi)-substituted ortho-carborane [(LSi:)C]2 B10 H10 (termed SiCCSi) is reported (NHSi=N-heterocyclic silylene; L=PhC(NtBu)2 ). Its suitability to serve as a reliable bis(silylene) chelating ligand for transition metals is demonstrated by the formation of [SiCCSi]NiBr2 and [SiCCSi]Ni(CO)2 complexes. The CO stretching vibration modes of the latter indicate that the Si(II) atoms in the SiCCSi ligand are even stronger σ donors than the P(III) atoms in phosphines and C(II) atoms in N-heterocyclic carbene (NHC) ligands. Moreover, the strong donor character of the [SiCCSi] ligand enables [SiCCSi]NiBr2 to act as an outstanding precatalyst (0.5 mol % loading) in the catalytic aminations of arenes, surpassing the activity of previously known molecular Ni-based precatalysts (1-10 mol %).

A Bis(silylene)‐Substituted ortho‐Carborane as a Superior Ligand in the Nickel‐Catalyzed Amination of Arenes

AbstractThe synthesis and structure of the first 1,2‐bis(NHSi)‐substituted ortho‐carborane [(LSi:)C]2B10H10 (termed SiCCSi) is reported (NHSi=N‐heterocyclic silylene; L=PhC(NtBu)2). Its suitability to serve as a reliable bis(silylene) chelating ligand for transition metals is demonstrated by the formation of [SiCCSi]NiBr2 and [SiCCSi]Ni(CO)2 complexes. The CO stretching vibration modes of the latter indicate that the SiII atoms in the SiCCSi ligand are even stronger σ donors than the PIII atoms in phosphines and CII atoms in N‐heterocyclic carbene (NHC) ligands. Moreover, the strong donor character of the [SiCCSi] ligand enables [SiCCSi]NiBr2 to act as an outstanding precatalyst (0.5 mol % loading) in the catalytic aminations of arenes, surpassing the activity of previously known molecular Ni‐based precatalysts (1–10 mol %).