Copper-Catalyzed Direct Oxidative C–H Amination of Benzoxazoles with Formamides or Secondary Amines under Mild Conditions

Photoinduced C-H arylation of 1,3-azoles via copper/photoredox dual catalysis

The visible light-induced C-H arylation of azoles has been accomplished by dual-catalytic system with the aid of an inexpensive ligand-free copper(i)-catalyst in combination with a suitable photoredox catalyst. An organic photoredox catalyst, 10-phenylphenothiazine (PTH), was identified as effective, cost-efficient and environmentally-benign alternative to commonly-used, expensive Ir(iii)-based complexes. The method proved applicable for the C-H arylation of various azole derivatives, including oxazoles, benzoxazoles, thiazoles, benzothiazoles as well as more challenging imidazoles and benzimidazoles. Moreover, the derivatization of complex molecules and the gram scale synthesis of the natural product balsoxin reflected the synthetic utility of the developed strategy. Mechanistic studies were indicative of a single electron transfer-based (SET) mechanism with an aryl radical as key intermediate.

Metal-free visible light mediated direct C-H amination of benzoxazole with secondary amines

An efficient visible light mediated, eosin Y catalyzed direct C-H oxidative amination of benzoxazoles with secondary amines has been developed, which providing a straightforward, green, and environmentally benign access to a wide variety of substituted benzoxazole-2-amines under mild reaction conditions. The biological studies such as drug-likeness and molecular docking are also carried out on the molecule.

Recent Advances in Aerobic Oxidative of C-H Bond by Molecular Oxygen Focus on Heterocycles

Aerobic oxidative cross-coupling represents one of the most straightforward and atom-economic methods for construction of C-C and C-X (X=N, O, S, or P) bonds using air as a sustainable external oxidant. The oxidative coupling of C-H bonds in heterocyclic compounds can effectively increase their molecular complexity by introducing new functional groups through C-H bond activation, or by formation of new heterocyclic structures through cascade construction of two or more sequential chemical bonds. This is very useful as it can increase the potential applications of these structures in natural products, pharmaceuticals, agricultural chemicals, and functional materials. This is a representative overview of recent progress since 2010 on green oxidative coupling reactions of C-H bond using O2 or air as internal oxidant focus on Heterocycles. It aims to provide a platform for expanding the scope and utility of air as green oxidant, together with a brief discussion on research into the mechanisms behind it.

Palladium-catalyzed C-H dimethylamination of 1-chloromethyl naphthalenes with N,N-dimethylformamide as the dimethyl amino source

Palladium-catalyzed remote C-H dimethylamination of 1-chloromethylnaphthalenes using N,N-dimethylformamide as the dimethylamino source is described for the first time. The dimethylamination took place exclusively at the 4-position of 1-chloromethylnaphthalenes in 2-methyltetrahydrofuran under mild conditions to afford 1-(N,N-dimethylamino)-4-alkylnaphthalenes in good to high yields. The halogen atom remained intact during the dimethylamination of 1-chloromethylnaphthalenes. A P,N bidentate ligand was conveniently synthesized and successfully utilized as the ligand in the Kumada-Corriu reaction.

Room-Temperature Dialkylamination of Chloroheteroarenes Using a Cu(II)/PTABS Catalytic System

The dimethylamino functionality has significant importance in industrially relevant molecules and methodologies to install these efficiently are highly desirable. We report herein a highly efficient, room-temperature dimethylamination of chloroheteroarenes performed via the in-situ generation of dimethylamine using N,N-dimethylformamide (DMF) as precursor wiith a large substrate scope that includes various heteroarenes, purines as well as commercially relevant drugs such as altretamine, ampyzine and puromycin precursor.

C2-Selective, Functional-Group-Divergent Amination of Pyrimidines by Enthalpy-Controlled Nucleophilic Functionalization

Synthesis of heteroaryl amines has been an important topic in organic chemistry because of their importance in small-molecule discovery. In particular, 2-aminopyrimidines represent a highly privileged structural motif that is prevalent in bioactive molecules, but a general strategy to introduce the pyrimidine C2-N bonds via direct functionalization is elusive. Here we describe a synthetic platform for site-selective C-H functionalization that affords pyrimidinyl iminium salt intermediates, which then can be transformed into various amine products in situ. Mechanism-based reagent design allowed for the C2-selective amination of pyrimidines, opening the new scope of site-selective heteroaryl C-H functionalization. Our method is compatible with a broad range of pyrimidines with sensitive functional groups and can access complex aminopyrimidines with high selectivity.

Catalytic Direct Cyanomethylenation of C(sp3)-H Bonds via a One-Step Double C-C Bond Formation

An elegant and catalytic procedure for the one-step cyanomethylenation of C(sp³)-H bonds adjacent to benzazoles and ketones is described herein using DMF as a C-1 unit and TMSCN as the cyanide source. The copper-mediated reaction between DMF and TMSCN gives a cyanomethylene radical intermediate that reacts with 2-alkylbenzazoles or alkylketones to furnish desired cyanomethylenated compounds under palladium catalysis. Subsequent interconversion of cyanomethylenated products makes the protocol synthetically attractive.

Hypervalent Iodine(III) Promoted Tandem Reaction of o-Fluoroanilines with Formamides to Construct 2-Aminobenzoxazoles

A simple and practical synthesis of 2-aminobenzoxaoles has been developed from commercially available o-fluoroanilines, and formamides. The process can be performed in the absence of metal catalyst with high levels...

Metal-catalyzed reactions for the C(sp2)–N bond formation: achievements of recent years

The review deals with the main catalytic methods for the C(sp2)–N bond formation, including Buchwald–Hartwig palladium-catalyzed amination of aryl and heteroaryl halides, renaissance of the Ullmann chemistry, i.e., the application of catalysis by copper complexes to form the carbon–nitrogen bond, and Chan–Lam reactions of (hetero)arylboronic acids with amines. Also, oxidative amination with C–H activation, which has been booming during the last decade, is addressed. Particular attention is paid to achievements in the application of heterogenized catalysts.

The bibliography includes 350 references.

Copper-Mediated ortho-C-H Amination Using DMF as the Amine Source

We report herein a copper-mediated ortho-C-H amination of anilines using oxalamide as the directing group and DMF as the amination reagent. This protocol tolerates various functional groups and shows good heterocyclic compatibility. Late-stage dimethylamination of drugs demonstrated the synthetic practicality of the protocol. Mechanistic experiments indicate that a radical pathway may be involved in the reaction.

Accessing C2-Functionalized 1,3-(Benz)azoles through Transition Metal-Catalyzed C-H Activation

The skeletal presence of 1,3-azoles in a variety of bioactive natural products, pharmacophores, and organic materials demands the derivatization of such heteroarenes regioselectively. Plenty of cross-coupling as well as cyclocondensation reactions have been performed to build up these skeletons but remained commercially unrealizable. A couple of severe drawbacks are faced by these traditional protocols that require a more straightforward strategy to obviate them. Transition metal-catalyzed C-H functionalization has emerged as a superior alternative in that context. 1,3-Azoles and their benzo counterparts have been extensively functionalized exploiting both noble and earth-abundant transition metals. Lately, C-2 functionalization have gained much traction due to the ease of attaining high regioselectivity and installation of synthetically manipulative functionalities. This critical review presents a bird's eye view of all major C-2 functionalization of (benz)azoles catalyzed by a diverse set of metals performed over the past 15 years.

Copper(ii) ions supported on functionalized graphene oxide: an organometallic nanocatalyst for oxidative amination of azoles via C–H/C–N bond activation

Graphene oxide (GO) was chemically modified with para-aminobenzoic acid (PABA) to immobilize copper(ii) ions on its surface and used as a nanocatalyst for the oxidative C (sp²)–H bond amination reaction.

One-Pot Multicomponent Reaction of Catechols, Ammonium Acetate, and Aldehydes for the Synthesis of Benzoxazole Derivatives Using the Fe(III)-Salen Complex

The Fe(III)-salen complex has been applied successfully as a catalyst for the novel, simple, efficient, and one-pot multicomponent synthesis of benzoxazole derivatives from catechols, ammonium acetate as the nitrogen source, and aldehydes (nontoxic and cheap alternatives of amines) for the first time. Using this procedure, a wide range of benzoxazoles was successfully synthesized in the presence of a catalyst in EtOH under mild conditions, and all products were obtained in excellent yields. To the best of our knowledge, this method is the first example of the multicomponent synthesis of benzoxazole derivatives using these starting materials. The notable features such as the use of air that is considered as a benign oxidant and EtOH as a green solvent, ease of product separation, readily available and inexpensive aldehydes, and mild conditions make our procedure more efficient and practical for organic synthesis. Moreover, the current protocol is successfully applied to synthesize desirable products on a large scale.

The silver catalyzed direct C-H functionalization of quinones with dialkyl amides

DMA and other dialkylamides were successfully used as synthons for the C-H functionalization of quinones. This novel amidoalkylation reaction works with a variety of substituted quinones and dialkyl/alkyl amides, such as DMF, NMP and NMA, and the corresponding products were obtained in moderate to good yields. The amidoalkylation of quinones is demonstrated for the first time. A suitable mechanism and the synthetic utility of these compounds are demonstrated. The molecular docking of compound 5 with an Alzheimer's disease (AD) associated AChE target site was studied.

Copper-Catalyzed Oxidative Synthesis of α-Ketoamides from Aryl Methyl Ketones and N-Bromobutanimide Using N,N-Dimethylformamide as Dimethylamine Source

A novel and practical Cu(OAc)2-catalyzed oxidative synthesis of α-ketoamides from aryl methyl ketones and N-bromobutanimide (NBS) using N,N-dimethylformamide (DMF) as dimethylamine (HNMe2) source and solvent has been developed under mild conditions. DMF was used as a HNMe2 source and can be easily converted into HNMe2 by acid hydrolysis. The mechanistic studies indicate that Cu(OAc)2 plays a dual role in providing both catalyst and oxidant.

Terminal methyl as a one-carbon synthon: synthesis of quinoxaline derivatives via radical-type transformation

An iron-promoted method for the construction of pyrrolo[1,2-a]quinoxaline derivatives has been developed. Various solvents with terminal methyl group, including ethers, amines and dimethyl sulfoxide, were utilized as carbon sources for the synthesis.

Metal-Free Synthesis of 2- N, N-Dialkylaminobenzoxazoles Using Tertiary Amines as the Nitrogen Source

The unprecedented reaction of tertiary amines with 2(3 H)-benzoxazolones has been investigated. In the presence of the Ph₃P-I₂ reagent system, the reaction of both acyclic and cyclic aliphatic tertiary amines led to the formation of 2- N, N-dialkylaminobenzoxazoles with the selective cleavage of an alkyl group. Especially, N-(2-iodoethyl)piperazinyl derivatives were rapidly produced in good yields when using DABCO as the nitrogen source. Only in the cases when the nucleophilicity of the substrates exceeds that of the amine, competitive self-condensation of benzoxazolones then proceeds preferentially. ³¹P{¹H}-NMR study suggested the involvement of an aryloxyphosphonium intermediate and/or possibly 2-iodobenzoxazole which activates the C-2 position of benzoxazolones toward nucleophilic aromatic substitution.

Direct synthesis of 2-oxo-acetamidines from methyl ketones, aromatic amines and DMF via copper-catalyzed C(sp3)-H amidination

A convenient method for the synthesis of 2-oxo-acetamidines from methyl ketones using aromatic amines and DMF as nitrogen sources is reported via copper-catalyzed C(sp3)-H amidination. Various methyl ketones react readily with aromatic amines and DMF, producing 2-oxo-acetamidines in yields of 47 to 92%. This protocol features the simultaneous formation of C-N and C[double bond, length as m-dash]N bonds using DMF and aromatic amines as two different nitrogen sources. It thus provides an efficient approach to construct acyclic amidines via three C(sp3)-H bond amidination. Based on the preliminary experiments, a plausible mechanism of this transformation is disclosed.

Cu-Catalyzed carbamoylation versus amination of quinoline N-oxide with formamides

Carbamoylation and amination of quinoline with formamides was developed via copper-catalyzed C–C and C–N bond formations.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Oxidation-induced C-H amination leads to a new avenue to build C-N bonds

In this work, we develop an oxidation-induced C-H functionalization strategy, which not only leads to a new avenue to build C-N bonds, but also leads to different site-selectivity compared with "classic directing-groups". The high selectivity of our new catalytic system originates from the heterogeneous electron-density distribution of the radical cation species which are induced by single electron transfer between the aromatics and oxidant-Cu(ii) species.

Origins of high catalyst loading in copper(i)-catalysed Ullmann-Goldberg C-N coupling reactions

A mechanistic investigation of Ullmann-Goldberg reactions using soluble and partially soluble bases led to the identification of various pathways for catalyst deactivation through (i) product inhibition with amine products, (ii) by-product inhibition with inorganic halide salts, and (iii) ligand exchange by soluble carboxylate bases. The reactions using partially soluble inorganic bases showed variable induction periods, which are responsible for the reproducibility issues in these reactions. Surprisingly, more finely milled Cs2CO3 resulted in a longer induction period due to the higher concentration of the deprotonated amine/amide, leading to suppressed catalytic activity. These results have significant implications on future ligand development for the Ullmann-Goldberg reaction and on the solid form of the inorganic base as an important variable with mechanistic ramifications in many catalytic reactions.

Transition Metal-Catalyzed C-H Amination: Scope, Mechanism, and Applications

Catalytic transformation of ubiquitous C-H bonds into valuable C-N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C-H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

Palladium-catalyzed intermolecular carbonylative cross-coupling of heteroaryl C(sp2)–H bonds with amines: an efficient strategy for oxidative aminocarbonylation of azoles

We report the first intermolecular carbonylative cross-coupling of heteroaryl C(sp²)–H bonds with amines using oxygen as the green oxidant.

Nickel-catalyzed carbonylation of arylboronic acids with DMF as a CO source

By using N,N-dimethylformamide (DMF) as a CO source, nickel-catalyzed carbonylation of arylboronic acids was demonstrated as an efficient and facile protocol for the synthesis of diaryl ketones.

Metal-free phosphonation of benzoxazoles and benzothiazoles under oxidative conditions

A metal-free C-2 phosphonation of benzoxazoles and benzothiazoles with trialkyl phosphites was described.