Copper-Mediated Direct Alkoxylation of Arenes Using an N,O-Bidentate Directing System

Synthesis of functionalized alkenes via Cu(I)-catalysed allylation of acetanilides using Morita-Baylis-Hillman bromides

An easy access to functionalized alkenes has been developed by the C-H functionalization of anilides with Morita-Baylis-Hillman (MBH) bromides in the presence of copper chloride, TBHP and acetic acid. Unsubstituted as well as ortho/meta-substituted anilides exclusively give rise to the para-allylated products, whereas para-substitution brings about the formation of ortho-allylated anilides.

Copper-catalyzed regioselective C2-H chlorination of indoles with para-toluenesulfonyl chloride

A copper-catalyzed, pyrimidine directed regioselective C-H chlorination of indoles with para-toluenesulfonyl chloride (TsCl) has been developed. The reactions proceeded smoothly in the presence of 20 mol% of Cu(OAc)₂ as the catalyst and TsCl as the chlorine source, delivering C2-chlorinated indoles with structural diversity in moderate to excellent yields. Mechanistic studies suggested that single electron transfer (SET) from Cu(II) to TsCl accompanied by the release of the p-toluenesulfonyl radical and the related Cu(III)Cl species might be involved in the reactions.

Pd(II)-Catalyzed Chemoselective Acetoxylation of C(sp2)-H and C(sp3)-H Bonds in Tertiary Amides

Palladium-catalyzed chemoselective C(sp²)-H and C(sp³)-H acetoxylation of synthetically useful tertiary amides is reported under relatively mild reaction conditions. This protocol proceeds through the assistance of a weakly coordinated directing group (C═O) and requires low catalyst (1.0 mol %) loading. Diverse functionalities, such as C(sp²)-Cl, C(sp³)-Cl, -CF₃, -COOEt, and -NO₂ groups, including morpholinyl, piperazinyl, and pyrrolidinyl heterocycles, are compatible under the reaction conditions. Further functionalization of this protocol is demonstrated by hydrolysis to alcohols, alcohol-acids, as well as reduction to tertiary amines. A preliminary kinetic isotope effect study supported the rate-limiting C-H bond activation process.

Copper-catalyzed chemoselective C-H functionalization of quinoxalin-2(1H)-ones with hexafluoroisopropanol

An unexpected three-component reaction of quinoxalin-2(1H)-ones, tert-butyl peroxybenzoate (TBPB), and hexafluoroisopropanol (HFIP) is described. Under CuBr-catalyzed and TBPB-oxidized conditions, a variety of hydroxyhexafluoroisobutylated quinoxalin-2(1H)-ones were formed. Furthermore, the first hexafluoroisopropoxylation of the quinoxalin-2(1H)-ones with HFIP is also demonstrated with Cu2O as the catalyst and PhI(OAc)2 as the oxidant. These new transformations of HFIP furnish previously unknown and potentially useful fluorinated quinoxalin-2(1H)-one derivatives.

Copper-Catalyzed Direct C(sp3)-H Alkoxylation to Access Quaternary α-Alkoxylated Amino Acid Derivatives

A copper-catalyzed C(sp³)-H alkoxylation was developed to prepare quaternary α-alkoxylated amino acid derivatives in good yields. This protocol can be applied to a series of α-amino acids bearing a variety of functional group substituents. Facile removal of the auxiliary directing group and tolerance of condensation conditions for amide bond formation enable the potential application of this method in the discovery of new peptide drugs in the future.

Copper-Catalyzed Oxalamide-Directed ortho-C-H Amination of Anilines with Alkylamines

A copper-catalyzed oxalamide-directed ortho-C-H amination of anilines has been developed by using 1 atm of air as the sole oxidant. The protocol shows excellent functional group tolerance, and some heterocyclic amines including indole, benzothiophene, benzothiazole, quinoline, isoquinoline, and quinoxaline could be compatible in the reaction. The late-stage diversification of medicinal drugs demonstrates the synthetic utility of this protocol.

Bidentate Directing Groups: An Efficient Tool in C-H Bond Functionalization Chemistry for the Expedient Construction of C-C Bonds

During the past decades, synthetic organic chemistry discovered that directing group assisted C-H activation is a key tool for the expedient and siteselective construction of C-C bonds. Among the various directing group strategies, bidentate directing groups are now recognized as one of the most efficient devices for the selective functionalization of certain positions due to fact that its metal center permits fine, tunable, and reversible coordination. The family of bidentate directing groups permit various types of assistance to be achieved, such as N,N-dentate, N,O-dentate, and N,S-dentate auxiliaries, which are categorized based on the coordination site. In this review, we broadly discuss various C-H bond functionalization reactions for the formation of C-C bonds with the aid of bidentate directing groups.

Mechanistic insights of Cu(ii)-mediated ortho-C-H amination of arenes by capturing fleeting intermediates and theoretical calculations

The capture of reactive intermediates empowers chemists to conjecture the detail of a chemical transformation. Here we explore the mechanism of a C-H amination by intercepting short-lived intermediates in real time using online mass spectrometry. Computational study unravels the favorable pathway of the proposed dual mechanism of the reaction.

Cu(II)-Mediated Ortho-C-H Amination of Arenes with Free Amines

Copper-mediated direct ortho-C-H amination of arenes has been accomplished with the aid of easily removable bidentate pyridine N-oxide as a directing group. The use of free cyclic secondary amines and anilines as aminating agents and inexpensive copper acetate makes the strategy more effective and favorable from the economic point of view. This reaction is compatible with a wide range of functional groups to synthesize a variety of amine-containing products of high interest. This method also allows the short synthesis of the central scaffold of pharmaceutically relevant Staphylococcus aureus Sortase A inhibitors.

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.

Cobalt-catalyzed peri-selective alkoxylation of 1-naphthylamine derivatives

A cobalt-catalyzed C(sp²)-H alkoxylation of 1-naphthylamine derivatives has been disclosed, which represents an efficient approach to synthesize aryl ethers with broad functional group tolerance. It is noteworthy that secondary alcohols, such as hexafluoroisopropanol, isopropanol, isobutanol, and isopentanol, were well tolerated under the current catalytic system. Moreover, a series of biologically relevant fluorine-aryl ethers were easily obtained under mild reaction conditions after the removal of the directing group.

Copper-mediated regioselective C-H etherification of naphthylamides with arylboronic acids using water as an oxygen source

The copper-mediated regioselective C-H activation and C-O bond formation of naphthylamides with arylboronic acids has been developed using water as an oxygen source. The kinetic isotope study suggests that C-H bond activation is the rate-determining step. The H2O18 labelling experiment reveals the incorporation of oxygen from water. The substrate scope, functional group diversity and post synthetic utilities are the important practical features.

Nickel-catalyzed regioselective arylation of aromatic amides with aryl iodides enabled by an N,O-bidentate directing group

A bidentate directing group enabled ortho-arylation of C(sp²)–H bonds in aromatic carboxamides with aryl iodides under nickel-catalysis was developed.

Benzene C-H Etherification via Photocatalytic Hydrogen-Evolution Cross-Coupling Reaction

Aryl ethers can be constructed from the direct coupling between the benzene C-H bond and the alcohol O-H bond with the evolution of hydrogen via the synergistic merger of photocatalysis and cobalt catalysis. Utilizing the dual catalyst system consisting of 3-cyano-1-methylquinolinum photocatalyst and cobaloxime, intermolecular etherification of arenes with various alcohols and intramolecular alkoxylation of 3-phenylpropanols with formation of chromanes are accomplished. These reactions proceed at remarkably mild conditions, and the sole byproduct is equivalent hydrogen gas.

Reconnaissance of reactivity of an Ag(ii)SO4 one-electron oxidizer towards naphthalene derivatives

Ag(ii)SO₄ – a powerful oxidizer – allows for single-pot oxidative aromatic coupling of naphthalene and its 1- and 2-substituted derivatives.

Borylation, silylation and selenation of C–H bonds in metal sandwich compounds by applying a directing group strategy

Carbon–heteroatom bond formation in metal-sandwich compounds using C–H activation by selective directing groups.

Palladium-Catalyzed Ortho-Alkoxylation of N-Benzoyl α-Amino Acid Derivatives at Room Temperature

An efficient palladium-catalyzed ortho-alkoxylation of N-benzoyl α-amino acid derivatives at room temperature has been explored. This novel transformation, using amino acids as directing groups, Pd(OAc)₂ as catalyst, alcohols as the alkoxylation reagents, and PhI(OAc)₂ as the oxidant, showed wide generality, good functional tolerance, and high monoselectivity and regioselectivity.

Pd(OAc)2-catalysed regioselective alkoxylation of aryl (β-carbolin-1-yl)methanones via β-carboline directed ortho-C(sp(2))-H activation of an aryl ring

Synthesis of (2-alkoxyphenyl)(9H-pyrido[3,4-b]indol-1-yl)methanone via Pd(OAc)2-catalyzed regioselective alkoxylation of aryl (β-carbolin-1-yl) methanones employing β-carboline directed ortho-C(sp(2))-H activation of an aryl ring under oxidative conditions is described.

Recent advances in copper-mediated chelation-assisted functionalization of unactivated C–H bonds

Recent advances in copper-mediated (both stoichiometric and catalytic) chelation-assisted functionalization of unactivated C–H bonds are reviewed.

Copper-mediated etherification of arenes with alkoxysilanes directed by an (2-aminophenyl)pyrazole group

(2-Aminophenyl)pyrazole directed copper mediated C–H etherification of (hetero)arenes is described.

Mechanistic insights into cobalt(ii/iii)-catalyzed C-H oxidation: a combined theoretical and experimental study

Cobalt-mediated C-H functionalization has been the subject of extensive interest in synthetic chemistry, but the mechanisms of many of these reactions (such as the cobalt-catalyzed C-H oxidation) are poorly understood. In this paper, possible mechanisms including single electron transfer (SET) and the concerted metalation-deprotonation (CMD) pathways of the CoII/CoIII-catalyzed alkoxylation of C(sp2)-H bonds have been investigated for the first time using the DFT method. CoII(OAc)2 has been employed as an efficient catalyst in our previous experimental study, but the calculated results unexpectedly indicated that the intermolecular SET pathway with CoIII as the actual catalyst might be the most favorable pathway. To support this theoretical prediction, we have explored a series of Cp*CoIII(CO)I2 catalyzed C(sp2)-H bond alkoxylations, extending the application of cobalt-catalyzed functionalization of C-H bonds. Furthermore, kinetic isotope effect (KIE) data, electron paramagnetic resonance (EPR) data, and TEMPO inhibition experiments also support the SET mechanism in both the Co-catalyzed alkoxylation reactions. Thus, this work should support an understanding of the possible mechanisms of the CoII/CoIII-catalyzed C(sp2)-H functionalization, and also provide an example of the rational design of novel catalytic reactions guided by theoretical calculations.

Recent Advances in the C-H-Functionalization of the Distal Positions in Pyridines and Quinolines

This review summarizes recent developments in the C-H-functionalization of the distal positions of pyridines, quinolines and related azaheterocycles. While the functionalization of the C2 position has been known for a long time and is facilitated by the proximity to N1, regioselective reactions in the distal positions are more difficult to achieve and have only emerged in the last decade. Recent advances in the transition metal-catalyzed distal C-H-functionalization of these synthetically-important azaheterocycles are discussed in detail, with the focus on the scope, site-selectivity and mechanistic aspects of the reactions.

Cross-dehydrogenative coupling for the intermolecular C-O bond formation

The present review summarizes primary publications on the cross-dehydrogenative C-O coupling, with special emphasis on the studies published after 2000. The starting compound, which donates a carbon atom for the formation of a new C-O bond, is called the CH-reagent or the C-reagent, and the compound, an oxygen atom of which is involved in the new bond, is called the OH-reagent or the O-reagent. Alcohols and carboxylic acids are most commonly used as O-reagents; hydroxylamine derivatives, hydroperoxides, and sulfonic acids are employed less often. The cross-dehydrogenative C-O coupling reactions are carried out using different C-reagents, such as compounds containing directing functional groups (amide, heteroaromatic, oxime, and so on) and compounds with activated C-H bonds (aldehydes, alcohols, ketones, ethers, amines, amides, compounds containing the benzyl, allyl, or propargyl moiety). An analysis of the published data showed that the principles at the basis of a particular cross-dehydrogenative C-O coupling reaction are dictated mainly by the nature of the C-reagent. Hence, in the present review the data are classified according to the structures of C-reagents, and, in the second place, according to the type of oxidative systems. Besides the typical cross-dehydrogenative coupling reactions of CH- and OH-reagents, closely related C-H activation processes involving intermolecular C-O bond formation are discussed: acyloxylation reactions with ArI(O2CR)2 reagents and generation of O-reagents in situ from C-reagents (methylarenes, aldehydes, etc.).

Copper-mediated ortho C–H sulfonylation of benzoic acid derivatives with sodium sulfinates

Copper-mediated direct ortho C–H bond sulfonylation of benzoic acid derivatives with sodium sulfinates was achieved by employing an 8-aminoquinoline moiety as the bidentate directing group. Various aryl sulfones were synthesized in good yields with excellent regioselectivity.