Synthesis of α-CF3 Amides via Palladium-Catalyzed Carbonylation of 2-Bromo-3,3,3-trifluoropropene

Amide compounds are important organic compounds, which play an important role in biomedical chemistry, materials science, life science, and other fields. The synthesis of α-CF₃ amides, especially compounds containing 3-(trifluoromethyl)-1,3,4,5-tetrahydro-2H-benzo[b][1,4]diazepine-2-one, has long been a challenge due to the tensile properties and instability of the rings. Here, we report an example of palladium-catalyzed carbonylation of CF₃-containing olefin to form α-CF₃ acrylamide. By controlling the ligands, we can get different amide compounds as products. This method has good substrate adaptability and functional group tolerance.

Recent Strategies in Nickel-Catalyzed C–H Bond Functionalization for Nitrogen-Containing Heterocycles

N-heterocycles are ubiquitous in natural products, pharmaceuticals, organic materials, and numerous functional molecules. Among the current synthetic approaches, transition metal-catalyzed C–H functionalization has gained considerable attention in recent years due to its advantages of simplicity, high atomic economy, and the ready availability of starting materials. In the field of N-heterocycle synthesis via C–H functionalization, nickel has been recognized as one of the most important catalysts. In this review, we will introduce nickel-catalyzed intramolecular and intermolecular pathways for N-heterocycle synthesis from 2008 to 2021.

Ligand-Enabled β-C(sp3 )-H Lactamization of Tosyl-Protected Aliphatic Amides Using a Practical Oxidant

The development of C(sp3 )-H functionalization reactions that use common protecting groups and practical oxidants remains a significant challenge. Herein we report a monoprotected aminoethyl thioether (MPAThio) ligand-enabled β-C(sp3 )-H lactamization of tosyl-protected aliphatic amides using tert-butyl hydrogen peroxide (TBHP) as the sole oxidant. This protocol features exceedingly mild reaction conditions, reliable scalability, and the use of practical oxidants and protecting groups. Further derivatization of the β-lactam products enables the synthesis of a range of biologically important motifs including β-amino acids, γ-amino alcohols, and azetidines.

Directing Group Strategies in Rhodium-Catalyzed C-H Amination

Construction of a carbon-nitrogen bond is one of the most prevalent operations in nature and organic synthesis. The resulting amino compounds are privileged structural fragments in natural products, pharmaceutical drugs,...

Transition-Metal-Catalyzed, Coordination-Assisted Functionalization of Nonactivated C(sp3)-H Bonds

Transition-metal-catalyzed, coordination-assisted C(sp³)-H functionalization has revolutionized synthetic planning over the past few decades as the use of these directing groups has allowed for increased access to many strategic positions in organic molecules. Nonetheless, several challenges remain preeminent, such as the requirement for high temperatures, the difficulty in removing or converting directing groups, and, although many metals provide some reactivity, the difficulty in employing metals outside of palladium. This review aims to give a comprehensive overview of coordination-assisted, transition-metal-catalyzed, direct functionalization of nonactivated C(sp³)-H bonds by covering the literature since 2004 in order to demonstrate the current state-of-the-art methods as well as the current limitations. For clarity, this review has been divided into nine sections by the transition metal catalyst with subdivisions by the type of bond formation. Synthetic applications and reaction mechanism are discussed where appropriate.

Copper(i)-catalyzed radical carboamination reaction of 8-aminoquinoline-oriented buteneamides with chloroform: synthesis of-β-lactams

A novel Cu(CH₃CN)₄PF₆-catalyzed carboamination reaction of 8-aminoquinoline-oriented buteneamides with chloroform to afford 4-(2,2,2-trichloroethyl)-β-lactams is described. The reaction proceeded at 110 °C in air with di-t-butyl peroxide. Preliminary studies indicated that the reaction undergoes a free radical mechanism via a Cu(i)/Cu(ii)/Cu(iii) catalytic cycle.

A general strategy for the synthesis of α-trifluoromethyl- and α-perfluoroalkyl-β-lactams via palladium-catalyzed carbonylation

β-Lactam compounds play a key role in medicinal chemistry, specifically as the most important class of antibiotics. Here, we report a novel one-step approach for the synthesis of α-(trifluoromethyl)-β-lactams and related products from fluorinated olefins, anilines and CO. Utilization of an advanced palladium catalyst system with the Ruphos ligand allows for selective cycloaminocarbonylations to give diverse fluorinated β-lactams in high yields.

A Guide to Directing Group Removal: 8-Aminoquinoline

The use of directing groups allows high levels of selectivity to be achieved in transition metal-catalyzed transformations. Efficient removal of these auxiliaries after successful functionalization, however, can be very challenging. This review provides a critical overview of strategies used for removal of Daugulis' 8-aminoquinoline (2005-2020), one of the most widely used N,N-bidentate directing groups. The limitations of these strategies are discussed and alternative approaches are suggested for challenging substrates. Our aim is to provide a comprehensive end-users' guide for chemists in academia and industry who want to harness the synthetic power of directing groups-and be able to remove them from their final products.

C-N and C-O Bond Formation in Copper-Catalyzed/Mediated sp3 C-H Activation: Mechanistic Studies from Experimental and Computational Aspects

Mechanistic studies on Cu-catalyzed/mediated sp³ C-H amidation and acetoxylation are investigated from experimental and computational aspects. The concerted metalation-deprotonation (CMD) mechanism rather than a radical-involved pathway is proved to occur in amidation and acetoxylation reactions, and this is the rare example of the CMD mechanism involved in the more challenging sp³ C-H activations. Theoretical calculations demonstrated that CMD is the rate-determining step either for methylic or benzylic positions in amidation and acetoxylation reactions, and intermolecular nucleophilic addition of acetate anions is more favorable than the ring opening of β-lactams and intramolecular acetoxylation. These mechanistic studies on the divergent and condition-dependent product formation are critical for developing Cu-promoted C-H functionalization via the CMD mechanism.

Testing the limits of radical-anionic CH-amination: a 10-million-fold decrease in basicity opens a new path to hydroxyisoindolines via a mixed C-N/C-O-forming cascade

An intramolecular C(sp3)-H amidation proceeds in the presence of t-BuOK, molecular oxygen, and DMF. This transformation is initiated by the deprotonation of an acidic N-H bond and selective radical activation of a benzylic C-H bond towards hydrogen atom transfer (HAT). Cyclization of this radical-anion intermediate en route to a two-centered/three-electron (2c,3e) C-N bond removes electron density from nitrogen. As this electronegative element resists such an "oxidation", making nitrogen more electron rich is key to overcoming this problem. This work dramatically expands the range of N-anions that can participate in this process by using amides instead of anilines. The resulting 107-fold decrease in the N-component basicity (and nucleophilicity) doubles the activation barrier for C-N bond formation and makes this process nearly thermoneutral. Remarkably, this reaction also converts a weak reductant into a much stronger reductant. Such "reductant upconversion" allows mild oxidants like molecular oxygen to complete the first part of the cascade. In contrast, the second stage of NH/CH activation forms a highly stabilized radical-anion intermediate incapable of undergoing electron transfer to oxygen. Because the oxidation is unfavored, an alternative reaction path opens via coupling between the radical anion intermediate and either superoxide or hydroperoxide radical. The hydroperoxide intermediate transforms into the final hydroxyisoindoline products under basic conditions. The use of TEMPO as an additive was found to activate less reactive amides. The combination of experimental and computational data outlines a conceptually new mechanism for conversion of unprotected amides into hydroxyisoindolines proceeding as a sequence of C-H amidation and C-H oxidation.

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.

Transition metal-catalyzed sp3 C-H activation and intramolecular C-N coupling to construct nitrogen heterocyclic scaffolds

Nitrogen heterocycles are of great medicinal importance, and the construction of nitrogen heterocyclic scaffolds has been one of the focuses in synthetic organic chemistry. Recently, the strategy of transition metal-catalyzed sp3 C-H activation and intramolecular C-N coupling to construct nitrogen heterocyclic scaffolds has been well developed. Palladium, copper, silver, nickel, cobalt, ruthenium and rhodium catalysis were successfully used for the construction of nitrogen heterocyclic scaffolds, aziridines, azetidines, pyrrolidines, pyrrolidine-2,5-diones, indolines, isoindolines, isoindolinones, tetrahydropyridines, oxazolidinones, oxazinanones, β-lactams, γ-lactams etc., which have been synthesized by the sp3 C-H activation strategy. Here, we summarize the progress of transition metal-catalyzed sp3 C-H activation/intramolecular C-N bond formation, and introduce both the reaction development and mechanisms in numerous synthetically useful intramolecular sp3 C-H catalytic aminations/amidations.

Catalytically Relevant Intermediates in the Ni-Catalyzed C(sp2)-H and C(sp3)-H Functionalization of Aminoquinoline Substrates

This Article describes the synthesis and characterization of cyclometalated aminoquinoline Ni^II σ-aryl and σ-alkyl complexes that have been proposed as key intermediates in Ni-catalyzed C-H functionalization reactions. These Ni^II complexes serve as competent catalysts for the C-H functionalization of aminoquinoline derivatives with I₂. They also react stoichiometrically with I₂ to form either aryl iodides or β-lactams within minutes at room temperature. Furthermore, they react with Ag^I salts at -30 °C to afford isolable five-coordinate Ni^III species. The Ni^III σ-aryl complexes proved inert toward C(sp²)-I bond-forming reductive elimination under all conditions examined (up to 140 °C in DMF). In contrast, a Ni^III σ-alkyl analogue underwent C(sp³)-N bond-forming reductive elimination at 140 °C in DMF to afford a β-lactam product. However, despite the ability of this latter Ni^III species to participate in stoichiometric product formation, the complex was not a competent catalyst for β-lactam formation. Overall, these results suggest against the intermediacy of Ni^III species in these C-H functionalization reactions.

Nickel-catalyzed anti-Markovnikov hydroarylation of alkenes

We have developed a nickel-catalyzed hydroarylation of alkenes using aryl halides as coupling partners. Excellent anti-Markovnikov selectivity is achieved with aryl-substituted alkenes and enol ethers. We also show that hydroarylation occurs with alkyl substituted alkenes to yield linear products. Preliminary examination of the reaction mechanism suggests irreversible hydrometallation as the selectivity determining step of the hydroarylation.

Chelation-assisted C-N cross-coupling of phosphinamides and aryl boronic acids with copper powder at room temperature

A protocol for the chelation-assisted C-N cross-coupling of phosphinamides and aryl boronic acids with copper powder under an oxygen atmosphere is reported. This reaction proceeds efficiently to afford fully substituted unsymmetrical N-arylation phosphinamides at room temperature in excellent yields. Diverse unstable functional groups on the benzene ring of aryl boronic acids such as vinyl, formyl, acetyl, sulfonyl, acetylamino, cyano, nitro, and trifluoromethyl can be accommodated.

A practical copper-catalyzed approach to β-lactams via radical carboamination of alkenyl carbonyl compounds

Functionalized β-lactams are highly important motifs in synthetic chemistry. We report an efficient and novel approach to the synthesis of β-lactams via a copper(i)-catalyzed cascade process involving C(benzyl)-H radical abstraction, intermolecular alkene addition, and intramolecular amination reaction. Variously substituted alkenes were synthesized from vinylacetic acid, leading to the corresponding β-lactams in moderate to good yields. Preliminary studies indicate that the reaction undergoes a free radical mechanism via a Cu(i)/Cu(ii)/Cu(iii) catalytic cycle.

The decarboxylative C–H heteroarylation of azoles catalysed by nickel catalysts to access unsymmetrical biheteroaryls

The direct decarboxylative C–H heteroarylation of azoles with heteroaryl carboxylic acids through nickel catalysts has been developed.

A computational mechanistic study of Ni(0)-catalyzed annulation of aromatic amides with alkynes: the effects of directing groups

The mechanism of Ni(0)-catalyzed annulation of aromatic amides with alkynes was studied theoretically to investigate the effects of directing groups.

Cobalt-catalysed unactivated C(sp3)–H amination: two-state reactivity and multi-reference electronic character

A remarkable two-state reactivity scenario and an unusual multi-reference character have been computationally found in Co-catalysed C(sp³)–H amination. In addition, the investigation on the additive, aminating reagent, metal center, and auxiliary ligand provides implications for development of new catalytic C–H functionalization systems.

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 Direct C-H Thiolation of Aromatic Amides with Disulfides: Application to the Synthesis of Quetiapine

A direct C(sp²)-H thiolation of aromatic amides with disulfides was developed. The coupling reaction proceeds between the thioether radical and cobaltacycle intermediate. This method exhibits a relatively broad substrate scope and high functional group compatibility. A mechanistic study indicates that the cobalt(IV) intermediate is probably formed during the course of the reaction. The thiolation product can be transformed to Quetiapine, which is an atypical antipsychotic agent approved for the treatment of schizophrenia and bipolar disorder.

Complementary Strategies for Directed C(sp3 )-H Functionalization: A Comparison of Transition-Metal-Catalyzed Activation, Hydrogen Atom Transfer, and Carbene/Nitrene Transfer

The functionalization of C(sp3 )-H bonds streamlines chemical synthesis by allowing the use of simple molecules and providing novel synthetic disconnections. Intensive recent efforts in the development of new reactions based on C-H functionalization have led to its wider adoption across a range of research areas. This Review discusses the strengths and weaknesses of three main approaches: transition-metal-catalyzed C-H activation, 1,n-hydrogen atom transfer, and transition-metal-catalyzed carbene/nitrene transfer, for the directed functionalization of unactivated C(sp3 )-H bonds. For each strategy, the scope, the reactivity of different C-H bonds, the position of the reacting C-H bonds relative to the directing group, and stereochemical outcomes are illustrated with examples in the literature. The aim of this Review is to provide guidance for the use of C-H functionalization reactions and inspire future research in this area.

Recent advances in β-lactam synthesis

During the past century, β-lactams have been identified as the core of penicillin and since then several strategies have been developed for their synthesis.

Nickel-catalyzed direct C–H bond sulfenylation of acylhydrazines

An efficient Ni-catalyzed direct C–H bond sulfenylation of acylhydrazines for the synthesis of diverse diaryl sulfides.

Nickel catalyzed site selective C–H functionalization of α-aryl-thioamides

A nickel catalyzed C–H bond functionalization reaction has been used for the first time to study an intramolecular site-selective C–S bond formation of arenes.