Gold-Catalyzed Hydroarylation of Alkenes with Dialkylanilines

Chemoselective Hydroheteroarylation of Alkenes via Photoredox-Neutral Proton- and BF3-Mediated Electron Transfer

Herein, we have developed a complementary entry to enable hydroheteroarylation of alkenes involving basically photoredox dearomatizative heterocyclic carbon radical formation through acid-coupled electron transfer followed by Giese addition. While protonic solvent and thiophenol additive enabled two molecular hydroheteroarylations of alkenes, the nonproton environment with BF3 altered the chemoselectivity over cascade hydroheteroarylation of alkenes by radical addition of heteroaromatics with two molecular alkenes. This chemoselectivity can be mechanistically attributed to the dynamically favored hydrogen atom transfer via the cyclic transition state.

Metal-free introduction of primary sulfonamide into electron-rich aromatics

We report herein a direct and practical synthesis of arylsulfonamides from electron-rich aromatic compounds by using in situ generated N-sulfonylamine as the active electrophile. Substrates include derivatives of aniline, indole, pyrrole, furan, styrene and so on. The reaction proceeds under mild conditions and tolerates many sensitive functional groups such as alkyne, acetate, the trifluoromethoxy group or acetoxymethyl ester. Applications of this method for the construction of metal ion sensors and fluorogenic dye have been demonstrated, thus highlighting the potential of this method for probe development.

H2 O ⋅ B(C6 F5 )3 -Catalyzed para-Alkylation of Anilines with Alkenes Applied to Late-Stage Functionalization of Non-Steroidal Anti-Inflammatory Drugs

Anilines are core motifs in a variety of important molecules including medicines, materials and agrochemicals. We report a straightforward procedure that allows access to new chemical space of anilines via their para-C-H alkylation. The method utilizes commercially available catalytic H2 O ⋅ B(C6 F5 )3 and is highly selective for para-C-alkylation (over N-alkylation and ortho-C-alkylation) of anilines, with a wide scope in both the aniline substrates and alkene coupling partners. Readily available alkenes are used, and include new classes of alkene for the first time. The mild reaction conditions have allowed the procedure to be applied to the late-stage-functionalization of non-steroidal anti-inflammatory drugs (NSAIDs), including fenamic acids and diclofenac. The formed novel NSAID derivatives display improved anti-inflammatory properties over the parent NSAID structure.

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

Kinetic studies on the intramolecular hydroamination of protected variants of 2,2-diphenylpent-4-en-1-amine were carried out under a variety of conditions with cationic gold catalysts supported by phosphine ligands. The impact of ligand on gold, protecting group on nitrogen, and solvent and additive on reaction rates was determined. The most effective reactions utilized more Lewis basic ureas, and more electron-withdrawing phosphines. A DCM/alcohol cooperative effect was quantified, and a continuum of isotope effects was measured with low KIE's in the absence of deuterated alcoholic solvent, increasing to large solvent KIE's when comparing reactions in pure MeOH to those in pure MeOH-d4. The effects are interpreted both within the context of a classic gold π-activation/protodeauration mechanism and a general acid-catalyzed mechanism without intermediate gold alkyls.

Ligand Promoted Pd-Catalyzed High para-Selective C-H Olefination

Achieving high para-selective C-H functionalized products of benzoic acid derivatives using a designed template is still a daunting challenge because the carbonyl group also could coordinate with metal to activate the ortho-C-H bond. Herein, we report the ligand promoted high para-selective C-H olefination of benzoic acid derivatives; we screened a series of ligands increasing the ratio of p:others from 62:38 to 96:4. This work may find application in the construction of para-substituted benzoic acid derivatives.

Catalyst- and Additive-free, Regioselective 1,6-Hydroarylation of para-Quinone Methides with Anilines in HFIP

A simple and efficient method for the synthesis of diarylmethyl-functionalized anilines through the hexafluoroisopropanol (HFIP)-mediated regioselective 1,6-hydroarylation reaction of para-quinone methides (p-QMs) with anilines under catalyst- and additive-free conditions is reported. Various kinds of p-QMs and amines (e. g. primary, secondary and tertiary amines) are well tolerated in this transformation without the pre-protection of amino group, and the corresponding products could be generated with good to excellent yields and satisfactory regioselectivity under the optimized reaction conditions. In addition to adaptable amine compounds, indoles and their derivatives are also compatible with this reaction system. This transformation can be easily extended to a gram scale-synthesis level to synthesize the target product. Furthermore, it is worth noting that some complex small aniline molecules with biological activity can be selectively modified using this method. The possible reaction mechanism is proposed through the step-by-step control experiments and DFT calculations, showing that the key process for achieving the regioselective 1,6-hydroarylation of p-QMs is the hydrogen bonding effect of HFIP to substrates.

Hydration Reactions Catalyzed by Transition Metal-NHC (NHC = N-Heterocyclic Carbene) Complexes

The catalytic addition of water to unsaturated C-C or C-N π bonds represent one of the most important and environmentally sustainable methods to form C-O bonds for the production of synthetic intermediates, medicinal agents and natural products. The traditional acid-catalyzed hydration of unsaturated compounds typically requires strong acids or toxic mercury salts, which limits practical applications and presents safety and environmental concerns. Today, transition-metal-catalyzed hydration supported by NHC (NHC = N-heterocyclic carbene) ligands has attracted major attention. By rational design of ligands, choice of metals and counterions as well as mechanistic studies and the development of heterogeneous systems, major progress has been achieved for a broad range of hydration processes. In particular, the combination of NHC ligands with gold shows excellent reactivity compared with other catalytic systems; however, other systems based on silver, ruthenium, osmium, platinum, rhodium and nickel have also been discovered. Ancillary NHC ligands provide stabilization of transition metals and ensure high catalytic activity in hydration owing to their unique electronic and steric properties. NHC-Au(I) complexes are particularly favored for hydration of unsaturated hydrocarbons due to soft and carbophilic properties of gold. In this review, we present a comprehensive overview of hydration reactions catalyzed by transition metal-NHC complexes and their applications in catalytic hydration of different classes of π-substrates with a focus on the role of NHC ligands, types of metals and counterions.

Metal-Free Aerobic C-N Bond Formation of Styrene and Arylamines via Photoactivated Electron Donor-Acceptor Complexation

This study processes a facile and green approach for the Markovnikov-selective hydroamination of styrene with naphthylamine through irradiation with UV LED light (365 nm) via an electron donor-acceptor complexation between naphthylamines and oxygen in situ. This protocol showcases the synthetic potential for aerobic C-N bond formation without using a metal catalyst and photosensitizer. Three naphthylamines were examined and afforded desired C-N bond formation product in moderate yield.

Palladium-Catalyzed para-C-H Arylation of Anilines with Aromatic Halides

Controlling regioselectivity in C-H functionalizations is a key challenge in chemical method development. In arenes, functionalizations are most difficult to direct towards the C-H group furthest away from a substituent, in its para position. We herein demonstrate how the para-C-H arylation of anilines with non-activated aryl halides, elusive to date, is achieved by a base-assisted "metalla-tautomerism" approach. A proton is abstracted from the aniline substrate and replaced by an arylpalladium species, generated from the aryl halide coupling partner. In this step, the palladium is directed away from the N- to the tautomeric para-C-H position by a large phosphine ligand combined with a triphenylmethyl shielding group. The triphenylmethyl group is easily installed and removed, and can be recycled.

Transition-metal-catalyzed C-H bond alkylation using olefins: recent advances and mechanistic aspects

Transition metal catalysis has contributed immensely to C-C bond formation reactions over the last few decades, and alkylation is no exception. The superiority of such methodologies over traditional alkylation is evident from minimal reaction steps, shorter reaction times, and atom economy while also allowing control over regio- and stereo-selectivity. In particular, hydrocarbonation of alkenes has grabbed increased attention due its fundamental ability to effectively and selectively synthesise a wide range of industrially and pharmaceutically relevant moieties. This review attempts to provide a scientific viewpoint and a systematic analysis of the recent developments in transition-metal-catalyzed alkylation of various C-H bonds using simple and activated olefins. The key features and mechanistic studies involved in these transformations are described briefly.

Ligand-Promoted Fluorinated Olefination of Isatins at the C5 Position via a Palladium Catalyst

A palladium-catalyzed nondirected fluorinated olefination was developed. The oxalyl amide ligand greatly improved the yield of the reaction. A wide variety of isatin derivatives were well tolerated and yielded the corresponding products in moderate to good yields. Various fluorinated olefins were also compatible. The application and synthesis of bioactive compounds such as a Metisazone derivative highlight the synthetic value of this approach.

AgNTf2-Catalyzed Regioselective C-H Alkenylation of N,N-Dialkylanilines with Ynamides

Regioselective C-H alkenylation of N,N-dialkylanilines with ynamides was developed using AgNTf₂ as a catalyst. This approach represents a facile hydroarylation of ynamides, allowing for the introduction of an alkenyl group exclusively at the para position of aniline derivatives. As a result, a series of 4-alkenyl N,N-dialkylanilines were synthesized with excellent regioselectivities.

Silver-Catalyzed Regioselective 1,6-Hydroarylation of para-Quinone Methides with Anilines and Phenols

A simple and efficient method for the silver-catalyzed regioselective 1,6-hydroarylation of para-quinone methides (p-QMs) with anilines and phenols has been established. Without the need for pre-protection, a broad range of...

Gold-Catalyzed Hydroarylation Reactions: A Comprehensive Overview

The hydroarylation of alkynes, alkene, and, allene is a cost-effective and efficient way to incorporate unsaturated moieties into aromatic substrates. This review focuses on gold-catalyzed hydroarylation, which produces aromatic alkenes,...

Base-Promoted Cobalt-Catalyzed Regio- and Enantioselective para-Friedel-Crafts Alkylation of Aniline Derivatives

Herein we disclose a highly efficient enantioselective para-C-H alkylation of aniline derivatives promoted by a base/Co/indeno-pybox ligand system. This methodology leads to the efficient construction of a series of enantioenriched aniline derivatives bearing all-carbon quaternary stereocenters. In addition, several special biologically or medicinally active indoles are facilely synthesized by our Co-catalyzed asymmetry synthesis method. Density functional theory calculations and experiment results suggest that the (acac)^- anion of Co(acac)₂ plays a very important role in chiral control during the nucleophilic reaction.

Selective Acid-Catalyzed Hydroarylation of Nonactivated Alkenes with Aniline Assisted by Hexafluoroisopropanol

The catalytic hydroarylation of nonactivated alkenes with aniline is a reaction of high interest, aiming at providing C-functionalized aniline derivatives that are important precursors for the fabrication of polyurethanes. However, this reaction remains a longstanding goal of catalysis, as it requires one to simultaneously address two important goals: (1) the very low reactivity of nonactivated alkenes and (2) control of the hydroarylation/hydroamination selectivity. As a result, the hydroarylation of aniline is mostly restricted to activated alkenes (i.e., featuring ring strain, conjugation, or activation with electron-donating or -withdrawing groups). Here we show that the combination of bismuth triflate and hexafluoroisopropanol (HFIP) leads to the formation of highly active catalytic species capable of promoting the hydroarylation of various nonactivated alkenes, such as 1-octene, 1-heptene, and 1-undecene, among others, with aniline with high selectivity (71-92%). Through a combined experimental and computational investigation, we propose a reaction pathway where HFIP stabilizes the rate-determining transition state through a H-bond interaction with the triflate anion, thus assisting the acid catalyst in the hydroarylation of nonactivated alkenes. From a practical point of view, this work opens a catalytic access to C-functionalized aniline derivatives from two cheap and abundant feedstocks in a 100% atom-economical fashion.

Boron-Catalyzed Hydroarylation of 1,3-Dienes with Arylamines

Catalytic hydroarylation reactions of conjugated dienes are achieved using tris(pentafluorophenyl)borane as a Lewis acid catalyst under mild reaction conditions. This new protocol shows a broad substrate scope for the highly regioselective functionalization of sterically hindered aniline derivatives. Experimental and extensive density functional theory mechanistic studies show that the complex of residual water and B(C₆F₅)₃ plays a crucial role in the aryl-assisted protonation of conjugated dienes, forming allyl cation intermediates that induce the facile electrophilic aromatic substitution of aniline substrates.

Optimizing Catalyst and Reaction Conditions in Gold(I) Catalysis-Ligand Development

This review considers phosphine and N-heterocyclic carbene complexes of gold(I) that are used as (pre)catalysts for a range of reactions in organic synthesis. These are divided according to the structure of the ligand, with the narrative focusing on studies that offer a quantitative comparison between the ligands and readily available or widely used existing systems.

Gold-Catalyzed Access to Isophosphinoline 2-Oxides

Gold(I)-catalyzed reactions of electron-poor alkynes are still a challenging process. A straightforward synthesis of phosphorus-based heterocycles, namely, 2-phenyl 1H-isophosphinoline 2-oxides 1, is reported. The reaction used PPh₃AuCl precatalyst in combination with triflic acid under microwave activation and afforded isophosphinoline 2-oxides 1 in moderate to quantitative yields through a fully regioselective 6-endo-dig hydroarylation cyclization, paving the way toward an effective synthesis of phosphorus heterocycles.

Group 11 Borataalkene Complexes: Models for Alkene Activation

A series of linear late transition metal (M=Cu, Ag, Au and Zn) complexes featuring a side-on [B=C]- containing ligand have been isolated and characterised. The [B=C]- moiety is isoelectronic with the C=C system of an alkene. Comparison across the series shows that in the solid-state, deviation between the η2 and η1 coordination mode occurs. A related zinc complex containing two [B=C]- ligands was prepared as a further point of comparison for the η1 coordination mode. The bonding in these new complexes has been interrogated by computational techniques (QTAIM, NBO, ETS-NOCV) and rationalised in terms of the Dewar-Chatt-Duncanson model. The combined structural and computational data provide unique insight into catalytically relevant linear d10 complexes of Cu, Ag and Au. Slippage is proposed to play a key role in catalytic reactions of alkenes through disruption and polarisation of the π-system. Through the preparation and analysis of a consistent series of group 11 complexes, we show that variation of the metal can impact the coordination mode and hence substrate activation.

Benzylic C-H addition of aromatic amines to alkenes using a scandium catalyst

An efficient and selective benzylic C(sp³)-H addition of o-CH₃-substituted tertiary aromatic amines to alkenes has been achieved using an anilido-oxazoline ligand supported scandium catalyst, which provides an atom-economic method for the synthesis of a new family of alkylated tertiary anilines. A wide range of amine and alkene substrates are compatible with the catalyst system.

Silver-Catalysed Hydroarylation of Highly Substituted Styrenes

Hydroarylation is an effective strategy to rapidly increase the complexity of organic structures by transforming flat alkene moieties into three-dimensional frameworks. Many strategies have already been developed to achieve the hydroarylation of styrenes, however most of these reports examine the hydroarylation of unpolar, β-mono- or β-unsubstituted styrenes, while exploring mainly electron-rich benzene nucleophiles. Herein, we report a mild and general catalytic system for the selective hydroheteroarylation of multiply substituted styrenes and heteroaromatic styrenes. Mechanistic analysis of the reaction led to the discovery of commercially available 2,2':5',2''-terthiophene as a key reagent.

Electron-deficient boron-based catalysts for C-H bond functionalisation

In contrast to transition metal-catalysed C-H functionalisation, highly efficient construction of C-C and C-X (X = N, O, S, B, Si, etc.) bonds through metal-free catalytic C-H functionalisation remains one of the most challenging tasks for synthetic chemists. In recent years, electron-deficient boron-based catalyst systems have exhibited great potential for C-H bond transformations. Such emerging systems may greatly enrich the chemistry of C-H functionalisation and main-group element catalysis, and will also provide enormous opportunities in synthetic chemistry, materials chemistry, and chemical biology. This article aims to give a timely comprehensive overview to recognise the current status of electron-deficient boron-based catalysis in C-H functionalisation and stimulate the development of more efficient catalytic systems.

Nickel-Catalyzed Asymmetric Synthesis of α-Arylbenzamides

A nickel-catalyzed asymmetric reductive hydroarylation of vinyl amides to produce enantioenriched α-arylbenzamides is reported. The use of a chiral bisimidazoline (BIm) ligand, in combination with diethoxymethylsilane and aryl halides, enables the regioselective introduction of aryl groups to the internal position of the olefin, forging a new stereogenic center α to the N atom. The use of neutral reagents and mild reaction conditions provides simple access to pharmacologically relevant motifs present in anticancer, SARS-CoV PLpro inhibitors, and KCNQ channel openers.

On the Superior Activity of In(I) versus In(III) Cations Toward ortho-C-Alkylation of Anilines and Intramolecular Hydroamination of Alkenes

An efficient ortho-C-alkylation of unprotected anilines with a variety of styrenes and alkenes using a univalent cationic indium(I) catalyst is reported. Mechanistic studies revealed that the reaction likely proceeds via a tandem hydroamination/Hofmann-Martius rearrangement. The high compatibility between the cationic indium(I) complex and primary anilines led us to develop an In(I)⁺-catalyzed hydroamination of alkenes using unprotected primary and secondary alkenylamines. Computations support the catalytic activity of naked In(I)⁺ ions, with an outer sphere mechanism for the C-N bond formation and a potentially inner sphere protodemetallation.

B(C6 F5 )3 -Catalyzed Tandem Friedel-Crafts and C-H/C-O Coupling Reactions of Dialkylanilines

Tandem Friedel-Crafts (FC) and C-H/C-O coupling reactions catalyzed by tris(pentafluorophenyl) borane (B(C₆ F₅ )₃ ) were achieved without using any other additive in the absence of solvent. This process can be used for the reactions between a series of dialkylanilines and vinyl ethers with good isolated yields of bis(4-dialkylaminophenyl) compounds. Based on combined theoretical and experimental studies, the possible reaction mechanism was proposed. B(C₆ F₅ )₃ can activate the C=C and C-O bond for FC and C-H/C-O coupling reactions respectively. The FC reaction is slow, which is followed by a fast C-H/C-O coupling.

Experimental and theoretical study on the cyclic(alkyl)(amino)carbene-copper catalyzed Friedel-Crafts reaction of N,N-dialkylanilines with styrenes

The Friedel-Crafts reaction of alkalinous substrates is challenging because of the coordination between amines and traditional acid catalysts. Based on theoretical research, we designed a catalytic process for the Friedel-Crafts reactions of N,N-dialkylanilines in the presence of CAAC-CuCl [CAAC = cyclic(alkyl)(amino)carbene] and KB(C₆F₅)₄. Experimental results show that the catalytic system is suitable for a series of N,N-dialkylanilines and styrenes with good to excellent yields of para-selectivity products. The results are comparable to those obtained in carbene-gold catalyzed processes.

Air-Stable Oxyallyl Patterns and a Switchable N-Heterocyclic Carbene

Oxyallyl derivatives are typically elusive compounds. Even recently reported "stabilized" 1,3-diaminooxyallyl species are still highly reactive and have short lifetimes at room temperature. Herein, we report the synthesis and preliminary study of mesoionic pyrimidine derivatives that feature 1,3-bis(dimethylamino)oxyallyl patterns with an unprecedented level of stabilization. The latter are not only insensitive towards air and moisture, but they are also compatible with the formation of an ancillary stable N-heterocyclic carbene moiety. As the oxyallyl pattern is proton-responsive, it allows the reversible switching of the electronic properties of the carbene, as a ligand.

Highly Chemo-, Site-, and Enantioseletive para C-H Aminoalkylation of N-Monosubstituted Aniline Derivatives Affording 3-Amino-2-oxindoles

In general, enantioselective C-H functionalization of N-monosubstituted anilines is a highly challenging task owing to the competitive chemoselective N-H bond insertion reactions. In this paper, we reported a direct highly chemo-, site-, and enantioselective para C-H aminoalkylation of N-monosubstituted aniline derivatives with isatin-derived ketimines in the presence of chiral phosphoric acids (CPAs) and offered a practical strategy for para asymmetric C-H functionalization of anilines containing N-H bonds.

Versatility and adaptative behaviour of the P^N chelating ligand MeDalphos within gold(i) π complexes

The hemilabile P^N ligand MeDalphos enables access to a wide range of stable gold(i) π-complexes with unbiased alkenes and alkynes, as well as electron-rich alkenes and for the first time electron-poor ones. All complexes have been characterized by multi-nuclear NMR spectroscopy and whenever possible, by X-ray diffraction analyses. They all adopt a rare tricoordinate environment around gold(i), with chelation of the P^N ligand and side-on coordination of the alkene, including the electron-rich one, 3,4-dihydro-2H-pyrane. The strength of the N → Au coordination varies significantly in the series. It is the way the P^N ligand accommodates the electronic demand at gold, depending on the alkene. Comparatively, when the chelating P^P ligand (ortho-carboranyl)(PPh₂)₂ is used, gold(i) π-complexes are only isolable with unbiased alkenes. The bonding situation within the gold(i) P^N π-complexes has been thoroughly analyzed by DFT calculations supplemented by Charge Decomposition Analyses (CDA), Natural Bond Orbital (NBO) and Atoms-in-Molecules (AIM) analyses. Noticeable variations in the donation/back-donation ratio, C[double bond, length as m-dash]C weakening, alkene to gold charge transfer and magnitude of the N → Au coordination were observed. Detailed examination of the descriptors for the Au/alkene interaction and the N → Au coordination actually revealed intimate correlation between the two, with linear response of the MeDalphos ligand to the alkene electronics. The P^N ligand displays non-innocent and adaptative character. The isolated P^N gold(i) π-complexes are reactive and catalytically relevant, as substantiated by the chemo and regio-selective alkylation of indoles.

Scandium-Catalyzed para-Selective Alkylation of Aromatic Amines with Alkenes

An efficient para-alkylation of primary and secondary anilines with a variety of sterically encumbered alkenes using a simple β-diketiminato scandium catalyst is reported. This protocol features 100% atom economy, excellent chemo- and regioselectivity, broad substrate scope, and good functional group tolerance. Mechanistic studies disclosed that the reaction probably proceeded via a tandem hydroamination/Hofmann-Martius rearrangement.

The debut of chiral cyclic (alkyl)(amino)carbenes (CAACs) in enantioselective catalysis

The popularity of NHCs in transition metal catalysis has prompted the development of chiral versions as electron-rich neutral stereodirecting ancillary ligands for enantioselective transformations. Herein we demonstrate that cyclic (alkyl)(amino)carbene (CAAC) ligands can also engage in asymmetric transformations, thereby expanding the toolbox of available chiral carbenes.