Triazole‐Assisted Ruthenium‐Catalyzed CH Arylation of Aromatic Amides

Site‐selective ruthenium(II)‐catalyzed direct arylation of amides was achieved through C?H cleavages with modular auxiliaries, derived from easily accessible 1,2,3‐triazoles. The triazolyldimethylmethyl (TAM) bidentate directing group was prepared in a highly modular fashion through copper(I)‐catalyzed 1,3‐dipolar cycloaddition and allowed for ruthenium‐catalyzed C?H arylations on arenes and heteroarenes, as well as alkenes, by using easy‐to‐handle aryl bromides as the arylating reagents. The triazole‐assisted C?H activation strategy was found to be widely applicable, to occur under mild reaction conditions, and the catalytic system was tolerant of important electrophilic functionalities. Notably, the flexible triazole‐based auxiliary proved to be a more potent directing group for the optimized ruthenium(II)‐catalyzed direct arylations, compared with pyridyl‐substituted amides or substrates derived from 8‐aminoquinoline.     

Thioketone‐Directed Palladium(II)‐Catalyzed C−H Arylation of Ferrocenes with Aryl Boronic Acids

A palladium(II)‐catalyzed thioketone‐chelation‐assisted direct C?H arylation of ferrocenes is described. With thioketone as an efficient directing group, various monoaryl‐ and diaryl‐substituted thiocarbonylferrocenes were obtained by palladium‐catalyzed direct C?H functionalization in high yields under mild and base‐free reaction conditions. Furthermore, the arylated thiocarbonylferrocene could undergo diverse transformations.     

Palladium‐Catalyzed γ‐C(sp3)−H Arylation of Thiols by a Detachable Protecting/Directing Group

Reported herein is a palladium‐catalyzed, directed γ‐C(sp³)?H arylation of protected thiols. The key is to utilize Michael acceptors as a dual reagent to install a protecting/directing group on thiols by a thiol‐Michael click reaction, and remove it later under basic conditions. The C?H arylation proceeds with high functional‐group tolerance and the deprotected thiols can be further transformed into other sulfur‐containing compounds. This unique mode of activation could open the door for site‐selective functionalization of thiols or other sulfur‐containing compounds at unactivated positions.     

Aniline Carbamates: A Versatile and Removable Motif for Palladium‐Catalyzed Directed CH Activation

The aniline carbamate is introduced as a new removable directing group for C?H activation. Its versatility and ability as a directing group are demonstrated by its use in the ortho‐arylation of a wide variety of aniline derivatives under palladium(II) catalysis, with symmetric diaryliodonium salts as aryl donors. The reaction differs from previously reported arylations in its selectivity and its mechanism, as elucidated by kinetic and isotopic experiments. The directing group can also be easily removed under a variety of conditions.     

Readily Removable Directing Group Assisted Chemo‐ and Regioselective C(sp3)H Activation by Palladium Catalysis

Currently used directing groups for selective aliphatic β‐functionalization of carbonyl compounds show excellent reactivity and selectivity with an amide as a linker. Described herein is 2‐piconimide, used for the first time with commercially available 2‐picolinamide/2‐picolic acid as precursors, to direct C? H arylation/alkenylation by palladium catalysis. The directing group is essential for promoting the sequnetial primary and secondary C(sp³)? H arylation with different aryl iodides in one substrate. The directing group was easily removed under simple reaction conditions at room temperature.     

PdII‐Catalyzed Mild CH ortho Arylation and Intramolecular Amination Oriented by a Phosphinamide Group

A novel protocol for the Pd‐catalyzed ortho‐arylation of aryl phosphinamide with boronic acid is reported. By using phosphinamide as a new directing group, the reaction proceeds efficiently under mild conditions at 40 °C. Mechanistic studies reveal that the reaction proceeds via a Pd^II to Pd⁰ cycle. The phosphinamide group is also shown to be an effective orienting group for direct C?H amination.     

Late‐Stage Diversification of Peptides by Metal‐Free CH Arylation

The bioorthogonal late‐stage diversification of functionalized oligopeptides was accomplished through a metal‐free, site‐selective C?H arylation of engineered indole derivatives under mild reaction conditions.     

Palladium‐Catalyzed Arylation of Unactivated γ‐Methylene C(sp3)H and δ‐CH Bonds with an Oxazoline‐Carboxylate Auxiliary

A palladium‐catalyzed arylation of unactivated γ‐methylene C(sp³)?H and remote δ‐C?H bonds by using an oxazoline‐carboxylate directing group has been developed. Arylation occurs with a broad substrate scope and high tolerance of functional groups (i.e., halogen, nitro, cyano, ether, trifluoromethyl, amine, and ester). The oxazoline‐type auxiliary can be removed under acidic conditions.     

Late‐Stage Peptide Diversification by Bioorthogonal Catalytic CH Arylation at 23 °C in H2O

The step‐economical late‐stage diversification of tryptophan‐containing peptides was accomplished through chemo‐ and site‐selective palladium‐catalyzed C?H arylation under exceedingly mild reaction conditions. Thus, the C?H functionalization occurred efficiently at 23 °C with a catalyst loading as low as 0.5 mol %, and/or in H₂O.     

Iridium‐Catalyzed ortho‐Arylation of Benzoic Acids with Arenediazonium Salts

In the presence of catalytic [{IrCp*Cl₂}₂] and Ag₂CO₃, Li₂CO₃ as the base, and acetone as the solvent, benzoic acids react with arenediazonium salts to give the corresponding diaryl‐2‐carboxylates under mild conditions. This C? H arylation process is generally applicable to diversely substituted substrates, ranging from extremely electron‐rich to electron‐poor derivatives. The carboxylate directing group is widely available and can be removed tracelessly or employed for further derivatization. Orthogonality to halide‐based cross‐couplings is achieved by the use of diazonium salts, which can be coupled even in the presence of iodo substituents.     

Expedient Iron‐Catalyzed C−H Allylation/Alkylation by Triazole Assistance with Ample Scope

Triazole assistance set the stage for a unified strategy for the iron‐catalyzed C?H allylation of arenes, heteroarenes, and alkenes with ample scope. The versatile catalyst also proved competent for site‐selective methylation, benzylation, and alkylation with challenging primary and secondary halides. Triazole‐assisted C?H activation proceeded chemo‐, site‐, and diastereo‐selectively, and the modular TAM directing group was readily removed in a traceless fashion under exceedingly mild reaction conditions.     

Steric Effect of Carboxylate Ligands on Pd‐Catalyzed Intramolecular C(sp2)–H and C(sp3)–H Arylation Reactions

A bulky carboxylic acid bearing three cyclohexylmethyl substituents at the α‐position, namely, tri(cyclohexylmethyl)acetic acid, is demonstrated to act as an efficient ligand source in Pd‐catalyzed intramolecular C(sp²)?H and C(sp³)?H arylation reactions. The reactions proceed smoothly under mild reaction conditions, even at room temperature due to the steric bulk of the carboxylate ligands, which accelerates the rate‐determining C?H bond activation step in the catalytic cycle.     

Mild Palladium Catalyzed ortho C‐H Bond Functionalizations of Aniline Derivatives

This account collects the developments and transformations which avoid the utilization of harsh reaction conditions in the field of palladium catalyzed, ortho‐directed C?H activation of aniline derivatives from the first attempts to up‐to‐date results, including the results of our research laboratory. The discussed functionalizations performed under mild conditions include acylation, olefination, arylation, alkylation, alkoxylation reactions. Beside the optimization studies and the synthetic applications mechanistic investigations are also presented.     

AgONO‐Assisted Direct CH Arylation of Heteroarenes with Anilines

A novel copper‐catalyzed C?H arylation of heteroarenes with anilines by an in situ diazonium reaction is established by using silver nitrite (AgONO) as an unconventional nitrosating reagent under acid‐free conditions. It provides a complementary approach for the C?H arylation of electron‐rich heteroarenes with aromatic amines affording a variety of heterobiaryls in moderate to good yields.     

Nickel‐Catalyzed C−H Chalcogenation of Anilines

The C?H thiolation of aniline derivatives was accomplished with a versatile nickel(II) catalyst under ligand‐free conditions. The robust nature of the nickel catalysis system was reflected by the C?H thiolation with a good functional group tolerance and an ample scope, employing anilines possessing removable directing groups. The widely applicable nickel catalyst also allowed for aniline C?H selenylations, while mechanistic studies provided strong support that the rate‐determining step is the C?H activation.     

Mixed Directing‐Group Strategy: Oxidative C−H/C−H Bond Arylation of Unactivated Arenes by Cobalt Catalysis

A mixed directing‐group strategy for inexpensive [Co(acac)₃]‐catalyzed oxidative C?H/C?H bond arylation of unactivated arenes has been disclosed. This strategy enables the arylation of a wide range of benzamide and arylpyridines effectively to afford novel bifunctionalized biaryls, which are difficult to achieve by common synthetic routes. Two different pathways, namely, a single‐electron‐transmetalation process (8‐aminoquinoline‐directed) and a concerted metalation–deprotonation process (pyridine‐directed), were involved to activate two different inert aromatic C?H bonds. Moreover, the aryl radicals have been trapped by 2,6‐di‐tert‐butyl‐4‐methylphenol to form benzylated products. This unique strategy should be useful in the design of other arene C?H/C?H cross‐couplings as well.     

Ligand‐Enabled Catalytic CH Arylation of Aliphatic Amines by a Four‐Membered‐Ring Cyclopalladation Pathway

A palladium‐catalyzed C? H arylation of aliphatic amines with arylboronic esters is described, proceeding through a four‐membered‐ring cyclopalladation pathway. Crucial to the successful outcome of this reaction is the action of an amino‐acid‐derived ligand. A range of hindered secondary amines and arylboronic esters are compatible with this process and the products of the arylation can be advanced to complex polycyclic molecules by sequential C? H activation reactions.     

Iron‐Catalyzed C?H Bond Activation for the ortho‐Arylation of Aryl Pyridines and Imines with Grignard Reagents

Direct arylation of the ortho‐C? H bond of an aryl pyridine or an aryl imine with an aryl Grignard reagent has been achieved by using an iron‐diamine catalyst and a dichloroalkane as an oxidant in a short reaction time (e.g., 5 min) under mild conditions (0 °C). The use of an aromatic co‐solvent, such as chlorobenzene and benzene, and slow addition of the Grignard reagent are essential for the high efficiency of the reaction. The present arylation reaction has distinct merits over the previously developed reaction that used an arylzinc reagent, such as its reaction rate and atom economy. Selective C? H bond activation occurs in the presence of a leaving group, such as a tosyloxy, chloro, and bromo group. Studies on a stoichiometric reaction and kinetic isotope effects shed light on the reaction intermediate and the C? H bond‐activation step.     

One‐Pot Tandem Photoredox and Cross‐Coupling Catalysis with a Single Palladium Carbodicarbene Complex

The combination of conventional transition‐metal‐catalyzed coupling (2 e^? process) and photoredox catalysis (1 e^? process) has emerged as a powerful approach to catalyze difficult cross‐coupling reactions under mild reaction conditions. Reported is a palladium carbodicarbene (CDC) complex that mediates both a Suzuki–Miyaura coupling and photoredox catalysis for C?N bond formation upon visible‐light irradiation. These two catalytic pathways can be combined to promote both conventional transition‐metal‐catalyzed coupling and photoredox catalysis to mediate C?H arylation under ambient conditions with a single catalyst in an efficient one‐pot process.     

An Enantioselective Bidentate Auxiliary Directed Palladium‐Catalyzed Benzylic C−H Arylation of Amines Using a BINOL Phosphate Ligand

A new enantioselective palladium(II)‐catalyzed benzylic C?H arylation reaction of amines is enabled by the bidentate picolinamide (PA) directing group. This reaction provides the first example of enantioselective benzylic γ‐C?H arylations of alkyl amines, and proceeds with up to 97 % ee. The 2,2′‐dihydroxy‐1,1′‐binaphthyl (BINOL) phosphoric acid ligand, Cs₂CO₃, and solvent‐free conditions are essential for high enantioselectivity. Mechanistic studies suggest that multiple BINOL ligands are involved in the stereodetermining C?H palladation step.