Iron-catalyzed C(sp(2))-H bond functionalization with organoboron compounds

Highly mono-selective ortho-trifluoromethylation of benzamides via 8-aminoquinoline assisted Cu-promoted C–H activations

A highly mono-selective ortho-trifluoromethylation of benzamides was achieved via Cu-promoted C–H activations employing an 8-aminoquinoline group as the bidentate directing group and Togni reagent II as the CF₃ source.

Cobalt-promoted selective arylation of benzamides and acrylamides with arylboronic acids

A novel cobalt-promoted arylation of aryl C–H bonds with arylboronic acids has been realized by using 8-aminoquinoline as the directing group. A notable feature of this newly developed protocol is that acrylamides, which cannot be arylated using copper salts as the promoter, can also be efficiently arylated.

Aminoquinoline-assisted vinylic C–H arylation of unsubstituted acrylamide for the selective synthesis of Z olefins

A method for Pd-catalyzed, aminoquinoline-directed arylation of vinylic C–H bonds with aryl iodides has been developed. This reaction represents a rare example of Pd-catalyzed vinylic C–H functionalization of unsubstituted acrylamide, allowing for preparation of Z-olefins.

Oxidative C-H Activation Approach to Pyridone and Isoquinolone through an Iron-Catalyzed Coupling of Amides with Alkynes

An iron catalyst combined with a mild organic oxidant promotes both C-H bond cleavage and C-N bond formation, and forms 2-pyridones and isoquinolones from an alkene- or arylamide and an internal alkyne, respectively. An unsymmetrical alkyne gives the pyridone derivative with high regioselectivity, this could be due to the sensitivity of the reaction to steric effects because of the compact size of iron.

Selective Alkenylation and Hydroalkenylation of Enol Phosphates through Direct C-H Functionalization

An efficient and selective Rh-catalyzed direct CH functionalization reaction of enol phosphates was developed. The method is applicable to a variety of coupling partners, including activated alkenes, alkynes, and allenes, and leads to the formation of various valuable alkenylated and hydroalkenylated enol phosphates through the action of the phosphate directing group. The versatility and utility of the coupling products were demonstrated through further transformations into synthetically useful building blocks.

Mono-Oxidation of Bidentate Bis-phosphines in Catalyst Activation: Kinetic and Mechanistic Studies of a Pd/Xantphos-Catalyzed C-H Functionalization

Kinetic, spectroscopic, crystallographic, and computational studies probing a Pd-catalyzed C-H arylation reaction reveal that mono-oxidation of the bis-phosphine ligand is critical for the formation of the active catalyst. The bis-phosphine mono-oxide is shown to be a hemilabile, bidentate ligand for palladium. Isolation of the oxidative addition adduct, with structural elucidation by X-ray analysis, showed that the mono-oxide was catalytically competent, giving the same reaction rate in the productive reaction as the Pd(II)/xantphos precursor. A dual role for the carboxylate base in both catalyst activation and reaction turnover was demonstrated, along with the inhibiting effect of excess phosphine ligand. The generality of the role of phosphine mono-oxide complexes in Pd-catalyzed coupling processes is discussed.

Iron-Catalyzed Directed C(sp(2))-H and C(sp(3))-H Functionalization with Trimethylaluminum

Conversion of a C(sp(2))-H or C(sp(3))-H bond to the corresponding C-Me bond can be achieved by using AlMe3 or its air-stable diamine complex in the presence of catalytic amounts of an inorganic iron(III) salt and a diphosphine along with 2,3-dichlorobutane as a stoichiometric oxidant. The reaction is applicable to a variety of amide substrates bearing a picolinoyl or 8-aminoquinolyl directing group, enabling methylation of a variety of (hetero)aryl, alkenyl, and alkyl amides. The use of the mild aluminum reagent prevents undesired reduction of iron and allows the reaction to proceed with catalyst turnover numbers as high as 6500.

Exploration of earth-abundant transition metals (Fe, Co, and Ni) as catalysts in unreactive chemical bond activations

Activation of inert chemical bonds, such as C-H, C-O, C-C, and so on, is a very important area, to which has been drawn much attention by chemists for a long time and which is viewed as one of the most ideal ways to produce valuable chemicals. Under modern chemical bond activation logic, many conventionally viewed "inert" chemical bonds that were intact under traditional conditions can be reconsidered as novel functionalities, which not only avoids the tedious synthetic procedures for prefunctionalizations and the emission of undesirable wastes but also inspires chemists to create novel synthetic strategies in completely different manners. Although activation of "inert" chemical bonds using stoichiometric amounts of transition metals has been reported in the past, much more attractive and challenging catalytic transformations began to blossom decades ago. Compared with the broad application of late and noble transition metals in this field, the earth-abundant first-row transition-metals, such as Fe, Co, and Ni, have become much more attractive, due to their obvious advantages, including high abundance on earth, low price, low or no toxicity, and unique catalytic characteristics. In this Account, we summarize our recent efforts toward Fe, Co, and Ni catalyzed "inert" chemical bond activation. Our research first unveiled the unique catalytic ability of iron catalysts in C-O bond activation of both carboxylates and benzyl alcohols in the presence of Grignard reagents. The benzylic C-H functionalization was also developed via Fe catalysis with different nucleophiles, including both electron-rich arenes and 1-aryl-vinyl acetates. Cobalt catalysts also showed their uniqueness in both aromatic C-H activation and C-O activation in the presence of Grignard reagents. We reported the first cobalt-catalyzed sp(2) C-H activation/arylation and alkylation of benzo[h]quinoline and phenylpyridine, in which a new catalytic pathway via an oxidative addition process was demonstrated to be much preferable. Another interesting discovery was the Co-catalyzed magnesiation of benzylic alcohols in the presence of different Grignard reagents, which proceeded via Co-mediated selective C-O bond activation. In C-O activation, Ni catalysts were found to be most powerful, showing the high efficacy in different kinds of couplings starting form "inert" O-based electrophiles. In addition, Ni catalysts exhibited their power in C-H and C-C activation, which have been proven by us and pioneers in this field. Notably, our developments indicated that the catalytic efficacy in cross coupling between aryl bromides and arenes under mild conditions was not the privilege of several noble metals; most of the transition metals exhibited credible catalytic ability, including Fe, Co, and Ni. We hope our studies inspire more interest in the development of first row transition metal-catalyzed inert chemical bond functionalization.

Stereo- and chemoselective cross-coupling between two electron-deficient acrylates: an efficient route to (Z,E)-muconate derivatives

A Ru-catalyzed direct oxidative cross-coupling reaction of acrylates was developed. It offers a straightforward and atom-economical protocol for the synthesis of functionalized (Z,E)-muconate derivatives in moderate to good yields with good stereo- and chemoselectivities. The conjugated muconates bearing differentiable terminal functionality can be selectively transformed into versatile synthetic intermediates widely used in organic synthesis.

Cobalt(III)-catalyzed synthesis of indazoles and furans by C-H bond functionalization/addition/cyclization cascades

The development of operationally straightforward and cost-effective routes for the assembly of heterocycles from simple inputs is important for many scientific endeavors, including pharmaceutical, agrochemical, and materials research. In this article we describe the development of a new air-stable cationic Co(III) catalyst for convergent, one-step benchtop syntheses of N-aryl-2H-indazoles and furans by C-H bond additions to aldehydes followed by in situ cyclization and aromatization. Only a substoichiometric amount of AcOH is required as an additive that is both low-cost and convenient to handle. The syntheses of these heterocycles are the first examples of Co(III)-catalyzed additions to aldehydes, and reactions are demonstrated for a variety of aromatic, heteroaromatic, and aliphatic derivatives. The syntheses of both N-aryl-2H-indazoles and furans have been performed on 20 mmol scales and should be readily applicable to larger scales. The reported heterocycle syntheses also demonstrate the use of directing groups that have not previously been applied to Co(III)-catalyzed C-H bond functionalizations. Additionally, the synthesis of furans demonstrates the first example of Co(III)-catalyzed functionalization of alkenyl C-H bonds.

Nickel-catalyzed synthesis of diarylsulfides and sulfones via C–H bond functionalization of arylamides

The sulfenylation and sulfonylation of (sp²)C–H bonds of benzamides were achieved with the aid of a bidentate directing group.

Copper catalysed amidation of aryl halides through chelation assistance

Using 8-aminoquinoline-based alkyl and aryl carboxamides, the direct N-arylation was achieved in good yields in the presence of a copper catalyst via chelation-assisted reaction.

Selective remote C–H sulfonylation of aminoquinolines with arylsulfonyl chlorides via copper catalysis

Copper-catalysed remote C−H bond sulfonylation of aminoquinolines using commercially available and inexpensive arylsulfonyl chlorides as the sulfonylation reagents is described.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.

Geminal bis(silane)-controlled regio- and stereoselective oxidative Heck reaction of enol ethers with terminal alkenes to give push–pull 1,3-dienes

A geminal bis(silane)-controlled regio- and stereoselective oxidative Heck reaction of enol ethers with terminal alkenes has been developed. The reaction proceeds with α,β-coupling regioselectivity to give push–pull Z,E-1,3-dienes in good yields.