NHC-Pd(II)-Im complex showed efficient catalytic activity toward the direct CH bond arylation of (benzo)thiophenes with the challenging aryl chlorides. Under the suitable conditions, all reactions proceeded smoothly to give the desired CH bond arylated products in acceptable to high yields, giving an inexpensive and alternative methodology for the arylation of (benzo)thiophenes.

We herein reported the N-heterocyclic carbene–palladium(II)–1-methylimidazole complex catalyzed direct C–H bond arylation of imidazo[1,2-a]pyridines with aryl chlorides. Under suitable conditions, all reactions between various imidazo[1,2-a]pyridines and aryl chlorides worked well to give the desired C3–H arylated products in acceptable to high yields, giving a convenient and alternative method for the direct C–H bond arylation of imidazo[1,2-a]pyridines, using economic and easily available aryl chlorides as the arylating reagents.

NHC–Pd(II)–Im complex 1 has proven to be an efficient catalyst in the reaction between tetralones 2 and aryl chlorides 3, giving the α-arylated tetralones 4 in good to high yields. In addition, if the above reaction mixture was exposed to air at room temperature for another 3 h, the normal α-arylated products 4 can be fully oxidized to 2-aryl-2′-hydroxytetralones 6 in good yields in a one-pot procedure. Furthermore, if the reaction mixture containing the oxidized products 6 was treated with TsOH/toluene solution under reflux for 19 h, the final aromatized products, 2-aryl-naphthalen-1-ols 5 can be achieved in acceptable to moderate yields. All reactions can tolerate various substituents on the tetralones 2 and aryl chlorides 3, thus giving an efficient method for the α-arylation of tetralones and further transformation of the products, and also enriching the applications of NHC–Pd(II) complexes in organic synthesis.

The first example of sole direct C–H bond arylation of benzo[b]furans with aryl chlorides was achieved catalyzed by a well-defined NHC-Pd(II)-Im complex. Under the suitable conditions, all reactions involving kinds of benzo[b]furans and (hetero)aryl chlorides proceeded well to give the desired C2-arylated benzo[b]furans in sole regioselectivity in acceptable to high yields, providing an efficient and economic pathway for the direct C2–H bond arylation of benzo[b]furans.

The first example of phosphine-free, NHC–Pd(II) complex catalyzed direct C–H bond benzylation of (benzo)oxazoles with benzyl chlorides was reported in this paper. Under the suitable conditions, all reactions worked well enough to give the desired C2-benzylated products in good to almost quantitative yields, providing a facile and straight pathway for the C–H bond benzylation of (benzo)oxazoles within short time.

The direct C–H bond arylation of (benzo)oxazoles with aryl chlorides was achieved catalyzed by a well-defined NHC–Pd(II)–Im complex. Under the optimal conditions, various aryl chlorides were successfully applied as the arylating reagents to achieve the 2-aryl (benzo)oxazoles in acceptable to high yields, providing a convenient and alternative method for the direct C–H bond arylation of (benzo)oxazoles and enriching the chemistry of the NHC–Pd(II) complex in organic synthesis.

We report here the NHC–Pd(II)–Im complex 1-catalyzed direct C–H bond functionalization of the C9 position of fluorenes with aryl chlorides and further transformation of the resulting products in a one-pot procedure. Under the optimal conditions, arylated fluorenes can be obtained in moderate to almost quantitative yields using various activated and unactivated (hetero)aryl chlorides as the arylating reagents. Furthermore, if the mixture from the arylation reaction is exposed to air, the C9-oxidized products can be obtained in acceptable to good yields in a one-pot procedure. In addition, alkyl groups can also be efficiently introduced to the above mixture from the arylation reaction, producing further C9-alkylated products in good to almost quantitative yields in a one-pot procedure, thus providing an expedient, inexpensive and practical strategy for the mono- and di-functionalization of fluorenes.

(Benz)imidazoles can be efficiently functionalized by (hetero)aryl chlorides via direct C–H bond arylation in the presence of a well-defined NHC-Pd(II)-Im complex. Under the optimal conditions, various activated, unactivated, and deactivated (hetero)aryl chlorides were successfully applied as the arylating reagents to achieve the 2-(hetero)aryl (benz)imidazoles in acceptable to high yields, giving a facile and alternative methodology for the direct C–H bond arylation of (benz)imidazoles.

NHC-Pd(II)-Im complex 1 was found to be an effective catalyst for the α-arylation of unprotected oxindoles with aryl chlorides to give products 4 in 44–98% yields under a N2 atmosphere. Furthermore, if the reactions were first performed under conditions identical to those for the α-arylation reaction for 12 h and then exposed to air for another 3 h, 3-aryl-3-hydroxy-2-oxindoles 5 can be obtained in 49–84% yields in a one-pot procedure.

The two-component, three-molecule reactions between 2,3-dihydroinden-1-ones and aryl chlorides were achieved in the presence of an NHC–Pd(II)–Im complex. Under the optimal conditions, all reactions performed well to give the corresponding products in moderate to high yields.

Readily available NHC–Pd(II)–Mp complexes 2 showed efficient catalytic activity toward the Suzuki–Miyaura coupling of aryl sulfamates with arylboronic acids or potassium phenyltrifluoroborate, giving the expected coupling products in good to high yields. It should be noted that this is the first example so far of the phosphine-free, NHC–Pd(II) complexes catalyzed Suzuki–Miyaura coupling of aryl sulfamates with arylboronic acids.

Although they are highly strained, methylenecyclopropanes (MCPs) are readily accessible molecules that have served as useful building blocks in organic synthesis. MCPs can undergo a variety of ring-opening reactions because the release of cyclopropyl ring strain (40 kcal/mol) can provide a thermodynamic driving force for reactions and the π-character of the bonds within the cyclopropane can afford the kinetic opportunity to initiate the ring-opening. Since the 1970s, the chemistry of MCPs has been widely explored in the presence of transition metal catalysts, but less attention had been paid to the Lewis or Brønsted acid mediated chemistry of MCPs. During the past decade, significant developments have also been made in the Lewis or Brønsted acid mediated reactions of MCPs. This Account describes chemistry developed in our laboratory and by other researchers.Lewis and Brønsted acids can be used as catalysts or reagents in the reactions of MCPs with a variety of substrates, and substituents on the terminal methylene or on the cyclopropyl ring of MCPs significantly affect the reaction pathways. During the past decade, we and other researchers have found interesting transformations based on this chemistry. These new reactions include the ring expansion of MCPs, cycloaddition reactions of MCPs with aldehydes and imines, cycloaddition reactions of MCPs with nitriles in the presence of strong Brønsted acid, radical reactions of MCPs with 1,3-dicarbonyl compounds, intramolecular Friedel–Crafts reactions of MCPs with arenes, acylation reactions of MCPs, and the reaction of MCPs with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers.These Lewis or Brønsted acid mediated reactions of MCPs can produce a variety of new compounds such as cyclobutanones, indenes, tetrahydrofurans, and tetrahydroquinolines. Finally, we have also carried out computational studies to explain the mechanism of the Brønsted acid mediated reactions of MCPs with acetonitrile.

A well-defined NHC–Pd(II)–Im complex 1 was found to be an effective catalyst for the Suzuki–Miyaura coupling of aryl sulfonates including tosylates and phenylsulfonates with arylboronic acids, giving the desired coupling products in good to high yields. Acceptable yields can also be achieved even by using the less reactive mesylates as the substrates. It is worthy of noting here that this is the first example of NHC–Pd(II) complex-catalyzed Suzuki–Miyaura coupling of aryl sulfonates with arylboronic acids, enriching an inexpensive, convenient, and alternative method for the synthesis of biaryl compounds.

We report herein that amides are excellent N-sources in the NHC–Pd(II)–Im complex 1 catalyzed amination of aryl chlorides. In the presence of KOtBu, various aryl chlorides and amides can react smoothly to give the corresponding aminated products in moderate to almost quantitative yields at room temperature within 6 h.

N-Heterocyclic carbene–rhodium(I) complexes derived from N-benzyl substituted proline have been successfully synthesized and were found to be efficient catalysts for the 1,4-conjugate addition of arylboronic acids to enones in neat water at 40 °C. Under the optimal reaction conditions, all reactions gave the addition products in good to high yields.

The PdCl2-promoted reactions of methylenecyclopropanes (MCPs) 1 bearing diaryl substituents on the terminal double bond were carefully investigated. The solvents employed significantly affected the reaction outcomes. It was found that dimeric allylpalladium(II) complexes 2a–2f can be obtained as the sole products in acceptable to good yields under mild reaction conditions with THF as the solvent, while dimeric allylpalladium(II) complexes 2a–2f along with another type of dimeric allylpalladium(II) complexes 4a–4e can be obtained in good to high total yields if N,N-dimethylacetamide (DMAc) was used as the solvent. Moreover, using N,N-dimethylformamide (DMF) as the solvent in the presence of water, it was found that water can also participate in the reaction to form another type of dimeric allylpalladium(II) complex 6 as the minor product. All of these dimeric allylpalladium(II) complexes reported in the paper have been characterized by X-ray crystal structure diffraction.

We report here the NHC–Pd(II)–Im complex 1-catalyzed direct C–H bond functionalization of the C9 position of fluorenes with aryl chlorides and further transformation of the resulting products in a one-pot procedure. Under the optimal conditions, arylated fluorenes can be obtained in moderate to almost quantitative yields using various activated and unactivated (hetero)aryl chlorides as the arylating reagents. Furthermore, if the mixture from the arylation reaction is exposed to air, the C9-oxidized products can be obtained in acceptable to good yields in a one-pot procedure. In addition, alkyl groups can also be efficiently introduced to the above mixture from the arylation reaction, producing further C9-alkylated products in good to almost quantitative yields in a one-pot procedure, thus providing an expedient, inexpensive and practical strategy for the mono- and di-functionalization of fluorenes.

The PdCl2-promoted reactions of methylenecyclopropanes (MCPs) 1 bearing diaryl substituents on the terminal double bond were carefully investigated. The solvents employed significantly affected the reaction outcomes. It was found that dimeric allylpalladium(II) complexes 2a–2f can be obtained as the sole products in acceptable to good yields under mild reaction conditions with THF as the solvent, while dimeric allylpalladium(II) complexes 2a–2f along with another type of dimeric allylpalladium(II) complexes 4a–4e can be obtained in good to high total yields if N,N-dimethylacetamide (DMAc) was used as the solvent. Moreover, using N,N-dimethylformamide (DMF) as the solvent in the presence of water, it was found that water can also participate in the reaction to form another type of dimeric allylpalladium(II) complex 6 as the minor product. All of these dimeric allylpalladium(II) complexes reported in the paper have been characterized by X-ray crystal structure diffraction.

Readily available NHC–Pd(II)–Mp complexes 2 showed efficient catalytic activity toward the Suzuki–Miyaura coupling of aryl sulfamates with arylboronic acids or potassium phenyltrifluoroborate, giving the expected coupling products in good to high yields. It should be noted that this is the first example so far of the phosphine-free, NHC–Pd(II) complexes catalyzed Suzuki–Miyaura coupling of aryl sulfamates with arylboronic acids.

NHC–Pd(II)–Im complex 1 has proven to be an efficient catalyst in the reaction between tetralones 2 and aryl chlorides 3, giving the α-arylated tetralones 4 in good to high yields. In addition, if the above reaction mixture was exposed to air at room temperature for another 3 h, the normal α-arylated products 4 can be fully oxidized to 2-aryl-2′-hydroxytetralones 6 in good yields in a one-pot procedure. Furthermore, if the reaction mixture containing the oxidized products 6 was treated with TsOH/toluene solution under reflux for 19 h, the final aromatized products, 2-aryl-naphthalen-1-ols 5 can be achieved in acceptable to moderate yields. All reactions can tolerate various substituents on the tetralones 2 and aryl chlorides 3, thus giving an efficient method for the α-arylation of tetralones and further transformation of the products, and also enriching the applications of NHC–Pd(II) complexes in organic synthesis.

We herein reported the N-heterocyclic carbene–palladium(II)–1-methylimidazole complex catalyzed direct C–H bond arylation of imidazo[1,2-a]pyridines with aryl chlorides. Under suitable conditions, all reactions between various imidazo[1,2-a]pyridines and aryl chlorides worked well to give the desired C3–H arylated products in acceptable to high yields, giving a convenient and alternative method for the direct C–H bond arylation of imidazo[1,2-a]pyridines, using economic and easily available aryl chlorides as the arylating reagents.