Palladium-Catalyzed Para-Selective Difluoromethylation of Arene Esters.

Highly efficient, palladium-catalyzed, para-selective difluoromethylation of arene esters has been developed using [1,1'-biphenyl]-2-dicyclohexylphosphine as the effective ligand. A wide variety of arene esters bearing various functional groups were all compatible with the reaction conditions, leading to para-difluoromethylated products in moderate to good yields. Moreover, benzoylamide and benzenesulfonamide were also well-tolerated, suggesting that this novel catalyst system has broad applications to a variety of substrates.

A Ligand-Enabled Palladium-Catalyzed Highly para-Selective Difluoromethylation of Aromatic Ketones.

A practical and highly para-selective C-H difluoromethylation of aromatic ketones has been developed by employing tetrakis(triphenylphosphine)palladium(0) as the catalyst and triphenylphosphine as the ligand. In addition to general aromatic ketones, this transformation was compatible with bioactive compounds and well-known drugs, such as oxybenzone, ketoprofen, zaltoprofen, and propafenone. Moreover, a mechanistic study revealed that a palladium intermediate coordinated by a carbonyl group promotes highly para-selective difluoromethylation.

Ruthenium(II)-Catalyzed C-H Difluoromethylation of Ketoximes: Tuning the Regioselectivity from the meta to the para Position.

A highly para-selective CAr -H difluoromethylation of ketoxime ethers under ruthenium catalysis has been developed. A wide variety of ketoxime ethers are compatible with the reaction, which leads to the corresponding para-difluoromethylated products in moderate to good yield. A mechanistic study clearly showed that chelation-assisted cycloruthenation is the key factor in the para selectivity of the difluoromethylation of ketoxime ethers. Density functional theory was used to gain a theoretical understanding of the para selectivity.

Ligand-Controlled Selective Synthesis of Indoles and Benzofurans from Secondary Anilines.

A ligand-controlled method for the selective synthesis of indoles and benzofurans from secondary anilines has been discovered. A six-ring palladacycle intermediate may be involved in this process by olefins as a transient directing mediator to give indoles. The indole/benzofuran ratio can be easily tuned by the MPAA ligand. Various substituted secondary anilines were well-tolerated, affording the corresponding products in moderate to good yields. Indole-derived drugs such as JWH-081, BB-22, and ML-098 could be obtained using our new method to achieve their precursors. Preliminary mechanistic studies indicated that BQ is the key factor in avoiding the ß-H elimination of insertion species.

Ligand-Enabled ortho-Selective C-H Olefination of Tertiary Aniline Derivatives.

A highly ortho-selective CAr-H olefination of tertiary anilines without a directing group was developed. This reaction tolerated various substituted arenes and olefin coupling partners, affording ortho-olefination products in moderate to good yields. Preliminary mechanistic studies showed that N-Ac-d-Ala, Ag2CO3, and BQ were the key factors for tuning the regioselectivity from para to ortho. Density functional theory was used to achieve a theoretical understanding of the ortho selectivity.

A Direct Approach to Decoration of Bioactive Compounds via C-H Amination Reaction.

The development of new methods to achieve the direct synthesis of bioactive organic molecules is always an important topic in organic synthesis. We hereby demonstrate that N-methoxyamide is an excellent amino source in the iridium-catalyzed intermolecular C-H amination reaction. The linkage of two bioactive organic molecules can be well achieved with this new protocol. More than 20 examples of decorated bioactive compounds were reported, which can facilitate the discovery of new bioactive molecules.

Highly Site-Selective Formation of Perfluoroalkylated Anilids via a Protecting Strategy by Molybdenum Hexacarbonyl Catalyst.

Introducing a perfluoroalkyl group on the aromatic ring with high site selectivity remains a challenging area in organofluorine chemistry. We herein report a highly para-selective C-H perfluoroalkylation of aniline substrates using the molybdenum hexacarbonyl catalyst. Various substituted anilids derived from anilids were well-tolerated, affording the corresponding products in moderate to good yields. Preliminary mechanism studies and density functional theory calculations revealed the coordination of Mo catalyst with amides as the key factor to realize para selectivity.

Palladium-Catalyzed Carboxylate-Assisted Ethoxycarboxylation of Aromatic Acids To Synthesize Monoethyl Phthalate Derivatives with Ethyl Bromodifluoroacetate.

A novel and efficient approach for direct carbonation of aromatic acids with ethyl bromodifluoroacetate as the carbonyl source is reported. A broad range of substrates bearing various functional groups were tolerated, leading to monoalkyl phthalate derivatives in moderate to good yields.

Ruthenium(II)-enabled para-selective C-H difluoromethylation of anilides and their derivatives.

Transition-metal-catalyzed direct site-selective functionalization of arene C-H bonds has emerged as an innovative approach for building the core structure of pharmaceutical agents and other versatile complex compounds. However, para-selective C-H functionalization has seldom been explored, only a few examples, such as steric-hindered arenes, electron-rich arenes, and substrates with a directing group, have been reported to date. Here we describe the development of a ruthenium-enabled para-selective C-H difluoromethylation of anilides, indolines, and tetrahydroquinolines. This reaction tolerates various substituted arenes, affording para-difluoromethylation products in moderate to good yields. Results of a preliminary study of the mechanism indicate that chelation-assisted cycloruthenation might play a role in the selective activation of para-CAr-H bonds. Furthermore, this method provides a direct approach for the synthesis of fluorinated drug derivatives, which has important application for drug discovery and development.

Rhodium(III)-Catalyzed Selective Monoarylation of ß or γ C(sp3)-H Bonds Assisted by a Trimethylpyrazole Group.

The selective arylation of unactivated ß or challenging γ primary and secondary ß-C(sp3)-H bonds has been developed with a Cp*Rh(III) catalyst assisted by a trimethylpyrazole group. A rarely reported six-membered rhodacycle has been identified in rhodium-catalyzed C(sp3)-H activation reactions. Preliminary mechanistic studies have revealed that a concerted metalation-deprotonation pathway might be involved in the C-H activation step.

Pd-catalysed ligand-enabled carboxylate-directed highly regioselective arylation of aliphatic acids.

α-amino acids bearing aromatic side chains are important synthetic units in the synthesis of peptides and natural products. Although various ß-C-H arylation methodologies for amino acid derivatives involving the assistance of directing groups have been extensively developed, syntheses that directly employ N-protected amino acids as starting materials remain rare. Herein, we report an N-acetylglycine-enabled Pd-catalysed carboxylate-directed ß-C(sp3)-H arylation of aliphatic acids. In this way, various non-natural amino acids can be directly prepared from phthaloylalanine in one step in good to excellent yields. Furthermore, a series of aliphatic acids have been shown to be amenable to this transformation, affording ß-arylated propionic acid derivatives in moderate to good yields. More importantly, this ligand-enabled direct ß-C(sp3)-H arylation could be easily scaled-up to 10 g under reflux conditions, highlighting the potential utility of this synthetic method.

Transformation of masked benzyl alcohols to o-aminobenzaldehydes through C-H activation: a facile approach to quinazolines.

Direct transformation of a directing group to important synthetic units would provide a high atom efficiency synthetic approach in synthetic chemistry. Herein, a convenient protocol for the synthesis of o-aminobenzaldehyde and benzoxazole derivatives from benzyl alcohols has been developed by employing (N,N-dimethyl)oxamoyl amide as a directing group in a palladium-catalyzed intramolecular amination. Furthermore, the attached directing center may not only be transformed into the product, but may also be further applied to generate synthetically important quinazoline and quinoline units. Finally, a high atom efficiency one-pot, two-step approach to form quinazolines from benzyl alcohol derivatives has been achieved in good yields, thus demonstrating its high utility.

Rhodium(III)-Catalyzed Oxidative C-H/C-H Cross-Coupling of Heteroarenes and Masked Benzylamines.

The first example of oxidative C-H/C-H cross-coupling of oxalyl amide-protected benzylamines and various heteroarenes in the presence of a rhodium(III) catalyst has been developed. The route provides a means of synthesizing ortho-heteroarylated benzylamines. The methodology presents broad substrate scope, great functional group tolerance, and good to excellent yields in the synthesis of substituted benzylamines. The study also reveals that the thienoisoquinoline derivatives can be accessed through the intramolecular amination of thiophenyl-substituted benzylamines with palladium(II).

Polyoxometalate supported complexes as effective electron-transfer mediators in dye-sensitized solar cells.

Two Anderson-type heteropolyanion-supported copper phenanthroline redox couples have been successfully introduced into dye-sensitized solar cells, which can significantly increase the short-circuit photocurrent, open-circuit voltage and the conversion efficiency by 2.2 times, 26.8% and 3.93 times respectively, compared to the pristine copper phenanthroline redox couple.