The first example for the ruthenium-catalyzed ligand-directed meta-selective C-H mono- and difluoromethylation is developed, affording a variety of new meta-mono- and difluoromethylated 2-phenylpyridines, 2-phenylpyrimidines, and 1-phenylpyrazoles in moderate-to-good yields. This new transformation exhibits broad substrate scope, good functional group tolerance, and high efficiency, and offers a practical approach to synthesize mono- and difluoromethylated arenes. Mechanistic studies indicate that a reaction pathway involving palladium-initiated radical species is involved in the catalytic cycle. The new dual catalytic system consisting of compatible ruthenium(II) and palladium(0) complexes enables the key processes of C-H activation and mono-/difluoromethyl-radical formation to occur and achieves the meta-selective functionalization efficiently. In addition, the present protocol can also be extended to non-fluoromethylation.

The direct decarboxylative meta-selective C−H acylation of a wide range of arenes is established via the ruthenium-catalyzed ortho-metalation strategy. This procedure, using Ru 3 (CO) 12 as the catalyst and α-oxocarboxylic acids as the acylation source, featured broad substrate scope, good functional group tolerance, and high regioselectivity. Mechanistic studies demonstrated that a radical process and an 18e-octahedral ruthenium species were involved in this reaction. The present work provides a new strategy for the regioselective metaacylation reactions and will be a powerful tool for the development of pharmaceutical and materials science.

A palladium-catalyzed decarboxylative ortho-acylation of tertiary benzamides with α-oxocarboxylic acids by weak O-coordination has been described. This reaction proceeds smoothly with a high monoacylation selectivity, affording ortho-acylated benzamides in moderate to good yields. When secondary benzamides are employed as the substrates, the formed ortho-acylated benzamides undergo further intramolecular cyclization to provide isoindolinone derivatives. In addition, several transformations of the synthesized ortho-acylated benzamides into a diversity of synthetically valuable products have been demonstrated.

Generally, steric tuning of the ortho positions of an aryl group and of the ligand backbone are the two major strategies to modify the ligand structure of an α-diimine system in the olefin polymerization field. In this study, a series of unsymmetrical dual steric α-diimine palladium and nickel complexes bearing bulky axial diarylmethyl moieties and an equatorial bulky dibenzobarrelene backbone were considered. The nickel complexes exhibited high activities (ca. 106 g/(mol h)) in ethylene polymerization even at 90 °C, yielding very high molecular weight (up to 1.27 million g/mol) polyethylenes with particularly high branching densities (up to 126/1000C). Interestingly, the resultant polyethylene products from Ni1 and Ni3–Ni5 with methyl substituents on the less bulky side showed very high branching densities even at high pressure and low temperature (104–121/1000C at 30 °C and 6 atm), and the branching density is hardly affected by the reaction temperature. Correspondingly, the palladium complexes Pd1 and Pd3–Pd5 displayed moderate activities (ca. 105 g/(mol h)), yielding highly branched polyethylene with a high molecular weight (up to 272 kg/mol) in ethylene polymerization. In comparison, complex Pd2 showed lower activities (ca. 104 g/(mol h)), generating lower branched polyethylene with a much lower molecular weight (1.7–3.2 kg/mol). Moreover, these palladium complexes exhibited low copolymerization activities and gave E-MA copolymers of low to moderate molecular weights (1–2 kg/mol with Pd2; 6–47 kg/mol with Pd1 and Pd3–Pd5) with average incorporation ratios (1.3–3.8 mol %). The bulky axial diarylmethyl substituents and equatorial bulky dibenzobarrelene backbone with a smaller steric o-methyl group on the less bulky side constitute a unique ligand environment conducive to chain walking in the nickel-catalyzed ethylene polymerization system.

The first palladium-catalyzed ortho-amidation of ketoximes has been developed with oxamic acids as the amidation source. The reaction with N-monosubstituted substrates undergoes further intramolecular cyclization to provide 3-methyleneisoindolinones.

The first cascade diastereoselective synthesis of oxazoloisoindolinones via the palladium-catalyzed decarboxylative ortho-acylation of N-benzoyl α-amino acid derivatives followed by double intramolecular cyclizations has been demonstrated. This reaction, using α-amino acids as directing groups and α-oxocarboxylic acids as the acylation source, features a broad substrate scope, good functional group tolerance, high regioselectivity, and excellent diastereoselectivity.

Transition metal-catalyzed C-H activation has attracted extensive attention because of its excellent functional group tolerance and high efficiency. Among them, palladium-catalyzed reactions exhibit versatile catalytic cycles and have mild conditions compared to others. Therefore, the palladium-catalyzed C-H activation has been employed broadly as a practical strategy in synthetic chemistry during the past decade. Since the first example of palladium-catalyzed decarboxylative C-H acylation using α-oxocarboxylic acids was reported in 2008, a lot of substrates have been employed to synthesize acylated products due to the easily available α-oxocarboxylic acids as well as the importance of acylation. However, the transition metal-catalyzed C-H esterification via decarbonylation is still limited. Our group previously developed the first directed C-H esterification of methyl ketoximes and 2-phenylpyridines by using potassium oxalate monoester as the decarboxylative reagent. Encouraged by this impressive result as well as the importance of salicylate derivatives in drug discovery, herein we disclose the efficient palladium-catalyzed decarboxylative esterification of 2-aryloxpyridines. This reaction proceeds smoothly with potassium oxalate monoester, affording the desired products in moderate to good yields (50%～82%). Compared to our previous work, the electron-donating pyridinyloxy (PyO) group as the directing group and six-membered metallocycle intermediate dramatically enhance the practicability and substrate tolerance of the present method. In addition, one of the products has been chosen as the model compound to deprotect the directing group to get the valuable salicylate derivative. The present method not only provides an efficient and convenient protocol for the synthesis of ethyl salicylate derivatives, but also enriches the diversity of Pd(II)/Pd(IV) catalytic reactions. A general procedure for the esterification of 2-aryloxypyridines 1 with potassium oxalate monoester 2 is as following: a mixture of 1 (0.5 mmol), Pd(OAc) 2 (10 mol%), K 2 S 2 O 8 (1.0 mmol), Ag 2 CO 3 (1.0 mmol), 2 (1.0 mmol), D-CSA (0.125 mmol), and 1,4-dioxane (2.5 mL) in a 25 mL tube was heated at 80 ℃ for a suitable time. The reaction mixture was cooled to room temperature, and concentrated in vacuo. Purification of the residue by column chromatography on silica gel with petroleum ether and ethyl acetate as the eluent provided the desired product 3.