Cobalt-catalyzed arylation of aldimines via directed C-H bond functionalization: addition of 2-arylpyridines and self-coupling of aromatic aldimines

A cobalt-N-heterocyclic carbene catalyst, in combination with an appropriate Grignard reagent, promotes a chelation-assisted aromatic C-H functionalization reaction via addition to an aromatic aldimine.     

Ruthenium-catalyzed direct C-H bond arylations of heteroarenes

Ruthenium-catalyzed C-H bond arylations of indoles, thiophenes, and pyrroles were accomplished in a highly chemo- and site-selective manner through the use of removable directing groups.     

Rhodium(III)-catalyzed arylation of Boc-imines via C-H bond functionalization

The first rhodium-catalyzed arylation of imines proceeding via C-H bond functionalization is reported. Use of a non-coordinating halide abstractor is important to obtain reactivity. Aryl-branched N-Boc-amines are formed, and a wide range of functionality is compatible with the reaction.     

Palladium-catalyzed direct C-H bond alkynylations of heteroarenes using gem-dichloroalkenes

Palladium-catalyzed direct alkynylations of heteroarenes were accomplished with inexpensive gem-dichloroalkenes as user-friendly electrophiles, which set the stage for a modular, step-economical synthesis of diversely decorated heteroaryl alkynes with ample scope.     

Metal-free, visible-light-mediated direct C-H arylation of heteroarenes with aryl diazonium salts

Visible light along with 1 mol % eosin Y catalyzes the direct C-H bond arylation of heteroarenes with aryl diazonium salts by a photoredox process. We have investigated the scope of the reaction for several aryl diazonium salts and heteroarenes. The general and easy procedure provides a transition-metal-free alternative for the formation of aryl-heteroaryl bonds.     

Iron-catalyzed direct arylation through directed C-H bond activation

An iron-catalyzed C-C bond formation reaction of a nitrogen-containing aromatic compound with an arylzinc reagent takes place at 0 degrees C in a good to quantitative yield. The reaction involves a C-H bond activation directed by a neighboring nitrogen atom. The important additives in this reaction are 1,10-phenanthroline, tetramethylethylenediamine, and 1,2-dichloro-2-methylpropane, in the absence of which a very low product yield was observed.     

Palladium-catalyzed C-N bond formation via direct C-H bond functionalization. Recent developments in heterocyclic synthesis

The formation of carbon-nitrogen bonds by reaction between a nitrogen atom and an unactivated carbon-hydrogen bond is a highly atom-economical process that attracted the attention of the chemists in the last two decades. The widely useful amination and hydroamination reactions, which furnish acyclic or cyclic products, give access to various nitrogen-containing basic and fine chemicals. This review highlights recent progress in the development of palladium-catalyzed reactions that occur by direct functionalization of simple carbon-hydrogen bonds to give heterocyclic products. Pd(0)- and Pd(II)-catalyzed reactions are described separately, emphasizing the different behavior of the metal in these two oxidation states.     

Arylation of heterocycles via rhodium-catalyzed C-H bond functionalization

[reaction: see text] A new method for the rhodium-catalyzed arylation of a variety of heterocycles has been developed. The reaction provided moderate to good yields of the arylated products. A preliminary mechanistic investigation of this reaction revealed the intermediacy of an isolable N-heterocyclic carbene complex.     

Palladium(0) nanoparticles-catalyzed ligand-free direct arylation of benzothiazole via C-H bond functionalization

Palladium nanoparticles, generated in situ efficiently catalyzes direct 2-C-H arylation of benzothiazole without requirement of any ligand. A wide range of substituted aryl and heteroaryl iodides participate in this reaction producing a series of 2-aryl/heteroaryl-benzothiazoles in high yields.     

Palladium-catalyzed C-H bond direct alkynylation of 5-membered heteroarenes: a well-defined synthetic route to azole derivatives containing two different alkynyl groups

A widely applicable oxidative coupling of 5-membered heteroarenes and terminal alkynes that uses a combination of palladium and silver salts was developed. Under suitable conditions, imidazole and benzimidazole, which are sluggish under similar previously reported oxidative coupling conditions, as well as imidazo[1,5-a]pyridines, oxazole, benzoxazole, thiazole, and benzothiazole could be alkynylated. In addition, the bromine atom on the substrates was intact under the reaction conditions, and conventional Sonogashira coupling did not occur at all. With these reactivities in hand, a well-defined synthetic route to imidazo[1,5-a]pyridines and thiazole containing two different alkynyl groups was achieved in a simple manner. In addition, linear correlations were observed between the fluorescence wavelength and the Hammett substituent constants of aryl groups, not only on the C1- but also on the C3-alkynyl group of the obtained 1,3-bis(arylethynyl)imidazo [1,5-a]pyridines.     

Base-mediated intermolecular sp2 C-H bond arylation via benzyne intermediates

A transition-metal-free method for arylation of heterocycle and arene carbon-hydrogen bonds by aryl chlorides and fluorides has been developed. The reactions proceed via aryne intermediates and are highly regioselective with respect to the C-H bond coupling component.     

Copper-catalyzed direct C-H oxidative trifluoromethylation of heteroarenes

This article describes the copper-catalyzed oxidative trifluoromethylation of heteroarenes and highly electron-deficient arenes with CF(3)SiMe(3) through direct C-H activation. In the presence of catalyst Cu(OAc)(2), ligand 1,10-phenanthroline and cobases tert-BuONa/NaOAc, oxidative trifluoromethylation of 1,3,4-oxadiazoles with CF(3)SiMe(3) proceeded smoothly using either air or di-tert-butyl peroxide as an oxidant to give the corresponding trifluoromethylated 1,3,4-oxadiazoles in high yields. Di-tert-butyl peroxide was chosen as the suitable oxidant for oxidative trifluoromethylation of 1,3-azoles and perfluoroarenes. Cu(OH)(2) and Ag(2)CO(3) were the best catalyst and oxidant for direct oxidative trifluoromethyaltion of indoles. The optimum reaction conditions enable oxidative trifluoromethylation of a range of heteroarenes that bear numerous functional groups. The prepared trifluoromethylated heteroarenes are of importance in the areas of pharmaceuticals and agrochemicals. The preliminary mechanistic studies of these oxidative trifluoromethylations are also reported.     

Mechanism of the rhodium(III)-catalyzed arylation of imines via C-H bond functionalization: inhibition by substrate

Rh(III)-catalyzed arylation of imines provides a new method for C-C bond formation while simultaneously introducing an α-branched amine as a functional group. This detailed mechanistic study provides insights for the rational future development of this new reaction. Relevant intermediate Rh(III) complexes have been isolated and characterized, and their reactivities in stoichiometric reactions with relevant substrates have been monitored. The reaction was found to be first order in the catalyst resting state and inverse first order in the C-H activation substrate.     

Pd-Catalyzed C-3 functionalization of indolizines via C-H bond cleavage

New transition metal-catalyzed methods for the arylation of indolizines by the direct cleavage of C-H bonds have been developed. A wide range of aryltrifluoroborate salts react with indolizines in the presence of Pd(OAc)(2) catalyst and AgOAc oxidant to give the arylated indolizines in high yields. Both electron-donating and electron-withdrawing groups perform smoothly while bromide and chlorine substituents are tolerated. In addition, the indolizines display similar reactivities in the Pd-catalyzed reaction with 3-phenylpropiolic acid to afford the corresponding C-3 alkynylated indolizines. These methods allow the direct functionalization of indolizines in one step.     

Sequential hydrocarbon functionalization: allylic C-H oxidation/vinylic C-H arylation

A Pd(II)/sulfoxide-catalyzed sequential allylic C-H oxidation/vinylic C-H arylation of alpha-olefins to furnish E-arylated allylic esters in high regio- and E:Z selectivities (>20:1) is reported. The broad scope of this method with respect to the alpha-olefin, carboxylic acid, and aryl boronic acid enables the rapid assembly of densely functionalized fragments for complex molecule synthesis from cheap, abundant hydrocarbon starting materials. The Pd(II)/sulfoxide-catalyzed vinylic C-H arylation of electronically unbiased olefins with aryl boronic acids proceeds under oxidative, acidic conditions and mild temperatures (room temperature to 45 degrees C).