Yanghui Zhang

Palladium-Catalyzed Benzylation of Carboxylic Acids with Toluene via Benzylic C–H Activation

Direct benzylation of carboxylic acids with toluene has been developed via palladium-catalyzed C-H acyloxylation under 1 atm of oxygen. This reaction demonstrates good functional group tolerance and high yields, providing a facile, atom-economic, and efficient method for the synthesis of benzyl esters.

Silver-catalyzed C-H trifluoromethylation of arenes using trifluoroacetic acid as the trifluoromethylating reagent.

Direct trifluoromethylation of arenes using TFA as the trifluoromethylating reagent was achieved with Ag as the catalyst. This reaction not only provides a new protocol for aryl C-H trifluoromethylation, but the generation of CF3· from TFA may prove useful in other contexts and could potentially be extended to other trifluoromethylation reactions.

Palladium-Catalyzed C–H Ethoxycarbonyldifluoromethylation of Electron-Rich Heteroarenes

The first Pd-catalyzed C-H ethoxycarbonyldifluoromethylation with BrCF2CO2Et has been developed. The use of a bidentate phosphine ligand (Xantphos) is critical for the reaction to occur. A variety of electron-rich heteroarenes, including indoles, furans, thiophenes, and pyrroles, can be ethoxycarbonyldifluoromethylated in moderate to excellent yields. The reactions take place at the C-H bonds adjacent to the heteroatoms with high regioselectivity. This method provides a new protocol for the introduction of difuoroalkyl groups into electron-rich heteroarenes.

An Approach to Tetraphenylenes via Pd-Catalyzed C–H Functionalization

Tetraphenylenes not only are theoretically and experimentally interesting but also have potential applications in a variety of fields such as materials science, supramolecular chemistry, and asymmetric catalysis. A facile and efficient approach is reported for the syntheis of tetraphenylene and its derivatives from 2-iodobiphenyls via Pd-catalyzed C-H activation. A range of substituted tetraphenylenes can be synthesized using this method, and the reaction can be performed on gram scale with relatively high efficiency, demonstrating its practical utility. This novel approach provides easy access to tetraphenylenes and should facilitate research on the application of this type of fascinating molecules.

Synthesis of Fluorenes Starting from 2-Iodobiphenyls and CH2Br2 through Palladium-Catalyzed Dual C–C Bond Formation

A facile and efficient approach is developed for the synthesis of fluorene and its derivatives starting from 2-iodobiphenyls and CH2Br2. A range of fluorene derivatives can be synthesized under relatively mild conditions. The reaction proceeds via a tandem palladium-catalyzed dual C-C bond formation sequence through the key dibenzopalladacyclopentadiene intermediates, which are obtained from 2-iodobiphenyls through palladium-catalyzed C-H activation.

Sequential Difunctionalization of 2-Iodobiphenyls by Exploiting the Reactivities of a Palladacycle and an Acyclic Arylpalladium Species

A novel sequential difunctionalization reaction of 2-iodobiphenyl has been developed by exploiting the distinct reactivities of a palladacycle and an acyclic arylpalladium species. In this tandem reaction, an in situ formed dibenzopalladacyclopentadiene reacts selectively with an alkyl halide, after which the thus formed acyclic arylpalladium species selectively undergoes a Heck reaction with an alkene. This work demonstrates the strong relationship between the coordination mode of a transition metal complex and its reactivity, which could shed light on the mechanisms of other transition-metal-catalyzed reactions and offer the opportunity to develop other synthetically enabling organic transformations.

Synthesis of Triphenylenes Starting from 2-Iodobiphenyls and Iodobenzenes via Palladium-Catalyzed Dual C–H Activation and Double C–C Bond Formation

A novel and facile approach for the synthesis of triphenylenes has been developed via palladium-catalyzed coupling of 2-iodobiphenyls and iodobenzenes. The reaction involves dual palladium-catalyzed C-H activations and double palladium-catalyzed C-C bond formations. A range of unsymmetrically functionalized triphenylenes can be synthesized with the reaction. The approach features readily available starting materials, high atom- and step-economy, and access to various unsymmetrically functionalized triphenylenes.

Palladium‐Catalyzed C−H Silylation through Palladacycles Generated from Aryl Halides

A highly efficient palladium-catalyzed disilylation reaction of aryl halides through C-H activation has been developed for the first time. The reaction has broad substrate scope. A variety of aryl halides can be disilylated by three types of C-H activation, including C(sp2 )-H, C(sp3 )-H, and remote C-H activation. In particular, the reactions are also unusually efficient. The yields are essentially quantitative in many cases, even in the presence of less than 1 mol % catalyst and 1 equivalent of the silylating reagent under relatively mild conditions. The disilylated biphenyls can be converted into disiloxane-bridged biphenyls.

3.23 Carbon–Carbon σ -Bond Formation via C H Bond Functionalization

Transition-metal-catalyzed C H functionalization has gained considerable interest and made noticeable progress during the past decades, because of its attractive advantages over traditional organic reactions relying on the transformation and conversion of functional groups. In this context, carbon–carbon σ-bond formation via C H activation has been a major focus of studies. In the presence of transition metals as catalysts, C H bonds can be transformed into C C bonds by reacting with a variety of reaction partners employed in traditional transition-metal-catalyzed cross-coupling reactions, including (pseudo)halides, organometallics, C C multiple bonds, and polar multiple bonds. Furthermore, dual C H activation has also gained much attention because it produces no chemical wastes other than hydrogen. A wide array of transition metals have been shown to be effective for C C bond formation via C H activation, which not only include palladium, rhodium, and ruthenium catalysts but also less expensive and toxic copper, iron, and nickel complexes.

Palladium-Catalyzed Alkylation with Alkyl Halides by C(sp3)−H Activation

Utilizing halogens as traceless directing goups represents an attractive strategy for C-H functionalization. A two C-H alkylation system, initiated by the oxidative addition of organohalides to Pd0 , has been developed. The first reaction involves an intermolecular alkylation of palladacycles to form C(sp3 )-C(sp2 ) bonds followed by C(sp2 )-H activation/cyclization to deliver alkylated benzocyclobutenes as the final products. In the second reaction, two C-C bonds are formed by the reaction of palladacycles with CH2 Br2 , and provides a facile and efficient method for the synthesis of indanes. The alkylated benzocyclobutene products can be transformed into tricyclic hyrocarbons, and the indane derivatives are essential structural motifs in bioactive and odorant molecules.