Recent Advances in Palladium‐Catalyzed Cross‐Coupling Reactions at ppm to ppb Molar Catalyst Loadings

The development of nanoparticle–polymer-hybrid-based heterogeneous catalysts with high reactivity and good recyclability is highly desired for their applications in the chemical and pharmaceutical industries. Herein, we have developed a novel synthetic strategy by choosing a predesigned metal-anchored building block for in situ generation of metal (Pd) nanoparticles in the stable, porous, and crystalline covalent organic framework (COF), without using conventional reducing agents. In situ generation of Pd nanoparticles in the COF skeleton is explicitly confirmed from PXRD, XPS, TEM images, and 15N NMR spectral analysis. This hybrid material is found to be an excellent reusable heterogeneous catalyst for the synthesis of biologically and pharmaceutically important 2-substituted benzofurans from 2-bromophenols and terminal alkynes via a tandem process with the turnover number up to 1101. The heterogeneity of the catalytic process is unambiguously verified by a mercury poisoning experiment and leaching test....

Predesigned Metal-Anchored Building Block for In Situ Generation of Pd Nanoparticles in Porous Covalent Organic Framework: Application in Heterogeneous Tandem Catalysis

(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.

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex-catalyzed direct C-H bond arylation of (benz)imidazoles with aryl chlorides.

A novel and efficient palladium-catalyzed cascade annulation/arylthiolation reaction has been developed to afford functionalized 3-sulfenylbenzofuran and 3-sulfenylindole derivatives in moderate to good yields from readily available 2-alkynylphenols and 2-alkynylamines in ionic liquids. This protocol provides a valuable synthetic tool for the assembly of a wide range of 3-sulfenylbenzofuran and 3-sulfenylindole derivatives with high atom- and step-economy and exceptional functional group tolerance. Moreover, the employment of ionic liquids under mild reaction conditions makes this transformation green and practical. Furthermore, this approach enriched current C–S bond formation chemistry, making a valuable and practical method in synthetic and medicinal chemistry.

Assembly of 3-Sulfenylbenzofurans and 3-Sulfenylindoles by Palladium-Catalyzed Cascade Annulation/Arylthiolation Reaction

A very easy method is described here for direct preparation of palladium(II) carboxymethylcellulose (CMC-PdII) by ion exchange of sodium carboxymethylcellulose (CMC-Na) and PdCl2. When the resulting CMC-PdII was employed as a catalyst in Suzuki−Miyaura and Mizoroki−Heck cross-coupling reactions, PdII was reduced in situ to Pd0 and further grown on CMC to afford carboxymethylcellulose-supported palladium nanoparticles (CMC-Pd0). The as-generated CMC-Pd0 proved to be an efficient catalyst for these mentioned cross-coupling reactions under mild aerobic conditions. The CMC-PdII and CMC-Pd0 were fully characterized by FT-IR, ICP-AES, XPS, XRD, SEM, EDX, TEM, and TGA. The characterized results demonstrated that the true catalytic species are Pd0 nanoparticles. Moreover, the catalyst showed no significant loss of efficiency after six catalytic cycles.

Carboxymethylcellulose-Supported Palladium Nanoparticles Generated in Situ from Palladium(II) Carboxymethylcellulose: An Efficient and Reusable Catalyst for Suzuki–Miyaura and Mizoroki–Heck Reactions

One-pot synthesis of 2-substituted benzo[b]furans via Pd–tetraphosphine catalyzed coupling of 2-halophenols with alkynes

Palladium nanoparticles generated from allylpalladium chloride in situ: A simple and highly efficient catalytic system for Mizoroki–Heck reactions

A simple and efficient strategy for the synthesis of 1-propenylnaphthols from readily accessible 3-arylallylnaphthyl ethers has been developed. By using K2CO3 as base and 2-methoxyethanol as solvent, direct access to a wide range of 1-propenylnaphthols can be achieved in generally good yield (up to 99%) with high stereoselectivity toward the Z isomer. The control experiments indicate that the reaction proceeds through a sequential Claisen rearrangement/isomerization process. Furthermore, starting from the same material, the highly valuable 3-arylnaphtho[2,1-b]furans can be obtained in N,N-dimethylformamide and in the presence of Ag2O as the oxidant via a one-pot sequential Claisen rearrangement/isomerization/cyclization reaction. Mechanistic studies confirm that 1-propenylnaphthols are the key intermediates to form the 3-arylnaphtho[2,1-b]furans. In addition, these two operationally simple and practical protocols could be scaled up to a gram level.

An Approach to the Synthesis of 1-Propenylnaphthols and 3-Arylnaphtho[2,1-b]furans.

A Simple and Efficient Access to Naphtho[b]furans by Claisen Rearrangement/Cyclization of Bromonaphthyl 3‐Phenylallyl Ethers

The use of iodonaphtalene (IX) as arylating agent affords the corresponding enol ether (X) instead of allyl aryl ethers.

Wei Wang

Papers

One-pot synthesis of 2-substituted benzo[b]furans via Pd–tetraphosphine catalyzed coupling of 2-halophenols with alkynes

Palladium nanoparticles generated from allylpalladium chloride in situ: A simple and highly efficient catalytic system for Mizoroki–Heck reactions

An Approach to the Synthesis of 1-Propenylnaphthols and 3-Arylnaphtho[2,1-b]furans.

A Simple and Efficient Access to Naphtho[b]furans by Claisen Rearrangement/Cyclization of Bromonaphthyl 3‐Phenylallyl Ethers

An Efficient Palladium‐Catalyzed Synthesis of Cinnamyl Ethers from Aromatic Halides, Phenols, and Allylic Chloride