Jingbo Lan

Palladium(II)-Catalyzed Oxidative C−H/C−H Cross-Coupling of Heteroarenes

An efficient methodology for the synthesis of unsymmetrical biheteroaryl molecules has been developed via Pd(II)-catalyzed oxidative C-H/C-H cross-coupling of heteroarenes. An inversion in reactivity and selectivity has been achieved successfully to perform the desired heterocoupling. This process allows the heterocoupling of not only electron-rich N-containing heteroarenes (e.g., xanthines, azoles, and indolizines) but also electron-poor pyridine N-oxides with various thiophenes or furans.

Copper-Catalyzed Direct C Arylation of Heterocycles with Aryl Bromides: Discovery of Fluorescent Core Frameworks†

A window of opportunity: A general copper-catalyzed C-H bond-activation path allows arylation of heterocycles with a wide range of aryl bromides (see scheme). The reaction shows excellent regioselectivity and exhibits good functional group tolerance. The 8-aryl xanthines exhibit fluorescence in a variety of solvents and show promise as reagents for biological imaging.

Palladium-Catalyzed Oxidative CH/CH Cross-Coupling of Indoles and Pyrroles with Heteroarenes†

The bi-heteroaryl structural motif is prevalent in polymers, advanced materials, liquid crystals, ligands, molecules of medicinal interest, and natural products. Transition-metalcatalyzed cross-coupling reactions of a heteroaryl halide or surrogate with a heteroaryl metal represents one of the most powerful and reliable methodologies for the preparation of bi-heteroaryl compounds. However, from the viewpoint of synthetic simplicity, atom economy, and sustainable chemistry, direct oxidative coupling between heteroarenes through a double C H activation would be the most ideal strategy for connecting two heteroarenes, thus avoiding prefunctionalization of both of substrates prior to the coupling reaction. In recent years, a few groups disclosed their pioneering work directed toward transition-metal-catalyzed oxidative C H/ C H cross-coupling between a directing-group-containing arene and an arene, between two simple arenes, and between a heteroarene and an arene. In sharp contrast, metal-catalyzed direct oxidative C C couplings between two heteroarenes have a limited substrate scope. Arguably the remaining challenge in this area is to develop a compatible method for a variety of heteroarenes since such species have often been documented to undergo homocoupling, and have inadequate stability for participating in the coupling process. In addition, the presence of heteroarenes may lead to low reactivity and selectivity in coupling reactions because of the binding of the heteroatom in both the substrate and product to the metal complex. Recently, we reported the first Pd(OAc)2-catalyzed copper-salt-activated oxidative C H/C H cross-coupling of xanthines, azoles, and pyridine N-oxides with thiophenes and furans. Quite recently, Ofial and coworkers described the efficient palladium-catalyzed dehydrogenative cross-couplings of benzothiazole and benzimidazoles with N-, O-, and S-containing azoles. (Hetero)arylated indoles and pyrroles represent important structural elements for pharmaceuticals, fragrances, dyes, agrochemicals, materials, and natural products (Scheme 1). Transition-metal-catalyzed direct oxidative C H/C H coupling methods to form (hetero)arylated indoles and pyrroles pose a great synthetic challenge because the indole and

Oxidative C–H/C–H Coupling Reactions between Two (Hetero)arenes

Transition metal-mediated C-H bond activation and functionalization represent one of the most straightforward and powerful tools in modern organic synthetic chemistry. Bi(hetero)aryls are privileged π-conjugated structural cores in biologically active molecules, organic functional materials, ligands, and organic synthetic intermediates. The oxidative C-H/C-H coupling reactions between two (hetero)arenes through 2-fold C-H activation offer a valuable opportunity for rapid assembly of diverse bi(hetero)aryls and further exploitation of their applications in pharmaceutical and material sciences. This review provides a comprehensive overview of the fundamentals and applications of transition metal-mediated/catalyzed oxidative C-H/C-H coupling reactions between two (hetero)arenes. The substrate scope, limitation, reaction mechanism, regioselectivity, and chemoselectivity, as well as related control strategies of these reactions are discussed. Additionally, the applications of these established methods in the synthesis of natural products and exploitation of new organic functional materials are exemplified. In the last section, a short introduction on oxidant- or Lewis acid-mediated oxidative Ar-H/Ar-H coupling reactions is presented, considering that it is a very powerful method for the construction of biaryl units and polycylic arenes.

Rhodium or Ruthenium‐Catalyzed Oxidative CH/CH Cross‐Coupling: Direct Access to Extended π‐Conjugated Systems

Doubling up: a chemo- and regioselective oxidative cross-coupling between various N-heteroarene-containing arenes and heteroarenes has been carried out by rhodium- or ruthenium-catalyzed twofold C-H activation, to deliver an array of highly functionalized π-conjugated systems.

Synthesis of di(hetero)aryl sulfides by directly using arylsulfonyl chlorides as a sulfur source

A new, efficient protocol for the synthesis of di(hetero)aryl sulfides is described. Cheap and easily available arylsulfonyl chlorides as a sulfur source reductively couple with electron-rich (hetero)arenes (e.g., indolizines, indoles, electron-rich benzenes, etc.) in the presence of triphenylphosphine to afford di(hetero)aryl thioethers in good yields.

Palladium‐Catalyzed Desulfitative CH Arylation of Heteroarenes with Sodium Sulfinates

The structural motif with aryl–heteroaryl bonds is a predominant substructure of many biologically active compounds, natural products, pharmaceuticals, and functional materials. Transition-metal-catalyzed direct C H arylation of heteroaromatics has recently received a great deal of attention as an efficient approach for the straightforward synthesis of aryl–heteroaryl units. Over the past several years, the scope of the arylating reagents has been extended from aryl halides to various surrogates such as arenesulfonates, arylsilanes, aryl boronic acids, aryltrifluoroborates, diaryl iodonium salts, and aromatic carboxylic acids. Despite remarkable advances in these types of transformations, the search for new reliable alternative arylating reagents is still critically important from both scientific and practical standpoints. Arylsulfonyl chlorides (ArSO2Cl) have been widely used as sulfonylating agents for formation of S O, S N and S C bonds, and have recently been demonstrated as electrophilic partners in transition-metal-catalyzed desulfitative C C cross-coupling reactions. Despite readily availability, inexpensiveness, and high versatility, the active arylsulfonyl chlorides generally suffer from moisture sensitivity with the release of the acidic HCl gas. Thus, the air stable and easy to handle arylsulfinic acids (or salts) would serve as the ideal arylating reagent for the C C bond-forming reactions through the liberation of sulphur dioxide gas. Nevertheless, to date, sulfinic acids (or salts) are rarely used as the aryl source in transition-metal-catalyzed desulfinative reactions, whereas current research is mainly focused on sulfonylation reagents. The presently known desulfitative C C bond formation reactions include Heck-type coupling, and coupling between aldehydes or nitriles and arenesulfinic acid salts to aryl ketones; however, the extension of the reaction to the direct C H arylation of heteroaromatics remains unresolved. In line with our continuous efforts to forge aryl–heteroaryl bonds, we herein wish to develop an efficient desulfitative C H arylation of a wide range of heteroarenes with arenesulfinic acid sodium salts to enrich the current synthetic methodologies. However, we may face a series of hindrances: 1) In comparison with alkenes, it is well known that N-heteroarenes themselves are susceptible to oxidative homocoupling and decomposition with transition-metal-catalyzed oxidative conditions; and 2) aromatic sulfinic acid sodium salts were observed to easily encounter desulfitative self-coupling in the presence of a Pd species and an oxidant (Scheme 1). Thus, to achieve the heterocou-

Ultrasound-Induced Switching of Sheetlike Coordination Polymer Microparticles to Nanofibers Capable of Gelating Solvents

We herein demonstrate a new gelation mechanism based on a readily available coordination polymer {Zn(bibp)(2)(OSO(2)CF(3))(2)}(n), in which ultrasound changes the morphology of the material from sheetlike microparticles into nanofibers, resulting in the immobilization of organic solvents.

A simple copper salt catalysed the coupling of imidazole with arylboronic acids in protic solventDedicated to Professor Xie Ming-Gui on the occasion of his 65th birthday.

In the presence of a catalytic amount of a simple copper salt, the coupling of imidazole with arylboronic acids was performed in methanol to give corresponding N-arylimidazoles in almost quantitative yields; this coupling reaction could also be performed in aqueous solutions to give N-arylimidazoles in excellent yields.

Helical nonracemic tubular coordination polymer gelators from simple achiral molecules

A novel class of helical nonracemic tubular coordination polymers, which can immobilize a wide range of solvents at very low concentrations, have been synthesized for the first time in the absence of chiral influences and appended groups.