Dongbing Zhao

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.

Indole Synthesis by Rhodium(III)-Catalyzed Hydrazine-Directed CH Activation: Redox-Neutral and Traceless by NN Bond Cleavage†

Fishing for complements! There is an alternative to the useful Fischer indole synthesis. The new method utilizes the same retrosynthetic disconnection but is based on a Rh(III) -catalyzed directed CH activation step and a successive coupling with alkynes.

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.

Recent Progress in Coupling of Two Heteroarenes

The biheteroaryl structural motif is prevalent in polymers, advanced materials, liquid crystals, ligands, molecules of medicinal interest, and natural products. Many types of synthetic transformations have been known for the construction of heteroaryl-heteroaryl linkages. Coupling reactions provide one of the most efficient ways to achieve these biheterocyclic structures. In this review, four types of coupling reactions are discussed: 1) transition-metal-catalyzed coupling reactions of heteroaryl halides or surrogates with heteroarylmetals; 2) direct inter- and intramolecular heteroarylations of C sp 2-H bonds of heteroarenes with heteroaryl halides or pseudohalides; 3) oxidative C-H/C-H homo- and cross-couplings of two unpreactivated heteroarenes; and 4) transition-metal-catalyzed decarboxylative cross-coupling reactions between haloheteroarenes or heteroarenes and heteroarenecarboxylic acids. The general purpose of this review is to give an exhaustive and clear picture in heteroaryl-heteroaryl bond formation as well as its application in the synthesis of natural products, pharmaceuticals, catalyst ligands, and materials.

Cobalt(III)‐Catalyzed Directed CH Coupling with Diazo Compounds: Straightforward Access towards Extended π‐Systems

The first highly efficient and scalable cobalt-catalyzed directed C-H functionalization with carbene precursors is presented. This methodology provides a modular route towards a new class of conjugated polycyclic hydrocarbons with tunable emission wavelengths both in solution and in the solid state.

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

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.

Copper-catalyzed decarboxylative cross-coupling of alkynyl carboxylic acids with aryl halides

The copper-catalyzed decarboxylative reactions of alkynyl carboxylic acids with aryl halides were performed under relatively mild reaction conditions. Benzofurans could be further prepared smoothly by a one-pot domino protocol on the basis of decarboxylative cross-coupling of 2-iodophenol.

Phosphoryl-Related Directing Groups in Rhodium(III) Catalysis: A General Strategy to Diverse P-Containing Frameworks

Herein, a rhodium(III)-catalyzed oxidative C-H activation of simple arylphosphonates and phosphonamides with subsequent coupling with alkenes (olefination), internal alkynes (hydroarylation and oxidative cyclization), or simple arenes to give access to diverse P-containing functional frameworks is reported.

Self-Assembled Bifunctional Catalysis Induced by Metal Coordination Interactions: An Exceptionally Efficient Approach to Enantioselective Hydrophosphonylation†

Enantiomerically enriched a-hydroxy-functionalized phosphonates and phosphonic acids have been widely employed to synthesize pharmaceutically and biologically active compounds. Catalytic asymmetric hydrophosphonylation by addition of an appropriate phosphorus nucleophile to the carbonyl bond can provide a very convenient route to the corresponding optically active a-hydroxy phosphonates, which is probably the most general and widely applied approach. Much effort has been directed towards the development of this important type of asymmetric reaction. Shibasaki and co-workers described the first highly enantioselective addition of aldehydes with dimethyl phosphite using a heterobimetallic multifunctional catalyst based on 1,1’-bi-2naphthol (binol). However, the catalytic system only gave rise to moderate enantioselectivities for aliphatic aldehydes. A breakthrough was achieved with the C1-symmetric [Al(salalen)] complex by Katsuki and co-workers (salalen= salen/salan hybrid; salen=N,N,-bis(salicylidene)ethylene diamine; salan=N,N,-bis(O-hydroxybenzyl)-1,2-diaminoethane). Quite recently, Feng and co-workers presented another highly enantioselective example promoted by the tridentate Schiff base/Al complexes. However, among these most outstanding examples, relatively high catalyst loadings and/or extended reaction times were generally required to induce acceptable conversions. Clearly, the development of more efficient and practical catalytic systems for a broad range of phosphites and aldehydes (both aromatic and aliphatic) is a highly challenging topic. The strategy of synergistic activation by two or more reactive centers constitutes a versatile approach for the development of high-performance asymmetric catalysis. Recently, the concept of self-assembly by metal–organic coordination has been successfully employed to construct combinatorial chiral catalysts. We wish to report the combination of the two concepts mentioned above to obtain a new type of bifunctional catalyst generated by the metalorganic self-assembly of substituted binols and cinchona alkaloids in combination with Ti(OiPr)4 [13] for the asymmetric hydrophosphonylation of aldehydes. The chiral Lewis base moiety (cinchona alkaloid) in these self-assembled bifunctional catalysts spontaneously coordinates to the central metal of the chiral Lewis acidic moiety (binol–Ti complex) to form the metal–organic assemblies (Figure 1).