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A series of N-heterocyclic carboxylate-stabilized N-heterocyclic carbene palladium complexes have been synthesized and fully characterized. The solid-state structures indicate that each of the palladium centers is coordinated by an N-heterocyclic carbene, a chloride and a bidentate N,O-donor N-heterocyclic carboxylate ligand. The catalytic performance of the complexes was screened and the results revealed that the complexes exhibit moderate to high catalytic activities for the direct C─H bond arylation of benzoxazoles with aryl bromides.

A general method for visible light-induced copper-catalyzed arylation of sp2 C—H bonds of azoles has been developed. The method employs aryl halide as the coupling partner, lithium alkoxide as base. A variety of azoles including benzooxazole and benzothiazole can be arylated. Furthermore, electron-poor heterocycles such as thiophene possessing one electron-withdrawing group can also be arylated.

A highly efficient palladium-catalyzed arylation of azoles at the C2-position using 1-aryltriazenes as aryl reagents was developed. Azoles including oxazoles, thiazoles, imidazoles, 1,3,4-oxadiazoles, and oxazolines could react with 1-aryltriazenes smoothly to generate the corresponding products in good to excellent yields, and various substitution patterns were tolerated toward the reaction.

A Ni-catalyzed C?F bond functionalization of unactivated aryl fluorides with oxazoles as coupling partners was developed. Various arylated oxazoles could be obtained in moderate to good yields in the presence of Ni(cod)2/IMes catalytic system.

An unsymmetrical pincer N-heterocyclic carbene-nitrogen-phosphine (CNP) and its palladium complexes PdCl2(κ2-CP) (4) and [PdCl(κ3-CNP)]PF6 (5·PF6) were synthesized. NMR spectra disclosed that the transformation of complex 4 structure occurred in the solution. Further NMR experimental and single crystal structure analysis of complex 4 provided unequivocal and structural evidence for the formation of complex [PdCl(κ3-CNP)]Cl (5·Cl) in the solution of complex 4. The catalytic performance of palladium complexes 4 and 5·PF6 was investigated with the direct Csp2-H arylation of benzoxazoles with aryl bromides. Notably, aryl bromides could give up to 97% arylation products in the presence of 0.5% complex 4. For ortho-substituted substrates, the steric hindrance had a significant impact, but product yields could be improved remarkably by extending reaction time. This result implied the catalytic active species in this system was stable and kept in a long lifetime. The flexible backbone and unsymmetrical pincer structure with a flank N-heterocyclic carbine should be a feasible strategy to realize an efficient catalytic transformation. This simple catalyst system first realized the direct arylation of aryl bromides with a catalyst loading as low as 0.25% without excessive base and copper as assistant catalyst.

The synthesis of novel chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized N-heterocyclic carbenes (NHCs) via direct metallation of the precursor imidazolium salts is presented. The structure has been characterized unambiguously by X-ray single crystal analysis. Catalytic activity investigation showed that the complexes catalyse the direct C-H bond arylation of (benzo)oxazoles efficiently when using tBuOLi as base and DMF as solvent.

A new and efficient method for preparation of benzimidazoles, benzoxazoles, and benzothiazoles from reactions of different carboxylic acids with o-phenylenediamine, o-aminophenol, and o-aminothiophenol in the presence of triphenylphosphine/trichloroisocyanuric acid system is presented. The desired products have been characterised on the basis of spectral (infrared, NMR, mass spectrometry) data, and the mechanism of their formation is proposed. The remarkable advantages are the inexpensive and readily available reagent, simple procedure, mild conditions, and good-to-excellent yields.

An efficient, environmentally friendly, and economical new method for arylation reactions of azoles with arylboronic acids via copper-iron-catalyzed C-H and C-B bond activation has been developed. The protocol tolerates a series of functional groups, such as methoxy, nitro, cyano, chloro, and trifluoromethyl groups.

A copper-catalyzed direct ring-opening double N-arylation of benzoxazoles with aryl iodides has been developed. The present system exhibits high selectivity despite competition from C-arylation. The selectivity between ring-opening N-arylation and C-arylation was controlled by the choice of reaction vessel. The nitrile bound bis(triphenylphosphine)copper cyanide was identified as the active catalytic species for both reactions, and when combined with a nitrile-containing solvent, enhanced the reaction efficiency.

Palladium-catalyzed desulfitative and denitrogenative arylation of azoles with arylsulfonyl hydrazides has been achieved. A broad scope of azoles and arylsulfonyl hydrazides has been used to produce arylated azoles in high yields.

A Pd (OAc)2-catalyzed direct arylation of benzoxazole C-H bonds has been achieved with iodobenzene diacetates as the arylation reagent in moderate to good yields. The procedure tolerates a series of functional groups, such as methoxy, nitro, cyano, chloro, and bromo groups.

A practical, efficient Pd(OAc)2/Cu(II)/PPh3 cocatalytic system has been developed. With only 1 mol% Pd(OAc)2, 20 mol% copper(II) salt, and 0.5 equiv of inexpensive PPh3 as ligand, the direct arylation of benzoazoles with aryl bromides could be performed smoothly in mild condition, affording the desired arylated benzoazoles in good yields (75-93%).

Not so challenging after all! The first general examples of the direct arylation of heteroarenes by using challenging aryl mesylates as electrophiles are disclosed. These easy reaction conditions also allow the functionalization of other heterocycles, such as caffeine, triazole and benzathiazole (see scheme). Copyright

(Chemical Equation Presented) A toss up: A highly active palladium complex enabled the first direct arylation of heteroarenes through C-H bond functionalization using tosylates or mesylates as electrophiles with ample scope.

To develop potent transthyretin (TTR) amyloidogenesis inhibitors that also display high binding selectivity in blood, it proves useful to systematically optimize each of the three substructural elements that comprise a typical inhibitor: the two aryl rings and the linker joining them. In the first study, described herein, structural modifications to one aryl ring were evaluated by screening a library of 2-arylbenzoxazoles bearing thyroid hormone-like aryl substituents on the 2-aryl ring. Several potent and highly selective amyloidogenesis inhibitors were identified that exhibit minimal thyroid hormone nuclear receptor and COX-1 binding. High resolution crystal structures (1.3-1.5 ?) of three inhibitors (2f, 4f, and 4d) in complex with TTR were obtained to characterize their binding orientation. Collectively, the results demonstrate that thyroid hormone-like substitution patterns on one aryl ring lead to potent and highly selective TTR amyloidogenesis inhibitors that lack undesirable thyroid hormone receptor or COX-1 binding.

A new method for the direct, copper-catalyzed arylation of heterocycle C-H bonds by aryl halides has been developed. In addition to electron-rich five-membered heterocycles, electron-poor pyridine oxides can also be arylated. The best results are obtained by using a combination of lithium tert-butoxide base, aryl iodide coupling partner, and copper iodide catalyst. Copyright