Syntheses and Properties of Donor−Acceptor-Type 2,5-Diarylthiophene and 2,5-Diarylthiazole

Palladium-Catalyzed Coupling Reactions of Bromothiophenes at the C−H Bond Adjacent to the Sulfur Atom with a New Activator System, AgNO3/KF

[reaction: see text] Bromothiophene derivatives react with aryl iodides catalyzed by a palladium complex in the presence of a silver(I) nitrate/potassium fluoride system to induce coupling at the C-H bond, while the carbon-bromine bond is intact. The produced coupling product bearing the C-Br bond allows further palladium-catalyzed C-C bond-forming reactions in reasonable yields.

One-Pot Construction of Pyrazoles and Isoxazoles with Palladium-Catalyzed Four-Component Coupling

[reaction: see text] Four-component coupling of a terminal alkyne, hydrazine (hydroxylamine), carbon monoxide, and an aryl iodide furnishes pyrazole or isoxazole derivatives in the presence of a palladium catalyst. The reaction proceeds at room temperature and an ambient pressure of carbon monoxide in an aqueous solvent system.

Regioselective Synthesis of 1,5-Diaryl-1H-imidazoles by Palladium-Catalyzed Direct Arylation of 1-Aryl-1H-imidazoles

[reaction: see text] A variety of 1,5-diaryl-1H-imidazoles have been regioselectively synthesized by direct coupling of 1-aryl-1H-imidazoles with aryl iodides or bromides in DMF in the presence of CsF as the base and a catalyst precursor consisting of a mixture of Pd(OAc)2 and AsPh3. The data obtained in this synthetic study support a reaction mechanism involving an electrophilic attack of an arylpalladium(II) halide species onto the imidazole ring. Interestingly, some imidazole derivatives synthesized in this study have been found to exhibit significant cytotoxic activity against human tumor cell lines.