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.

Syntheses and properties of donor-acceptor-type 2,5-diarylthiophene and 2,5-diarylthiazole.

[structure: see text] Syntheses of differently substituted 2,5-diarylthiophenes and 2,5-diarylthiazoles are carried out with the palladium-catalyzed C-H substitution reaction using AgF as an activator. Remarkably strong photoluminescence is observed in 2,5-diarylthiophene. Differences between the physical properties of liquid crystalline characteristics and cyclic voltammograms of thiophene and thiazole are also studied.

Photoluminescent and liquid-crystalline properties of donor-acceptor-type 2,5-diarylthiazoles.

The synthesis of donor-acceptor-type 2,5-diarylthiazoles that bear electron-donating N,N-dialkylamine and electron-withdrawing cyano groups at the 2- and 5-position, respectively, were carried out with transition-metal-catalyzed C-H arylation reactions developed by us. The compounds were synthesized by the C-H arylation of unsubstituted thiazole at the 2-position with a palladium/copper catalyst in the presence of tetrabutylammonium fluoride (TBAF) as an activator. Further C-H arylation of the 2-arylated thiazole at the 5-position was carried out by the palladium-catalyzed reaction in the presence of silver(I) fluoride to afford the donor-acceptor-type 2,5-diarylthiazoles with N,N-dialkylamine groups of different chain lengths. The UV/Vis absorption, photoluminescence, and electrochemical behavior were similar regardless of chain length, whereas liquid-crystalline behavior and thermal characteristics were found to be dependent on the alkyl-chain length. The compounds with N,N-diethylamine or N-butyl-N-methyl groups showed a stable liquid-crystalline phase over a wide temperature range as well as higher stability to thermal decomposition.

Palladium-catalyzed C-H homocoupling of bromothiophene derivatives and synthetic application to well-defined oligothiophenes.

Synthesis of oligothiophenes of well-defined structures that possess 2-8 thiophene units is performed with a new synthetic strategy involving C-H homocoupling of bromothiophenes and cross-coupling with organostannanes. Tolerance of the carbon-bromine bond to the palladium-catalyzed C-H homocoupling results in oligothiophenes bearing C-Br bonds at the terminal thiophene rings, which allow further transformation by the catalysis of a transition-metal complex.

Palladium-catalyzed C-H homocoupling of thiophenes: facile construction of bithiophene structure.

Palladium-catalyzed C-H homocoupling of thiophene derivatives takes place in the presence of silver(I) fluoride or acetate. A variety of bithiophenes are obtained in good to excellent yields. In particular, the reaction of 2-bromothiophene proceeds at room temperature to afford 5,5'-dibromo-2,2'-bithiophene, where the bromine atom is completely intact in the palladium-catalyzed reaction. XRD analysis reveals that silver fluoride is reduced to silver(0) during the reaction.

Facile synthesis of 2,5-diarylthiazoles via palladium-catalyzed tandem C-H substitutions. Design of tunable light emission and liquid crystalline characteristics.

A mild and regioselective C-H substitution reaction of thiazole by the catalysis of the palladium/copper system is found to proceed in the presence of tetrabutylammonium fluoride under mild conditions. Applying the new reaction, we synthesized various 2,5-diarylthiazoles that exhibit light-emitting and liquid crystalline characteristics in good yields. The color of light emission is tunable by the introduction of the substituent. Differently substituted 2,5-diarylthiazoles are found to exhibit a stable liquid crystal phase in a wide temperature range.