Search

One-pot halogen dance/Negishi cross-coupling of readily available 2,5-dibromothiophenes is described. A lithium diisopropylamide (LDA)-mediated halogen dance reaction resulted in the formation of thermodynamically stable α-lithiodibromothiophenes, which were transmetalated with ZnCl2 and subjected to Negishi cross-coupling to provide the corresponding arylated dibromothiophenes in one pot. The resultant β-bromo group was much less reactive than the remaining α-bromo group, which was used in a one-pot double Suzuki-Miyaura cross-coupling, enabling facile synthesis of multiply arylated thiophenes. [ABSTRACT FROM AUTHOR]

Preparation of 2-furylthiazole-4-carboxylic acid methyl ester is achieved in four steps from biomass-derived heteroaromatic compound furfural and a natural amino acid L-cysteine. One-pot bromination and following palladium-catalyzed arylation with arylboronates of the thus obtained furylthiazole at the furan ring gives arylated furylthiazole in excellent yields. Further arylation at the C–H bond of the thiazole ring (5-position) in the presence of AgF as an additive leads to diarylated furylthiazoles, which show strong photoluminescence. Homocoupling at the C–H bond of thiazole is also carried out with AgF to afford the corresponding further conjugated product composed of eight (hetero)aromatic rings. [ABSTRACT FROM AUTHOR]

Addition-elimination reactions of an arylaluminum reagent with vinylarenes is achieved mediated by a rhodium catalyst. The reaction of dimethyl(phenyl)aluminum with a rhodium(I) catalyst takes place to afford ( E)-stilbene. The reaction is promoted by the addition of ketone as an additive to give ( E)-stilbene in a quantitative yield. A nickel complex bearing cyclopentadienyl (Cp) and N-heterocyclic carbene (NHC) ligands also catalyzes the reaction to afford 1,2-diarylethenes accompanied by a small amount of the saturated byproduct, 1,2-diarylethanes. [ABSTRACT FROM AUTHOR]

Rhodium-catalyzed addition/elimination of arylaluminum reagents with vinylarenes was achieved to obtain stilbene derivatives. The reaction of diethyl(phenyl)aluminum with styrene in the presence of the chloro(1,5-cyclooctadiene)rhodium(I) dimer, [RhCl(cod)]2, and diisopropyl ketone (2,4-dimethyl-3-pentanone) as an additive occurred to give ( E)-stilbene in quantitative yield. The use of other arylaluminum reagents afforded β-arylated products in good to excellent yields. This reaction was found to be promoted by ketones as additives, which are reduced to the corresponding alcohols, as confirmed by analysis of the crude reaction mixture by 1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Deprotonative metalation of chlorothiophene takes place with a catalytic amount of cis-2,6-dimethylpiperidine (DMP) and an alkyl Grignard reagent at room temperature for three hours to give the corresponding thienyl Grignard reagent. Polymerization leading to head-to-tail-type poly(3-substituted thiophene) with the thus metalated chlorothiophene proceeds in the presence of a nickel catalyst bearing an N-heterocyclic carbene (NHC) ligand. Palladiumcatalyzed cross-coupling reaction with aryl bromides also gives arylated thiophenes in good to excellent yields while the C-Cl bond remains intact. [ABSTRACT FROM AUTHOR]

The synthesis of linear and branched oligothiophenes of well-defined structures is performed with regioselective deprotonation of 3-substituted thiophenes and nickel-catalyzed cross-coupling of the thus formed metalated species with a bromothiophene. The reaction of 3-hexylthiophene with EtMgCl and 2,2,6,6-tetramethylpiperidine (TMP-H, 10 mol %) induces the metalation selectively at the 5-position by use of the catalytically generated hindered magnesium amide (TMPMgCl) and the subsequent reaction of a 2-halo-3-hexylthiophene (bromide or chloride) in the presence of a nickel catalyst affords a head-to-tail (HT)-type dimer. By repeating the same sequence, the linear oligothiophene up to a 4-mer is synthesized in good yield. The reaction of 3-hexylthiophene with 2,3-dibromothiophene also takes place to afford a branched oligothiophene 3-mer in quantitative yield. The obtained 3-mer is also metalated at the sterically less-hindered position in a regioselective manner furnishing a 7-mer in >99 % yield after a further coupling reaction with 2,3-dibromothiophene. These dendrimers react with several multifunctionalized organic electrophiles, leading to a variety of branched oligothiophenes. [ABSTRACT FROM AUTHOR]

Abstract: Silicone, poly(diorganosiloxane), serves as an organosilicon reagent for palladium-catalyzed cross-coupling reactions. Treatment of poly[(aryl)methylsiloxane], poly[(alkenyl)methylsiloxane], or cyclic oligosiloxanes with various aryl iodides in the presence of silver(I) oxide (Ag2O) or tetrabutylammonium fluoride (TBAF) and a catalytic amount of palladium affords the corresponding cross-coupling product in a good to excellent yield. The reaction of silicone with aryl chlorides in the presence of K2CO3/H2O as an activator proceeded to afford biaryl derivatives in moderate to excellent yields. A wide range of aryl chlorides bearing an electron-donating or electron-withdrawing substituent on the aromatic ring are tolerated. [Copyright &y& Elsevier]