Kassem Beydoun

Palladium‐Based Catalytic System for the Direct C3‐Arylation of Furan‐2‐carboxamides and Thiophene‐2‐carboxamides

The palladium‐catalyzed direct arylation of furans or thiophenes that contained secondary carboxamides at the C2 position proceeded regioselectively at either the C3 or C5 positions, depending on the reaction conditions. The nature of the base was crucial for controlling the regioselectivity of the reaction. We had previously observed that, in the presence of potassium acetate, direct arylation at the C5 position was favored. Herein, we report that the use of cesium carbonate as the base and xylene as the solvent selectively afforded the C3‐arylated furans or thiophenes. The reactivity of furan‐2‐carboxamides and thiophene‐2‐carboxamides were similar. The reaction tolerated a range of functional groups on the aryl bromide and also heteroaryl bromide substrates.

A straightforward access to photochromic diarylethene derivatives via palladium-catalysed direct heteroarylation of 1,2-dichloroperfluorocyclopentene

A novel and efficient palladium-catalysed direct di-heteroarylation of 1,2-dichloroperfluorocyclopentene with a variety of heteroarenes is reported, giving rise to 1,2-di(heteroaryl)ylperfluorocyclopentene photochromic compounds. The reaction proceeds with thiazoles, thiophenes or furan derivatives and tolerates various substituents.

Palladium-Catalyzed Direct Arylation of Luminescent Bis-Cyclometalated Iridium(III) Complexes Incorporating C^N- or O^O-Coordinating Thiophene-Based Ligands: an Efficient Method for Color Tuning.

We report the palladium-catalyzed direct 5-arylation of both metalated and nonmetalated thiophene moieties of iridium complexes 2, 3, and 4 with aryl halides via C-H bond functionalization. This method opens new routes to varieties of Ir complexes in only one step, allowing easy modification of the nature of the ligand. The photophysical properties of the new functionalized complexes have been studied by means of absorption and emission spectroscopy. The extension of the π-conjugated system induces a bathochromic and hyperchromic shift of the absorption spectra, an effect reproduced by first principle calculations. Indeed, the bathochromic shifts are related to a more delocalized nature of the excited-states. All complexes are photoluminescent in the red region of the spectrum. This study establishes that arylation of the thienyl ring affects strongly the electronic properties of the resulting complexes, even when the thienyl ring is remote and not directly metalated to the iridium center, as in the thienyltrifluoroacetonate complex 4.

Direct heteroarylation of 5-bromothiophen-2-ylpyridine and of 8-bromoquinoline via palladium-catalysed C–H bond activation: simpler access to heteroarylated nitrogen-based derivatives

The palladium-catalysed direct heteroarylation of the pyridyl-containing substrates, 2-(5-bromothiophen-2-yl)pyridine and 8-bromoquinoline, proceeds in moderate to high yields with a variety of heteroarenes in the presence of 1–2 mol% of a palladium catalyst. This approach allows the access to polyheteroaromatics which are interesting building blocks as (N⁁C)-chelate ligands. The reaction proceeds regioselectively at the C5 position of thiophenes, thiazoles, furans or pyrroles and tolerates various substituents such as formyl, acetyl, ester, nitrile or chloro on the heteroarene. Therefore, this method allows a straightforward modulation of the electron density distribution on such derivatives.

Direct arylation of dithienylperfluorocyclopentenes via palladium -catalysed C–H bond activation : a simpler access to photoswitches

The palladium-catalysed direct arylation of dithienylperfluorocyclopentene (DTE) derivatives proceeds in moderate to high yields with a variety of aryl bromides in the presence of 5 mol% Pd(OAc)2/dppb as the catalyst, and KOAc as the base. The use of cyclopentyl methyl ether as the solvent was found to be crucial to avoid the decomposition of the reactants and products. The reaction proceeds regioselectively at C5 of thiophenes, and tolerates various substituents such as formyl, acetyl, ester, nitrile or nitro on the aryl bromide. Therefore, this method allows a straightforward modulation of the electron density distribution on DTE derivatives.

Palladium-catalysed direct polyheteroarylation of di- or tribromobenzene derivatives: a one step synthesis of conjugated poly(hetero)aromatics

The palladium catalysed polyheteroarylation of benzene, biphenyl, fluorene, naphthalene or antracene derivatives via C–H bond functionalisation allows the synthesis of a wide variety of functionalised conjugated poly(hetero)aromatics in only one step. This simple method provides a powerful tool to material chemists allowing to tune easily the physical properties of materials.

Direct 2-Arylation of Thiophene Using Low Loading of a Phosphine-Free Palladium Catalyst

Abstract The direct coupling of aryl halides with thiophene would be a considerable advantage for sustainable development because of only HBr associated with a base as by-product is formed and the number of steps to prepare these compounds is less than in more classical coupling reactions. We observed that through the use of only 0.2 mol% Pd(OAc)2 as the catalyst, a range of aryl bromides undergoes coupling via a C-H bond activation/functionalization reaction with thiophene to give 2-arylated thiophenes in good yields. In most cases, only traces of polyarylated thiophenes were detected when a large excess of thiophene was employed. This air-stable catalyst can be used with a wide variety of aryl bromides.

Palladium catalytic system for inhibition of O-arylation type reaction and regioselective direct arylation at C2 of phenols

The palladium-catalysed arylation of free OH phenol derivatives proceeds regioselectively either at C2 or at OH with a variety of electron-deficient aryl bromides or heteroaryl bromides. The nature of the base was found to be crucial to control the regioselectivity of the reaction. In the presence of potassium acetate, the direct arylation at C2 is favoured; whereas, under the same reaction conditions, the use of potassium carbonate gave selectively the O-arylation type products.