Helvetica Chimica Acta最新文献

A new one-phase process for hydroarylation of C₆₀ fullerene using arylboronic acids and a rhodium catalyst in an aromatic solvent containing soluble protic additives is described. Yields of monohydroarylated product with tert-butanol and water as the protic additive range from 14 to 50 % depending on which arylboronic acid is used after reaction times of 4 hours or less which is a significant improvement from the outcome of reactions carried out using conditions from the literature. Accurate monitoring of reaction outcomes was achieved by a combination of UV-Vis spectroscopy and ¹H-NMR spectroscopy: C₆₀ conversion was determined using an analytical HPLC-UV-vis method employing commonly available columns for the separation, while product formation was quantified by ¹H-NMR spectroscopy with an internal standard. Moreover, two new arylboronic acids carrying 4-alkynyl aryl substituents, synthesized using Sonogashira couplings, are reported, as well as the use of these in the hydroarylation of C₆₀.

A method for the hydroalkylation of 1,1-diarylalkenes has been developed using magnesium hydride (MgH₂) generated in situ by the solvothermal treatment of magnesium iodide (MgI₂) with sodium hydride (NaH) in ethereal solvents. The process is initiated by the hydromagnesiation of 1,1-diarylalkenes with MgH₂ to generate 1,1-diarylethylmagnesium species, which are immediately alkylated with ethereal solvents to construct a diaryl quaternary carbon center in the hydroalkylation products.

The incorporation of the vinylene motif into conjugated molecules notably elevates the HOMO level, augmenting both emissive and conductive properties while enhancing responsiveness to external stimuli. This study focuses on the regioselective C−H/C−H coupling of N-vinylcarbazole with thiophenes, offering an efficient route to N-vinylene-incorporated conjugated molecules for the development of organic electronic materials. Traditional palladium-catalyzed Fujiwara-Moritani (FM) reactions proved ineffective for C−H alkenylation with N-vinylcarbazole. In response, we have developed an iron-catalyzed twofold alkenylation method for conjugated thiophenes with N-vinylcarbazole, utilizing trimethylaluminum as the base and diethyl oxalate as the oxidant. This reaction occurs regioselectively at the C₂−H (or C₅−H) bond of the thiophenes and the terminal position of N-vinylcarbazole. It also successfully produces short thiophene polymers end-capped with N-vinylcarbazole, demonstrating the potential for synthesizing polymeric donor materials. The enamine products exhibit blue-to-green emission, high fluorescence quantum yield, and visible light responsivity for stereo-isomerization, indicating promising applications in organic electronics.

The synthesis of glycosides generally requires the use of building blocks that need to be readily prepared, avoiding tricky reaction steps and boring purifications. Thioglycosides represent key donor intermediates for their activation in glycosylation reactions and for their great stability. Moreover, the presence of a benzylidene moiety confers to the molecule a double advantage: it can influence the stereochemistry of the glycosylation reaction and can be selectively opened to generate different species having a free secondary hydroxyl group. Here, the preparation of p-Tolyl 1-thio-4,6-O-benzylidene-2,3-di-O-benzyl-β-d-pyranoses of glucose, galactose, and mannose are described. The global procedure involved the exploitation of simple reactions and crystallization techniques, having a chromatographic purification for the last step only.

A series of sulfonamide azobenzenes bearing alkyl substituents of increasing steric bulk at the position ortho to the N=N bond and their corresponding chloro(hexamethylbenzene)ruthenium(II) complexes were synthesized. The latter bearing mono-substituted ligands exhibited an exocyclic azo bond under the E configuration, and underwent reversible E→Z photoisomerization upon irradiation with visible light, followed by thermal Z→E back isomerization upon resting in the dark at 20 °C. In contrast, the corresponding 2,6-dimethyl substituted azobenzene complex, while also exhibiting an exocyclic azo bond, was isolated as the Z-isomer and underwent uncommon solvent dependent irreversible photodissociation of azobenzene ligand upon visible light irradiation. Valuable insights into the photophysical and structural properties of these complexes were gained by combination of computational and X-ray diffraction studies.

Supported metal hydrides are key reactive intermediates in various catalytic processes, such as hydrogenation and dehydrogenation, but are often challenging to characterize spectroscopically. Here, deuterium solid state nuclear magnetic resonance spectroscopy is used to understand the structure of the corresponding silica-supported zirconium hydrides after H/D exchange as an illustrative example of supported metal hydrides, which have been shown to display notable reactivity towards small molecules (e. g., CO₂ and N₂O) and to activate both C−H and C−C bonds, hence their use in to the conversion of hydrocarbons (alkanes, polyolefins etc.)

A practical, efficient approach for the synthesis of C4-arylated 2-quinolones from propargylic chlorides and anilines has been developed. The synthesis process involves subsequent oxidations of the initial products, tetrahydroquinolines and quinolinium ions, eventually leading to desired quinolones. A mechanism for the transformation is proposed based on a meticulous examination of intermediates and comprehensive control experiments. With a thorough understanding of the reaction mechanism, the applicability of the reaction scope is expanded.