Helvetica Chimica Acta最新文献

This review describes applications of radical reactions developed in the authors’ laboratory for the modification of carbohydrates. It focuses on tin-free variation on the Barton-McCombie deoxygenation; on reductive de-iodination; on intermolecular radical additions of xanthates; on allylations and vinylations of xanthates and iodides, with emphasis on allylations using allylic alcohols activated as fluoropyridyl ethers; and, finally, on the synthesis of mercaptosugars.

The incorporation of nitrogen into small molecules is one of the highest-demanded transformations in modern synthetic chemistry. Alkene difunctionalization and aziridination offer desirable approaches to the incorporation of these amino synthons from feedstock precursors. Although amino groups can be added to alkenes following alkene reaction with an initiation reagent, the most desirable approach involves direct addition of the nitrogen group to the alkene, allowing for a range of possible secondary functionalization outcomes. Although many of these strategies have been accomplished through the use of transition metals, the utility of a transition metal-free approach is still at the forefront of synthetic chemistry, both in development and demand. This review aims to present a comprehensive review of the history and current state-of-the-art in the transition metal-free, direct addition of nitrogen to alkenes.

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.