Helvetica Chimica Acta最新文献

Radical anions constitute an important class of reactive intermediates. Here, we investigate the suitability of electrospray-ionization (ESI) mass spectrometry for their qualitative and quantitative analysis. To this end, we have probed solutions of 14 different benzoquinones and nitrobenzenes in the presence or absence of the reductant CoCp₂. The latter greatly helped in the formation and detection of radical anions, but even without, analytes of sufficiently high electron affinity could accept an electron upon cathodic reduction during the ESI process and, thus, became observable. Analytes with low electron affinities escaped from detection because the corresponding radical anions did not form to a sufficient extent and/or underwent electron detachment during the ESI process and the consecutive ion transfer. Furthermore, we studied the effect of the analyte concentration, different reducing agents as well as the solvent and demonstrated the utility of the present approach for the mechanistic elucidation of reactions involving radical anions.

Transannular π-cyclizations and heterocyclizations are characteristic for electrophilic addition reactions to medium-sized cycloalka-1,5-dienes. Transannular O-heterocyclizations have been frequently observed in reactions of cycloocta-1,5-diene and derivatives, but rarely for larger rings. Now this reaction type has been extended for diastereoisomeric cyclododeca-1,5,9-trienes to form 2,9-disubstituted 13-oxabicyclo[8.2.1]tridec-5-enes, creating four stereogenic centers in racemic form in one step. Ozonolytic cleavage of the remained double bond provided cis-1,5-dialkylated tetrahydrofuran derivatives bearing functional groups like halogen or hydroxyl in β- and β′-positions regarding the tetrahydrofuran-oxygen and carboxyl functions at the ends of both alkyl groups. Applying differently substituted cyclododeca-1,5-diene derivatives such as epoxides or vicinal diols as starting materials, diastereoisomers of the above-mentioned tetrahydrofurans have been prepared in four or five steps. These compounds have the potential to serve as Lego-like building blocks for syntheses of annonaceous acetogenins.

The abrupt reorganization of the electronic configuration of spin-crossover (SCO) compounds upon the transition from the low-spin (LS) to the high-spin (HS) state leads to significant changes in their structural, optical, and magnetic properties. As spin-transitions can be triggered by a variety of external stimuli such as variations in temperature, pressure, or through light irradiation, these systems have attracted considerable attention for the design of multifunctional and stimuli-responsive molecular materials. In this context, the synergistic coupling of SCO and luminescent properties holds great promise for the development of molecular spintronic devices capable of correlating the luminescence with an external perturbation, or of probing the magnetic state of the metal center through variations in emission intensity. This contribution provides a comprehensive overview of the field of luminescent SCO materials, with particular emphasis on systems that exhibit a genuine interplay between the two properties, both in materials and at the molecular level.

The strategic generation of α-fluoro radicals underpins powerful routes to fluorine-rich architectures of high value in molecular design. Here, we disclose an operationally simple, catalyst-free method for the photochemical activation of α-halo fluorinated precursors using visible light and two inexpensive additives, sodium iodide and 2,6-lutidine. This mild protocol enables in-situ halide exchange and subsequent homolytic C–I bond scission to generate α-fluoro radicals under ambient conditions. The generality of the platform is demonstrated across esters, sulphones, and nitriles, facilitating intermolecular coupling with alkenes, heteroarenes, and propellanes to access diverse fluorinated scaffolds. Mechanistic studies support the formation of a weak electron donor–acceptor complex that mediates bond activation, while the benign conditions permit merger with energy transfer catalysis for stereodivergent product formation.

To celebrate the 125th anniversary of the Swiss Chemical Society, we present a review and perspective to highlight the recent research in breath analysis that has been conducted in Switzerland, with a particular focus on secondary electrospray ionization mass spectrometry (SESI-HR-MS). We focus on breath analysis research from 2019, the publication year of the last major review. We highlight where improvements are needed in experimental and clinical protocols and outline the current gaps in the field, to support the implementation of breath analysis into the clinical domain.

This perspective highlights a distinctive class of symmetric molecular architectures, methylene-bridged calixarene polyhedral, that, despite long-standing theoretical interest, have not yet been synthesized. It consolidates all previously proposed members of this family, introduces a new representative, and assesses their synthetic feasibility through computational strain analyses. Five polyhedra were examined: methanospherophane, Cram's prototype carcerand, two augmented prismatic dimers, and the newly postulated calix[5]arene-based icosidodecahedron. Homodesmotic hydrogenolysis reactions were employed to estimate strain energies, complemented by angular deviation analysis from ideal collinearity (180°). Among all candidates, the methanospherophane emerged as the only nearly strain-free structure, while Cram's carcerand and the icosidodecahedron exhibited significant strain. The prismatic dimers showed intermediate stability. Methanospherophane thus emerges as the leading candidate for the first successful synthesis, potentially opening the door to this fascinating class of methylene-bridged calixarene polyhedra.

Imidazole is a versatile heteroaromatic ring whose properties can be systematically tuned through substitution. N-alkylation or N-arylation yields imidazolium cations, which are frequently low-melting and are then described as ionic liquids (ILs), and as precursors to N-heterocyclic carbene (NHC) ligands. Substitution at the 4- and 5-positions modulates the electronic and steric profiles of the five-membered ring. Imidazole and imidazolium derivatives not only serve as solvents, catalysts, and cocatalysts in the reduction of CO₂, but also act as electrolytes in dye-sensitized solar cells (DSSCs) and as hole-transport materials and multifunctional additives in perovskite solar cells (PSCs). Hence, the combination of imidazole/imidazolium-based materials with versatile structures can bridge molecular design with high-performance catalysis and photovoltaics. This mini-review aims to survey imidazole/imidazolium-scaffold structures and their applications in sustainable chemistry and energy conversion, providing a perspective on the structure–function relationships and future directions.