Péter Kisszékelyi

When steric effects decide: N-heterocyclic carbene catalysed mechanochemical deuteration of aromatic aldehydes results in either C-1 deuteration or formation of α-deutero acyloins depending on the steric strain of the Breslow intermediate.

Photocatalysis provides a sustainable approach to chemical synthesis by enabling energy-efficient transformations under mild conditions. In this study, we present a comprehensive method that combines the development of photocatalytic reactions with process optimization, using a standardized 3D-printed photoreactor platform. We utilized the organophotocatalyst 4CzIPN to systematically optimize the visible-light-mediated carbon–carbon bond formation between the CH-acidic methyl cyanoacetate and 1,1-diphenylethylene. This optimization was performed through a 2⁴ full factorial design of experiments (DoE) resulting in a 48% improvement in yield (up to 91%). To address the persistent challenge of reproducibility in photochemical research, we employed a custom-designed, 3D-printed, open-access photoreactor. This design allows for standardized conditions and enhanced process optimization. We conducted a systematic investigation of various reaction parameters, including the conditions and the substrate scope. To assess the sustainability of the process, we introduced a modified energy economy factor specifically tailored for photoreactions, which illustrates a significant increase in energy efficiency. Finally, we demonstrate the possible implementation of the optimized reaction in continuous flow synthesis, underscoring the practical applicability of this methodology for advancing the design of scalable and sustainable photochemical manufacturing.

Mechanochemically‐assisted multicomponent Povarov reaction catalyzed by chiral BINOL‐derived TRIP organocatalyst enabled the stereoselective synthesis of various tetrahydroquinolines in good yields and high enantiomeric purities. This represents a new example for the thus far less explored stereoselective transformations under mechanochemical conditions utilizing noncovalent asymmetric organocatalysis. A series of conventional and alternative solvents was tested for the liquid‐assisted grinding. The solvent additive has a considerable influence on the stereocontrol of the reaction. The mechanochemical reaction setup offers better mass intensity values than the solution‐based variant. The isolation of the addition intermediate and significant effect of solvent polarity suggests a stepwise polar mechanism. DFT calculation provided insights into the stereoinduction of the reaction.

Ferrocene thioamides are potential alternatives for classical oxoamide‐type ferrocene ligands with broad applications in metal‐catalyzed transformations as well as substrates for CH activations and applications in other fields. A reaction of ferrocenecarboxaldehyde with various amines and sulfur promoted by sodium sulfide furnishes a wide range of ferrocene thioamides via the Willgerodt–Kindler multicomponent reaction. The detailed solvent screening reveals that amide‐type solvents are highly beneficial for the reaction. The steric hindrance of bulky amine substrates limits the reaction. While secondary amines require only conventional heating, primary amines yield better results with microwave irradiation at higher temperatures. The mechanism is investigated using nuclear magnetic resonance kinetic measurements, which show that Na ₂ S acts as a promoter, rather than a catalyst, of the reaction.

Three variants of 2-(pyridine-2-yl)-1H-benzimidazole bidentate ligands, with distinct pentyl substituents (n-pentyl (L1), (2S)-2-methylbutyl (L2S), and (2R)-2-methylbutyl (L2R)), were synthesized and employed to prepare magnetically bistable cobalt(II) and iron(II) complexes. The cobalt(II) complexes [Co(L1)(κ²-NO₃)₂(CH₃CN)] (1), [Co(L2S)(κ²-NO₃)₂(H₂O)] (2S), [Co(L2R)(κ²-NO₃)₂(H₂O)] (2R) and [Co(L2)(κ²-NO₃)₂(H₂O)] (2rac) exhibit field supported slow relaxation of magnetisation, while the iron(II) complexes [Fe(L2S)₃](CF₃SO₃)₂·H₂O·CH₃NO₂·C₅H₁₂O (3S) and [Fe(L2S)₃]·1.5H₂O (3R) exhibit thermal spin crossover allocated above room temperature. Structural analysis revealed that the heptacoordinated cobalt(II) complexes adopt a distorted pentagonal bipyramidal geometry, whereas the iron(II) compounds contain hexacoordinated complex cations. Coordination compounds incorporating the chiral ligands L2S and L2R are optically active, with their enantiomeric relationship confirmed by circular dichroism spectroscopy. Computational studies provided insights into electron density distributions and bonding energetics (DFT and QT-AIM), predicted zero-field splitting parameters (CASSCF/NEVPT2), and quantified energies of the d-orbital, ligand field terms and their multiplets (via AILFT). Magnetic investigations of the cobalt(II) complexes yielded experimental ZFS parameters and revealed distinct magnetization relaxation mechanisms: 1 exhibits relaxation governed by a phonon bottle-neck process, whereas 2S and 2R involve a combination of Raman and direct relaxation processes. Notably, compounds 2S and 2R, despite being enantiomers and isostructural, exhibited distinct relaxation dynamics, attributable to differential phonon coupling pathways modulated by the chiral substituents. This is the first report demonstrating enantiomer-dependent slow relaxation of magnetisation behaviour in cobalt(II)-based SMMs. These findings underscore the critical role of stereochemistry in modulating spin dynamics and magnetic bistability, providing design principles for future chiral magnetic materials.

Guaiazulene-derived carbocations react with metal enolates. These reactions afford guaiazulene-containing carbonyl derivatives and reaction progress can be easily monitored by UV-Vis or fluorescence spectroscopy.

Synthesizing organocatalysts is often a long and cost-intensive process, therefore, the recovery and reuse of the catalysts are particularly important to establish sustainable organocatalytic transformations. In this work, we demonstrate the synthesis, application, and recycling of a new lipophilic cinchona squaramide organocatalyst. The synthesized lipophilic organocatalyst was applied in Michael additions. The catalyst was utilized to promote the Michael addition of cyclohexyl Meldrum’s acid to 4-chloro-trans-β-nitrostyrene (quantitative yield, up to 96% ee). Moreover, 1 mol % of the catalyst was feasible to conduct the gram-scale preparation of baclofen precursor (89% yield, 96% ee). Finally, thanks to the lipophilic character of the catalyst, it was easily recycled after the reaction by replacing the non-polar reaction solvent with a polar solvent, acetonitrile, with 91–100% efficiency, and the catalyst was reused in five reaction cycles without the loss of activity and selectivity.

Metal enolates are useful intermediates and building blocks indispensable in many organic synthetic transformations. Chiral metal enolates obtained by asymmetric conjugate additions of organometallic reagents are structurally complex intermediates that can be employed in many transformations. In this review, we describe this burgeoning field that is reaching maturity after more than 25 years of development. The effort of our group to broaden possibilities to engage metal enolates in reactions with new electrophiles is described. The material is divided according to the organometallic reagent employed in the conjugate addition step, and thus to the particular metal enolate formed. Short information on applications in total synthesis is also given.

Arylboronates are helpful building blocks in organic synthesis. Here, we present an efficient mechanochemical synthesis of arylboronates from arene diazonium salts. Importantly, this transformation was significantly enhanced by sodium chloride, which probably promotes the decomposition of diazonium salts via anion exchange. Chloride anions also participate in the formation of strongly reducing Cl−B anion radical intermediate that promotes radical chain reaction. The reaction proceeds more efficiently with a small amount of polar solvent as a liquid‐assisted grinding additive. Quantum chemical calculations support the mechanistic proposal.