Robby Vroemans

A family of molecular anionic calcium alkyl complexes is described. Compared with their neutral analogues, these anionic systems show markedly higher basicity, exemplified by the templated twofold deprotonation of benzene to give an inverse-crown areneide complex.

Abstract

Anionic calcium alkyl complexes have been synthesised through the reduction of ethylene by an anionic calcium hydride. The alkyl complexes are demonstrated to be superbasic, rapidly deprotonating ethers below room temperature, leading to C─O bond cleavage. In reactions with benzene, selective 1,4-metalation of benzene is observed, forming an inverse-crown areneide complex. This transformation, previously inaccessible to calcium, proceeds via a stepwise mechanism, which can also be facilitated by co-complexation with organometallic reagents such as tert-butyllithium and phenylpotassium.

Mechanochemical degradation of polystyrene into benzene through ball milling is demonstrated for the first time. The benzene generated can be used to synthesize the styrene monomer for a closed-loop recycling or be converted into benzophenone through a mechanochemical cascade Friedel–Crafts acylation for upcycling.

Abstract

Synthetic plastics sourced from petroleum have gained widespread use since the 1950s. Polystyrene (PS) is one of the most extensively used plastics, as it is colorless, has high mechanical strength, and exhibits excellent chemical and thermal stability; however, it is also one of the least recycled plastics because of the high cost and low profit in recycling. Herein, we demonstrate a mechanochemical recycling approach that allows PS to be efficiently degraded into benzene when it is ground in a ball mill with AlCl₃. For example, when 165 kDa PS pellets are milled with AlCl₃, the extent of degradation reaches 90% at 15 min. Isotope labeling experiments indicate that both ambient water and the polymer backbone can be proton sources for the formation of benzene. The benzene generated in the mechanochemical degradation can be used to synthesize styrene, which can be repolymerized to produce polystyrene, allowing for the closed-loop recycling of PS. In addition, a mechanochemical Friedel–Crafts acylation between the generated benzene and the subsequently added benzoic anhydride produces benzophenone in 40%–50% yield. The mechanochemical degradation process demonstrated here is solvent-free, cost-effective, and energy-efficient, providing a promising route for the chemical recycling and upcycling of PS.

Synlett
DOI: 10.1055/a-2701-6009

Enantioselective protonation/deuteration has emerged as a pivotal transformation in modern synthetic chemistry, offering strategic control over stereochemistry at tertiary chiral carbon centers while enabling the selective incorporation of isotopic labels. Recent advancements in chiral catalysts, photochemical activation, and dual-catalytic systems have significantly expanded the scope of enantioselective protonation/deuteration, allowing for efficient and sustainable protocols under mild reaction conditions. Herein, we disclose our recent progress in photochemical enantioselective protonation/deuteration via boron migration, which provides a robust and unified platform for the enantioselective construction of tertiary C–H stereocenters under precisely controlled chiral hydrogen-bonding catalysis. Beyond its capacity to incorporate protons or deuterium atoms, the expansion of the toolkit for chiral hydrogen-bonding catalysis, and the application of boron migration in asymmetric synthesis represent two key innovations in this work, contributing to the development of more versatile asymmetric reactions.
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Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

A rapid synthesis of azosulfones can be accomplished in a vibrational mechanical mill, giving up to quantitative yields in as little as 30 min. The tolerance of the method is demonstrates on a broad substrate scope and is successfully used to produce 30 different products. Spectroscopic and computational studies provide insight into the process and its selectivity.

Azosulfones represent a potent and stable surrogate for diazonium salts. Their wide application in C–H functionalizations catalyzed by transition metals and visible light is well-known in organic chemistry. Here, a single-step mechanochemical synthesis of azosulfones is reported, starting from readily available precursors, which has high conversion efficacy −80%–99% isolated yields are obtained in most cases. A substrate scope of 30 different compounds is obtained. This method requires no solvent, it is quick and has potential in terms of scalability and tolerance toward a broad range of functional groups, which makes it attractive for synthesis. Spectroscopic and computational studies are performed to explain the observed reactivity patterns.

Publication date: 1 February 2026

Source: Coordination Chemistry Reviews, Volume 548, Part 1

Author(s): Haifei Kang, Ranran Yang, Wenying Wei, Kun Liu, Yingxin Xu, Xiaopei Wu, Honglian Dai

Electrochemical dehydration reactions are a fascinating and underexplored field of research in the domain of electrosynthesis. They offer a sustainable alternative to hazardous and harsh dehydration reagents. In this review, the recent progress that has been made in this emerging research topic is surveyed.

Electrochemical dehydration reaction is a fascinating and underexplored field of research, which has started to attract significant attention in recent years. Dehydration reactions are characterized by the formal removal of water in the course of the transformation, and they are among the most fundamental types of reactions found throughout chemistry. Examples are esterification reactions, amidation reactions, and the synthesis of carbon-heteroatom multiple bonds. In general, dehydration reactions are not considered to be redox reactions, because no oxidation states change in the substrate from which water is eliminated or in the dehydration reagent that is utilized. At first glance, there does not seem to be a link between dehydration reactions and redox chemistry. In recent years, however, it has been demonstrated that dehydration reactions can be carried out by electrolysis. Given the enormous importance of dehydration reactions from academic to technical scale, electrochemical dehydration reactions offer a more sustainable approach to such transformations. In this review, the recent progress is surveyed and the opportunities of this new and evolving field are highlighted. Electrochemical dehydration reactions are an interesting new discipline in the emerging domain of electroorganic chemistry, which is currently experiencing a remarkable renaissance to establish itself as a 21st-century technique.

This review presents recent advances in the chemistry of expanded helicenes, defined as helicenes containing linearly fused benzene rings, as novel aromatic compounds. This review begins with a summary of their structural classification, followed by the synthesis, structures, properties, and chiroptical performance of expanded helicenes of various shapes, such as hexagons, triangles, and rhombuses.

Abstract

Expanded helicenes are interesting compounds created by modifying the original helicene structure through the incorporation of linearly fused benzene rings, enlarging the helical diameter. Motivated by Tilley et al.’s report of a key expanded helicene structure in 2017, several research groups have synthesized such nonplanar aromatic compounds, aiming to explore their impressive structures, properties, and chiroptical performance. This review highlights recent advances in the expanded helicene chemistry through experimental and theoretical studies. The shape and length of helical structures depend on the number and combination of angularly and linearly fused benzene rings. Helical structures are classified using notations, and specific compounds corresponding to each structural form, namely, hexagonal, triangular, rhombic, or others, are introduced herein. As an extension of the molecular design, examples of nonhexagonal and heteroaromatic ring-embedded expanded helicenes are presented. Specifically, this review focuses on how the diameters, lengths, and turn numbers of helical structures depend on dynamic processes involving helical inversion and chiroptical properties (circular dichroism (CD) and circularly polarized luminescence (CPL)). The characteristics and perspectives of this molecular design are also discussed.

Single component does double duty! Arylsulfinate salts or arylsulfonyl chlorides alone act as the source of both the arylsulfonyl and arylsulfide fragments via electrochemical autocatalytic processes to generate diarylthiosulfonate. Wide substrate scope was demonstarted with minimum waste generation.

Abstract

A facile and straightforward electrochemical method for synthesizing diaryl thiosulfonates is reported. The process involves a combination of consecutive in situ electrochemical–autocatalytic processes, followed by a C─S coupling sequence, to enable the formation of diaryl thiosulfonates using either arylsulfinate salts or arylsulfonyl chlorides alone. Thus, unlike previous methods, it avoids using stoichiometric thiol or disulfide reaction partners, over-stoichiometric promoters, metal-based redox reagents, or catalysts, thereby minimizing the formation of undesired products and chemical waste. A range of arylsulfinate salts/arylsulfonyl chlorides was screened under the reaction conditions, yielding the corresponding diaryl thiosulfonates in moderate-to-good yields.

Chiral azacrown ethers from threitol were synthesized, and their catalytic activity and reusability were investigated in liquid–liquid and solid–liquid phase-transfer reactions together with some previously synthesized catalysts. Some structure-effect relationships were explored, while the recoverability of the crown ethers was demonstrated. In some cases, the selectivity was preserved through three cycles.

Abstract

In enantioselective reactions, several catalysts can be used, such as chiral crown ethers, which form a special group of them. In addition to the reaction conditions, the structure of the catalyst used also affects the outcome of the reaction. In the case of carbohydrate-based crown ethers, we previously found that the monoaza-15-crown-5 structure is the most effective, and the generated enantiomeric excess is influenced by the substituent of the nitrogen, the protecting groups of the carbohydrate, and the source of chirality. In this study, macrocycles derived from l-threitol were synthesized with a similar structure, and their catalytic activity and reusability were tested and compared in different model reactions along with some previously prepared compounds. Several types of effect-structure relationships were pointed out, while the enantiomeric excess varied widely. We demonstrated the recoverability of the crown ethers by acidic extraction and subsequent liberation of the azacrown moiety. The regeneration process was investigated more thoroughly in scaled-up reactions, where the selectivity of the catalysts preserved for three examined cycles.

10-Azidotetrazolo[1,5-a][1,10] phenanthroline: schematic diagram, disordered crystal structure, ESP plot of the optimized structures, fluorescence of the sample in acetonitrile under 365 nm UV light.

Abstract

In our quest for novel An/Ln separating ligands, we have synthesized a heterocyclic precursor based on phenanthroline and identified it as 10-azidotetrazolo[1,5-a][1,10] phenanthroline. This asymmetric heterocyclic azide has been synthesized in four reaction steps in good yield and is well characterized via experimental methods. Thermal analysis shows that this compound is reasonably stable as an azide. The heterocycle shows fluorescent properties with a distinctive red shift of the emissions and excitation peaks. A single-crystal XRD study shows that the molecule is planar and exhibits total molecular disorder with molecules in the crystal structure present in a major:minor conformation ratio of 0.91:0.09 and related by a 180° flip. In addition, quantum-theoretical investigation suggests that such a product with one fused tetrazolo ring is the most stable one out of other alternatives. This molecule presents a relatively rare case of azido-tetrazole tautomerism in 1.10-phenanthroline.

Nature, Published online: 21 August 2025; doi:10.1038/d41586-025-02547-1