Tomas Horsten

The Front Cover illustrates the concept of “Back to the Electro-Future,” where classical named reactions are reimagined through electro-organic synthesis. Electrical sparks linking traditional laboratory glassware with an electrochemical cell symbolize electron-driven activation. This imagery represents how electricity revitalizes well-known transformations, offering sustainable and modern approaches to established reactions in organic chemistry. More information can be found in the Review by M. Kim, I. Choi and co-workers (DOI: 10.1002/cssc.70613).

A new class of 1-azabicyclo[1.1.0]butanes (ABBs) is synthesized, and the first electrochemical method for synthesizing chemo-selective trifluoromethanesulfonylated and trifluoromethylated azetidine derivatives from ABBs. This strategy involves the anodic oxidation of ABB to generate a nitrogen-centered radical cation, a rare [2, 3]-sigmatropic shift of the sulfone, and selective oxidation of Langlois' reagent. The generated azetidines were integrated into drug motifs, demonstrating their utility. Mechanistic investigations through control experiments, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) provided deep insights into the reaction pathways.

ABSTRACT

Due to the favorable pharmaceutical properties of the azetidine ring, it can serve as a bioisostere to replace saturated heterocycles such as piperazines, piperidines, and pyrrolidines in drug discovery. The diverse methods for azetidine synthesis are still limited and challenging. Herein, we design a new class of 1-azabicyclo[1.1.0]butanes (ABBs) and report the first electrochemical protocol for the synthesis of chemo-selective trifluoromethanesulfonylated and trifluoromethylated azetidine derivatives via direct anodic oxidation. The key features of this strategy involve: (i) electrochemical anodic oxidation of ABB to form a N-centered radical cation, (ii) a rare [2,3]-sigmatropic shift of sulfone, (iii) selective oxidation of Langlois’ reagent (NaSO₂CF₃), and (iv) the kinetic study of the developed methodology. The strategy exhibits broad substrate scope and scalability, making it practical. Installation of generated azetidines into marketed drug motifs, including ibuprofen, naproxen, and olaparib derivative, demonstrates the method's utility. Mechanistic investigations, supported by control experiments, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS), provided key insights into the reaction pathway. This electrochemical approach advances the strain-release chemistry of ABBs and offers a promising platform for future developments.

This review systematically summarizes the research progress on the electrocatalytic reduction of furfural, elucidates the formation mechanisms of furfuryl alcohol, 2-methylfuran, and hydrofuroin, describes the methods for reaction pathway control through reaction environment and catalyst engineering, proposes core principles for catalyst design, and outlines future research challenges in this field.

Furfural serves as a critical bridge connecting lignocellulosic feedstocks with the biorefinery industry. Its catalytic upgrading, particularly hydrogenation and reduction, constitutes a core pathway for synthesizing diverse chemicals and biofuels. In recent years, the electrochemical reduction of furfural has gained significant interest, driven by the large-scale development of renewable electricity and its mild reaction conditions. This review comprehensively summarizes recent advances in the electrocatalytic reduction of furfural into value-added chemical products (such as furfuryl alcohol, 2-methylfuran, and hydrofuroin). It places a strong emphasis on the comprehensive elucidation of reaction mechanisms and advanced strategies for modulating reaction pathways through catalyst design, thereby establishing the groundwork for future electrocatalyst development. Furthermore, it provides a detailed discussion of key experimental characterization techniques and theoretical computational methods employed in mechanistic and active site studies, while outlining the challenges and future directions in this field.

An efficient electrochemical intermolecular annulation of diarylphosphine oxides with alkynes is established. Using DABCO as an organic mediator, benzo[b]phosphole oxides are synthesized under transition-metal- and oxidant-free conditions. High-surface-area carbon electrodes are essential for the reaction. The electrochemical reaction proceeded via phosphine radical intermediates through multiple reaction pathways.

The electrochemical intermolecular annulation of diarylphosphine oxides with alkynes for the synthesis of benzo[b]phosphole oxides has been reported. The reaction proceeded under transition-metal- and oxidant-free conditions via indirect electrolysis, using 1,4-diazabicyclo[2.2.2]octane as a mediator. High-surface-area carbon electrodes, such as carbon felt and reticulated vitreous carbon, are essential for this reaction. Several diarylphosphine oxides and alkynes were applied to electrochemical annulation, and the corresponding benzo[b]phosphole oxides were obtained. Mechanistic studies suggested that the reaction proceeds via radical intermediates generated through multiple pathways.

Silver-catalyzed [3 + 2] cycloaddition of aryldiazonium salts and (diazomethyl)dimethylphosphine oxide is developed as an approach to 2,5-disubstituted tetrazoles bearing a P(O)(Alkyl)₂ group. The method has wide scope and low susceptibility toward electronic and steric effects in the diazonium salt component.

A convenient approach to 2,5-disubstituted tetrazoles bearing a dialkylphosphine oxide substituent at the C-5 position is developed. The method involves silver-catalyzed [3 + 2] cycloaddition of (diazomethyl)dialkylphosphine oxide and aryl diazonium salts. The proposed reaction is compatible with various substituents at the aryl ring and has low susceptibility to their electronic and steric effects. Several heterocyclic diazonium salts were also involved into the transformation successfully. The proposed reaction pathway may include synchronous [3 + 2] cycloaddition or two-step formation of the tetrazole ring starting with electrophilic attack of aryl diazonium salt at the diazoalkane carbon atom.

Selective electrochemical benzylic C─H pyridination is achieved in an undivided flow cell using a tailored pyridine. Electronic tuning suppresses competing aromatic substitution and enables the formation of versatile benzylic pyridinium intermediates, which undergo diverse downstream transformations to afford primary benzylamines and a wide range of carbon- and heteroatom-functionalized products under practical and scalable conditions.

ABSTRACT

C─H diversification strategies that enable access to various C─X (X = heteroatom) and C─C bonds are of central importance in synthetic chemistry. Here we present a benzylic C─H diversification protocol that merges electrochemical C─H pyridination with subsequent aminolysis or substitution to access unprotected benzylamines and a wide range of benzylic products. The electrochemical transformation proceeds in an undivided flow cell under oxidant- and transition-metal-free conditions and shows broad generality across electron-rich, electron-deficient, and halogenated alkylarenes. A key element is the use of a tailored pyridine with appropriate electronic properties, which suppresses undesired aromatic substitution while facilitating aminolysis and nucleophilic substitution of the pyridinium intermediate. The practicality of this method is underscored by a continuous operation in parallel microreactors, which furnished more than 100 g of benzylamine product.

Co/CoO heterostructured composites supported on reduced graphene oxide (rGO) are prepared via rapid synthesis based on magnetic induction heating for 10 s, and the sample prepared at 400 A exhibits the best bifunctional activity toward HER and OER in alkaline media. In electrochemical water splitting, the performance is over 260 mV better than that based on commercial benchmarks.

ABSTRACT

Metal/carbon-based nanocomposites have attracted significant interest for electrochemical water splitting due to their unique interfacial electronic structures, abundant active sites, and catalytic bifunctionality toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, Co/CoO-rGO composites consisting of Co/CoO heterostructured nanoparticles encapsulated within a graphitized carbon scaffold are produced via magnetic induction heating at controlled currents for 10 s with cobalt(II) nitrate and reduced graphene oxide (rGO) loaded on nickel foam and effectively catalyze both HER and OER in alkaline media. Among the series, the sample prepared at 400 A for 10 s exhibits the best performance, featuring an overpotential of −144 mV for HER and +390 mV for OER at 10 mA cm^{− 2} and 50 mA cm^{− 2}, respectively. The bifunctional activity can then be exploited for full water splitting, where a low cell voltage of 1.61 V is needed to generate a current density of 10 mA cm⁻², 260 mV better than that with commercial Pt/C and RuO₂. The remarkable performance is attributed to the synergistic interaction between the Co and CoO domains, enhanced charge transfer at the heterojunction interface, and conductive carbon support. These results highlight the potential of Co/CoO-based nanocomposites as efficient and low-cost catalysts for overall water splitting and the scalability of the MIH technology.

Electrochemical dehydration of carboxamides to nitriles is achieved using thiocyanate-mediated activation, avoiding stoichiometric reagents. In an undivided cell at ambient conditions, 18 aromatic and aliphatic substrates give good-to-excellent yields (up to 84%) with functional-group tolerance. Cyclic voltammetry supports an EC-type-mediated oxidation. The method is scalable with minimal loss in efficiency, offering a mild and sustainable route to nitriles.

An efficient electrochemical strategy for the dehydration of carboxamides to their corresponding nitriles is reported. This method replaces conventional dehydrating reagents with a thiocyanate-mediated electrochemical activation, providing a safer, milder, and more sustainable alternative. Under optimized conditions in an undivided cell, 18 examples of aromatic and aliphatic carboxamides were smoothly converted to the corresponding nitriles at ambient temperature in good-to-excellent yields (up to 84%). Hexafluoroisopropanol proved to be essential for reaction efficiency, while tetrabutylammonium thiocyanate acted as a redox mediator, as confirmed by cyclic voltammetry studies, which revealed an EC-type-mediated oxidation process. The method demonstrates broad functional-group tolerance, including halogenated, methoxylated, and sterically hindered substrates, as well as complex molecules derived from pharmaceuticals and natural products. Importantly, the protocol was successfully scaled up eightfold with minimal loss in yield, illustrating its robustness and practical applicability. Mechanistically, anodic oxidation of thiocyanate generates highly reactive species that activate the amide functionality, leading to nitrile formation via an oxidative dehydration pathway, while hydrogen evolution occurs at the cathode. This work expands the synthetic utility of electrochemical dehydration reactions and offers a valuable, environmentally responsible route to nitrile-containing compounds of broad relevance for pharmaceuticals, agrochemicals, and materials science.

Catalysis Rules! The year 2025 marks the 20^th anniversary of diarylprolinol silyl ethers in asymmetric organocatalysis. During the first decade after their discovery, these catalysts have been established as one of the most versatile tools in aminocatalysis. Although now considered mature, recent years have witnessed renewed innovation. We outlined these developments, demonstrating that this remains a rapidly evolving field.

ABSTRACT

A new chapter starts now. Since its discovery in 2005, the diarylprolinol silyl ether catalytic concept has emerged as a general and reliable aminocatalytic tool for the synthesis of enantioenriched molecules. Recently its combination with emerging technologies, as well as its application in more complex molecular systems has opened new avenues for novel enantioenriched scaffolds. In this review, we will highlight these recent developments, unfolding five primary categories that define new horizons in the use of diarylprolinol silyl ethers: Photochemical-, electrochemical-, dual-catalytic transformations, higher-order cycloadditions and applications in total synthesis of complex natural products.

Lignins from γ-valerolactone organosolv fractionation were depolymerised in ethanol using unsupported molybdenum catalysts. Over 90% yields of low-molecular-weight lignin oil were obtained with minimal char formation, yields of the aromatic monomers being 7–16 wt%. Furthermore, we show how the product properties, like molecular weight and hydroxyl content, can be tuned by modifying the depolymerisation conditions.

Lignin is an attractive feedstock for a wide variety of applications ranging from aromatic chemicals and transportation fuels to resins and coatings. Emerging biorefinery concepts, like the organosolv process, enable the separation of all the lignocellulose components, and moreover, produce lignins of high quality and purity susceptible to valorisation by depolymerisation. In this work, we focus on the depolymerisation of lignins obtained by γ-valerolactone (GVL) organosolv fractionation of four biomass feedstocks, eucalyptus, white birch, sugarcane bagasse and Scots pine. We demonstrate that lignins extracted with the GVL process are depolymerised using unsupported molybdenum-based catalysts under reductive conditions in supercritical ethanol. As a result, over 90% yields of low-molecular-weight lignin oils are obtained with minimal char formation, yields of the aromatic monomers being 7–16 wt%. Furthermore, the design of experiments method is used to analyse the effect of depolymerisation conditions, catalyst, hydrogen loading and temperature, on the yields and properties of the product fractions. Notably, we show that the properties of the lignin oils and monoaromatics can be tuned towards the targeted application by modifying the depolymerisation conditions.

A mechanochemical Kolbe–Schmitt reaction of disodium catecholate enables the synthesis of mono- and dicarboxylated catechols at low temperature and CO₂ pressure. Directly derivatizing the resulting carboxylic acid and phenolic moieties in the obtained mixture provides plasticizer blends with efficiencies competitive to commercial benchmarks.

ABSTRACT

Catechol, an important aromatic platform molecule which can be derived from biomass, was carboxylated by mechanochemical Kolbe–Schmitt reaction of disodium catecholate with CO₂, providing a mixture of mono- and dicarboxylated catechol derivatives. While classical protocols require harsh reaction conditions, involving a high temperature and/or CO₂ pressure, a mild ball milling method was developed. This represents the first mechanochemical Kolbe–Schmitt reaction featuring a low CO₂ pressure and reactivity at room temperature. From the individual catechol-based mono- and dicarboxylic acid reaction products, a library of novel renewable plasticizers was synthesized through esterification of the carboxylic acid functionalities and O-acylation of the phenolic hydroxy groups. The resulting esters were evaluated in poly(vinylchloride) (PVC) and poly(lactic acid) (PLA), revealing plasticizing efficiencies competitive to benchmark commercial plasticizers. These efficiencies were maintained when the best performing ester substitution pattern was installed on the ball mill-derived mixture of mono- and dicarboxylated catechols, making resource intensive separation (e.g. chromatographic separation) of these ortho-dihydroxybenzene(di)carboxylic acids redundant.