A highly enantioselective cyanation of imines (up to >99 % ee) has been developed using well-designed C₂-symmetric hydrogen bonding catalysts. This catalytic system is distinguished by its low catalyst loading (S/C up to 1000), high efficiency, extremely broad substrate scope, scalability and mild reaction conditions.

Abstract

A highly enantioselective cyanation of imines (up to >99 % ee) has been developed using well-designed C₂-symmetric hydrogen bonding catalysts. The catalytic strategy was characterized with low catalyst loading (0.1–1 mol %), easily accessible catalysts with diverse functional groups, and catalytic base additives. A wide range of imines, including the challenging N-Boc and N-Cbz protected ketimines and aldimines, as well as fluoroalkylated ketimines, were investigated under mild conditions to afford the products with good to excellent yields (up to 99 % yield) and high enantioselectivity (up to >99 % ee). Control experiments revealed that the multiple hydrogen bonding catalysts enhanced the reactivity and enantioselectivity of the Strecker reaction initiated by the base.

Two new metal-free photocatalytic cyclopropanations employing eosin in the green solvent ethanol have been developed and then applied to the synthesis of colibactin warhead models. Using the models, we show what features can lead to nucleophilic addition at the cyclopropyl unit and which ones favor a ring expansion-addition sequence. We also show that copper could be responsible for catalyzing the known oxidation of the colibactin-DNA adduct.

Abstract

Herein, we report the synthesis of a series of colibactin warhead model compounds using two newly developed metal-free photocatalytic cyclopropanation reactions. These mild cyclopropanations expand the known applications of eosin within synthesis. A halogen atom transfer reaction mode has been harnessed so that dihalides can be used as the cyclopropanating agents. The colibactin warhead models were then used to provide new insight into two key mechanisms in colibactin chemistry. An explanation is provided for why the colibactin warhead sometimes undergoes a ring expansion-addition reaction to give fused cyclobutyl products while at other times nucleophiles add directly to the cyclopropyl unit (as when DNA adds to colibactin). Finally, we provide some evidence that Cu(II) chelated to colibactin may catalyze an important oxidation of the colibactin-DNA adduct. The Cu(I) generated as a result could then also play a role in inducing double strand breaks in DNA.

This review aims to provide an overview of the key obstacles encountered by vanadium-based cathodes toward practical aqueous zinc-ion batteries, encompassing dissolution, by-product formation, and limited ion diffusion. Additionally, it highlights the latest advancements made in tackling these challenges and proposes potential directions for future research in this domain.

Abstract

Aqueous zinc-ion batteries (ZIBs) are gaining significant attention for their numerous advantages, including high safety, high energy density, affordability, and environmental friendliness. However, the development of ZIBs has been hampered by the lack of suitable cathode materials that can store Zn²⁺ with high capacity and reversibility. Currently, vanadium-based materials with tunnel or layered structures are widely researched owing to their high theoretical capacity and diversified structures. However, their long-term cycling stability is unsatisfactory because of material dissolution, phase transformation, and restrictive kinetics in aqueous electrolytes, which limits their practical applications. Different from previous reviews on ZIBs, this review specifically addresses the critical issues faced by vanadium-based cathodes for practical aqueous ZIBs and proposes potential solutions. Focusing on vanadium-based cathodes, their ion storage mechanisms, the critical parameters affecting their performance, and the progress made in addressing the aforementioned problems are also summarized. Finally, future directions for the development of practical aqueous ZIB are suggested.

Two wide-band-capturing donor-acceptor conjugates featuring bis-styrylBODIPY and perylenediimide have been newly synthesized, and the occurrence of ultrafast excitation transfer from the singlet excited perylenediimide to BODIPY, and subsequent electron transfer from the excited BODIPY to PDI have been demonstrated.

Abstract

Two wide-band-capturing donor-acceptor conjugates featuring bis-styrylBODIPY and perylenediimide (PDI) have been newly synthesized, and the occurrence of ultrafast excitation transfer from the ¹PDI* to BODIPY, and a subsequent electron transfer from the ¹BODIPY* to PDI have been demonstrated. Optical absorption studies revealed panchromatic light capture but offered no evidence of ground-state interactions between the donor and acceptor entities. Steady-state fluorescence and excitation spectral recordings provided evidence of singlet-singlet energy transfer in these dyads, and quenched fluorescence of bis-styrylBODIPY emission in the dyads suggested additional photo-events. The facile oxidation of bis-styrylBODIPY and facile reduction of PDI, establishing their relative roles of electron donor and acceptor, were borne out by electrochemical studies. The electrostatic potential surfaces of the S₁ and S₂ states, derived from time-dependent DFT calculations, supported excited charge transfer in these dyads. Spectro-electrochemical studies on one-electron-oxidized and one-electron-reduced dyads and the monomeric precursor compounds were also performed in a thin-layer optical cell under corresponding applied potentials. From this study, both bis-styrylBODIPY⋅ ⁺ and PDI⋅⁻ could be spectrally characterizes and were subsequently used in characterizing the electron-transfer products. Finally, pump–probe spectral studies were performed in dichlorobenzene under selective PDI and bis-styrylBODIPY excitation to secure energy and electron-transfer evidence. The measured rate constants for energy transfer, k _ENT, were in the range of 10¹¹ s⁻¹, while the electron transfer rate constants, k _ET, were in the range of 10¹⁰ s⁻¹, thus highlighting their potential use in solar energy harvesting and optoelectronic applications.

Wide-band-capturing artificial photosynthetic model compounds featuring bisstyrylBODIPY and perylene diimide have been newly synthesized to probe excited-state energy and electron transfer. Excited-state DFT and free-energy calculations supported the occurrence of such photo events. Pump–probe spectroscopy provided the ultimate evidence wherein the measured rate constants for energy transfer were in the range of 10¹¹ s⁻¹, while the electron transfer rate constants were in the range of 10 s⁻¹, thus highlighting their potential use in solar energy harvesting. More information can be found in the Research Article by F. Fernández-Lázaro, Á. Sastre-Santos, F. D'Souza et al. (DOI: 10.1002/chem.202301686).

Direct amination of benzene is demonstrated with a plasma microreactor. Using ammonia plasma, this process was optimized by studying the influence of temperature, residence time and power of the plasma. Various compounds were evaluated to study influence of double bond, conjugation, and aromaticity. Under optimized conditions, direct amination of benzene gave of total yield of 3.8 %.

Abstract

Amine derivatives, including aniline and allylic amines, can be formed in a single-step process from benzene and an ammonia plasma in a microreactor. Different process parameters such as temperature, residence time, and plasma power were evaluated to improve the reaction yield and its selectivity toward aminated products and avoid hydrogenated or oligomerized products. In parallel, simulation studies of the process have been carried out to propose a global mechanism and gain a better understanding of the influence of the different process parameters. The exploration of diverse related alkenes showed that the double bonds, conjugation, and aromatization influenced the amination mechanism. Benzene was the best reactant for amination based on the lifetime of radical intermediates. Under optimized conditions, benzene was aminated in the absence of catalyst with a yield of 3.8 % and a selectivity of 49 % in various amino compounds.

Sulfur trioxide acts as a strong oxidizer towards halides as well as pseudohalides. Therefore, reactions of sulfur trioxide with cyanide anions do usually not lead to the formation of cyanido-sulfates anion but to oxidation of the cyanide ion. This problem can be avoided if a sulfur trioxide-pyridine complex is used instead of neat sulfur trioxide. In this way, the oxidation power is sufficiently reduced, and the pyridine molecule can be replaced by the cyanide anion under formation of the cyanido-sulfate anion, SO₃CN⁻. Thus sulfur trioxide gets rid of the badly smelling pyridine molecule, however, at the expense of gaining the toxic cyanide anion. More information can be found in the Research Article by M. S. Wickleder and co-workers (DOI: 10.1002/chem.202301761).