Search Results (119)

For those who did not follow the invention and development of enantioselective catalysis, this review introduces pertinent historical aspects of the field and presents the scientific concepts of asymmetric bio- and organocatalysis. They are powerful technologies applied in organic laboratories and industry. They realize chiral amplification by converting inexpensive achiral substrates and reagents into enantiomerically enriched products using readily recoverable solvents, if any are used. Racemic substrates can also be deracemized catalytically. More sustainable fabrications are now available that require neither toxic metallic species nor costly reaction conditions in terms of energy, atmosphere control, product purification, and safety. Nature has been the source of the first asymmetric catalysts (microorganisms, enzymes, alkaloids, amino acids, peptides, terpenoids, sugars, and their derivatives). They act as temporary chiral auxiliaries and lower the activation free energy of the reaction by altering the reaction mechanism. Reductions, oxidations, carbon-carbon and carbon-heteroatom bond-forming reactions are part of the process panoply. Asymmetric catalyzed multicomponent and domino reactions are becoming common. Typical modes of activation are proton transfers, hydrogen bonded complex formation, charged or uncharged acid/base pairing (e.g., σ-hole catalysts), formation of equilibria between achiral aldehydes and ketones with their chiral iminium salt or/and enamine intermediates, umpolung of aldehydes and ketones by reaction with N-heterocyclic carbenes (NHCs), phase transfer catalysis (PTC), etc. Often, the best enantioselectivities are observed with polyfunctional catalysts derived from natural compounds, but not always. They may combine to form chiral structures containing nitrogen, phosphorus, sulfur, selenium, and iodine functional moieties. Today, man-made enantiomerically enriched catalysts, if not enantiomerically pure, are available in both enantiomeric forms. Being robust, they are recovered and reused readily. Full article

Chemical complexity is not a nuisance to be minimized in origin of life research, it is an enabling condition. This second edition of the Special Issue on the Origin of Life in Chemically Complex Messy Environments gathers contributions that embrace multicomponent mixtures, dynamic geochemical settings, and nonequilibrium processes. The papers collected here survey surface hydrothermal routes to reactive nitriles, groundwater evolution of alkaline lakes, and transition metal sulfide-driven amino acid and amide formation without cyanide. They report one pot nucleoside and nucleotide synthesis from formamide over cerium phosphate, review non aqueous organophosphorus pathways, and probe peptide rich mixtures and formose type networks under serpentinization associated minerals. The issue also advances conceptual frameworks, including atmospheric photochemical signatures for biosignature discrimination, the role of chiral mineral surfaces in enantioseparation, and computational simulations of the origin of LUCA. Together, these studies position messy chemistry as a crucible that turns chemical diversity and environmental heterogeneity into routes toward organization and function. Full article

Coordination complexes play a crucial role in modern research. 4-benzopyranone-2-carboxylic acid is a fascinating class of molecules with numerous applications, including the synthesis of pharmaceuticals and valuable chiral compounds. Antibacterial and tuberculostatic medicines, HIV protease inhibitors, intermediates in organic synthesis, and organic catalysis are only a few of the biological applications of chiral complexes. In this study, the synthesis of four metal complexes, C₃₀H₂₈N₂NiO₁₂ [Ni(bzpyr)₂(py)₂(H₂O)₂] (I), C₃₀H₂₄CoN₂O₁₀ [Co(bzpyr)₂(py)₂(H₂O)₂] (II), C₂₀H₂₀O₁₃Zn [Zn(bzpyr)₂(H₂O)₃] (III), and C₃₀H₂₂CuN₂O₉ [Cu(bzpyr)₂(py)₂(H₂O)] (IV), is reported via direct reactions of 4-benzopyranone-2-carboxylic acid with metal salts and pyridine in anhydrous ethanol. Single-crystal X-ray diffraction analysis revealed that complexes I and II crystallize in the chiral space group P-1, whereas III and IV crystallize in the centrosymmetric space group P2₁/c. The structures of these complexes were further characterized by infrared spectroscopy, UV-Visible Diffuse Reflectance Spectroscopy, electrospray ionization mass spectrometry (ESI-MS), elemental analysis, nuclear magnetic resonance, electron paramagnetic resonance spectroscopy and single-crystal X-ray diffraction. In addition, the cytotoxic activities of complexes I–IV were evaluated against the human tumor cell lines K562, A549, HepG2, MDA-MB-231, and SW480, and molecular docking studies were conducted on the four complexes. Full article

The Kabachnik–Fields (KF) reaction is a versatile three-component method for the condensation of amines, carbonyl compounds, and P–H reagents, enabling efficient synthesis of α-aminophosphonates—key bioactive and functional molecules. This review critically examines the literature from the last 25 years. However, with regard to mechanistic aspects, selected earlier seminal studies are also considered when necessary to provide a coherent and comprehensive mechanistic framework. Advances in catalyst-free methodologies, sustainable synthetic approaches, and Lewis and Brønsted acid catalysis are discussed, alongside developments in enantioselective KF reactions in the presence of chiral metal complexes or organocatalysts. Full article

Chiral coordination compounds are of growing interest due to their structural diversity and wide applicability. Besides chirality, alcohol and especially oxime-functionalized limonene derivatives confer water solubility, stability, and the appropriate reactivity to enable their use in asymmetric catalysis—such as allylic substitution, alkynylation, transfer hydrogenation, and selective C–C bond formation. Biologically, they have shown promising anticancer, antibacterial, and antibiofilm activity. This review presents an integrated overview of the synthesis, properties, and applications of chiral transition metal complexes featuring ligands derived from inexpensive, naturally occurring R- and S-limonene substrates, and explore their roles in catalysis and biological activity. Full article

This review updates the field of enantioselective copper-catalysed domino reactions promoted by chiral green copper catalysts, covering the literature since 2017. These complexes are derived from a diversity of chiral ligands, including mostly bisoxazolines and biphosphines along with monophosphines, N-heterocyclic carbenes, proline derivatives, phosphoric acids, phosphoramidates, and different types of N,N-ligands. The review shows that asymmetric copper catalysis, that suits the growing demand for greener processes, offers a real opportunity to replace toxic and expensive metals in the near future. Full article

We propose a single-phase chiral elastic metamaterial capable of simultaneously exhibiting negative effective mass density and negative bulk modulus in the ultrasonic frequency range. The unit cell consists of a regular hexagonal frame connected to a central circular mass through six obliquely oriented, slender aluminum beams. The design avoids the manufacturing complexity of multi-phase systems by relying solely on geometric topology and chirality to induce dipolar and rotational resonances. Dispersion analysis and effective parameter retrieval confirm a double-negative frequency region from 30.9 kHz to 34 kHz. Finite element simulations further demonstrate negative refraction behavior when the metamaterial is immersed in water and subjected to 32 kHz and 32.7 kHz incident plane wave. Equifrequency curves (EFCs) analysis shows excellent agreement with simulated refraction angles, validating the material’s double-negative performance. This study provides a robust, manufacturable platform for elastic wave manipulation using a single-phase metallic metamaterial design. Full article

Axially chiral compounds play a pivotal role in organic synthesis, materials science, and pharmaceutical development. Among the various strategies for their construction, enantioselective iodination and bromination have emerged as powerful and versatile approaches, enabling the introduction of halogen functionalities that serve as valuable synthetic handles for further transformations. This review highlights recent advances in atroposelective iodination and bromination, with a particular focus on the synthesis of axially chiral biaryl and heterobiaryl frameworks. Key catalytic systems are discussed, including transition metal complexes, small-molecule organocatalysts, and high-valent metal catalysts in combination with chiral ligands or transient directing groups. Representative case studies are presented to elucidate mechanistic pathways, stereochemical induction models, and synthetic applications. Despite notable progress, challenges remain, such as expanding substrate scope, improving atom economy, and achieving high levels of regio- and stereocontrol in complex molecular settings. This review aims to provide a comprehensive overview of these halogenation strategies and offers insights to guide future research in the atroposelective synthesis of axially chiral molecules. Full article

Fluorinated organic molecules have become indispensable in modern chemistry, owing to the unique properties imparted by fluorine to other compounds, including enhanced metabolic stability, controlled lipophilicity, and improved bioavailability. The site-selective incorporation of fluorine atoms into organic frameworks is essential in pharmaceutical, agrochemical, and material science research. In recent years, catalytic fluorination has become an important methodology for the efficient and selective incorporation of fluorine atoms into complex molecular architectures. This review highlights advances in catalytic fluorination reactions over the past six years and describes the contributions of transition metal catalysts, photocatalysts, organocatalysts, and electrochemical systems that have enabled site-selective fluorination under a variety of conditions. Particular attention is given to the use of well-defined fluorinating agents, including Selectfluor, N-fluorobenzenesulfonimide (NFSI), AlkylFluor, Synfluor, and hypervalent iodine reagents. These reagents have been combined with diverse catalytic systems, such as AgNO₃, Rh(II), Mo-based complexes, Co(II)-salen, and various organocatalysts, including β,β-diaryl serine catalysts, isothiourea catalysts, and chiral phase-transfer catalysts. This review summarizes proposed mechanisms reported in the original studies and discusses examples of electrophilic, nucleophilic, radical, photoredox, and electrochemical fluorination pathways. Recent developments in stereoselective and more sustainable protocols are also examined. By consolidating these strategies, this article provides an up-to-date perspective on catalytic fluorination and its impact on synthetic organic chemistry. Full article

Chiral ansa-η⁵-complexes of transition metals have shown remarkable efficacy in organometallic synthesis and catalysis. Additionally, enantiomerically pure ansa-complexes hold promise for the development of novel chiral materials and pharmaceuticals. The discovery and synthesis of a diverse range of group IVB and IIIB metal complexes represents a significant milestone in the advancement of stereoselective catalytic methods for constructing metal-C, C-C, C-H, and C-heteroatom bonds. The synthesis of enantiomerically pure metallocenes can be accomplished through several strategies: utilizing optically active precursors of η⁵-ligands, separation of diastereomers of complexes with enantiomerically pure agents, and synthesis via the stereocontrolled reactions of enantiomerically pure σ-complexes with prochiral anions of η⁵-ligands. This review focuses on the analysis of various nuances of the synthesis of enantiomerically pure ansa-η⁵-complexes of titanium and lanthanum families. Their applicability as effective catalysts in asymmetric carbomagnesiation, carbo- and cycloalumination, oligo- and polymerization, Diels–Alder cycloaddition, reactions of zirconaaziridines, cyclization, hydrosilylation, hydrogenation, hydroamination, and other processes are highlighted as well. Full article

The development of new, more effective, and selective anticancer agents is one of the most important tasks of modern medicinal chemistry. Recently, we have found that non-classical Pd(II) pincer complexes derived from thiophosphoryl-appended picolinamides exhibit promising cytotoxic properties. In this work, the potential of this class of metal-based derivatives was studied on an extended family of Pd(II) complexes with a deprotonated amide core featuring thiophosphoryl pendant arms, readily obtained by the direct cyclopalladation of new functionalized amide ligands upon interaction with PdCl₂(NCPh)₂ under mild conditions. The ligands, in turn, were obtained by conventional amide coupling methods using (aminobenzyl)- and (aminomethyl)diphenylphosphine sulfides as the key precursors and different N- and S-donor-substituted carboxylic acids. The effect of an acid component and carbon chirality in the ligand framework on the bioactivity of the resulting Pd(II) pincer complexes was elucidated by evaluating their cytotoxicity against different solid and blood cancer cell lines, apoptosis induction ability, and P-glycoprotein (P-gp) affinity, which revealed the high anticancer potential of some of them, and in particular, the potential to overcome drug resistance associated with P-gp overexpression. The representative palladocycle was also shown to possess moderate antibacterial activity. Full article

Vibrational circular dichroism (VCD) enhancement by low-lying electronic states (LLESs) is a fascinating phenomenon, but accounting for it theoretically remains a challenge despite significant research efforts over the past 20 years. In this article, we synthesized two transition metal complexes using the tetradentate Schiff base ligands (R,R)- and (S,S)-N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine with Co(II) and Mn(III), referred to as Co(II)-salen-chxn and Mn(III)-Cl-salen-chxn, respectively. Their stereochemical properties were explored through a combined experimental chiroptical spectroscopic and theoretical approach, with a focus on Co(II)-salen-chxn. Extensive conformational searches in CDCl₃ for both high- and low-spin states were carried out and the associated infrared (IR), VCD, ultraviolet-visible (UV-Vis) absorption, and electronic circular dichroism (ECD) spectra were simulated. A good agreement between experimental and simulated data was achieved for IR, VCD, UV-Vis, and ECD, except in the case of VCD of Co(II)-salen-chxn which exhibits significant intensity enhancement and monosignate VCD bands, attributed to the LLESs. Interestingly, detailed comparisons with Mn(III)-Cl-salen-chxn and previously reported Ni(II)-salen-chxn and Cu(II)-salen-chxn complexes suggest that the enhancement factor is predicted by the current density functional theory simulations. However, the monosignate signatures observed in the experimental Co(II) VCD spectrum were not captured theoretically. Based on the experiment and theoretical VCD and ECD comparison, it is tentatively suggested that Co(II)-salen-chxn exists in both low- and high-spin states, with the former being dominant, while Mn(III)-Cl-salen-chxn in the high-spin state. The study indicates that VCD enhancement by LLESs is at least partially captured by the existing theoretical simulation, while the symmetry consideration in vibronic coupling provides further insight into the mechanisms behind the VCD sign-flip. Full article

Ionic liquids have been utilized in numerous significant applications within the field of chemistry, particularly in organic chemistry, due to their unique physical and chemical properties. In the realm of asymmetric transition-metal-catalyzed transformations, chiral ionic-liquid-supported ligands and their corresponding transition-metal complexes have facilitated these processes in unconventional solvents, especially ionic liquids and water. These innovative reaction systems enable the recycling of transition-metal catalysts while producing optically active organic molecules with comparable or even higher levels of chemo-, regio-, and stereoselectivity compared to their parent catalysts. In this short review, we aim to provide an overview of the structures of chiral ionic-liquid-supported ligands and the synthetic pathways for these ligands and catalysts. Various synthetic methodologies are demonstrated based on the conceptual frameworks of diverse chiral ionic-liquid-supported ligands. We systematically present the structures and comprehensive synthetic pathways of the chiral ionic-liquid-supported ligands and the typical corresponding transition-metal complexes that have been readily applied to asymmetric processes, categorized by their parent ligand framework. Notably, the crucial experimental procedures are delineated in exhaustive detail, with the objective of enhancing comprehension of the pivotal aspects involved in constructing chiral ionic-liquid-tagged ligands and compounds for both scholars and readers. Considering the current limitations of such ligands and catalysts, we conclude with remarks on several potential research directions for future breakthroughs in the synthesis and application of these intriguing ligands. Full article

Four mononuclear bioefficient zinc coordination complexes [Zn(NN)₃](ClO₄)₂ (A–D) involving chiral bidentate Schiff base ligands have been synthesized and characterized by IR, ¹H, and ¹³C NMR spectroscopy and mass spectrometry. X-ray crystal structures of three of the zinc complexes revealed that the zinc metal ion is hexacoordinated, exhibiting a distorted octahedral geometry where both the nitrogen atoms (NN = pyridyl and imine) of imines are coordinated to the central zinc ion. The isolated zinc complexes were evaluated for their antimicrobial activity in vitro against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, displaying varying levels of growth inhibition. An acute toxicity test conducted using Artemia salina and Swiss albino mice showed that the zinc complexes A–D were non-toxic towards A. salina at concentrations below 414, 564, 350, and 385 µM, respectively, and did not affect liver biochemical parameters, although pyknosis was induced in hepatocytes of the treated mice. Full article

The use of chiral organic ligands as linkers and metal ion nodes with specific coordination geometry is an effective strategy for creating homochiral structures with potential ferroelectric properties. Natural Cinchona alkaloids, e.g., quinine and cinchonine, as compounds with a polar quinuclidine fragment and aromatic quinoline ring, are suitable candidates for the construction of molecular ferroelectrics. In this work, the compounds [CnZnCl₃]·MeOH and [CnZnBr₃]·MeOH, which crystallize in the ferroelectric polar space group P2₁, were prepared by reacting the cinchoninium cation (Cn) with zinc(II) chloride or zinc(II) bromide. The structure of [CnZnBr₃]·MeOH was determined from single-crystal X-ray diffraction analysis and was isostructural with the previously reported chloride analog [CnZnCl₃]·MeOH. The compounds were characterized by infrared spectroscopy, and their thermal stability was determined by thermogravimetric analysis and temperature-modulated powder X-ray diffraction experiments. The intermolecular interactions of the different cinchoninium halogenometalate complexes were evaluated and compared. Full article