Search

The preparation of heterocyclic compounds using 1,3-dipolar cycloaddition chemistry is now well recognized in the fields of organic synthesis, drug discovery efforts, polymer chemistry, and materials science. As highlighted in this review, a growing area of interest in organic synthesis involves the enantioselectivity aspects of dipolar cycloaddition chemistry for the preparation of many different classes of natural products. Asymmetric synthesis of natural products using chiral substrates has been elegantly accomplished over the past decade using an assortment of dipole intermediates and represents the focus of this review article.

A novel Cu(II)-catalyzed cross-dehydrogenative coupling reaction of N′-aryl acylhydrazines and dialkyl phosphites has been developed for the synthesis of phosphorylhydrazides by using NMO as an external oxidant and AgNO3 as additive. Various N′-aryl acylhydrazines were mildly and regioselectively converted to corresponding phosphorylhydrazides with good to excellent yields.

Ceria (CeO2) is used as support material in heterogeneous catalysts since decades and, recently, ceria itself was also demonstrated to be catalytically active for some reactions. Atomistic and electronic structure details of the functioning of ceria in catalysis can nowadays be successfully uncovered with the help of computational modeling based on the density functional theory (DFT). Yet, the majority of such computational studies undertaken so far relied on extended models of surfaces, which are adequate for the description of surface science processes and phenomena, but neglect the nanostructured nature of ceria in many catalysts. This Perspective focuses on discussing DFT calculations of various nanostructured models of ceria and its composites relevant for catalysis. Pivotal consequences of ceria nanostructuring for its role in catalysts derived from the computational studies are documented and supported by experimental results. The presented case studies shed light on several actively debating issues of ceria usage in catalysis and other applications. For instance: What makes ceria nanoparticles in a certain size range dramatically more reactive in oxidative processes? Is the oxygen storage capacity of ceria solely due to its ability to easily form and heal oxygen vacancies or do alternative mechanisms also operate at the nanoscale? How prone are metal particles deposited on ceria to sintering or dispersion and how is this interplay controlled by the nanostructuring of the support? Under what conditions will the transfer of lattice oxygen atoms from ceria support to the metal particles deposited thereon become energetically favorable? How can the electron transfer across the metal-ceria interface be measured and its peculiarities rationalized? The discussed examples show that accounting for ceria nanostructuring in catalysts is essential for performing trustworthy computational modeling. Such realistic description is possible thanks to a variety of the recently developed dedicated models representative of ceria at the nanoscale.

An efficient and easily scalable NHC–copper(I) halide-catalyzed addition of terminal alkynes to 1,1,1-trifluoromethyl ketones, carried out on water for the first time, is reported. A series of addition reactions were performed with as little as 0.1–2.0 mol % of [(NHC)CuX] (X=Cl, Br, I, OAc, OTf) complexes, providing tertiary propargylic trifluoromethyl alcohols in high yields and with excellent chemoselectivity from a broad range of aryl- and more challenging alkyl-substituted trifluoromethyl ketones (TFMKs). DFT calculations were performed to rationalize the correlation between the yield of catalytic alkynylation and the sterics of N-heterocyclic carbenes (NHCs), expressed as buried volume (%VBur), indicating that steric effects dominate the yield of the reaction. Additional DFT calculations shed some light on the differential reactivity of [(NHC)CuX] complexes in the alkynylation of TFMKs. The first enantioselective version of a direct alkynylation in the presence of C1-symmetric NHC–copper(I) complexes is also presented.

The Chan–Evans–Lam reaction is a valuable C–N bond forming process. However, aryl boronic acid pinacol (BPin) ester reagents can be difficult coupling partners that often deliver low yields, in particular in reactions with aryl amines. Herein, we report effective reaction conditions for the Chan–Evans–Lam amination of aryl BPin with alkyl and aryl amines. A mixed MeCN/EtOH solvent system was found to enable effective C–N bond formation using aryl amines while EtOH is not required for the coupling of alkyl amines.

‘Hierarchy’ is a property which can be attributed to a manifold of different immaterial systems, such as ideas, items and organisations or material ones like biological systems within living organisms or artificial, man-made constructions. The property ‘hierarchy’ is mainly characterised by a certain ordering of individual elements relative to each other, often in combination with a certain degree of branching. Especially mass-flow related systems in the natural environment feature special hierarchically branched patterns. This review is a survey into the world of hierarchical systems with special focus on hierarchically porous zeolite materials. A classification of hierarchical porosity is proposed based on the flow distribution pattern within the respective pore systems. In addition, this review might serve as a toolbox providing several synthetic and post-synthetic strategies to prepare zeolitic or zeolite containing material with tailored hierarchical porosity. Very often, such strategies with their underlying principles were developed for improving the performance of the final materials in different technical applications like adsorptive or catalytic processes. In the present review, besides on the hierarchically porous all-zeolite material, special focus is laid on the preparation of zeolitic composite materials with hierarchical porosity capable to face the demands of industrial application.

Two new compounds (I) and (II) are isolated, possessing a rare pentacyclic carbon skeleton typical for lichen metabolism, and quite unusual in the vegetal kingdom.

Surface- and tip-enhanced Raman spectroscopy (SERS and TERS) techniques exhibit highly localized chemical sensitivity, making them ideal for studying chemical reactions, including processes at catalytic surfaces. Catalyst structures, adsorbates, and reaction intermediates can be observed in low quantities at hot spots where electromagnetic fields are the strongest, providing ample opportunities to elucidate reaction mechanisms. Moreover, under ideal measurement conditions, it can even be used to trigger chemical reactions. However, factors such as substrate instability and insufficient signal enhancement still limit the applicability of SERS and TERS in the field of catalysis. By the use of sophisticated colloidal synthesis methods and advanced techniques, such as shell-isolated nanoparticle-enhanced Raman spectroscopy, these challenges could be overcome.

Many natural products that consist of quinoline core are found to be bioactive and the versatility of quinoline and its derivatives have attracted great attention in the field of drug development. As a result, in recent years, many green and sustainable synthetic approaches for the synthesis of structurally diverse quinolines have been developed. This review covers four main aspects, namely bioactive quinoline alkaloids, the biological activity and mechanism of action of quinoline-based compounds as well as various quinoline syntheses.

Formal homologation of sp2-hybridized boronic acids is achieved via cross-coupling of boronic acids with conjunctive haloaryl BMIDA components in the presence of a suitably balanced basic phase. The utility of this approach to provide a platform for diversity-oriented synthesis in discovery medicinal chemistry is demonstrated in the context of the synthesis of a series of analogues of a BET bromodomain inhibitor.

The advent of soft lithography allowed for an unprecedented expansion in the field of microfluidics. However, the vast majority of PDMS microfluidic devices are still made with extensive manual labor, are tethered to bulky control systems, and have cumbersome user interfaces, which all render commercialization difficult. On the other hand, 3D printing has begun to embrace the range of sizes and materials that appeal to the developers of microfluidic devices. Prior to fabrication, a design is digitally built as a detailed 3D CAD file. The design can be assembled in modules by remotely collaborating teams, and its mechanical and fluidic behavior can be simulated using finite-element modeling. As structures are created by adding materials without the need for etching or dissolution, processing is environmentally friendly and economically efficient. We predict that in the next few years, 3D printing will replace most PDMS and plastic molding techniques in academia.

This account critically surveys the field of side-chain transition metal-containing polymers as prepared by controlled living ring-opening metathesis polymerization (ROMP) of the respective metal-incorporating monomers. Ferrocene- and other metallocene-modified polymers, macromolecules including metal-carbonyl complexes, polymers tethering early or late transition metal complexes, etc. are herein discussed. Recent advances in the design and syntheses reported mainly during the last three years are highlighted, with special emphasis on new trends for superior applications of these hybrid materials.

The first examples of iminium catalyzed Nazarov cyclizations of divinyl ketones are presented. Experiments describing hydroxylamine catalysis of the cyclization of eight α-alkoxy divinyl ketones (60–79% yield) and one unactivated divinyl ketone (38% yield) are reported. Phenyl substitution at the β-position of the divinyl ketone inhibits cyclization, whereas β-alkyl substituted α-alkoxy divinyl ketones readily cyclize.

An efficient PBu3-catalyzed α-addition of the P(O)–H bond to ethyl phenylpropiolate has been developed. This strategy offers a facile method for the preparation of synthetically useful alkenyl phosphonates and phosphinates proceeding under neutral reaction conditions with high atom economy.

As new uses for larger scale energy storage systems are realized, new chemistries that are less expensive or have higher energy density are needed. While lithium-ion systems have been well studied, the availability of new energy storage chemistries opens up the possibilities for more diverse strategies and uses. One potential path to achieving this goal is to explore chemistries where a multivalent ion such as Ca2+ or Mg2+ is the active species. Herein, we demonstrate this concept for a Ca-ion system utilizing manganese hexacyanoferrate (MFCN) as the cathode to intercalate Ca reversibly in a dry nonaqueous electrolyte. Through characterization via X-ray absorption near-edge spectroscopy, it is determined that only the manganese changes oxidation state during cycling with Ca. X-ray diffraction indicates the MFCN maintains its crystallinity during cycling, with only minor structural changes associated with expansion and contraction. Furthermore, we have demonstrated the first rechargeable Ca-ion battery uti...

The title compound is prepared by dropwise addition of an aqueous NiCl2 solution to solid NaBH4 followed by annealing the precipitate at 375 °C in vacuo for 2 h.

The chemistry of the azido-bridged coordination clusters continues to attract the intense interest of synthetic inorganic chemists and scientists working in the interdisciplinary field of Molecular Magnetism. In this review we have focused on describing aspects of synthesis, structures and magnetic properties of azido-bridged 3d- and d/d′-metal clusters with nuclearities equal to or higher than 4. Some of the clusters display slow magnetic relaxation at very low temperatures, mainly due to the ferromagnetic metal⋯metal exchange interactions propagated through the end-on azido ligand. The chemistry of polynuclear, azido-bridged 3d-metal complexes embedded in lacunary polyoxometalates is also discussed.

A new polymorph of MnP4 was prepared by reaction of the elements via chemical vapor transport with iodine as transporting agent. The crystal structure was refined using single-crystal diffraction data (space group Cc, no. 9, a = 5.1049(8) A, b = 10.540(2) A, c = 10.875(2) A, β = 93.80(2)°). The phase is called γ-MnP4 as it is isostructural with γ-FeP4. It is the fourth reported binary polymorph in the MnP4 system, all of which are stacking variants of nets built with manganese and phosphorus atoms. In γ-MnP4, there are two Mn-Mn distances (2.93 and 3.72 A) arising from a Peierls-like distortion effectively forming Mn2 dumbbells in the structure. Magnetic and electrical conductivity measurements show diamagnetism and a small anisotropic band gap (100-200 meV) with significantly enhanced conductivity along the crystallographic a axis. Calculations of the electronic and vibrational (phonon) structures show the P-P and Mn-P bonds within the nets are mainly responsible for the stability of the phase. The similar bonding motifs of the polymorphs give rise to the existence of numerous dynamically stable variants. The calculated Helmholtz energy shows the polymorph formation to be closely tied to temperature with the 6-MnP4 structure favorable at low temperatures, the 2-MnP4 favorable between approximately 800 and 2000 K, and 8-MnP4 preferred at high temperatures.

Bis(diazo)piperidin-2-ones that are devoid of a donor substituent in the 4-position undergo a one-pot cyclopropanation/cascade dipole formation/cycloaddition reaction to produce novel azapolycycles.

The newly developed title complex proves efficient in the reductive amination of various aldehydes and ketones with primary aliphatic and aromatic amines as well as secondary amines.

The title compound is characterized by powder XRD, conductivity and Seebeck coefficient measurements, solid state NMR spectroscopy, nanoindentation measurements, and DFT calculations.

Using N′-aryl acylhydrazines as aryl donors, a novel copper(II)-catalyzed homo-coupling reaction of N′-aryl acylhydrazines has been developed for the synthesis of N′,N′-diaryl acylhydrazines. We also provided a complementary procedure for the preparation of unsymmetrical diaryl acylhydrazines via cross-coupling reaction. These protocols featured mild reaction conditions, wide functional group tolerance and highly regioselective products. Control experiments indicated that this kind of coupling reaction might undergo a transient acyl diazene intermediate.

The use of microwave radiation to drive chemical reactions has become ubiquitous in almost all fields of chemistry. In all of these areas it is principally due to rapid and convenient heating resulting in significantly higher rates of reaction, with other advantages including enhanced product selectivity and control of materials properties. Although microwave heating continues to grow as an enabling technology, fundamental research into the nature of microwave heating has not grown at the same rate. In the case of chemical reactions run in homogeneous solution, particularly synthetic organic reactions, there is considerable controversy over the origins of rate enhancement, with a fundamental question being whether there exist microwave-specific effects, distinct from what can be attained under conventional convective heating, that can accelerate a reaction rate. In this Perspective, we discuss unique aspects of microwave heating of molecules in solution and discuss the origin and nature of microwave-specific effects arising from the process of “selective heating” of reactants in solution. Integral to this discussion is work from the field of dielectric relaxation spectroscopy, which provides a model for selective heating by Debye relaxation processes. The Perspective also includes a critical discussion of hypotheses of non-thermal effects (alternatively classified here as resonant processes) and an outline of specific reaction parameters for chemical systems in which microwave-specific Debye relaxation processes can result in observable reaction rate enhancement.

α,β-Unsaturated N,N-dialkyl hydrazones undergo a mild [2 + 2] cycloaddition to allenamides when treated with a suitable gold catalyst. The method, which represents the first application of N,N-dialkyl hydrazones in gold catalysis, is compatible with a wide variety of substituents at the alkenyl moiety of the hydrazone component, proceeds with excellent levels of regio- and diastereoselectivity, and provides densely substituted cyclobutanes with good to excellent yields.

A wide variety of primary and secondary amines are suitable nucleophiles for the title reaction to form ring opening products with good levels of enantioselectivity.

Tetrahydro-3-benzazepines and tetrahydroisoquinolines are synthesized in one step from allenes and phenylethylamines or benzylamines, respectively. Mechanistically, it is assumed that activation of a C–H bond of an aromatic ring with Pd(II) occurs, directed by the primary amine, leading to the formation of a palladacycle into which an allene then undergoes insertion. The resulting π-allyl intermediate cyclizes to the products by an intramolecular allylic alkylation. The process is particularly useful with 2,3-butadienoates and amines having a quaternary carbon at the α-position.

The system CuF 2 -HF-H 2 O has been investigated at 0 °C. The solid phases in equilibrium with the solutions are CuF 2 · 2H 2 O and CuF 2 .

Three enantiomerically and geometrically pure building blocks representing fragments of the antifungal antibiotic viridenomycin have been prepared.

A second generation approach toward the synthesis of viridenomycin is described. Three key fragments of the molecule have been synthesized in stereochemically pure form. Initial studies toward the coupling of these fragments with the aim of assembling the macrocycle are detailed. Final efforts to reach the title compound are documented.

The Soai reaction and the Viedma deracemization of racemic conglomerate crystal mixtures are experimental pieces of evidence of the ability of enantioselective autocatalytic coupled networks to yield absolute asymmetric synthesis. Thermodynamically open systems or systems with non-uniform energy distributions may lead to chiral final states and, in systems able to come into thermodynamic equilibrium with their surroundings, to kinetically controlled absolute asymmetric synthesis. The understanding of network parameters and of the thermodynamic scenarios that may lead to spontaneous mirror symmetry breaking (SMSB) could assist in the development of new methods for asymmetric synthesis and enantioselective polymerizations (e.g., replicators), and to frame reasonable speculations on the origin of biological homochirality.

The secondary amines synthesized by the reaction between 2-aminophenols and aromatic aldehydes, via the reduction of the corresponding imines, were employed in the synthesis of new 2-hydroxy-2H-1,4-benzoxazine derivatives through a one-pot Petasis multicomponent reaction in good to excellent yields.

Apart from their exotic structure, radialenes have been employed as precursors of more complex polycyclic molecules. In this work we report the synthesis of the first compound having the benzo[5]radialene substructure, starting from simple materials. Such a compound proved to be a convenient diene in Diels–Alder reactions, for the preparation of highly functionalized fluorenes and benzo[b]fluorenes in a quimio- and stereocontrolled fashion.

NaB5C is prepared by solid state reaction of the elements in the molar ratio of Na:B:C = 6:5:1 (sealed boronated Ta tubes in evacuated quartz ampoule, 1000 °C, 6-8 h) and densified by high-pressure spark plasma sintering (923 K, 100 MPa, 90 min).

The domino reaction of hexanal derivative (I) with α,β-unsaturated aldehydes proceeds in the presence of a chiral diphenylsilylprolinol catalyst under mild conditions to give cyclohexene derivatives in good yields and with high enantioselectivities.

A new tunable chiral monophosphine was used as a ligand for asymmetric rhodium-catalyzed ring-opening of oxabenzonorbornadiene with amines, providing a series of chiral ring-opened products in high yields (up to 97%) and with high enantioselectivities (>99%).The reaction can be performed at rt to obtain the desired product with high enantioselectivity.

Model studies dealing with the Cu(II)- or Rh(II)-catalyzed carbenoid cyclization/cycloaddition cascade of several α-diazo indolo amido esters have been carried out as an approach to the alkaloid scandine. The Cu(II)-catalyzed reaction of an α-diazo indolo diester that contains a tethered oxa-pentenyl side chain was found to give rise to a reactive benzo[c]furan which undergoes a subsequent [4 + 2]-cycloaddition across the tethered π-bond. The reaction proceeds by the initial generation of a copper carbenoid intermediate which cyclizes onto the adjacent carbonyl group to give a reactive benzo[c]furan which in certain cases can be isolated. Disappointingly, the analogous reaction with the related amido indolo ester failed to take place, even when the tethered π-bond contained an electron-withdrawing carbomethoxy group. It would seem that the geometric requirements for the intramolecular cycloaddition of the furo[3,4-b]indole system with the tethered π-bond imposes distinct restrictions upon the bond angles ...

Highly enantioselective cascade reactions for the synthesis of fluoroindanes and chromanols derivatives are described. The cascade reactions consisted of either a double Michael reaction or Michael–hemiacetal formation via the addition of fluorobis(phenylsulfonyl)methane (FBSM) to enals. The final products were obtained in good yields with excellent stereoselectivities.

Covering: up to 2014 Dithiolopyrrolone (DTP) group antibiotics were first isolated in the early half of the 20th century, but only recently has research been reawakened by insights gained from the synthesis and biosynthesis of this structurally intriguing class of molecules. DTPs are characterized by an electronically unique bicyclic structure, which contains a compact disulfide bridge between two ene-thiols. Points of diversity within the compound class occur outside of the bicyclic core, at the two amide nitrogens. Such modifications distinguish three of the most well studied members of the class, holomycin, thiolutin, and aureothricin; the DTP core has also more recently been identified in the marine antibiotic thiomarinol, in which it is linked to a marinolic acid moiety, analog of the FDA-approved topical antibiotic Bactroban® (GlaxoSmithKline). Dithiolopyrrolones exhibit relatively broad-spectrum antibiotic activity against many Gram-positive and Gram-negative bacteria, as well as strains of Mycobacterium tuberculosis. Additionally, they have been shown to exhibit potent and selective anti-cancer activity. Despite this promising profile, there is still much unknown about the mechanisms of action for DTPs. Early reports suggested that they inhibit yeast growth at the level of transcription and that this effect is largely responsible for their distinctive microbial static properties; a similar mechanism is supported in bacteria. Elucidation of biosynthetic pathways for holomycin in Streptomyces clavuligerus and Yersinia ruckeri and thiomarinol in Alteromonas rava sp. nov. SANK 73390, have contributed evidence suggesting that multiple mechanisms may be operative in the activity of these compounds. This review will comprehensively cover the history and development of dithiolopyrrolones with particular emphasis on the biosynthesis, synthesis, biological activity and mechanism of action.

Magnetic clusters, i.e., assemblies of a finite number (between two or three and several hundred) of interacting spin centers which are magnetically decoupled from their environment, can be found in many materials ranging from inorganic compounds, magnetic molecules, artificial metal structures formed on surfaces to metalloproteins. The magnetic excitation spectra in them are determined by the nature of the spin centers, the nature of the magnetic interactions, and the particular arrangement of the mutual interaction paths between the spin centers. Small clusters of up to four magnetic ions are ideal model systems to examine the fundamental magnetic interactions which are usually dominated by Heisenberg exchange, but often complemented by anisotropic and/or higher-order interactions. In large magnetic clusters which may potentially deal with a dozen or more spin centers, the possibility of novel many-body quantum states and quantum phenomena are in focus. In this review the necessary theoretical concepts and experimental techniques to study the magnetic cluster excitations and the resulting characteristic magnetic properties are introduced, followed by examples of small clusters demonstrating the enormous amount of detailed physical information which can be retrieved. The current understanding of the excitations and their physical interpretation in the molecular nanomagnets which represent large magnetic clusters is then presented, with an own section devoted to the subclass of the single-molecule magnets which are distinguished by displaying quantum tunneling of the magnetization. Finally, some quantum many-body states are summarized which evolve in magnetic insulators characterized by built-in or field-induced magnetic clusters. The review concludes addressing future perspectives in the field of magnetic cluster excitations.