Assembly State of Catalytic Modules as Chiral Switches in Asymmetric Strecker Amino Acid Synthesis

Catalytic Asymmetric Synthesis of Chiral α,α-Dialkyl Aminonitriles via Reaction of Cyanoketimines

Chiral aminonitriles not only are broadly useful building blocks but also increasingly appear as structural motifs in bioactive molecules and pharmaceuticals. The catalytic asymmetric synthesis of chiral aminonitriles, therefore, has been intensively investigated, as reflected in numerous reports of catalytic asymmetric Strecker reactions. Despite such great progress, the catalytic asymmetric synthesis of chiral α,α-dialkyl aminonitriles in a highly selective and efficient manner is still a formidable challenge. Here, we report a new approach for the catalytic asymmetric synthesis of chiral α,α-dialkyl aminonitriles via reaction of cyanoketimines with enals. We demonstrate that this reaction could be carried out with as low as 20 ppm catalyst loading.

Asymmetric Cyanation of α-Ketimino Ester Derivatives with Chiral Ru-Li Combined Catalysts

Asymmetric cyanation of α-ketimino esters catalyzed by combined systems of amino acid/BINAP derivative/Ru(II) complexes and lithium compounds was examined. The use of an appropriate combination of amino acid and BINAP ligands achieved high enantioselectivity for a variety of α-alkynyl (Val/XylBINAP/Ru), α-alkenyl (Val/TolBINAP/Ru), and α-aryl imino esters (Val/XylBINAP/Ru) as well as an isatin-derived cyclic imino amide (t-Leu/BINAP/Ru) to afford the α-cyano-α-amino esters and the amide with an α-nitrogen-substituted quaternary chiral center with up to 98% ee.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Modular Organoboron Catalysts Enable Transformations with Unprecedented Reactivity

ConspectusElectron-deficient boron-based catalysts with metal-free but metallomimetic characteristics provide a versatile platform for chemical transformations. However, their catalytic performance is usually lower than that of the corresponding metal-based catalysts. Furthermore, many elaborate organoboron compounds are produced via time-consuming multistep syntheses with low yields, presenting a formidable challenge for large-scale applications of these catalysts. Given this context, the development of organoboron catalysts with the combined advantages of high efficiency and easy preparation is of critical importance.Therefore, we envisioned that the construction of a dynamic Lewis multicore system (DLMCS) by integrating the Lewis acidic boron center(s) and a Lewis basic ammonium salt in one molecule would be particularly efficient for on-demand applications because of the intramolecular synergistic effect. This Account summarizes our recent efforts in developing modular organoboron catalysts with unprecedented activities for several chemical transformations. A series of mono-, di-, tri-, and tetranuclear organoboron catalysts was readily designed and prepared in nearly quantitative yields over two steps using commercially available feedstocks. Notably, these catalysts can be modularly tailored by fine control over the electrophilic property of the Lewis acidic boron center(s), electronic and steric effects of the electropositive ammonium cation, linker length between the boron center and the ammonium cation, the number of boron centers, and the nucleophilic anion. This modular design allows systematic manipulation of the reactivity and efficacy of the catalysts, thus optimizing suitable catalysts for versatile chemical transformations. These include the coupling of CO₂ and epoxides, copolymerization of CO₂ and epoxides, ring-opening polymerization (ROP) of epoxides, and ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides.The utilization of mononuclear organoboron catalysts provided a turnover frequency of 11050 h^-1 for the CO₂/propylene oxide coupling reaction, an unprecedented efficiency of 5.0 kg of polymer/g of catalyst for the copolymerization of CO₂ and cyclohexene oxide, and a record-breaking catalytic efficiency of 7.4 kg of polymer/g of catalyst for the ROCOP of epoxides with cyclic anhydrides. A turnover number of 56500 was observed at a catalyst loading of 10 ppm for the ROP of epoxides using the dinuclear catalysts. The tetranuclear organoboron catalysts realized the previously intractable task of the copolymerization of CO₂ and epichlorohydrin, producing poly(chloropropylene carbonate) with the highest molecular weight of 36.5 kg/mol reported to date.Furthermore, the study revealed that the interaction between the dynamic Lewis multicore, that is, the intramolecular synergistic effect between the boron center(s) and the quaternary ammonium salt, plays a key role in mediating the catalytic activity and selectivity. This was based on investigations of the crystal structures of the catalysts, key intermediates, reaction kinetics, and density functional theory calculations. The modular tactics for the construction of organoboron catalysts presented in this Account should inspire more advanced catalyst designs.

Two [Ln4] molecular rings folded as compact tetrahedra

A new highly photo-switchable ligand furnishes supramolecular tetrahedral nanomagnets with Ln(iii) ions (Ln = Dy, Tb). Intramolecular weak interactions define the conformation of the ligand, quenching the photochromic activity.

The Crystal Structure of N-(1-Arylethyl)-4-methyl- 2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides as the Factor Determining Biological Activity Thereof

In order to detect new structural and biological patterns in a series of hetaryl-3-carboxylic acid derivatives, the optically pure (S)- and (R)-enantiomers of N-(1-arylethyl)-4-methyl- 2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides, their true racemates, and mechanical racemic mixtures have been synthesized in independent ways. The particular features of the 1Н- and 13С-NMR spectra of all synthesized substances, liquid chromato-mass spectrometric behavior thereof under electrospray ionization conditions, and also the results of polarimetric and X-ray diffraction studies have been discussed. Pharmacological screening on a model of carrageenan inflammation has found a clear relationship between the spatial structure of the studied objects and biological activity thereof. Enantiomers with chiral centers having (S)-configuration showed weak inhibition of pain and inflammatory reactions, while their mirror (R)-isomers exhibited very powerful analgesic and antiphlogistic properties under the same conditions, with the level of specific activity exceeding that of Lornoxicam and Diclofenac. Taking obtained data into account, a noticeable decrease in the activity of mechanical racemic mixtures, consisting of one-half of the “wrong” (S)-enantiomers, is quite natural. The true racemate of N-(1-phenylethyl)-amide proved itself in a similar way, while 4-methoxy-substituted analog thereof stood out against this background with unexpectedly high analgesic and anti-inflammatory activities. A comparative analysis of X-ray diffraction data has found that crystalline and molecular structure of racemic N-[1-(4-methoxyphenyl)ethyl]-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamide is completely different from that of the original enantiomers and, moreover, very unusual for racemates. Obviously, it is the factor determining the unique character of the biological effects of the said substance.

A Sc(OTf)3 catalyzed Mukaiyama–Mannich reaction of difluoroenoxysilanes with unactivated ketimines

The first example of a Mukaiyama–Mannich reaction of difluoroenoxysilanes with unactivated ketimines catalyzed by Sc(OTf)₃ is described.

Stereodivergent Catalysis

This review covers diastereo- and enantiodivergent catalyzed reactions in acyclic and cyclic systems using metal complexes or organocatalysts. Among them, nucleophilic addition to carbon-carbon and carbon-nitrogen double bonds, α-functionalization of carbonyl compounds, allylic substitutions, and ring opening of oxiranes and aziridines are considered. The diastereodivergent synthesis of alkenes from alkynes is also included. Finally, stereodivergent intramolecular and intermolecular cycloadditions and other cyclizations are also reported.

Nitronyl nitroxide based 2p-3d-4f chains with the magnetocaloric effect and slow magnetic relaxation

Four new nitronyl nitroxide radical based hetero-tri-spin one-dimensional compounds, namely [{Ln(hfac)3}3{Cu(hfac)2}{NIT-Ph(OMe)2}4]n (Ln = Gd (1), Tb (2), Dy (3), Er (4); hfac = hexafluoroacetylacetonate; NIT-Ph(OMe)2 = 2-(2',4'-dimethoxyphenyl)-4,4,5,5-tetramethyl-imidazolyl-1-oxyl-3-oxide) have been successfully prepared. Single crystal X-ray crystallographic analysis reveals that complexes 1-4 possess a 1D chain structure with a repeating [Cu-Rad-Ln-Rad-Ln-Rad-Ln-Rad] moiety in which Ln(hfac)3 and Cu(hfac)2 units are bridged by nitronyl nitroxide radicals through the NO groups. DC magnetic studies found that ferromagnetic interactions between metals and the coordinated NO groups are active in all four compounds. The Tb derivative displays frequency dependent ac magnetic susceptibilities, indicating slow magnetic relaxation behavior. The Gd complex shows an important cryogenic magnetocaloric effect with the entropy change (-ΔSm) of 13.5 J kg(-1) K(-1) at 2 K and a magnetic field of 7 T, representing the first example of Gd-radical molecular species exhibiting the magnetocaloric effect.

Solvent-dependent assemblies, structure diversities and magnetic properties of two homochiral Co(ii)/Na(i) coordination polymers

Two novel homochiral Co(ii)/Na(i) coordination polymers based on chiral tridentate S-H₃L ligand have been successfully synthesized and structurally characterized.

Enantioselective Strecker reaction of aldimines using potassium cyanide catalyzed by a recyclable macrocyclic V(v) salen complex

Chiral dimeric V(v) salen complexes have been synthesized and used as catalysts for asymmetric Strecker reaction of N-benzylimines using both KCN to produce chiral α-amino nitrile. The catalyst was recycled upto five times without loss in its activity.

Butterfly-like enantiomerically homochiral {CoII6CoIII4} clusters exhibiting both slow magnetic relaxation and ferroelectric property

A pair of butterfly-like enantiomerically homochiral [Co^II₆Co^III₄] clusters with both slow magnetic relaxation behaviour and ferroelectric property was synthesized.

New advances in dual stereocontrol for asymmetric reactions

Achieving dual stereocontrol in asymmetric reactions using a single enantiomer for the building of the chiral catalyst or auxiliary is a very important goal in enantioselective synthesis as it eliminates the need for having available the two enantiomers of the auxiliary or catalyst designed. Recent strategies and advances towards this goal during the last four years will be discussed throughout this review.

Polymetallic complexes linked to a single-frame ligand: cooperative effects in catalysis

In an eco-friendly development, catalysis represents the key approach for converting raw materials into valuable products, particularly convenient for multi-step transformations. Mimicking Nature seems the smartest way to design poly-functional assemblies leading to the design of "synergic" catalysts. This perspective focuses on the advances in the conception of polymetallic catalysts bonded to a single ligand frame.

Cooperative bimetallic catalysis in asymmetric transformations

The efficient synthesis of enantioenriched compounds is becoming increasingly important in modern organic, pharmaceutical, and materials chemistry. Recently, chiral cooperative bimetallic catalysts have emerged as a powerful tool to achieve high efficiency and selectivity in asymmetric transformations. This tutorial review highlights strategies and recent advances in cooperative bimetallic catalysts which have been developed for a variety of asymmetric transformations.