Asymmetric hydrogenation catalysis via ion-pairing in chiral ionic liquids

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Enantioselective Total Synthesis of (+)-KB343

A concise total synthesis of the complex guanidinium toxin KB343 is reported traversing through an unusual sequence of chemoselective transformations and strategic skeletal reorganization. The absolute configuration is confirmed through an enantioselective route, and the structures of all key intermediates and the natural product itself are unassailably confirmed through X-ray crystallographic analysis.

Dielectric Study of Tetraalkylammonium and Tetraalkylphosphonium Levulinate Ionic Liquids

Broadband dielectric spectroscopy in a broad temperature range was employed to study ionic conductivity and dynamics in tetraalkylammonium- and tetraalkylphosphonium-based ionic liquids (ILs) having levulinate as a common anion. Combining data for ionic conductivity with data obtained for viscosity in a Walden plot, we show that ionic conductivity is controlled by viscosity while a strong association of ions takes place. Higher values for ionic conductivities in a broad temperature range were found for the tetraalkylphosphonium-based IL compared to its ammonium homolog in accordance with its lower viscosity. Levulinate used in the present study as anion was found to interact and associate stronger with the cations forming ion-pairs or other complexes compared to the NTf₂ anion studied in literature. In order to analyze dielectric data, different fitting approaches were employed. The original random barrier model cannot well describe the conductivity especially at the higher frequencies region. In electric modulus representation, two overlapping mechanisms contribute to the broad low frequencies peak. The slower process is related to the conduction mechanism and the faster to the main polarization process of the complex dielectric permittivity representation. The correlation of the characteristic time scales of the previous relaxation processes was discussed in terms of ionic interactions.

Preliminary modelling as the first stage of targeted organic synthesis

The review aims to present a classification and applicability analysis of methods for preliminary molecular modelling for targeted organic, catalytic and biocatalytic synthesis. The following three main approaches are considered as a primary classification of the methods: modelling of the target – ligand coordination without structural information on both the target and the resulting complex; calculations based on experimentally obtained structural information about the target; and dynamic simulation of the target – ligand complex and the reaction mechanism with calculation of the free energy of the reaction. The review is meant for synthetic chemists to be used as a guide for building an algorithm for preliminary modelling and synthesis of structures with specified properties.

The bibliography includes 353 references.

Enantiomerization of Axially Chiral Biphenyls: Polarizable MD Simulations in Water and Butylmethylether

In this study, we investigate the influence of chiral and achiral cations on the enantiomerization of biphenylic anions in n-butylmethylether and water. In addition to the impact of the cations and solvent molecules on the free energy profile of rotation, we also explore if chirality transfer between a chiral cation and the biphenylic anion is possible, i.e., if pairing with a chiral cation can energetically favour one conformer of the anion via diastereomeric complex formation. The quantum-mechanical calculations are accompanied by polarizable MD simulations using umbrella sampling to study the impact of solvents of different polarity in more detail. We also discuss how accurate polarizable force fields for biphenylic anions can be constructed from quantum-mechanical reference data.

Levulinate amidinium protic ionic liquids (PILs) as suitable media for the dissolution and levulination of cellulose

Levulinate protic ionic liquids allow for the dissolution and the levulination of their parent polysaccharide.

Recent trends in organocatalyzed asymmetric reduction of prochiral ketones

This review depicts the recent practices followed in organocatalyzed asymmetric reduction of prochiral ketones, highlighting the main organocatalysts used for the past seven years.

Coordinating Chiral Ionic Liquids: Design, Synthesis, and Application in Asymmetric Transfer Hydrogenation under Aqueous Conditions

Hydrophilic coordinating chiral ionic liquids with an amino alcohol substructure were developed and efficiently applied to the asymmetric reduction of ketones. Their careful design and adaptability to the desired reaction conditions allow for these chiral ionic liquids to be used as the sole source of chirality in a ruthenium-catalyzed transfer hydrogenation reaction of aromatic ketones. When used in this reaction system, these chiral ionic liquids afforded excellent yields and high enantioselectivities.