A fast and efficient mechanochemical Ritter reaction between alcohols and nitriles under mild conditions is demonstrated. The reaction proceeds rapidly at room temperature in a solvent‐free or ...low‐solvent environment by using a Brønsted acid catalyst. Its general application has been verified through a substrate screening comprising a wide range of functionalized nitriles as well as secondary and tertiary alcohols.
Gentle Ritter: A fast and efficient mechanochemical Ritter reaction under mild conditions is described. The reaction proceeds rapidly at room temperature in a solvent‐free or low‐solvent environment by using sulfuric acid as catalyst.
This work investigated the cocatalytic activity of recently prepared guanidinium salts containing an oxanorbornane subunit in an (
)-proline-catalyzed aldol reaction. The activity was interpreted by ...the diastereoselectivity of the reaction (
/
ratio) and for the most interesting polycyclic guanidinium salt, the enantioselectivity of the reaction was determined. The results indicated a negative impact on the oxanorbornane unit if present as the flexible substituent. For most of the tested aldehydes, the best cocatalysts provided enantioselectivities above 90% and above 95% at room temperature and 0 °C, respectively, culminating in >99.5% for 4-chloro- and 2-nitrobenzaldehyde as the substrate. The barriers for forming four possible enantiomers were calculated and the results for two
enantiomers are qualitatively consistent with the experiment. Obtained results suggest that the representatives of furfurylguanidinium and rigid polycyclic oxanorbornane-substituted guanidinium salts are good lead structures for developing new cocatalysts by tuning the chemical space around the guanidine moiety.
The investigation of liquid crystal (LC) mixtures is of great interest in tailoring material properties for specific applications. The recent discovery of the twist-bend nematic phase (N
) has ...sparked great interest in the scientific community, not only from a fundamental viewpoint, but also due to its potential for innovative applications. Here we report on the unexpected phase behaviour of a binary mixture of twist-bend nematogens. A binary phase diagram for mixtures of imino-linked cyanobiphenyl (CBI) dimer and imino-linked benzoyloxy-benzylidene (BB) dimer shows two distinct domains. While mixtures containing less than 35 mol % of BB possess a wide temperature range twist-bend nematic phase, the mixtures containing 55-80 mol % of BB exhibit a smectic phase despite that both pure compounds display a Iso-N-N
-Cr phase sequence. The phase diagram shows that the addition of BB of up to 30 mol % significantly extends the temperature range of the N
phase, maintaining the temperature range of the nematic phase. The periodicity, obtained by atomic force microscopy (AFM) imaging, is in the range of 6-7 nm. The induction of the smectic phase in the mixtures containing 55-80 mol % of BB was confirmed using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. The origin of the intercalated smectic phase was unravelled by combined spectroscopic and computational methods and can be traced to conformational disorder of the terminal chains. These results show the importance of understanding the phase behaviour of binary mixtures, not only in targeting a wide temperature range but also in controlling the self-organizing processes.
The two main classes of liquid-crystal (LC) phases of rodlike molecules are nematics, where the rods align in the same direction (the nematic directorn), and smectics, where the rods not only are ...aligned but also form layers. The electro-optic effects in LC devices that are a backbone in today’s display industry mainly use the Fréedericksz transition, which is the bulk reorientation of a surface-anchored nematic by an electric field. Conventional (uniaxial) smectics do not present a Fréedericksz transition, because, due to their layered structure, the director reorientation would distort the layers, which would cost too much energy. In a worldwide ongoing effort to extend the variety of LC compounds suitable for applications in the display industry, bent-shaped molecules have recently raised much attention, since they present multiple new LC phases with unusual properties. In this paper, we report on a structural and electro-optic study of the LC phases of a bent-shaped dimer. On cooling from the isotropic liquid, this compound shows a usual nematic (N), a twist-bend nematic (NTB), and a biaxial smectic-Aphase (SmAb). Quite surprisingly, contrary to usual smectics,SmAbpresents a remarkable electro-optic response, with low (<4V) voltage threshold, no reorganization of the smectic layers, and low (<1ms) response time (i.e., 30 times faster than theNphase at higher temperature). We interpret this unexpected electro-optic effect as a Fréedericksz transition affecting the secondary directormof theSmAb, and we model it by analogy with the usual Fréedericksz transition of thendirector of the uniaxialNphase. Indeed, a Fréedericksz transition affecting onlymin this biaxial fluid smectic does not alter its layered structure and costs little energy. From the point of view of applications, thanks to its low relaxation time, this “biaxial” Fréedericksz transition could be exploited in electro-optic devices that require fast switching.
Herein we report a comprehensive study on novel carbonyl- and ethenyl-linked symmetric dimers that combine synthesis, mesomorphic properties and molecular modelling. The study has been focused on the ...impact of geometry imposed by the linkage group on the incidence of the twist-bend nematic (N
TB
) phase. Comparison of the mesomorphic properties of these two series complemented with computational studies of conformational space around the linkage group points molecular curvature and intramolecular torsion plays important role in the appearance of the N
TB
phase and can be regarded as the basic structural requirements for design of new twist-bend nematogen materials.
Kinetic resolution of a series of fluorinated styrene oxide derivatives was studied using halohydrin dehalogenase. A mutant HheC-W249P catalysed nucleophilic ring-opening with azide and cyanide ions ...with excellent enantioselectivity (E-values up to >200), which gives access to various enantiopure β-substituted alcohols and epoxides. It was found that the enzyme tolerates substrates in concentrations over 50 mM. However, different side reactions were observed at elevated concentrations and with prolonged reaction time. The biocatalytic azidolysis and cyanolysis of racemic 4-trifluoromethylstyrene oxide were performed on preparative scale, affording (R)-2-azido-1-(4-trifluoromethyl-phenyl)-ethanol in 38% yield and 97% ee, and (S)-3-hydroxy-3-(4-trifluoromethyl-phenyl)-propionitrile in 30% yield and 98% ee.
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•Halohydrin dehalogenase catalyses transformation of fluorinated aryl epoxides.•Enantioselective kinetic resolution was achieved (E-value up to >200).•Preparative azidolysis and cyanolysis reactions were performed at 20–50 mM scale.•Under elevated concentrations substrates were sensitive to spontaneous hydrolysis.
The synthesis and liquid-crystalline properties are reported for novel naphthyl-based diketones incorporating variant terminal chains and lateral fluoro- substitution. Newly prepared materials ...exhibit a broad temperature range of the nematic phase. The study demonstrates how subtle structural modifications can be exploited to alter the efficiency of molecular packing and consequently the thermal behaviour. Keywords: liquid crystals, bent-shaped dimers, naphthyl diketones.
The twist-bend nematic (NTB) phase of bent-shaped molecules has recently attracted much attention due to the spontaneous bend of its director field and the doubly-degenerate chirality of its ...heliconical structure. Despite intensive experimental and theoretical investigation worldwide, the main structural characteristics (pitch and conical angle) and elastic properties of the phase are still barely understood. This is mainly due to the difficulty in growing large single domains of the NTB phase, which prevents the application of the powerful electro-optical techniques developed for the nematic (N) phase. Moreover, the twist and bend distortions of the optic axis are forbidden by the pseudo-layered structure of the NTB phase, which makes its response to the field smectic-like instead of nematic-like. Therefore, the only macroscopic electric effect that can be observed deep in the NTB phase is the smectic-like “electroclinic” effect (ECENTB). Here, we achieve large monochiral NTB domains which remain uniform over a wide temperature range (20–60 °C) in thin (1.5 µm) planar cells, thus avoiding the so-called stripe- and rope-like textural instabilities. This allowed us to experimentally determine, using electro-optical measurements, the temperature dependence of the ECENTB response in four different NTB materials: namely the dimers CB7CB, CB9CB, CB6OCB, and BNA76. For all compounds, the thermal dependences of conical angle and pitch in the vicinity of the N-NTB transition follow the theoretically predicted power law behaviour. However, the agreement between the measured and predicted power law exponents remains only qualitative, which calls for improvement of the theoretical models.
A range of 1-aryl-allylamines were prepared in moderate to excellent enantioselectivity (ee 63.5%→99.9%) using lipase B from a
Candida antarctica catalyzed resolution of racemic amines. This is the ...first time that CaLB has been used for the resolution of 1-aryl-allylamines. Racemic amines were prepared starting from aromatic aldehydes with a 3,3-sigmatropic rearrangement of the acyclic imidates as the key step followed by trichloroacetamidate hydrolysis. Aldehydes were converted into acrylic esters using Knoevenagel reaction. After reduction, the corresponding alcohols were used for the preparation of trichloroacetimidates, which were then used in an Overman rearrangement.
New ethenyl-linked dimers which differ in the fluorine-substitution pattern were prepared and characterised. The investigation has been focused on the impact of electronic structure and non-covalent ...interactions associated with the presence of C-F bond on the stability of the N
TB
phase and overall thermal behaviour of the dimers. A joined computational and spectroscopy study showed that electrostatic interactions associated with C-F bond govern the conformational diversity of the mesogenic core without interfering with the molecular shape. The qualitative analysis of allowable inter-molecular interactions suggested that conformational diversity and flexibility of the fluorinated fragment influence the strength of intermolecular interactions and thus transitional properties, including stability of the N
TB
phase. These results provide an important insight into the relationship between the electronic structure, the strength of intermolecular interactions and transitional properties, providing a valuable contribution to the design of novel functional materials.
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