The 1,4‐conjugated addition of nitrogen centered nucleophiles to electron‐deficient alkenes is one of the most significant and widely used reactions in modern synthetic organic chemistry. To date, ...various protocols for the aza‐Michael reaction have been developed. However, these reports mainly focus on the use of strong Michael donors. In recent years, the conjugate addition of weak nitrogen nucleophiles to various Michael acceptors gained increasing popularity. Impressive progress in this area has been achieved by the use of more efficient catalyst systems. This review aims to provide a critical analysis of the results obtained in reactions of weak nucleophiles (azoles, pyrroles, indoles, carbamates, purines, amides, hydrazides, uraciles etc) with electron‐deficient alkenes which were reported over the past twelve years.
The application of micro-Raman spectroscopy was used for characterization of structural features of the high-k stack (h-k) layer of “silicon-on-insulator” (SOI) nanowire (NW) chip (h-k-SOI-NW chip), ...including Al2O3 and HfO2 in various combinations after heat treatment from 425 to 1000 °C. After that, the NW structures h-k-SOI-NW chip was created using gas plasma etching optical lithography. The stability of the signals from the monocrine phase of HfO2 was shown. Significant differences were found in the elastic stresses of the silicon layers for very thick (>200 nm) Al2O3 layers. In the UV spectra of SOI layers of a silicon substrate with HfO2, shoulders in the Raman spectrum were observed at 480–490 cm−1 of single-phonon scattering. The h-k-SOI-NW chip created in this way has been used for the detection of DNA-oligonucleotide sequences (oDNA), that became a synthetic analog of circular RNA–circ-SHKBP1 associated with the development of glioma at a concentration of 1.1 × 10−16 M. The possibility of using such h-k-SOI NW chips for the detection of circ-SHKBP1 in blood plasma of patients diagnosed with neoplasm of uncertain nature of the brain and central nervous system was shown.
Fluorinated α‐bromoenones have received considerable attention in the last decade. Their ability to react in 1.2‐ and 1.4‐addition modes, together with the presence of bromine, makes them valuable ...fluorinated building blocks in organic synthesis. This review focuses on the unusual and often unpredictable transformations of these compounds on treatment with nitrogen nucleophiles.
Recent achievements in improving understanding of the unusual reactivity of trifluoromethyl α‐haloalkenyl ketones are summarized in this microreview.
In the present work, a convenient and straightforward approach to the preparation of borylated amidines based on the
-dodecaborate anion B
H
NCCH
NHR-, R=H, Alk, Ar was developed. This method has two ...stages. A nitrile derivative of the general form B
H
NCCH
was obtained, using a modified technique, in the first stage. On the second stage the resulting molecular system interacted with primary amines to form the target amidine products. This approach is characterised by a simple chemical apparatus, mild conditions and high yields of the final products. The mechanism of the addition of amine to the nitrile derivative of the
-dodecaborate anion was studied, using quantum-chemical methods. The interaction between NH
and B
H
NCCH
ammonia was chosen as an example. It was found that the structure of the transition state determines the stereo-selectivity of the process. A study of the biological properties of borylated amidine sodium salts indicated that the substances had low toxicity and could accumulate in cancer cells in significant amounts.
Primary instability of the lid-driven flow in a cube is studied by a linear stability approach. Two cases, in which the lid moves parallel to the cube sidewall or parallel to the diagonal plane, are ...considered. It is shown that Krylov vectors required for application of the Newton and Arnoldi iteration methods can be evaluated by the SIMPLE procedure. The finite volume grid is gradually refined from
100
3
to
256
3
nodes. The computations result in grid converging values of the critical Reynolds number and oscillation frequency that allow for Richardson extrapolation to the zero grid size. Three-dimensional flow and most unstable perturbations are visualized by a recently proposed approach that allows for a better insight into the flow patterns and appearance of the instability. New arguments regarding the assumption that the centrifugal mechanism triggers the instability are given for both cases.
N‐Heterocyclic carbene (NHC) ligands are ubiquitously utilized in catalysis. A common catalyst design model assumes strong M–NHC binding in this metal–ligand framework. In contrast to this common ...assumption, we demonstrate here that lability and controlled cleavage of the M−NHC bond (rather than its stabilization) could be more important for high‐performance catalysis at low catalyst concentrations. The present study reveals a dynamic stabilization mechanism with labile metal–NHC binding and PdX3−NHC‐R+ ion pair formation. Access to reactive anionic palladium intermediates formed by dissociation of the NHC ligands and plausible stabilization of the molecular catalyst in solution by interaction with the NHC‐R+ azolium ion is of particular importance for an efficient and recyclable catalyst. These ionic Pd/NHC complexes allowed for the first time the recycling of the complex in a well‐defined form with isolation at each cycle. Computational investigation of the reaction mechanism confirms a facile formation of NHC‐free anionic Pd in polar media through either Ph–NHC coupling or reversible H–NHC coupling. The present study formulates novel ideas for M/NHC catalyst design.
Recycling matters! A reactive ionic palladium complex forms due to dissociation of the N‐heterocyclic carbene (NHC) ligand and subsequent stabilization by the interaction with the NHC‐R+ azolium ions, thus providing a powerful concept of ionic recyclable catalyst (see scheme).
Oscillatory instability of buoyancy convection in a laterally heated cube with perfectly thermally conducting horizontal boundaries is studied. The effect of the spanwise boundaries on the ...oscillatory instability onset is examined. The problem is treated by Krylov-subspace-iteration-based Newton and Arnoldi methods. The Krylov basis vectors are calculated by a novel approach that involves the SIMPLE iteration and a projection onto a space of functions satisfying all linearized and homogeneous boundary conditions. The finite volume grid is gradually refined from
100
3
to
256
3
finite volumes. A self-sustaining oscillatory process responsible for the instability onset is revealed, visualized and explained.
The development of new lightweight materials is required for the automotive industry to reduce the impact of carbon dioxide emissions on the environment. The lightweight, high-manganese steels are ...the prospective alloys for this purpose. Hot deformation is one of the stages of the production of steel. Hot deformation behavior is mainly determined by chemical composition and thermomechanical parameters. In the paper, an artificial neural network (ANN) model with high accuracy was constructed to describe the high Mn steel deformation behavior in dependence on the concentration of the alloying elements (C, Mn, Si, and Al), the deformation temperature, the strain rate, and the strain. The approval compression tests of the Fe-28Mn-8Al-1C were made at temperatures of 900-1150 °C and strain rates of 0.1-10 s
with an application of the Gleeble 3800 thermomechanical simulator. The ANN-based model showed high accuracy, and the low average relative error of calculation for both training (5.4%) and verification (7.5%) datasets supports the high accuracy of the built model. The hot deformation effective activation energy values for predicted (401 ± 5 kJ/mol) and experimental data (385 ± 22 kJ/mol) are in satisfactory accordance, which allows applying the model for the hot deformation analysis of the high-Mn steels with different concentrations of the main alloying elements.
We examine long-wavelength correlation functions of massive scalar fields in de Sitter spacetime. For the theory with a quartic self-interaction, the two-point function is calculated up to two loops. ...Comparing our results with the Hartree–Fock approximation and with the stochastic approach shows that the former resums only the cactus type diagrams, whereas the latter contains the sunset diagram as well and produces the correct result. We also demonstrate that the long-wavelength expectation value of the commutator of two fields is equal to zero both for spacelike and timelike separated points.
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