Aromaticity and Chirality: New Facets of Old Concepts.

The review summarizes the results of previous and the latest studies on aromaticity and related concepts. The electron counting rule for 3D-aromatic systems 2(n + 1) is shown to be a generalization of the 4n + 2 rule for planar molecules, and, vice versa, the latter can be derived from the former. The relative stability of the push-pull and captodative aromatic systems is shown to depend on the nature of the groups separated by the C=C bond in geminal or vicinal positions.

The Rivalry between Intramolecular Tetrel Bonds and Intermolecular Hydrogen Bonds in (O-Si) Chelates of N-Silylmethylamides and -ureas. A Theoretical Study.

The comparison of the results of theoretical calculations of (O-Si) chelates of N-silylmethylated amides and ureas with the axial chlorine or fluorine atom at silicon to the data of X-ray analysis of related compounds revealed the formation of covalent O-Si tetrel bonds (TB) or noncovalent O⋅⋅⋅Si tetrel bonds (NTB). The nature of the formed tetrel bond depends on the substituents at silicon and the polarity of the medium. The competition between the intramolecular TB and intermolecular hydrogen bonds (HB) with proton donors depends on the center of basicity involved in the formation of HB, which could be either oxygen or halogen.

The Reactions of Alkenes with Phenyl--triflylimino-λ-iodane: Solvent and Oxidant Impact.

The reactions of alkenes with phenyl--triflylimino-λ-iodane PhI=NTf () have been studied in different conditions. In methylene chloride, in the presence of -halosuccinimides, the products of mono and bis-triflamidation were obtained. In MeCN, the product of bromotriflamidation (with NBS) with solvent interception or of bis-triflamidation (with NIS) is formed.

Gas-Phase Structure of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane by GED and Theoretical Calculations.

The molecular structure and conformational and rotational composition of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane have been investigated by synchronous gas-phase electron diffraction/mass spectrometry GED/MS and theoretical calculations (B3LYP and M06-2X with cc-pVTZ and aug-cc-pVTZ basis sets) and compared to the X-ray structure.

2-Amino-1,3-benzothiazole: Endo -Alkylation with α-Iodo Methyl Ketones Followed by Cyclization.

Reactions of 2-amino-1,3-benzothiazole with aliphatic, aromatic and heteroaromatic α-iodoketones in the absence of bases or catalysts have been studied. The reaction proceeds by N-alkylation of the endocyclic nitrogen atom followed by intramolecular dehydrative cyclization. The regioselectivity is explained and the mechanism of the reaction is proposed.

Conjugative Stabilization versus Anchimeric Assistance in Carbocations.

In this study, an old concept of anchimeric assistance is viewed from a different angle. Primary cations with two different heteroatomic substituents in the α-position to the cationic carbon atom CHXY−CH2+ (X, Y = Me2N, MeO, Me3Si, Me2P, MeS, MeS, Br) can be stabilized by the migration of either the X or Y group to the cation center. In each case, the migration can be either complete, resulting in the transfer of the migrating group to the adjacent carbon atom and the formation of a secondary carbocation stabilized by the remaining heteroatom, or incomplete, leading to an anchimerically assisted iranium ion.

Iodine-Mediated Alkoxyselenylation of Alkenes and Dienes with Elemental Selenium.

A one-pot synthesis of linear and cyclic β-alkoxyselenides is developed through the iodine-mediated three-component reaction of elemental selenium with alkenes (dienes) and alcohols. Selenylation of 1,5-hexadiene gives 2,5-di(methoxymethyl)tetrahydroselenophene and 2-methoxy-6-(methoxymethyl)tetrahydro-2-selenopyran via the 5 and 6- cyclization. 1,7-Octadiene affords only linear 1:2 adduct with two terminal double bonds.

Synthetic Approaches to Biologically Active C-2-Substituted Benzothiazoles.

Numerous benzothiazole derivatives are used in organic synthesis, in various industrial and consumer products, and in drugs, with a wide spectrum of biological activity. As the properties of the benzothiazole moiety are strongly affected by the nature and position of substitutions, in this review, covering the literature from 2016, we focus on C-2-substituted benzothiazoles, including the methods of their synthesis, structural modification, reaction mechanisms, and possible pharmacological activity. The synthetic approaches to these heterocycles include both traditional multistep reactions and one-pot atom economy processes using green chemistry principles and easily available reagents.

A low-temperature dynamic H, C, and Se NMR study of 2,2'-selenodicyclohexanol.

2,2'-Selenodicyclohexanol 1 was shown to exist as two (all-trans-achiral and all-trans-chiral) stereoisomers with all C-Se and C-OH bonds in equatorial orientations. When the temperature is lowered, the H, C, and Se NMR spectra exhibit a strongly one-sided dynamic process, which involves sterically hindered rotation about the C-Se bond. Structures, free energy differences of the rotamers ΔG°, and the rotational barrier were determined and confirmed by quantum chemical calculations at the M06-2X/6-311++G**, M06-2X/cc-pVTZ, and MP2/6-311+G** levels of theory.

Modern Approaches to the Synthesis and Transformations of Practically Valuable Benzothiazole Derivatives.

The review is devoted to modern trends in the chemistry of 2-amino and 2-mercapto substituted benzothiazoles covering the literature since 2015. The reviewed heterocycles belong to biologically active and industrially demanded compounds. Newly developed synthesis methods can be divided into conventional multistep processes and one-pot, atom economy procedures, realized using green chemistry principles and simple reagents.

Theoretical Density Functional Theory Study of Electrocatalytic Activity of MN-Doped (M = Cu, Ag, and Zn) Single-Walled Carbon Nanotubes in Oxygen Reduction Reactions.

The mechanism of oxygen reduction reaction (ORR) on transition metal-doped nitrogen codoped single-walled nanotubes, CHMN (MN-CNT where M = Zn, Cu, or Ag; N = pyridinic nitrogen), has been studied with the density functional theory method at the ωB97XD/DGDZVP level of theory. The charge density analysis revealed two active sites of the catalyst toward ORR: the MN site and the C=C bond of the N-C=C-N metal-chelating fragment (C site). The structure of O-containing adsorbates (O , HOO*, O*, HO*, etc.

At the Experimental Limit of the NMR Conformational Analysis: Si and C NMR Study of the Conformational Equilibrium of 1-Phenyl-1--butylsilacyclohexane.

The low temperature (95 K) NMR study of 1-Ph-1-Bu-silacyclohexane () showed the conformational equilibrium to be extremely one-sided toward thePh,-Bu conformer. The barrier to interconversion has been measured (4.2-4.

Divergent reactivity of divinylsilanes toward sulfonamides in different oxidative systems.

Oxidative sulfonamidation of divinylsilanes with various sulfonamides in different solvents is reported. With -BuOI as an oxidant, halogenation is the main process, whereas aziridines are the minor products. With NBS in CHCl the products of bromination or bromosulfonamidation were obtained, whereas in MeCN or THF the Ritter-type solvent interception products are formed.

Trifluoromethanesulfonamide vs. Non-Fluorinated Sulfonamides in Oxidative Sulfamidation of the C=C Bond: An In Silico Study.

A theoretical analysis of the reaction of oxidative sulfamidation of several alkenes was performed in order to explain the various experimental observations and different reactivity of triflamide and non-fluorinated sulfonamides. Transformations occurring in the system alkene-sulfonamide in the presence of oxidative system (BuOCl + NaI) were analyzed at the MP2/DGDZVP//B3LYP/DGDZVP level of theory using the IEF-PCM method for taking into account the solvent acetonitrile (MeCN) effect. As the model substrates, styrene, trimethyl(vinyl)silane, dimethyl(divinyl)silane and diphenyl(divinyl)silane were chosen and mesylamide, triflamide, tosylamide and -nosylamide were taken as the reagents.

Structural and Conformational Aspects in the Chemistry of Heterocycles.

Heterocyclic compounds represent more than half of all known organic compounds, so the growing interest in this field of chemistry is not surprising [...

Single Si-Doped Graphene as a Catalyst in Oxygen Reduction Reactions: An In Silico Study.

Single Si-doped graphene CHSi with one carbon atom replaced by a three-coordinate silicon atom is studied by density functional theory (DFT) calculations as a catalyst for the oxygen reduction reactions (ORRs) in both acidic and alkaline media. The active sites for oxygen adsorption were determined from the distribution of the charge density difference analysis. At the equilibrium electrode potential, the most stable intermediate was found to have the structure HO*O*-CHSi with both oxygen atoms bound to the support, one of them being incorporated in between Si and C atoms, corresponding to the transfer of one hydrogen atom [H + e].

Silacyclohexanes, Sila(hetero)cyclohexanes and Related Compounds: Structure and Conformational Analysis.

Conformational analysis of Si-mono- and Si,Si-disubstituted silacyclohexanes as well as their analogues with a heteroatom(s) in the ring is reviewed with the focus on the recent results. Experimental measurements in the gas phase (gas electron diffraction, GED) and low temperature NMR spectroscopy (LT NMR) on H, C and Si nuclei are described along with theoretical calculations at the DFT and MP2 levels of theory. Structural and conformational specific features are shown to be principally different from those of the carbon predecessors - the corresponding cyclohexanes, oxanes, thianes and piperidines.

Solvent interception, heterocyclization and desilylation upon NBS-induced sulfamidation of trimethyl(vinyl)silane.

The reaction of trimethyl(vinyl)silane with sulfonamides in the presence of N-bromosuccinimide was shown to proceed regioselectively in methylene chloride under mild conditions and led to the products of bromosulfamidation in up to 88% yield. The obtained adducts undergo base-promoted dehydrobromination to give 2-trimethylsilyl-N-sulfonyl aziridines in a close to quantitative yield. In the reaction with trifluoromethanesulfonamide in acetonitrile or tetrahydrofuran, the Ritter-type (solvent-interception) products were obtained and converted to 1-triflyl-2-methyl-5-(trimethylsilyl)-2-imidazoline or 4-triflyl-3-(trimethylsilyl)-1,4-oxazocane in almost quantitative yield.

2-Indazole Tautomers Stabilized by Intra- and Intermolecular Hydrogen Bonds.

2-[(2-Indazol-3-yl)methylene]-1-indene-1,3(2)-dione and ()-2-[(2-indazol-3-yl)methylene]-2,3-dihydro-1-inden-1-one have been synthesized. In the crystal, the NH hydrogen atom of is disordered between the N(1) and N(2) atoms with the population ratio of 0.69:0.

Tetrel Bonding along the Pathways of Transsilylation and Alkylation of N-Trimethylsilyl- N-methylacetamide with Bifunctional (Chloromethyl)fluorosilanes.

A quantum chemical study has been carried out on the complexes formed in the first stage of the reaction of (chloromethyl)trifluorosilane with an ambident nucleophile, N-trimethylsilyl- N-methylacetamide, existing in the amide and imidate tautomeric forms. The analysis of molecular electrostatic potential maps of the electrophile molecule revealed the presence of two σ-holes belonging to the Si and C atoms. Each of the two tautomers of the nucleophile form complexes having O···Si, O···C, N···Si, and N···C bonds of different characters.

Conformational Preferences of the Phenyl Group in 1-Phenyl-1-X-1-silacyclo-hexanes (X = MeO, HO) and 3-Phenyl-3-X-3-silatetrahydropyrans (X = HO, H) by Low Temperature C NMR Spectroscopy and Theoretical Calculations.

New Si-phenyl-substituted silacyclohexanes and 3-silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosix-membered ring by low temperature C NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Ph ⇆ Ph equilibrium constants at 103 K are 2.

Photoinduced Intramolecular Bifurcate Hydrogen Bond: Unusual Mutual Influence of the Components.

A series of 7-hydroxy-2-methylidene-2,3-dihydro-1H-inden-1-ones with 2-pyrrolyl (3), 4-dimethylaminophenyl (4), 4-nitrophenyl (5), and carboxyl group (6) as substituents at the exocyclic double bond was synthesized in the form of the E-isomers (4-6) or predominantly as the Z-isomer (3) which in solution is converted to the E-isomer. The synthesized compounds and their model analogues were studied by NMR spectroscopy, X-ray analysis, and MP2 theoretical calculations. The E-isomers having intramolecular O-H···O═C hydrogen bond are converted by UV irradiation to the Z-isomers having bifurcated O-H···O···H-X hydrogen bond.

Molecular Structure and Conformational Analysis of 1-Phenyl-1-X-1-Silacyclohexanes (X = F, Cl) by Electron Diffraction, Low-Temperature NMR, and Quantum Chemical Calculations.

The molecular structure and conformational preferences of 1-phenyl-1-X-1-silacyclohexanes CHSi(Ph,X) (X = F (3), Cl (4)) were studied by gas-phase electron diffraction, low-temperature NMR spectroscopy, and high-level quantum chemical calculations. In the gas phase only three (3) and two (4) stable conformers differing in the axial or equatorial location of the phenyl group and the angle of rotation about the Si-C bond (axi and axo denote the Ph group lying in or out of the X-Si-C plane) contribute to the equilibrium. In 3 the ratio Ph:Ph:Ph is 40(12):55(24):5 and 64:20:16 by experiment and theory, respectively.