Application of the intramolecular Diels-Alder vinylarene (IMDAV) reaction for the synthesis of benzo-, carbocyclo-, thienothiopheneisoindolecarboxylic acids and its limitations.

Thienylallylamines, readily accessible from the corresponding thienyl aldehydes, react with maleic and trifluoromethylmaleic anhydrides leading to the formation of acids with a thieno[2,3-f]isoindole core. The reaction sequence involves two successive steps: acylation of the nitrogen atom of the initial allylamine and the intramolecular Diels-Alder vinylarene (IMDAV) reaction. The scope and limitations of the proposed method were thoroughly investigated. It has been revealed with the aid of X-ray analysis and DFT calculations that the key step, the IMDAV reaction, proceeds through an exo-transition state, giving rise to the exclusive formation of a single diastereomer of the target heterocycle. The obtained functionally substituted thieno[2,3-f]isoindole carboxylic acids are potentially useful substrates for further transformations and bioscreening. The antimicrobial evaluation of the obtained compounds revealed that 1-oxo-2-(3-(trifluoromethyl)phenyl)hexahydrobenzo[4,5]thieno[2,3-f]isoindole-10-carboxylic acid is the most active sample in the synthesized library. It exhibits antibacterial activity against sensitive strains of Gram-positive bacteria, including S. aureus, Enterococcus faecium, Bacillus cereus, and Micrococcus luteus, as well as the Gram-negative bacteria E. coli and Pseudomonas fluorescens, with MIC values ranging from 4 to 64 µg mL-1. 9-Oxo-8-phenyloctahydronaphtho[2,1-d]thieno[2,3-f]isoindole-10-carboxylic acid showed antifungal activity against yeast culture C. albicans with a MIC value of 32 µM.

Domino Approach for the Synthesis of Pyridinium Salts and 1,2,3,8a-Tetrahydroimidazo[1,2-a]pyridines from 2-Imidazolines and Propiolic Acid Esters.

Adducts of 1-alkyl-2-imidazolines and two molecules of alkyl propiolate, possessing an N-propargyl-ß-enaminoester fragment, easily undergo a domino reaction to form pyridinium salts with ß-(alkylammonio)ethyl group at the nitrogen atom in the presence of 2 equiv of a protic acid. Treatment of the above reaction mixture with a base gives 1,2,3,8a-tetrahydroimidazo[1,2-a]pyridines. Reaction of the latter compounds with acid chlorides affords pyridinium salts with ß-(alkylamido)ethyl moiety at the nitrogen atom.

Domino Three-Component N-Acylation/[4 + 2] Cycloaddition/Alder-ene Synthesis of Polysubstituted Benzo[f]isoindole-4-carboxylic Acids.

Diversely substituted, partially saturated benzo[f]isoindole-4-carboxylic acids were synthesized by a new three-component reaction (3CR) starting from cinnamic amines (3-arylallylamines), maleimides, and maleic anhydride. The process consists of N-acylation of the amines by maleic anhydride, intramolecular [4 + 2] cycloaddition in vinylarenes (the IMDAV reaction), and the concluding Alder-ene reaction between Diels-Alder intermediates and maleimides. All of the reaction steps proceed in a highly regio- and stereoselective manner, furnishing five adjacent chiral centers and leading to a single diastereoisomer of the title compound. The efficiency of the transformation is secured by thermal conditions or utilization of soft Lewis acids (Yb(OTf)3) as catalysts. The kinetics and mechanism of the 3CR were studied by using dynamic 19F NMR. Based on the NMR data and density functional theory (DFT) calculations, the IMDAV, not the Alder-ene, reaction is the rate-limiting step of the entire process.

Thiourea as a Stabilizer of Reduced Forms of Technetium─Tc(III) and Tc(IV): Experimental and Theoretical Studies of Complexes.

This paper presents synthetic methods for the preparation of Tc(III) and Tc(IV) coordination compounds with thiourea. We have shown that the main product of the synthesis is the complex [TcTu5X]X2, (Tu = (NH2)2CS, X = Cl, Br) and not [TcTu6]Cl3·4H2O, as previously thought. Tu2[TcX6]X2·3H2O is the main technetium-containing byproduct of the reaction. All reaction products, including byproducts, were characterized by X-ray diffraction analysis. We also measured the solubility for the obtained Tc(III) complexes. This research work considers the process of thermolysis of the obtained Tc(III) complexes and shows that the presence of sulfur atoms in the coordination sphere can inhibit the process of metal formation in an argon-hydrogen medium. The analysis of nonvalent interactions in Tc(III) complexes showed that the main contribution is made by van der Waals interactions of the H···H type (40.8-42.3%) and hydrogen bonds Hal···H/H···Hal and H···S/S···H, which are 41.6-44.5% in total. As the temperature decreases, the proportion of H···H contacts and H bonds decreases, and when the halogen (Cl by Br) is replaced, the proportion of H bonds increases and the proportion of van der Waals interactions decreases.

Intramolecular Re···O Nonvalent Interactions as a Stabilizer of the Polyoxorhenate(VII).

The first polyoxorhenate(VII) compound, pyrazolium polyoxorhenate ((C4N2H5)2Re4O15), and two new rhenium(VII) and technetium(VII) salts have been synthesized and studied. The structure of Tc2O7 has been reinvestigated. The [Re4O15]2- polyoxoanion contains four Re(VII) atoms: one with an octahedral environment and three with a tetrahedral environment. Polyoxorhenate is formed in the presence of a buffering agent, pyrazole, the latter maintaining pH = 2.5 during the formation of crystals. The [Re4O15]2- polyoxoanion has novel stoichiometry and the cis-conformation, likely due to the stabilizing intramolecular nonvalence interactions. For the first time, intramolecular interactions of the Re···O, Re···µ-O, and O···O are described (previously known were only intermolecular ones). In all of the compounds, intermolecular Re···O interactions are observed, which, however, in other compounds, do not lead to the formation of polyoxometalates. The Hirshfeld surface analysis showed that the main contribution to intermolecular interactions is made by the O···H/H···O contacts, van der Waals interactions of the H···H for cations, and the O···O for anions. DFT calculations of the [Re4O15]2- geometry, compared with the crystallographic data, revealed a deviation in the angles. Mass spectroscopy of the red polyoxometalate [Tc20O68]4- was carried out for the first time. Comparison of the results of MALDI and LI for the first known polyoxometalates of the manganese subgroup made it possible to find general patterns of oligomerization for rhenium and technetium compounds. The ESI-MS and LI-MS methods applied to solution and crystals Re compounds made it possible to prove rhenium being able to form not only [Re4O15]2- but also heavier polyoxoanions.

New Preparative Approach to Purer Technetium-99 Samples-Tetramethylammonium Pertechnetate: Deep Understanding and Application of Crystal Structure, Solubility, and Its Conversion to Technetium Zero Valent Matrix.

99Tc is one of the predominant fission products of 235U and an important component of nuclear industry wastes. The long half-life and specific activity of 99Tc (212,000 y, 0.63 GBq g-1) makes Tc a hazardous material. Two principal ways were proposed for its disposal, namely, long-term storage and transmutation. Conversion to metal-like technetium matrices is highly desirable for both cases and for the second one the reasonably high Tc purity was important too. Tetramethylammonium pertechnetate (TMAP) was proposed here as a prospective precursor for matrix manufacture. It provided with very high decontamination factors from actinides (that is imperative for transmutation) by means of recrystallisation and it was based on the precise data on TMAP solubility and thermodynamics accomplished in the temperature range of 3-68 °C. The structure of solid pertechnetates were re-estimated with precise X-ray structure solution and compared to its Re and Cl analogues and tetrabutylammonium analogue as well. Differential thermal and evolved gas analysis in a flow of Ar-5% H2 gas mixture showed that the major products of thermolysis were pure metallic technetium in solid matrix, trimethylammonium, carbon dioxide, and water in gas phase. High decontamination factors have been achieved when TMAP was used as an intermediate precursor for Tc.

Influence of Substituents in a Six-Membered Chelate Ring of HG-Type Complexes Containing an N→Ru Bond on Their Stability and Catalytic Activity.

An efficient approach to the synthesis of olefin metathesis HG-type catalysts containing an N→Ru bond in a six-membered chelate ring was proposed. For the most part, these ruthenium chelates can be prepared easily and in high yields based on the interaction between 2-vinylbenzylamines and Ind II (the common precursor for Ru-complex synthesis). It was demonstrated that the increase of the steric volume of substituents attached to the nitrogen atom and in the α-position of the benzylidene fragment leads to a dramatic decrease in the stability of the target ruthenium complexes. The bulkiest iPr substituent bonded to the nitrogen atom or to the α-position does not allow the closing of the chelate cycle. N,N-Diethyl-1-(2-vinylphenyl)propan-1-amine is a limiting case; its interaction with Ind II makes it possible to isolate the corresponding ruthenium chelate in a low yield (5%). Catalytic activity of the synthesized complexes was tested in RCM reactions and compared with α-unsubstituted catalysts obtained previously. The structural peculiarities of the final ruthenium complexes were thoroughly investigated using XRD and NMR analysis, which allowed making a reliable correlation between the structure of the complexes and their catalytic properties.

Towards Anion Recognition and Precipitation with Water-Soluble 1,2,4-Selenodiazolium Salts: Combined Structural and Theoretical Study.

The synthesis and structural characterization of a series of supramolecular complexes of bicyclic cationic pyridine-fused 1,2,4-selenodiazoles with various anions is reported. The binding of trifluoroacetate, tetrachloroaurate, tetraphenylborate, perrhenate, and pertechnetate anions in the solid state is regarded. All the anions interact with selenodiazolium cations exclusively via a pair of "chelating" Se⋯O and H⋯O non-covalent interactions, which make them an attractive, novel, non-classical supramolecular recognition unit or a synthon. Trifluoroacetate salts were conveniently generated via novel oxidation reaction of 2,2'-dipyridyl diselenide with bis(trifluoroacetoxy)iodo)benzene in the presence of corresponding nitriles. Isolation and structural characterization of transient 2-pyridylselenyl trifluoroacetate was achieved. X-ray analysis has demonstrated that the latter forms dimers in the solid state featuring very short and strong Se⋯O and Se⋯N ChB contacts. 1,2,4-Selenodiazolium trifluoroacetates or halides show good solubility in water. In contrast, (AuCl4)-, (ReO4)-, or (TcO4)- derivatives immediately precipitate from aqueous solutions. Structural features of these supramolecular complexes in the solid state are discussed. The nature and energies of the non-covalent interactions in novel assembles were studied by the theoretical methods. To the best of our knowledge, this is the first study that regards perrhenate and pertechnetate as acceptors in ChB interactions. The results presented here will be useful for further developments in anion recognition and precipitation involving cationic 1,2,4-selenodiazoles.

Synthesis, crystal structure and Hirshfeld surface analysis of bis-(caffeinium) hexa-chlorido-platinum(IV) in comparison with some related compounds.

The mol-ecular and crystal structure of the title compound, (C8H11N4O2)2[PtCl6], synthesized from hexa-chloro-platinic acid and caffeine in methanol, was studied by single-crystal X-ray diffraction. The caffeinium cations form a double layer via hydrogen bonds and π-stacking inter-actions. The Hirshfeld surface analysis showed that the largest contribution to the crystal packing is made by H⋯H (31.2%), H⋯Cl/Cl⋯H (22.6%), O⋯H/H⋯O (21.9%) contacts for the cation and H⋯Cl/Cl⋯H (79.3%) contacts for the anion.

Synthesis, crystal structure and Hirshfeld surface analysis of di-µ2-iodido-bis-[(2,2'-bi-quinoline-κ2 N,N')copper(I)].

The mol-ecular and crystal structures of the title compound, [Cu2I2(C18H12N2)2], were examined by single-crystal X-ray diffraction and Hirshfeld surface analysis. The Cu atom is coordinated in a distorted tetra-hedral geometry by two N atoms from the 2,2'-bi-quinoline ligands and the two µ2-bridging iodide ligands. The mol-ecules are in contact via π-π-stacking inter-actions. Hirshfeld surface analysis showed that the most important contributions to the inter-molecular inter-actions are H⋯H (39.7%), H⋯I/I⋯H (17.8%), C⋯H/H⋯C (17.5%), C⋯C (16.5%), N⋯C/C⋯N (3.9%) and N⋯H/H⋯N (3.5%).

Crystal structure and Hirshfeld surface analysis of 2,5-di-imino-8a-methyl-4,9-bis-(4-methyl-phen-yl)-7-oxo-6-phenyl-deca-hydro-2H-3,8-methano-pyrano[3,2-c]pyridine-3,4a-dicarbo-nitrile N,N-di-methyl-formamide monosolvate.

In the title compound, C32H29N5O2·C3H7NO, the bi-cyclo[3.3.1]nonane ring sys-tem adopts a half-chair/twist-boat conformation, with the phenyl rings in equatorial orientations with respect to the piperidine ring. The two oxane rings of the 2-oxabi-cyclo-[2.2.2]octane ring system exhibit a distorted boat conformation. Inter-molecular C-H⋯O and C-H⋯N hydrogen bonds connect the mol-ecules in the crystal, generating layers extending parallel to (100). These layers are connected by C-H⋯π inter-actions. A Hirshfeld surface analysis was per-formed to qu-antify the contributions of the different inter-molecular inter-actions, indicating that the most important contributions to the crystal packing are from H⋯H (52.5%), N⋯H/H⋯N (19.2%), C⋯H/H⋯C (18.8%) and O⋯H/H⋯O (8.3%) inter-actions.

Influence of the organic cation on the formation of hexahalotechnetates: X-ray, thermal and comparative analyses of non-covalent interactions.

In this work, we have reviewed non-covalent interactions in technetium hexahalide compounds and obtained eight new compounds of the CatnTcHal6 type, where Cat = dimethylammonium, tetramethylammonium, caffeinium, benzothiazolium, nicotinamidium, and pyrazolium, and Hal = Cl, Br. SCXRD studies were carried out for new compounds. In some compounds, halide anions and/or crystallization water were present. In the compounds obtained, an essential influence on the formation of structures and crystal packing is exerted by the molecules of crystallization water and halide ions. Diethylammonium and nicotinamidium compounds, whose structures do not contain other ions and contain sufficiently strong non-covalent interactions, best bind hexahalotechnetates. π-Stacking interactions, anion-π interactions, and halogen bonds were found in the structures. The percentage contribution of the H⋯Hal/Hal⋯H interactions in the transition from fluorine to bromine in TcHal62- anions decreases, while the contribution of interactions of other types increases. The greatest variety of interactions in anions is observed for compounds of caffeinium and nicotinamidium with TcBr62-. The paper considers the processes of thermolysis of some new and previously known CatnTcHal6 compounds with various cations. It is shown that the thermal stability of the compounds is only due to the properties of the organic cation and does not depend on the nature of the halogen. The proposed stages of the process of thermolysis of the TcHal62- anion, accompanied by the reduction of technetium to metal, have been established.

Synthesis, crystal structure and Hirshfeld surface analysis of 2-(perfluoro-phen-yl)acetamide in comparison with some related compounds.

The mol-ecular and crystal structures of the title compound, C8H4F5NO, were examined by single-crystal X-ray diffraction and Hirshfeld surface analysis. The title compound was synthesized by a new method at the interface of aqueous solutions of LiOH and penta-fluoro-phenyl-aceto-nitrile. In the crystal, hydrogen bonds and π-halogen inter-actions connect the mol-ecules into double layers. Analysis of the Hirshfeld surface showed that the most important contributions to the crystal packing are made by F⋯F (30.4%), C⋯F/F⋯C (22.9%), O⋯H/H⋯O (14.9%), H⋯F/F⋯H (14.0%) and H⋯H (10.2%) contacts. The Hirshfeld surfaces of analogues of the title compound were compared and the effect of perfluorination on the crystal packing was shown.

Crystal structure and Hirshfeld surface analysis of 5-acetyl-2-amino-4-(4-bromo-phen-yl)-6-oxo-1-phenyl-1,4,5,6-tetra-hydro-pyridine-3-carbo-nitrile.

The crystal structure of the title compound, C20H16BrN3O2, was determined using an inversion twin. Its asymmetric unit comprises two crystallographically independent mol-ecules (A and B) being the stereoisomers. Both mol-ecules are linked by pairs of N-H⋯O hydrogen bonds, forming a dimer with an R 2 2(16) ring motif. The dimers are connected by further N-H⋯O and N-H⋯N hydrogen bonds, forming chains along the c-axis direction·C-Br⋯π inter-actions between these chains contribute to the stabilization of the mol-ecular packing. Hirshfeld surface analysis showed that the most important contributions to the crystal packing are from H⋯H, C⋯H/H⋯C, O⋯H/H⋯O, Br⋯H/H⋯Br and N⋯H/H⋯N inter-actions.

Crystal structure and Hirshfeld surface analysis of 5-amino-5'-bromo-2'-oxo-2,3-di-hydro-1H-spiro-[imidazo[1,2-a]pyridine-7,3'-indoline]-6,8-dicarbo-nitrile dimethyl sulfoxide disolvate.

In the title compound, C16H11BrN6O·2C2H6OS, the 1,2,3,7-tetra-hydro-imid-azo[1,2-a]pyridine ring system and the oxindole moiety are both nearly planar [maximum deviations = 0.042 (2) and 0.115 (2) Å, respectively] and their planes form a dihedral angle of 86.04 (5)° with each other. Inter-molecular N-H⋯O, C-H⋯O and C-H⋯N hydrogen bonds link mol-ecules in the crystal through the O atoms of the solvent mol-ecules, generating a three-dimensional network. A Hirshfeld surface analysis was performed to further analyse the inter-molecular inter-actions.

5,5-Di-chloro-6-hy-droxy-dihydro-pyrimidine-2,4(1H,3H)-dione: mol-ecular and crystal structure, Hirshfeld surface analysis and the new route for synthesis with Mg(ReO4)2 as a new catalyst.

The mol-ecular and crystal structures of the title compound, C4H4Cl2N2O3, were investigated by single-crystal X-ray diffraction and a Hirshfeld surface analysis. The title compound was synthesized by a new type of reaction using Mg(ReO4)2 as a new catalyst and a possible mechanism for this reaction is proposed. The six-membered ring adopts a half-chair conformation. In the crystal, hydrogen bonds connect the mol-ecules into double layers, which are connected to each other by halogen bonds. The Hirshfeld surface analysis revealed that the most important contributions for the crystal packing are from O⋯H/H⋯O (35.8%), Cl⋯Cl (19.6%), Cl⋯H/H⋯Cl (17.0%), H⋯H (8.3%), C⋯O/O⋯C (4.3%), Cl⋯O/O⋯Cl (4.2%) and O⋯O (4.1%) contacts.