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A method is reported to control the stereoselectivity at C(20) in the syntheses of 20-R-21,21,21-trifluorothevinols, the opioid ligands incorporating fluorine atoms within the pharmacophore associated with the surroundings of the C(20) carbon atom.

New catalysts prepared by simple mixing of molecular iodine and inexpensive monodonor amines can efficiently catalyze the coupling of CO2 with different epoxides at moderate temperatures (60–90 °C), pressures (10–56 atm) and low (0.25–0.5 mol %) catalytic loading. The molecular systems can be considered as the simplest and most inexpensive catalyst for the reactions.

A group of available catalysts based on polyethylenimine quaternized with p-xylylene dichloride followed by subsequent exchange of anions was developed. The influence of the nature of halide ions and electronic and steric factors of the substituents in epoxides on the reaction rate of carbon dioxide addition to epoxides was studied. The catalytic capabilities of the adduct of polyethylenimine with iodine were considered.

The first [4]radialene complex of zirconocene 1Zr-Ph was obtained by the reaction of Negishi’s reagent with 1,4-diphenylbutadiyne. The structure of 1Zr-Ph has been determined by X-ray diffraction. ...

Three series of N-heterocyclic carbene analogues including Arduengo-type systems (HCNBut)2E (1; E = C, Si, Ge, Sn), their benzannulated derivatives C6H4(NCH2But)2E (2; E = C, Si, Ge, Sn, Pb), and amidophenolates C6H2But2(O)NButE (3; E = Ge, Sn, Pb) were studied by the electron density of delocalized bonds (EDDB) method. The results obtained confirmed the π-aromaticity of systems 1–3. The aromaticity series were obtained. The degree of aromaticity of heavy carbene analogues increases on going down Group 14 of the periodic system.

Benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) (isoBBT) is a new electron-withdrawing building block that can be used to obtain potentially interesting compounds for the synthesis of OLEDs and organic solar cells components. The electronic structure and delocalization in benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole), 4-bromobenzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole), and 4,8-dibromobenzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) were studied using X-ray diffraction analysis and ab initio calculations by EDDB and GIMIC methods and were compared to the corresponding properties of benzo[1,2-c:4,5-c′]bis[1,2,5]thiadiazole (BBT). Calculations at a high level of theory showed that the electron affinity, which determines electron deficiency, of isoBBT was significantly smaller than that of BBT (1.09 vs. 1.90 eV). Incorporation of bromine atoms improves the electrical deficiency of bromobenzo-bis-thiadiazoles nearly without affecting aromaticity, which increases the reactivity of these compounds in aromatic nucleophilic substitution reactions and, on the other hand, does not reduce the ability to undergo cross-coupling reactions. 4-Bromobenzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) is an attractive object for the synthesis of monosubstituted isoBBT compounds. The goal to find conditions for the selective substitution of hydrogen or bromine atoms at position 4 in order to obtain compounds containing a (het)aryl group in this position and to use the remaining unsubstituted hydrogen or bromine atoms to obtain unsymmetrically substituted isoBBT derivatives, potentially interesting compounds for organic photovoltaic components, was not set before. Nucleophilic aromatic and cross-coupling reactions, along with palladium-catalyzed C-H direct arylation reactions for 4-bromobenzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole), were studied and selective conditions for the synthesis of monoarylated derivatives were found. The observed features of the structure and reactivity of isoBBT derivatives may be useful for building organic semiconductor-based devices.

Using the recent aromatic criteria, the conjugation and aromatic properties of group 4 metallacyclocumulenes Cp2M-η4–(R)C═C═C═C–R (1) and Cp2M-η3(R–C═C═C═C(R)–R(C) ═CR) (2) (M = Ti, Zr, Hf) were st...

New tripodal 1,2,3-triazole ligands based on triphenylphosphine oxide platform with different linker lengths have been synthesized, and their structure has been determined by elemental analysis, 1H, 13C, and 31P NMR spectroscopy, mass spectrometry, and vibrational (IR and Raman) spectroscopy. The coordination and extraction properties of the new ligands have been studied in the complexation with uranyl nitrate and extraction of micro amounts of uranium(VI) from aqueous phase to 1,2-dichloroethane.

The aromaticity of three-membered monoheterocycles containing a group 14 or 4 element was investigated by using modern aromaticity criteria: structural, electronic (FBO), optical (vibrational spect...

Treatment of 4-phenyl-5H-1,2,3-dithiazole-5-thione with iodine in acetonitrile yielded crystalline product with thione-iodonium three-center halogen bond and triiodide anion bound with two iodine molecules by the typical halogen bonds. At the level of a theoretical study of electron density and its gradients, the similarity of electronic properties of the central iodine atom in bridged moiety [S−I−S]+ and in triiodide anion [I−I−I]− has been illustrated. The experimental and theoretical Raman spectra of iodonium salt are discussed: the assignment of the bands corresponding to the iodonium bridged fragment vibrations has been made on the basis of calculated ab initio data.

The synthesis, crystal structure, thermal stability, porosity and magnetic properties of three new layered coordination polymers [(M2(pQ)3)·4DMAA]n (M3+ = La3+ (1), Pr3+ (2), Nd3+ (3); pQ2− – the dianionic form of 2,5-dihydroxy-3,6-di-tert-butyl-para-quinone; DMAA = N,N′-dimethylacetamide) are reported. The coordination polymers obtained were investigated by solid-state electrochemistry which demonstrates multistep one-electron transformations caused by the presence of redox-active dioxolene ligands.

A series of new bis(pyrazol-3-yl)pyridines (LR) N,N′-disubstituted by 4-functionalized 2,6-dibromophenyl groups have been synthesized to study the effect of a distal substituent on the spin-crossover (SCO) behaviour of the iron(II) complexes [Fe(LR)2](ClO4)2 by variable-temperature magnetometry, NMR spectroscopy, and X-ray diffraction. The SCO-assisting tendency of the substituents with different electronic and steric properties (i.e., the bromine atom and the methyl group) in the para-position of the 2,6-dibromophenyl group is discussed. Together with earlier reported SCO-active iron(II) complexes with N,N′-disubstituted bis(pyrazol-3-yl)pyridines, these new complexes open the way for this family of SCO compounds to emerge as an effective ‘tool’ in revealing structure–function relations, a prerequisite for successful molecular design of switchable materials for future breakthrough applications in sensing, switching, and memory devices.

Experimental optical (UV–vis, Raman) and computational magnetic (NICS, GIMIC) criteria were used to study the aromaticity of group 14 N,O-heterocyclic carbenes tBuAPE (AP = amidophenolate, E = Ge, Sn, Pb). The UV–vis and Raman spectra of the monomeric compound with E = Ge were shown to differ significantly from those of dimeric compounds with E = Sn, Pb. The reason for these phenomena is suppression in the dimeric molecules of 10 π-electron aromaticity due to partial filling of the vacant pz orbital of the EII atom caused by intermolecular coordination N→EII. The monomeric forms of all molecules studied are aromatic according to all the criteria used.

The structure of the digermene (tBu2MeSi)2Ge=Ge(SiMetBu2)2 (1) was investigated by experimental (Raman and UV–vis) as well as computational (NCA, TD DFT and QTAIM) methods. Temperature-dependent Raman and UV–vis spectra have demonstrated that 1 does not dissociate into the corresponding germylenes on heating either to 120 °C as a solid or to 80 °C in solution, thus preserving the integrity of its double Ge=Ge bond. Raman and NCA results allowed one to estimate the region of the νGe=Ge vibrational frequency in the spectra of digermenes as 270–340 cm−1. When illuminated with a red laser beam of enhanced power (>5 mW), solid 1 undergoes a transformation followed by disappearance of the νGe=Ge Raman band. This process is evidently photodissociation caused by proximity of the red laser wavelength 632.8 nm to the intrinsic absorption of 1 at 616 nm. Temperature dependence of the Raman spectrum has revealed conformational isomerism in solid digermene 1 due to hindered rotation about the Ge–Si bonds, the conformers differing in mutual disposition of Me and bulky tBu groups.

1-Dimethylthiocarbamoyloxy-3-diphenylphosphinobenzene was used as a key precursor for the synthesis of a whole series of organophosphorus(V) pincer ligands combining thiocarbamate donor group with ...

Intramolecular hydrogen bonding competes with intermolecular hydrogen bonding in alkanols containing Ph2P(O) group. A character of H-bonding in secondary alkanols Ph2P(O) (CR2)nCH2CH(OH)Me, where n = 0 (1), n = 1, R = H (2), and n = 1, R = Me (3) in crystal state and solutions has been studied by X-ray diffraction, FTIR, and diffusion ordered NMR spectroscopy (DOSY). Quantum chemical calculations and QTAIM analysis of isolated alkanol molecules and their dimers have been performed. In spite of slight difference in the structure of linker between P(O) and OH groups, the studied alcohols in crystal exhibit three types of H-bonds: dimer with intermolecular H-bond, polymeric chains with intermolecular H-bond, and monomer with intramolecular H-bond. Experimental data agree well with structural data of quantum chemical calculations at the M06-2x/6-311G (d,p) level of theory. Energy values (thermodynamic parameters) of DFT-optimized structures for gauche and anti isomers and dimers have been calculated. According to FTIR data in solutions (0.1–0.0001 M), alcohol 1 is the most associated, association of alcohol 2 is much less expressed, while alcohol 3 remains as H-bound monomer. Particle size assessed by DOSY relative to Ph3CH does not change on dilution for alcohols 2 and 3 but varies for alcohol 1.

The structure and properties of nanocomposites based on organosoluble polyimide (PI) and branched functional metallosiloxane oligomers with different types of central metal atoms (Al, Cr, Fe, Zr, Hf and Nb) were investigated. Under the same weight content of the filler, the geometric parameters of the nanoparticles and thermal properties of the nanocomposites did not exhibit a direct relationship with the ability of the materials to withstand the incident flow of oxygen plasma. The atomic oxygenerosion resistance of the filled PI films was influenced by the composition of the hybrid fillerand the type of metal atom in the hybrid filler in the base metallosiloxane oligomer. To determine the effectiveness of the nanoparticles as protective elements of the polymer surface, the nanocomposite erosion yields pertaining to the concentration of the crosslinked organo&ndash, inorganic polymer forming the dispersed phase were determined and expressed in mmol per gram PI. The filler concentration in the polymer, expressed in these units, allows for comparison of the efficiency of different nanosize fillers for use in fabricating space survivable coatings. This can be important in the pursuit of new precursors, fillers for fabricating space survivable polymer composites.

1-Hydroxy-3-(5,7-dimethyl-2-oxo-1,2-dihydro-1,8-naphthyridin-1-yl)propylidenebisphosphonic acid has been synthesized. The structure of the acid and its precursors synthesized for the first time, 3-(5,7-dimethyl-2-oxo-1,2-dihydro-1,8-naphthyridin-1-yl)propionic acid and the corresponding methyl ester, in the solid state and in the DMSO solution has been elucidated by means of vibrational (IR and Raman) and multinuclear (1H, 13C, and 31P) NMR spectroscopy.

Electronic structure of the six-membered unsaturated N-heterocyclic silylene 1 was investigated by the experimental (Raman, IR, UV–vis) and theoretical methods of optical spectroscopy. The results obtained along with the refined NICS data confirm π-conjugated but not aromatic character of molecule 1 with its trans-diene fragment and participation of the vacant pz orbital of SiII atom in the conjugated system.

Vibrational spectroscopy studies of 11-vertex boron-containing clusters [B11H11]2–(1), [2-CB10H11]– (2), and 2,3-C2B9H11 (3) revealed two low-frequency large-amplitude modes in their spectra and, therefore, structural nonrigidity of these polyhedra in contrast to related 12-, 10-, and 6-vertex closo-clusters. The nonrigidity originates from specific features of the electron density distribution. According to calculations within the framework of the "Atoms in Molecule" (AIM) theory, these polyhedra are characterized by the lack of many bond paths localized on corresponding edges, in particular, between boron atoms with coordination numbers of 6 and 5 (6k and 5k). Consequently, these polyhedra are composed of not only trigonal faces, i.e., formally do not have the closo-structure that was traditionally ascribed to them based on formal count of (2n + 2) valence electrons. According to calculations of three-center delocalization indices, the absence of bond paths is not equivalent to the lack of interaction between corresponding atoms since this interaction occurs through open three-center bonds. The mechanism and reasons for signal averaging observed in 11B NMR spectra of compounds 1 and 2 in contrast to 3 are analyzed.

The electronic structure and the conjugation in allyltetrylenes Ar-E-η3-C3H4 (E= Si, Ge, Sn, Pb; Ar = С6H3Trip2 (1), Ph (1′)), which exhibit the unique symmetric η3-coordination among the allyl compounds of the main groups, were studied by the DFT based methods. The QTAIM molecular graph exhibits two metal-allyl bond paths, which form 4-membered metallacycles. The advance aromaticity criteria NICS-scan, electron density of delocalized bonds (EDDB) and gauge-including magnetically induced currents (GIMIC) were firstly applied to the 1. The method results demonstrate a strong cyclic delocalization for organometallics. According to the NICS and GIMIC values, the aromaticity degree diminishes in the series Si ~ Ge > Sn > Pb. According to the EDDB results, it increases in the series Si

The crystal structure and properties of (Z)-4-chloro-5-((2-((4-chloro-5H-1,2,3-dithiazol-5-ylidene)amino)phenyl)amino)-1,2,3-dithiazol-1-ium oligoiodide (C2/c) synthesized from the initial bis(4-сhloro-5H-1,2,3-dithiazolo-5-ylidene)benzene-1,2-diamine (P21/c) have been characterized by various experimental and theoretic methods. The superposition of atomic basin boundaries in the electron density and in the electrostatic potential does not confirm the halogen bonding between the triiodide anion and sulfur atoms in cation. On the other hand, in the studied oligoiodide, the charge-assisted iodine–iodine halogen bonds are observed between the strongly asymmetric triiodide and diiodine units; thus, the oligoiodide anion includes at least two diiodine fragments with bond lengths 2.7334(4) and 2.7786(5) A bound. This key trait has resulted in characteristic spectral and thermal features. Raman spectra do not contain typical triiodide bands but only those that are expectable for bound diiodine at 157 and 179 cm−1. Thermal decomposition has demonstrated release of both diiodine molecules within one decomposition stage without melting.

The nature of the apex-base bonds in organometallics of a novel class – pyramidanes [(Me 3 Si) 4 C 4 ]E (E = Ge, Sn, Pb) was shown to be covalent but with a high degree of polarity on the basis of the Raman data and the results of QTAIM analysis. NICS data suggest three-dimensional aromaticity of the C 4 E pyramid.

The vibrational spectra (IR and Raman) for seven-membered zirconacyclocumulenes of the type Cp2Zr[η3-R1C=C=C=C(R1)–C(R3)=CR2], R1= SiMe3, tBu, R2,R3=Ph, SiMe3, tBu, -C C-SiMe3, -C C-tBu] were obtained and studied using normal coordinate analysis. For metallacycles of this type, three lines are pronounced: ~1870 and ~1650 cm–1 bands corresponding to symmetric (ν1) and antisymmetric (ν2) vibrations of cumulene fragment, as well as at ~1400 cm–1 the νС=С vibration, respectively. These data are consistent with the geometric parameters of the cycles and the results of QTAIM analysis, within which the molecular graph demonstrated three Zr–C bond paths. For a crystalline sample of the Cp2Zr[η3-Me3SiC4(SiMe3)–C(Ph)=CPh] complex (2Zr(e)), irreversible isomerization under the action of a He-Ne laser into the cyclopentadiene structure Cp2Zr[η2-(Me3SiC C)C=C(SiMe3)–C(Ph)=CPh] with a pendant alkyne substituent. Based on the IR spectra data for the Cp2Zr[η3-Me3SiC4(SiMe3)–C(SiMe3)=C–C C-SiMe3] (2Zr(d)) complex, the preservation of the cyclocumulene structure in the dynamic process of its isomerization was proved.

Three new 3D metal–organic frameworks of lanthanum based on mixed anionic ligands, [(La2(pQ)2(BDC)4)·4DMF]n, [(La2(pQ)2(DHBDC)4)·4DMF]n, [(La2(CA)2(BDC)4)·4DMF]n (pQ—dianion of 2,5-dihydroxy-3,6-di-tert-butyl-para-quinone, CA—dianion of chloranilic acid, BDC-1,4-benzenedicarboxylate, DHBDC-2,5-dihydroxy-1,4-benzenedicarboxylate and DMF-N,N′-dimethylformamide), were synthesized using solvothermal methodology. Coordination polymers demonstrate the rare xah or 4,6T187 topology of a 3D framework. The homoleptic 2D-coordination polymer [(La2(pQ)3)·4DMF]n was obtained as a by-product in the course of synthetic procedure optimization. The thermal stability, spectral characteristics and porosity of coordination polymers were investigated.

Reaction of 1,2-bis(diphenylpsphoryl)benzene 1,2-[Ph2(O)P]2C6H4 (L) with f-element nitrates resulted in 1:1 and 1:2 complexes. The isolated complexes, namely, [UO2(L)(NO3)2]·MeCN (1), [UO2(L)2(NO3)](NO3)·MeCN (2), [Th(L)2(NO3)3](NO3)·MeCN·H2O (3), [La(L)2(NO3)3]·0.5MeCN·1.5H2O (4), and [Lu(L)2(NO3)2](NO3)·2MeCN (5) have been characterized by elemental analysis and IR spectroscopy. The structures of complexes 1, 2, and 5 have been determined by single-crystal X-ray crystallography. Intraligand π-stacking and interligand C H… π interaction have been observed in the crystalline complexes. The π-stacking and C H… π interaction energy in two uranyl complexes 1 and 2 have been estimated from Bader’s AIM theory calculations performed at the DFT level. Solution structure of all complexes has been investigated by IR and multinuclear (1H, 13C, and 31P) NMR spectroscopy. The formation of 1:3 complexes with lanthanum nitrate (IR, 31P NMR) has been examined. Preliminary extraction study of U(VI), Th(IV), and Ln(III) from 2 M HNO3 into 1,2-dichloroethane have shown that ligand L recovers U(VI), Th(IV), and La(III) in the same extent as its tetraphosphoryl analog 1,2,4,5-[Ph2(O)P]4C6H2 (L') but it recovers Eu(III), and Lu(III) by several times better than L'. Furthermore, an improved modified method for the synthesis of ligand L has been suggested.

According to an X-ray diffraction study, pyridine-2-selenenyl chloride (1) characterized by unusually high stability both in solutions and in the solid state adopts a dimeric structure formed by two secondary intermolecular Se···N interactions. However, it slowly transforms into zwitterionic T-shaped pyridinium-2-selenenyl dichloride (2) in a dichloromethane solution. Conformational features, electronic structures, and reactivities of 1 and 2 are discussed on the basis of experimental and theoretical (quantum chemical calculations) data.

New 1,8- and 1,6-naphthyridines containing a phosphoryl group in the side chain were synthesized via Friedlӓnder reaction by combining the appropriate aminonicotinic aldehydes and phosphoryl ketones in alcohol medium in the presence of basic catalysts (pyrrolidine or KOH). A series of phosphoryl-substituted 1,8-naphthyridines effectively extracted uranium(VI) from neutral aqueous solutions containing lanthanide(III) into 1,2-dichloroethane.

The reactions of 5-substituted furfurylamines with anhydrides of α,β-unsaturated carboxylic acids (acryloyl chloride and maleic anhydride) were studied. The first step of the reaction mechanism involved acylation of furfurylamine nitrogen atom, followed by a stereospecific, spontaneous intramolecular Diels–Alder reaction at the furan ring of the N-furfurylamide intermediates. When the starting materials were 5-alkyl-substituted furfurylamines, the expected 1-oxo-2,3,7,7a-hexahydro-1H-3a,6-epoxyisoindoles or the corresponding 7-carboxylic acids were obtained in up to 98% yields. The acylation of 5-aryl-substituted furfurylamines with maleic anhydride led to N-furfurylmaleic amides, which formed a dynamic equilibrium in solutions with adducts formed by intramolecular [4+2] cycloaddition, 3a,6-epoxyisoindole-7-carboxylic acids, as proved by NMR spectroscopy. X-ray structural analysis results show that these mixtures crystallized in the form of the cyclic tautomer.

Hybrid scorpionate ligand (OPPh2)2CHCH2C(O)Me (L) was synthesized and characterized by spectroscopic methods and X-ray diffraction. The selected coordination chemistry of L with UO2(NO3)2 and Ln(NO3)3 (Ln = La, Nd, Lu) has been evaluated. The isolated mono- and binuclear complexes, namely, [UO2(NO3)2L] (1), [{UO2(NO3)L}2(μ2-O2)]·EtOH (2), [La(NO3)3L2]·2.33MeCN (3), [Nd(NO3)3L2]·3MeCN (4), [Nd(NO3)2L2]+·(NO3)−·EtOH (5) and [Lu(NO3)3L2] (6) have been characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray structures have been determined for complexes 1-5. Intramolecular intraligand π-stacking interactions between two phenyl fragments of the coordinated ligand(s) were observed in all complexes 1-5. The π-stacking interaction energy was estimated from Bader's AIM theory calculations performed at the DFT level. Solution properties have been examined using IR and multinuclear ((1)H, (13)C, and (31)P) NMR spectroscopy in CD3CN and CDCl3. Coordination modes of L vary with the coordination polyhedron of the metal and solvent nature showing many coordination modes: P(O),P(O), P(O),P(O),C(O), P(O),C(O), and P(O). Preliminary extraction studies of U(VI) and Ln(III) (Ln = La, Nd, Ho, Yb) from 3.75 M HNO3 into CHCl3 show that scorpionate L extracts f-block elements (especially uranium) better than its unmodified prototype (OPPh2)2CH2.

The synthesis of an organometallic PdII pincer complex is realized for the first time via C H bond activation of the bis(thiocarbamate) ligand with PdCl2(NCPh)2 under mechanochemical conditions either by grinding of the reactants in a mortar or in a vibration ball mill at gram scale.

Synthesis and single-crystal X-ray diffraction study (SC-XRD) of the O,N-heterocyclic germylene Ge(PhAp) (1) containing chelate 4,6-di-tert-butyl-N-phenyl-o-amidophenolate ligand (PhApH2, where Ap – o-amidophenolate) are reported. Germylene 1 demonstrates a monomeric structure in contrast to earlier known related stannylene Sn(PhAp) (2) existing as a dimer. Diverse weak intermolecular interactions (Ge…Ge, CH…π(chelate) and Ge…π(arene)) were detected in the crystal packing of germylene 1. Hirshfeld surface analysis has been performed to evaluate such interactions. Reactivity of compounds 1 and 2 towards dithiodiiron hexacarbonyl has been examined. Low-valent germanium(II) and tin(II) centers are readily inserted into S-S bond of dithiodiiron hexacarbonyl with the formation of Fe4(µ4-ES4)(CO)12 (E: Ge(3); Sn(4)) and bis-ligand complexes of tetravalent metals E(PhAp)2. The resulting germanium(IV) and tin(IV) bis-o-amidophenolates were isolated as six-coordinated pyridine adducts E(PhAp)2(Py)2 (E: Ge(5); Sn(6)). All complexes were characterized by SC-XRD.

In this paper, a new kind of space-durable nanocomposites has been prepared using one-step in situ method of filling organosoluble polyimides (PI). Three types of metalloalkoxysiloxanes (tris-(diethoxymethylsiloxy) aluminum, tetrakis-(diethoxymethylsiloxy) zirconium, pentakis-(diethoxymethylsiloxy) niobium) were used as filler precursors. It is demonstrated that the nanosized filler particles formed in the polymer volume have a hybrid chemical structure and contain М-О-Si and Si–O–Si bonds. The in situ filling of PI preserves its unique thermal properties, increases the glass transition temperature, and maintains high stability to the thermal oxidation of the matrix PI. The atomic oxygen (AO) erosion resistance of the filled PI has been investigated by exposing its surface to a variety of AO fluences. The introduction of nanosized filler in PI contributes to a sharp, order-of-magnitude decrease in the AO erosion coefficient of the nanocomposite. The valence of the central metal atom of the precursor predetermines the silica-block content in the forming filler and its atomic oxygen AO-protective function. During the transition from a precursor with a trivalent metal atom to a precursor with a tetra- or pentavalent metal atom, the erosion coefficient of filled PI decreases at a constant fluence of AO. Taking into account that the M-O bond energy in a M-O-Si group is higher than the Si–O bond energy, the presence of such atoms as Zr or Nb in the chemical structure of the filler can act as a “reinforcing” element that increases the resistance of the protective layer against AO action.

A rare example of chemospecificity in the tandem Diels–Alder reaction of activated alkynes and bis-dienes has been revealed. The reaction between bis-furyl dienes and DMAD occurs at 25–80 °C and leads to kinetically controlled “pincer” adducts, 4a,8a-disubstituted 1,4:5,8-diepoxynaphthalenes. On the contrary, only thermodynamically controlled “domino” adducts (2,3-disubstituted 1,4:5,8-diepoxynaphthalenes) are formed in the same reaction at 140 °C. The “pincer” adducts can be transformed to the “domino” adducts at heating. The rate constants for reactions of both types were calculated using dynamic 1H NMR spectroscopy.