Search

The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and no external oxidant is required. A rate constant for the addition of a primary radical to N-methoxylepidinium >107 M−1 s−1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radicals to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction has been used for the preparation of unique pyridinylated terpenoids and was extended to a three-component carbopyridinylation of electron-rich alkenes including enol esters, enol ethers and enamides., N-Methoxypyridinium salts are exceptionally reactive radical traps that can be used in efficient radical chain reactions with organoboranes.

Halocyclization of alkenes is a powerful bond-forming tool in synthetic organic chemistry and a key step in natural product biosynthesis, but catalyzing halocyclization with high enantioselectivity remains a challenging task. Identifying suitable enzymes that catalyze enantioselective halocyclization of simple olefins would therefore have significant synthetic value. Flavin-dependent halogenases (FDHs) catalyze halogenation of arene and enol(ate) substrates. Herein, we reveal that FDHs engineered to catalyze site-selective aromatic halogenation also catalyze non-native bromolactonization of olefins with high enantioselectivity and near-native catalytic proficiency. Highly selective halocyclization is achieved by characterizing and mitigating the release of HOBr from the FDH active site using a combination of reaction optimization and protein engineering. The structural origins of improvements imparted by mutations responsible for the emergence of halocyclase activity are discussed. This expansion of FDH catalytic activity presages the development of a wide range of biocatalytic halogenation reactions., Catalytic enantioselective halocyclization of alkenes is an important bond forming tool and a key step in natural product biosynthesis, but so far no examples of the enzymatic counterpart of this reaction on simple achiral olefins have been reported. Here, the authors describe examples of engineered flavin-dependent halogenases that catalyze halolactonization of olefins with high enantioselectivity and near-native catalytic activity.

A novel approach for the formation of anomeric carbon-functionalized furanoside systems was accomplished through the employment of an oxo-rhenium catalyst. The transformation boasts a broad range of nucleophiles including allylsilanes, enol ethers, and aromatics in addition to sulfur, nitrogen, and hydride donors, able to react with an oxocarbenium ion intermediate derived from furanosidic structures. The excellent stereoselectivities observed followed the Woerpel model, ultimately providing 1,3-cis-1,4-trans systems. In the case of electron-rich aromatic nucleophiles, an equilibration occurs at the anomeric center with the selective formation of 1,3-trans-1,4-cis systems. This anomalous result was rationalized through density functional theory calculations. Different oxocarbenium ions such as those derived from dihydroisobenzofuran, pyrrolidine, and oxazolidine heterocycles can also be used as a substrate for the oxo-Re-mediated allylation reaction.

Little‐explored hydrosilylation of ketenes promoted by main‐group catalysts is reported. The boron Lewis acid tris(pentafluorophenyl)borane accelerates the slow uncatalyzed reaction of ketenes and hydrosilanes, thereby providing a convenient access to the new class of β,β‐di‐ and β‐monoaryl‐substituted aldehyde‐derived silyl enol ethers. Yields are moderate to high, and Z configuration is preferred. The corresponding silyl bis‐enol ethers are also available when using dihydrosilanes. The related trityl‐cation‐initiated hydrosilylation involving self‐regeneration of silylium ions is far less effective., β,β‐Di‐ and β‐monoaryl‐substituted silyl enol ethers derived from aldehydes are difficult to prepare. This rare class of compounds has been made accessible by a transition‐metal‐free hydrosilylation of ketenes with B(C6F5)3 as catalyst and Et3SiH as stoichiometric reductant. The substrate scope is decent, and the stereoselectivity moderate to good in selected cases.

Breslow intermediates (BIs) are the crucial nucleophilic amino enol intermediates formed from electrophilic aldehydes in the course of N‐heterocyclic carbene (NHC)‐catalyzed umpolung reactions. Both in organocatalytic and enzymatic umpolung, the question whether the Breslow intermediate exists as the nucleophilic enol or in the form of its electrophilic keto tautomer is of utmost importance for its reactivity and function. Herein, the preparation of charge‐tagged Breslow intermediates/keto tautomers derived from three different types of NHCs (imidazolidin‐2‐ylidenes, 1,2,4‐triazolin‐5‐ylidenes, thiazolin‐2‐ylidenes) and aldehydes is reported. An ammonium charge tag is introduced through the aldehyde unit or the NHC. ESI‐MS IR ion spectroscopy allowed the unambiguous conclusion that in the gas phase, the imidazolidin‐2‐ylidene‐derived BI indeed exists as a diamino enol, while both 1,2,4‐triazolin‐5‐ylidenes and thiazolin‐2‐ylidenes give the keto tautomer. This result coincides with the tautomeric states observed for the BIs in solution (NMR) and in the crystalline state (XRD), and is in line with our earlier calculations on the energetics of BI keto–enol equilibria., Breslow intermediates in the gas phase: In N‐heterocyclic carbene (NHC)‐catalyzed Umpolung, the reaction of the substrate aldehyde with the NHC gives the Breslow intermediate (BI) as pivotal species. The combination of IR ion spectroscopy with quantum chemical computations can determine whether the BI exists as a nucleophilic amino enol or as its keto tautomer in the gas phase, which is decisive for its reactivity both in enzymatic catalysis and in organocatalysis.

Aim. To synthesize 4-cyanoindolo[2,3-c]pyrilium salts and examine their reactivity towards N-nucleophiles. Results and discussion. The acylation reaction of 2-(indolyl-3)-2-aroylacetonitriles under acid catalysis conditions was studied. 4-Cyanoindolo[2,3-c]pyrillium borofluorides were obtained, and ketonitrile enolacylates were isolated as by-products of the reaction. Treatment of the 4-cyanoindolo[2,3-c]pyrilium salts with ammonia led to 4-cyano-β-carbolines while the interaction of the salts with hydrazine hydrate resulted in formation of pyrazolo[3’,4’:5,6]pyrido[3,4‑b]indoles – derivatives of a new heterocyclic system. The latter are formed via recyclization involving the pyran ring and the cyano group. Experimental part. Upon the treatment of 2-(indolyl-3)-2-aroylacetonitriles with acetic anhydride/tetrafluoroboric acid mixture, the acylation of the indole fragment in position 2 was followed by cyclization, resulting in formation of 4-сyanoindolo[2,3-c]pyrilium salts. The reactivity of the pyrylium salts was studied on the examples of their interaction with N-nucleophiles – ammonia and hydrazine hydrate. The structure of the compounds synthesized was confirmed by 1H NMR, IR spectroscopy and elemental analysis. Conclusions. It has been found that moderate yields of 4-сyanoindolo[2,3-c]pyrilium salts are the result of competing acylation of the hydroxyl group of enol ketonitrile, which blocks the pyran ring formation. Recylization of the salts with ammonia leads to 4-cyano-β-carbolines. Transformation of the pyran ring with hydrazine hydrate proceeds with the participation of the cyano group as a tandem reaction with formation of pyrazolo[3’,4’:5,6]pyrido[3,4-b]indoles. Received: 22.06.2020 Revised: 03.10.2020 Accepted: 23.10.2020

The key nucleophile was found to be neither an enamine nor an enol, but an enolate in the direct Michael reaction of α,β-unsaturated aldehydes and non-activated ketones catalyzed by two amine catalysts namely diphenylprolinol silyl ether and pyrrolidine. This is a rare example of an enolate from a ketone serving as a key intermediate in the asymmetric organocatalytic reaction involving secondary amine catalysts because the ketone enolates are generally generated using a strong base, and the enamine is a common nucleophile in this type of reaction., The key nucleophile was found to be neither an enamine nor an enol, but an enolate in the direct Michael reaction of α,β-unsaturated aldehydes and non-activated ketones catalyzed by two amine catalysts namely diphenylprolinol silyl ether and pyrrolidine.

The mol­ecular structure of the title compound comprises two parts, xanthene and iso­indole, sharing a central quaternary carbon atom. Both the xanthene and iso­indole moieties are nearly planar and are almost perpendicular., The mol­ecular structure of the title compound {systematic name: 3′,6′-bis(di­ethyl­amino)-2-[(2-hy­droxy­benzyl­idene)amino]­spiro­[isoindoline-1,9′-xan­then]-3-one}, C35H36N4O3 or RbSa, can be seen as being composed of two parts sharing a central quaternary carbon atom. Both the xanthene and iso­indole moieties are nearly planar: 14 atoms in the former moiety show an r.m.s. deviation of 0.0411 Å and eleven atoms in the latter moiety show an r.m.s. deviation of 0.0545 Å. These two planes are almost perpendicular to each other, the angle between the mean planes being 87.71 (2)°. The title compound appears to be in its enol form. The corresponding H atom was located and freely refined at a distance of 1.02 (3) Å from the O atom and 1.72 (2) Å from the N atom. The strong intra­molecular hydrogen bond O—H⋯N bridging the hydroxyl group and its neighboring nitro­gen atom forms an S(6) graph-set motif. Apart from the intra­molecular O—H⋯N hydrogen bond, C—H⋯O inter­actions are observed between two neighbouring RbSa mol­ecules related by an inversion center. The C—O donor–acceptor distance is 3.474 (2) Å. Moreover, C—H⋯π inter­actions are observed between the C—H bond of one of the ethyl groups and the centroid of the benzene ring of the iso­indole moiety. The C⋯centroid distance is 3.8191 (15) Å. No π–π inter­actions are observed in the crystal structure as the shortest distance between ring centroids is more than 4 Å. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H, C⋯H/H⋯C, O⋯H/H⋯O and N⋯H/H⋯N inter­actions. DFT calculations at the CAM-B3LYP/6–31 G(d) level were carried out to gain a better understanding of the relative energies and the tautomerization process between two possible conformers (keto and enol), as well as the transition state of the title compound.

An enantioselective catalytic synthesis of α‐acetoxylated ketones through I(I)/I(III) catalysis using a resorcinol/lactamide‐based chiral iodoarene is reported. Catalyst turnover by in situ generation of the active iodine(III) derivative is achieved by oxidation with mCPBA in the presence of acetic acid. The prior transformation of ketones to easily accessible acetyl enol ethers is beneficial and yields up to 97 % with enantioselectivities up to 88 % ee are obtained using only low catalyst loadings of only 5 mol % under mild reaction conditions., An efficient and easy acetoxylation of ketones via their enolethers is described. With low catalyst loadings of a chiral aryliodine high stereoselectivities can be obtained under mild reaction conditions.

Herein, ( E )-4-{[(2-amino-5-chlorophenyl)imino]methyl}-5-(hydro­xymethyl)-2-methylpyridin-3-ol [ HL ] Schiff base and its [Cu(L)Cl] complex were newly synthesized and characterized by several spectroscopic methods. In addition, density functional theory (DFT) methods were used for investigation of the tautomerization of the HL Schiff base, structural parameters of HL and [Cu(L)Cl] species, assignment of the IR vibrational bands and the NMR chem­ical shifts as well as natural bond orbital (NBO) analyses. The most stable tau­tomer of the HL Schiff base is the enol form of the meta isomer. The opti­mized geometry of the free HL Schiff base is not planar. The L - acts as a N2O tridentate ligand, which is bonded to Cu2+ via the deprotonated phenolic oxy­gen, and the amine and azomethine nitrogens. The [Cu( L )Cl] has a square pla­nar geometry in which the chloro ligand occupies the fourth coordination posit­ion. The DFT-computed values are in good consistency with the corresponding experimental values, confirming the suitability of the optimized geometries for HL and [Cu( L )Cl] species. According to the high-energy gaps, these com­pounds are stable. The atoms in molecule (AIM) analysis was used to evaluate strength of the bonding interactions and electron densities in structure of the compounds.

Deprotonative formation of biarylazacyclooctynone (BARAC) from the corresponding enol triflate is described. The reaction furnished the azacyclooctynone within one hour at –78 °C. This process could be performed in one pot from the starting ketone to provide a range of BARAC derivatives in moderate to excellent yields. The protocol enabled the gram-scale formation of the BARAC skeleton by reducing the number of reaction steps. Furthermore, the established method was applied to the synthesis of the BARAC derivative bearing a coumarin moiety.

A series of ruthenium-based catalysts supported on acid-activated montmorillonite (PILC) and interspersed with titanium (Ru/Ti-PILCs) were prepared with various amounts of ruthenium. Their catalytic performances in the selective oxidation of cyclohexene, using tert-butylhydroperoxide (TBHP) as oxidant were checked. The clay structure modification by acid activation and impregnation of transition metals resulted in an enhanced Lewis and Bronsted acidities. The Ru/Ti-PILCs materials were characterized using X-ray diffraction (XRD), surface area and pore volume measurements, surface acidity followed by Fourier transform infrared (FTIR) spectroscopy, chemical analysis, and Scanning Electron Microscopy (SEM). It was found that all catalysts can selectively oxidize cyclohexene through allylic oxidation leading mainly to 2-cyclohexene-1-one (Enone) as the major product, and 2-cyclohexene-1-ol (Enol) as secondary product. With the 5 %Ru/Ti-PILC, it was possible to reach 59 % cyclohexene total conversion, and 87 % selectivity into 2-cyclohexene-1-one and 13 % selectivity into 2-cyclohexene-1-ol. Copyright © 2019 BCREC Group. All rights reserved

Four new copper(II) complexes of the composition [Cu(H2L)(H2O)] have been synthesized by template method from reaction of copper(II) acetate, succinoyldihydrazine and some o-hydroxy aromatic aldehydes and ketones in aqueous methanol media. The composition of the complexes has been established on the basis of data obtained from analytical and mass spectral studies. The structure of the complexes has been discussed in the light of molar conductance, magnetic moment, Uv-vis, EPR and IR spectral studies. All of the complexes are non-electrolyte in DMSO. The μeff values for the complexes fall in the region 1.76–1.85 BM which rules out the possibility of any M–M interaction in the structural unit of the complexes. The ligands coordinate to the metal centre in enol form through phenolate/naphtholate oxygen atoms and azomethine nitrogen atoms. The NMR spectra show that ligands are present in anti-cis configuration in uncoordinated state. In all of the complexes the copper centre adopts square pyramidal stereochemistry. The unpaired electron is present in dx2-y2 orbital in the ground state for copper centre in the complexes. The electron transfer reactions for the complexes have been studied by cyclic voltammetry. Keywords: Copper(II) complexes, Succinoyldihydrazones, Magnetic moment, Spectroscopic studies

A general method for the hydroalkylation of electron-rich terminal and non-terminal alkenes such as enol esters, alkenyl sulfides, enol ethers, silyl enol ethers, enamides and enecarbamates has been developed. The reactions are carried out at room temperature under air initiation in the presence of triethylborane acting as a chain transfer reagent and 4-tert-butylcatechol (TBC) as a source of hydrogen atom. The efficacy of the reaction is best explained by very favorable polar effects supporting the chain process and minimizing undesired polar reactions. The stereoselective hydroalkylation of chiral N-(alk-1-en-1-yl)oxazolidin-2-ones takes place with good to excellent diastereocontrol., Giese reaction not anymore limited to electron poor alkenes! A general method for the radical mediated hydroalkylation of electron rich alkenes including enol ethers, silylenolethers, enamides, and enecarbamates has been developed.

The metallo-radical activation of ortho-allylcarbonyl-aryl N-arylsulfonylhydrazones with the paramagnetic cobalt(II) porphyrin catalyst [CoII(TPP)] (TPP = tetraphenylporphyrin) provides an efficient and powerful method for the synthesis of novel 8-membered heterocyclic enol ethers. The synthetic protocol is versatile and practical and enables the synthesis of a wide range of unique 1H-2-benzoxocins in high yields. The catalytic cyclization reactions proceed with excellent chemoselectivities, have a high functional group tolerance, and provide several opportunities for the synthesis of new bioactive compounds. The reactions are shown to proceed via cobalt(III)-carbene radical intermediates, which are involved in intramolecular hydrogen transfer (HAT) from the allylic position to the carbene radical, followed by a near-barrierless radical rebound step in the coordination sphere of cobalt. The proposed mechanism is supported by experimental observations, density functional theory (DFT) calculations, and spin trapping experiments.

Curcumin is a natural compound extracted from turmeric (Curcuma longa), which has shown remarkable anti-inflammatory, antibacterial, and possibly anticancer properties. The intense absorption in the visible domain and the possibility of intersystem crossing make curcumin attractive also for photodynamic therapy purposes. In the present contribution, we unravel, thanks to non-adiabatic surface hopping dynamics, the interplay between intersystem crossing and hydrogen transfer in the enol form, i.e. the most stable tautomer of curcumin. Most notably, we show that while hydrogen transfer is ultrafast and happens in the sub-ps regime, intersystem crossing is still present, as shown by the non-negligible population of the triplet state manifold after 2 ps. Hence, while the hydrogen transfer channel can act as a deactivating channel, curcumin, also in the red-shifted absorption enol form, can still be regarded as potentially favorable for photodynamic therapy applications.

Acyclic quaternary stereocenters are widely present in a series of biologically active natural products and pharmaceuticals. However, development of highly efficient asymmetric catalytic methods for the construction of these privileged motifs represents a longstanding challenge in organic synthesis. Herein, an efficient chiral phosphoric acid catalyzed direct asymmetric addition of α-alkynyl acyclic ketones with allenamides has been developed, furnishing the acyclic all-carbon quaternary stereocenters with excellent regioselectivities and high enantioselectivities. Extensive and detailed experimental mechanistic studies were performed to investigate the mechanism of this reaction. Despite a novel covalent allyl phosphate intermediate was found in these reactions, further studies indicated that a SN2-type mechanism with the ketone nucleophiles is not very possible. Instead, a more plausible mechanism involving the elimination of the allyl phosphate to give the α,β-unsaturated iminium intermediate, which underwent the asymmetric conjugate addition with the enol form of ketone nucleophiles under chiral anion catalysis, was proposed. In virtue of the fruitful functional groups bearing in the chiral products, the diverse derivatizations of the chiral products provided access to a wide array of chiral scaffolds with quaternary stereocenters., Acyclic quaternary stereocenters are widely present in a series of biologically active natural products and pharmaceuticals. Here the authors show an efficient chiral phosphoric acid catalyzed direct asymmetric addition of α-alkynyl acyclic ketones with allenamides to produce acyclic all-carbon quaternary stereocenters with excellent regioselectivities and high enantioselectivities

Apart from being one of the most important intermediates in chemical synthesis, broadly used in the formation of C–C bonds among other processes, the β-dicarbonyl structure is present in a huge number of biologically and pharmaceutically active compounds. In fact, mainly derived from the well-known antioxidant capability associated with the corresponding enol tautomer, β-diketones are valuable compounds in the treatment of many pathological disorders, such as cardiovascular and liver diseases, hypertension, obesity, diabetes, neurological disorders, inflammation, skin diseases, fibrosis, or arthritis; therefore, the synthesis of these structures is an area of overwhelming interest for organic chemists. This paper is devoted to the advances achieved in the last ten years for the preparation of 1,3-diketones, using different chemical (Claisen, hydration of alkynones, decarboxylative coupling) or catalytic (biocatalysis, organocatalytic, metal-based catalysis) methodologies: Additionally, the preparation of branched β-dicarbonyl compounds by means of α-functionalization of non-substituted 1,3-diketones are also discussed.

Three di-tert-butyl-substituted N-salicylideneaniline derivatives were synthesized, structurally characterized and their chromic properties investigated. Polymorphism was found to affect the photochromic behaviour of the first com­pound, while the second two com­pounds were found to display a temperature-induced phase transition. All of the structures contained an intra­molecular O—H⋯N hydrogen bond., The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluoro­phen­yl)imino]­meth­yl}phenol, C21H26FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chloro­phen­yl)imino]­meth­yl}phenol, C21H26ClNO, 2, and (E)-6-{[(4-bromo­phen­yl)imino]­meth­yl}-2,4-di-tert-butyl­phenol, C21H26BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C—O(H) and imine C=N bond lengths, and contained an intra­molecular O—H⋯N hydrogen bond alongside weaker inter­molecular C—H⋯O contacts.

Electronic properties and excited-state intramolecular proton transfer (ESIPT) processes of 2-(2′-hydroxyphenyl)benzothiazole (HBT) and its derivatives with different chemical structures (π-expansion, benzothiazole substituent and additional PT unit) have been theoretically investigated. The red-shifts of enol absorption peaks are found for all HBT derivatives regardless of chemical structures, whereas the blue-shifts or red-shifts of keto emission peaks are dependent on the orientation of π-expansion and the additional PT unit compared to HBT, which are rationalized by frontier molecular orbitals. Among designed HBT derivatives, a HBT having two PT units connected with π-expansion along the nodal plane is the best candidate for fluorescent probes because of its keto emission at 1159 nm with the largest Stokes shift. Moreover, potential energy curves and dynamic simulations confirm that the emission at much longer wavelength is from the di-keto species driven by double PT process. Based on this theoretical investigation, the keto emission of HBT derivatives in NIR region can be achieved by the combination of π-expansion along the nodal plane and additional PT unit.

A variety of synthetic methods have been developed for azulene derivatives due to their potential applications in pharmaceuticals and organic materials. Particularly, 2H-cyclohepta[b]furan-2-one and its derivatives have been frequently used as promising precursors for the synthesis of azulenes. In this review, we describe the development of the synthesis of azulenes by the reaction of 2H-cyclohepta[b]furan-2-ones with olefins, active methylenes, enamines, and silyl enol ethers as well as their reactivity and properties.

a bstract Carbonyl compounds employed as carbon nucleophiles have played a dominant role in synthetic organic chemistry; however, there is very limited use of these compounds as oxygen nucleophiles. In particular, there are only a few reports on the oxy-Michael addition of the enol forms of carbonyl nucleophiles. In this study, we present the asymmetric cycloetherification of enols, which are generated in situ from enone-bearing ketones, using chiral bifunctional organocatalysts bearing amino and squaramide groups. This transformation chemo- and enantioselectively afforded dihydropyran derivatives, which are the core structures of building blocks for synthesizing glycans.

Acid-catalyzed intramolecular vinylogous Mannich reactions and intramolecular Michael reactions affording pyrrolizinone-fused N-heterocycles from hydroxylactam derivatives bearing enals have been developed. Depending on the substituent on the hydroxylactam, the enal moiety acted either as a nucleophile (i.e., as an enol/enolate) or as an electrophile to react with the N-acyliminium ion or enamide generated from the hydroxylactam moiety, respectively. The reactions were demonstrated in the construction of fused N-heterocycles with 5- to 8-membered rings.

Strategies for altering the reaction pathway of reactive intermediates are of significant importance in diversifying organic synthesis. Enol silyl ethers, versatile enolate equivalents, are known to undergo one-electron oxidation to generate the radical cations that spontaneously form electrophilic α-carbonyl radicals via elimination of the silyl groups. Here, we demonstrate that close scrutiny of the property of the radical cations as strong C–H acids enables the identification of a catalyst system consisting of an iridium-based photosensitizer and 2,4,6-collidine for the generation of nucleophilic allylic radicals from enol silyl ethers through one-electron oxidation-deprotonation sequence under light irradiation without the desilylation of the radical cation intermediates. The resultant allylic radicals engage in the addition to electron-deficient olefins, establishing the selective allylic C-H alkylation of enol silyl ethers. This strategy is broadly applicable, and the alkylated enol silyl ethers can be transformed into highly functionalized carbonyl compounds by exploiting their common polar reactivity., Allylic C–H activation of enol silyl ethers via one-electron oxidation is usually accompanied by undesired desilylation. Here, under hybrid photoredox and Brønsted base catalysis, the authors show the mild functionalization of enol silyl ethers, providing a platform to access an array of complex carbonyl compounds.

By interaction of SnCl 4 with condensation products of dihydrazides of oxalic, terephthalic, malonic acids and R-benzoic aldehydes (R = Н, 4-N(CH 3 ) 2 , 2-OH) in acetonitrile, the following complexes were synthesized: with oxaloyl- [SnCl 4 (H 2 Oxb)]∙CH 3 CN (R = Н, I ), [SnCl 4 (Oxdb∙2H)]·2CH 3 CN (R = 4-N(CH 3 ) 2 , II ), [SnCl 4 (H 4 Oxs)]∙CH 3 CN (R = 2-OH, III ), терефталоїл- [(SnCl 4 )2(μ-Tfdb·2H)]∙2CH 3 CN (R = 4-N(CH 3 ) 2 , IV ), [SnCl 4 (μ-H 2 Tfs)]∙CH 3 CN (R = 2-OH, V ), malonoyldihydrazones- [SnCl 4 (μ-Maldb·2H)]·2CH 3 CN (R = 4-N(CH 3 ) 2 , VI ), [SnCl 4 (μ-H 2 Mals)] ∙ CH 3 CN (R = 2-OH, VII ). Their composition and structure are established by the methods of elemental analysis, conductometry, thermogravimetry, and IR spectroscopy. It was established that in the absence of a spacer (X = 0) in the dihydrazone molecules of R-benzoic aldehydes (R = H, 2-OH, 4-N(CH 3 ) 2 ) – oxaloyl dihydrazones, regardless of the presence of functional groups (CН=N, OH) as part of these molecules, SnCl 4 forms only mononuclear complexes I-III with the same O,O- coordination and composition of the coordination node, the charge of which is determined by a substituent (R) in the aldehyde fragment: R = H, 2-OH – {SnCl 4 O 2 }, R = 4-N(CH 3 ) 2 – {SnCl 4 O 2 } 2- . In the presence of a spacer in dihydrazone molecules, regardless of their stereochemical rigidity (X = -C 6 H 4 -, -CH 2 -), only if R = 2-OH, 4-N(CH 3 ) 2 , binuclear Sn(IV) complexes are formed with spatially separated coordination nodes, the composition of the nodes and the dihydrazone denatism is been determined by the substituent (R): R = 4-N(CH 3 ) 2 – {SnCl 4 ON} 2 - (tetra- in IV, VI ), R = 2-OH – {SnCl 3 O 2 N} (hexacoordinated ligand in V, VII ). Coordination of dihydrazones in a enol form, both in mono- ( II ) and in binuclear complexes ( IV, VI ), is a consequence of the presence of vacant nitrogen atoms in the aldehyde fragments of their molecules (R = 4-N(CH3)2); due to their protonation, a negative charge is compensated, which is localized in this case at the coordination sites of the zwitterionic complexes {SnCl 4 O 2 } 2- ( II ) and {SnCl 4 ON} 2- ( IV , VI ). The patterns of the formation of each spatially separated coordination node and the tautomeric form of the ligands in IV-VII are the same as in mononuclear tin(IV) complexes.

This study investigated a practical method for regiocontrolled synthesis of precursors of strained cyclohexynes and 1,2-cyclohexadienes, which is a one-pot procedure consisting of a rearrangement of silyl enol ether and subsequent formation of the enol triflates. Triethylsilyl enol ether, derived from cyclohexanone, was treated with a combination of LDA and t-BuOK in n-hexane/THF to encourage the migration of the silyl group to generate an α-silyl enolate. Subsequently, the α-silyl enolate was reacted with Comins’ reagent to yield the corresponding enol triflate. Finally, the α-silylated trisubstituted lithium enolate for the synthesis of 1,2-cyclohexadiene precursor was isomerized in the presence of a stoichiometric amount of water for one hour at room temperature to exclusively provide tetrasubstituted lithium enolate for the synthesis of cyclohexyne precursor in one pot.

The separation and isolation of many of the platinum group metals (PGMs) is currently achieved commercially using solvent extraction processes. The extraction of rhodium is problematic however, as a variety of complexes of the form [RhCln(H2O)6‐n](n−3)− are found in hydrochloric acid, making it difficult to design a reagent that can extract all the rhodium. In this work, the synergistic combination of a primary amine (2‐ethylhexylamine, LA) with a primary amide (3,5,5‐trimethylhexanamide, L1) is shown to extract over 85 % of rhodium from 4 M hydrochloric acid. Two rhodium complexes are shown to reside in the organic phase, the ion‐pair [HLA]3[RhCl6] and the amide complex [HLA]2[RhCl5(L1)]; in the latter complex, the amide is tautomerized to its enol form and coordinated to the rhodium centre through the nitrogen atom. This insight highlights the need for ligands that target specific metal complexes in the aqueous phase and provides an efficient synergistic solution for the solvent extraction of rhodium., A synergistic combination of a simple primary amine (LA) and a simple primary amide (L1) is shown to extract rhodium from hydrochloric acid. A range of experimental and computational techniques are used to elucidate the structures of two different complexes in the organic phase; the ion‐pair [HLA]3[RhCl6] and the amide complex [HLA]2[RhCl5(L1)]. In the latter complex, the amide is tautomerized to its enol form and coordinated through the nitrogen atom.

Metal complexes of Co(II), Ni(II) and Cu(II) complexes (1–3) with a new Schiff base (HL) have been prepared and characterized by elemental analyses IR, UV–Visible, magnetic measurements, 1H NMR, 13C NMR, and X-ray diffraction analysis. Coats-Redfern and Horowitz-Metzger techniques are used to measure the thermodynamic parameters of the ligand and its complexes. The spectral data indicated that the ligand (HL) acts as a monobasic tridentate coordinating via the oxygen of the carbonyl group in the enol form, the nitrogen atom of the azomethine (–C=N–) group and phenolic –OH group. On the basis of magnetic and electronic spectral data, an octahedral geometry for Co (II), Ni (II) and Cu (II) complexes have been proposed. The molecular modeling using DFT method is drawn showing the bond lengths, bond angles and quantum chemical parameters. Absorption spectra and viscosity measurements have examined the calf thymus DNA binding behavior of the ligand and its complexes. The docking active site interactions were evaluated to predict the activity of HL against COVID-19 by binding with SARS-CoV-2 principal protease that recovered from the RCSB protein data bank with PDB ID: 6Y84 and its anticancer activity with prostate cancer receptor 3qum. Therefore, HL is worth further investigations and clinical trials as a possible therapeutic agent for prostate cancer and COVID-19 disease caused by the novel SARS-CoV-2. Evaluation results of synthesized complexes against the human cancer cell lines MCF-7 and HepG-2 were published in comparison with positive controls in the viability assay of vinblastine and colchicine. DPPH free radical-scavenging assays used to determine the in vitro antioxidant activity of all complexes. Moreover, the ligand and some complexes were screened for in vitro antibacterial activity against Staphylococcus aureus as Gram +ve bacteria and Escherichia coli (E. coli) as Gram -ve bacteria using inhibition zone diameter.

The nucleophilic addition to nitrogen in 3-monosubstituted s-tetrazines under mild conditions is reported, by using silyl-enol ethers as the nucleophiles and mediated by BF3. The preference for this azaphilic addition over the usually observed inverse electron demand Diels-Alder reactions was determined experimentally and evaluated theoretically. In this regard, the influence of the effect of BF3-coordination to s-tetrazines was investigated thoroughly. The substrate dependency of this unusual reaction was rationalized by determination of the activation barriers and on the basis of the activation strain model by employing density functional theory. Lastly, the decomposition of the unstable adducts was examined and an interesting rearrangement to a triazine derived structure was observed.