Tailoring of the Properties of Amorphous Mesoporous Titanosilicates Active in Acetone Condensation.

Amorphous mesoporous materials are promising as catalysts for processes involving or forming bulk molecules. In a reaction such as acetone condensation to form mesitylene, an effective catalyst should not only have a developed porous structure but also have active centers of acidic and basic types. The sol-gel approach allows one to obtain titanosilicates with such characteristics.

The Dimerization and Oligomerization of Alkenes Catalyzed with Transition Metal Complexes: Catalytic Systems and Reaction Mechanisms.

Dimers and oligomers of alkenes represent a category of compounds that are in great demand in diverse industrial sectors. Among the developing synthetic methods, the catalysis of alkene dimerization and oligomerization using transition metal salts and complexes is of undoubted interest for practical applications. This approach demonstrates substantial potential, offering not only elevated reaction rates but also precise control over the chemo-, regio-, and stereoselectivity of the reactions.

The mechanism of the replacement of aluminum atoms in 1-ethyl-3-alkylalumolanes by boron atoms with boron halides.

In this study, the mechanism of the replacement reaction of an aluminum atom by a boron atom in the 1-ethyl-3-substituted alumolanes with boron halides is proposed. Theoretical and experimental justifications based on the DFT quantum chemical calculations of the energy parameters of possible reaction routes coupled with monitoring of the reaction between 1-ethyl-3-butylalumolane and BF·EtO, BCl and BBr using H, C, B and Al NMR spectroscopy are provided.

Catalytic Properties of Zirconocene-Based Systems in 1-Hexene Oligomerization and Structure of Metal Hydride Reaction Centers.

Despite large-scale investigations of homogeneous single-site metallocene catalysts and systems based on them, there are still unsolved problems related to the control of their activity and chemo- and stereoselectivity. A solution to these problems is required to develop efficient methods for the synthesis of practically useful products of alkene transformations, such as dimers, oligomers, and polymers. Here we studied the catalytic activity of structurally diverse zirconocenes (LZrCl, L = Cp, CMe, Ind, L = MeCCp, MeSiCp, MeCCp, -MeCInd, -HCInd, BIPh(Ind), HC[THInd]), and co-catalysts activating the system, namely HAlBu, MMAO-12, and (PhC)[B(CF)], at low activator/Zr ratios in a 1-hexene oligomerization reaction.

Crystallization of SAPO-11 Molecular Sieves Prepared from Silicoaluminophosphate Gels Using Boehmites with Different Properties.

In this article, we report the results of research the formation of silicoaluminophosphate gels under changing gel aging conditions and the influence of an aluminum source (boehmite), characterized by different properties. The samples of initial gels were characterized by XRF, X-ray diffraction, MAS NMR Al and P, and scanning electron microscopy (SEM). Products of crystallization were characterized by XRF, X-ray diffraction, MAS NMR Al and P, scanning electron microscopy (SEM), N-physical adsorption, and IR spectroscopy with pyridine adsorption.

Possibility of chiral recognition by adsorption on enantiomorphous crystals: the impact of crystal surface polarity.

Chiral crystals remain one of the probable sources of first minute chiral symmetry breaking, a trigger that potentially causes an as-yet unknown type of asymmetric autocatalysis during the formation of chiral biopolymers under the conditions of the Archean Earth. Therefore, studying adsorption processes on the surface of such crystals may help improve the understanding of the nature of the initial chiral shift. The adsorptive activity of non-porous crystals with respect to the majority of organic molecules essentially depends on the ability of a crystal surface to engage in specific intermolecular interactions.

Zirconocene dichlorides as catalysts in alkene carbo- and cyclometalation by AlEt: intermediate structures and dynamics.

A series of zirconocenes LZrCl (23 examples) were studied as catalysts in the reaction of alkenes with AlEt. The catalyst activity and reaction chemoselectivity were found to depend on the ligand structure in the complex and the nature of the solvent. The alkyl exchange in the triethylaluminum dimer was studied by NMR spectroscopy; a solvent effect on the alkyl exchange parameters was established.

Hybrid Molecules Based on Fullerene C60 and Dithienylethenes. Synthesis and Photochromic Properties. Optically Controlled Organic Field-Effect Transistors.

Hybrid molecules based on fullerene C and dithienylethene and its perfluorinated analog not inferior in the efficiency of phototransformations to the initial photochromic compounds were synthesized for the first time. The resulting pyrrolidinofullerenes containing photochromic moieties were used to fabricate organic field-effect transistors (OFETs) with output and transfer characteristics ten times exceeding similar characteristics of devices based on staring dithienylethenes. It was found that OFETs based on hybrid molecules with dithienylethenes are four times less efficient than devices based on hybrid molecules with perfluorinated analogs.

Glycyrrhetinic acid derivatives as Zika virus inhibitors: Synthesis and antiviral activity in vitro.

Zika virus (ZIKV) is an arbovirus of the Flaviviridae family (Flavivirus genus), causing serious neurological complications, such as Guillain-Barre Syndrome (GBS) in adults and fetal microcephaly. Licensed vaccines or specific antiviral agents against ZIKV do not currently exist. Therefore, the search and development of anti-ZIKV agents are particularly relevant and necessary.

Synthesis, structure, and antitumor activity of 2,9-disubstituted perhydro 2,3a,7b,9,10a,14b-hexaazadibenzotetracenes.

Catalytic methods for the synthesis of previously unknown 2,9-disubstituted 3b*,7a*,10b*,14a*--14c,14d-perhydro-2,3a,7b,9,10a,14b-hexaazadibenzotetracenes have been developed. The structures were established by 1D (H, C) and 2D (COSY, HSQC, HMBC) NMR spectroscopy, MALDI TOF/TOF mass spectrometry, and X-ray diffraction analysis. Primary screening of the synthesized perhydro hexaazadibenzotetracenes for antitumor activity was carried out.

Twist-chair conformation of the tetraoxepane ring remains unchanged in tetraoxaspirododecane diamines.

A detailed structural analysis has been performed for N,N'-bis(4-chlorophenyl)-7,8,11,12-tetraoxaspiro[5.6]dodecane-9,10-diamine, CHClNO, (I), N,N'-bis(2-fluorophenyl)-7,8,11,12-tetraoxaspiro[5.6]dodecane-9,10-diamine, CHFNO, (II), and N,N'-bis(4-fluorophenyl)-7,8,11,12-tetraoxaspiro[5.

How the oxazole fragment influences the conformation of the tetraoxazocane ring in a cyclohexanespiro-3'-(1,2,4,5,7-tetraoxazocane): single-crystal X-ray and theoretical study.

Single crystals of (2S,5R)-2-isopropyl-5-methyl-7-(5-methylisoxazol-3-yl)cyclohexanespiro-3'-(1,2,4,5,7-tetraoxazocane), CHNO, have been studied via X-ray diffraction. The tetraoxazocane ring adopts a boat-chair conformation in the crystalline state, which is due to intramolecular interactions. Conformational analysis of the tetraoxazocane fragment performed at the B3LYP/6-31G(d,2p) level of theory showed that there are three minima on the potential energy surface, one of which corresponds to the conformation realized in the solid state, but not to a global minimum.

First Example of Catalytic Synthesis of Difurazanohexahydrohexaazapyrenes and Study of Their Antitumor Activity.

Catalytic method for synthesis of hexahydrohexaazapyrenes bearing two annelated furazan moieties has been successfully developed. Structures of synthesized hexahydrodioxadecaazadicyclopenta[,]pyrenes have been determined on the basis of NMR data using 2D techniques, MALDI TOF/TOF mass spectrometry, and X-ray analysis. Primary screening of hexahydrodioxadecaazadicyclopenta[,]pyrenes for cytotoxic activity against the K562, Jurkat, U937, and HeLa tumor cell lines has been performed.

Ligand exchange processes in zirconocene dichloride-trimethylaluminum bimetallic systems and their catalytic properties in reaction with alkenes.

Ligand exchange processes in the systems LZrCl-AlMe (LZrCl: CpZrCl, (CpMe)ZrCl, (CMe)ZrCl, MeSiCpZrCl, MeSi(CMe)ZrCl, rac-MeC(2-Me-4-Bu-Cp)ZrCl, meso-MeC(2-Me-4-Bu-Cp)ZrCl, rac-MeC(3-Bu-Cp)ZrCl, IndZrCl, rac-HC(Ind)ZrCl, rac-MeC(Ind)ZrCl, rac-MeSi(Ind)ZrCl, rac-CH(Ind)ZrCl, rac-CH(THInd)ZrCl, rac-MeSi(THInd)ZrCl) and CpZrMeCl-AlMe (n = 1, 2) were studied by NMR spectroscopy with the goal to establish the structures and dynamic features of probable intermediates in the zirconocene-catalyzed reactions of alkenes with AlMe. The effect of solvent, the organoaluminum compound concentration and the addition of (ClAlMe) on the activation parameters of the alkyl exchange in the trimethylaluminum dimer was studied as well. The constants and activation parameters of the methyl group exchange in the monoalkyl-substituted ansa-complexes LZrMeCl (L = rac-MeC(2-Me-4-Bu-Cp), rac-MeC(3-Bu-Cp), rac-HCInd, rac-MeCInd, rac-MeSiInd, rac-HCInd) were established for the first time.

Intramolecular mobility of η(5)-ligands in chiral zirconocene complexes and the enantioselectivity of alkene functionalization by organoaluminum compounds.

The effect of solvent nature (CD2Cl2, d8-toluene, d8-THF) on the conformational behavior of neomenthyl-substituted zirconocenes CpInd*ZrCl2 (Cp = η(5)-C5H5, Ind* = η(5)-neomenthylindenyl), CpCp'ZrCl2 (Cp = η(5)-C5H5, Cp' = η(5)-neomenthyl-4,5,6,7-tetrahydroindenyl), and Ind*2ZrCl2 (Ind* = η(5)-neomenthylindenyl) was shown by means of dynamic NMR spectroscopy, and the constants and thermodynamic parameters of conformer exchange were determined. The experimental conformational composition of the complexes was compared with structures obtained by quantum chemical modeling using the DFT methods PBE/3ζ and M06-2X/cc-pVDZ(H, C, Cl)/cc-pVDZ-PP(Zr), which predicted three rotamers in the case of both CpInd*ZrCl2 and CpCp'ZrCl2, and seven rotational isomers for Ind*2ZrCl2, three of these being C2-symmetric and the others being asymmetric. The enantioselectivity of the conformationally mobile complex Ind*2ZrCl2 in the reactions of terminal alkenes with AlR3 (R = Me, Et) was compared with that of rigid ansa-complexes, rac-p-S, p-S-[Y(η(5)-C9H10)2]ZrX2 (Y = SiMe2, C2H4; X = S-binaphtholate).

Catalytic cyclometallation in steroid chemistry IV: Efficient method for the synthesis of tetrahydrothiophene, tetrahydroselenophen and cyclopentanone derivatives of (5α)-cholestane.

Catalytic cycloalumination of (3β,5α)-3-vinylcholestane and (3α,5α)-3-allylcholestane with Et3Al catalyzed by Cp2ZrCl2 was performed for the first time to give previously unknown aluminacyclopentanes in ∼90% yield; these products were converted in situ to carbo- and heterocyclic (5α)-cholestane derivatives.

A green synthesis in water of novel (1,5,3-dithiazepan-3-yl)alkanoic acids by the multicomponent reaction of amino acids, CH2O, and 1,2-ethanedithiol.

A library of new (1,5,3-dithiazepan-3-yl)alkanoic acids was prepared by the multicomponent cyclocondensation of amino acids, formaldehyde, and 1,2-ethanedithiol in water at room temperature for 1 to 5 h in high yields. This green procedure offers several advantages such as an operational simplicity, no catalyst, and no production of hazardous materials.

7α-alkylation and 7,7-bis-alkylation of 20-hydroxyecdysone with propargyl bromide in a lithium-ammonia solution and catalytic reductive spirocyclization of 7,7-bis(2-propyn-1-yl)-14-deoxy-Δ(8(14))-20-hydroxyecdysone.

7α-Alkylation and 7,7-bis-alkylation of 20-hydroxyecdysone with propargyl bromide in a lithium-ammonia solution resulted in the formation of 7α-(2-propyn-1-yl)- and 7,7-bis(2-propyn-1-yl)-14-deoxy-Δ(8(14))-20-hydroxyecdysone in 92% and 75% yield respectively. Upon catalytic hydrogenation (10% Pd-C) of 7,7-bis(2-propyn-1-yl) derivative spirocyclization occurs by geminal 2-propyn-1-yl groups.

Stereospecific 7α-alkylation of 20-hydroxyecdysone in a lithium-ammonia solution.

The reaction of 20-hydroxyecdysone with methyl or ethyl iodide or allyl bromide in a lithium-ammonia solution results in stereospecific 7α-alkylation to give 7α-methyl-, 7α-ethyl-, and 7α-allyl-14-deoxy-Δ(8(14))-20-hydroxyecdysones, respectively. By catalytic hydrogenation (Pd-C/MeOH), the 7α-allyl derivative was converted to 7α-n-propyl-14-deoxy-Δ(8(14))-20-hydroxyecdysone.

Hydroxylation and epimerization of ecdysteroids in alkaline media: stereoselective synthesis of 9α-hydroxy-5α-ecdysteroids.

Autoxidation of diacetonides of 20-hydroxyecdysone and ponasterone A under treatment with excess of NaOH in methanol leads to the formation of 9α-hydroxy-5α-ecdysteroids previously not described. Their structures have been determined by detailed NMR analysis. Catalytic hydrogenation (Pd-C, MeOH-MeONa) of hydroxylated ecdysteroids affords the 7,8α-dihydro-9α-hydroxy-5α-ecdysteroids.

Diastereotopic splitting in the 13C NMR spectra of sulfur homofullerenes and methanofullerenes with chiral fragments.

Using gauge-invariant atomic orbital PBE/3ζ quantum chemistry approach, (13)C NMR chemical shifts and diastereotopic splittings of sp(2) fullerenyl carbons of a number of sulfur homofullerenes and methanofullerenes have been predicted and discussed. An anisochrony of fullerene carbons is caused by a chiral center of attached moieties. Clearly distinguishable diastereotopic pairs (from 8 to 11) of fullerenyl carbons of homofullerenes were observed.

Catalytic cycloalumination in steroid chemistry II: selective functionalization of 2'-methylidene-2',3'-ethano-(5α)-cholestane.

The catalytic cycloalumination of 2'-methylidene-2',3'-ethano-(5α)-cholestane with Et3Al catalyzed by Cp2ZrCl2 was performed for the first time to give spiro[2',3'-ethano-(5α)-cholestane-2',3″-aluminacyclopentane] in a ~75% yield and with high stereoselectivity (>98%). The obtained cyclic organoaluminum compound was transformed in situ into heterocyclic spiran derivatives of 2',3'-ethano-(5α)-cholestane.

Catalytic cycloalumination in steroid chemistry: the introduction of a spirotetrahydrofuran or spirotetrahydroselenophene moiety into a 3'-methylene-(5α)-spirocholestane-3,1'-cyclobutane molecule.

Cycloalumination of 3'-methylene-(5α)-spirocholestane-3,1'-cyclobutane with triethylaluminum catalyzed by Cp(2)ZrCl(2) was accomplished for the first time to give (5α)-spirocholestane-3,1'-(6'-ethyl-6'-aluminaspiro [3.4] octane) in 89%. The latter, without isolation, was converted into spirotetrahydroselenophene or spirotetrahydrofuran.