Synthesis of anticonvulsant sulfamides. Theoretical study of the related mechanism

A theoretical study of the mechanisms associated with the synthesis of anticonvulsant symmetric N,N-substituted sulfamides is presented. Two possible synthetic routes are compared, which mainly differ in the use of pyridine as a nucleophilic agent in the reaction mechanism. Geometry optimization techniques and transition-state detection at the B3LYP/6-31G** level, modeling the solvent by means of an isodensity polarizable continuum approach, allow the most suitable method for the experimental process to be discerned.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

Predicting Stable Molecular Structures for (RNC)2AuIX Complexes

Calculations have been performed at the MP2 and DFT levels for investigating the reasons for the difficulties in synthesizing bis(isocyanide)gold(I) halide complexes. Three‐coordinated gold(I) complexes of the type (R₃P)₂Au^IX ( 1 ) can be synthesized, whereas the analogous isocyanide complexes (RNC)₂Au^IX ( 2 ) are not experimentally known. The molecular structures of (R₃P)₂Au^IX (X = Cl, Br, and I) and (RNC)₂Au^IX with X = halide, cyanide, nitrite, methylthiolate, and thiocyanate are compared and structural differences are discussed. Calculations of molecular properties elucidate which factors determine the strength of the gold‐ligand interactions in (RNC)₂Au^IX. The linear bonding mode of RNC favors a T‐shaped geometry instead of the planar Y‐shaped trigonal structure of (R₃P)₂Au^IX complexes that have been synthesized. An increased polarity of the Au–X bond in 2 leads to destabilization of the Y‐shaped structure. Chalcogen‐containing ligands or cyanide appear to be good X‐ligand candidates for synthesis of (RNC)₂Au^IX complexes.     

Synthesis and Characterization of the Silylated Hexaphenyl Carbodiphosphorane [Me3SiC(PPh3)2][CF3SO3]

The addition of trimethylsilyl trifluoromethanesulfonate TMS‐OTf (CF₃SO₃ = OTf, triflate) to hexaphenyl carbodiphosphorane PPh₃=C=PPh₃ ( 1 ) in toluene yields the silylated carbodiphosphorane [Me₃SiC(PPh₃)₂][OTf] ( 2 ). Compound 2 represents the first silylated carbodiphosphorane characterized in solution and in the solid state. 2 is an air‐sensitive compound but stable in solution and in the solid state in an inert atmosphere as shown by heteronuclear NMR experiments and also by X‐ray diffraction analysis. Compound 2 crystallizes in the monoclinic space group P2₁/n with the cell dimensions a = 1161.7(1), b = 1714.4(1), c = 1903.3(1) pm; β = 102.74(1)° and Z = 4. Structure, frontier orbitals, and dissociation energies for 2 were determined by density functional theory‐based computations highlighting the character of 2 as a Lewis acid adduct of a carbon(0) compound.     

Unprecedented Multicomponent Reaction of Indoles,CS2 and Nitroarenes: Stereoselective Synthesis of (Z)-3-((Arylamino)methylene)indoline-2-thiones

An efficient method for the stereoselective synthesis of (Z)-3-((arylamino)methylene)indoline-2-thiones have been developed via a novel multicomponent reaction of indoles, CS₂ and nitroarenes. A range of functionalized indoline-2-thiones were prepared in moderate to good yields from easily available starting materials. The indoline-2-thione products can be easily derivatized to give biologically active thieno[2,3-b]indole and thiopyrano[2,3-b]indole skeletons in high yields.     

Controlled Synthesis and Molecular Structures of Methoxy-, Amino-, and Chloro-Functionalized Disiloxane Building Blocks

Functionalized disiloxane units with defined structures are interesting molecular models for investigating the reactivity and chemoselectivity in transformations that are of interest in synthesis, surface chemistry, and materials science. (Mes)PhSi(OMe)₂ ( 1 ) (Mes = mesityl) and (Mes)PhSiCl₂ ( 5 ) were chosen as starting compounds for the controlled synthesis of methoxy-, amino-, and chloro-functionalized unsymmetric disiloxanes. Two synthesis routes towards (Mes)PhSi(OMe)(OSiPh₃) ( 3 ) were followed, one via the aminomethoxysilane (Mes)PhSi(OMe)(NC₄H₈) ( 2 ) and the other via the chlorodisiloxane (Mes)PhSiCl(OSiPh₃) ( 6 ). The amino-substituted disiloxane (Mes)PhSi(NC₄H₈)(OSiPh₃) ( 4 ) was obtained from the chloro derivative 6 with N-pyrrolidinyllithium, but the same reaction starting from compound 3 was not successful. All provided disiloxanes were structurally characterized by X-ray crystallography.     

Implications of Nitrogen Doping on Geometrical and Electronic Structure of the Fullerene Dimers

Because of its unsaturated bonds, C₆₀ is susceptible to polymerize into dimers. The implications of nitrogen doping on the geometrical and electronic structure of C₆₀ dimers have been ambiguous for years. A quarter‐century after the discovery of azafullerene dimer (C₅₉N)₂, we reported its single crystallographic structure in 2019. Herein, the unambiguous crystal structure information of (C₅₉N)₂ is elucidated specifically, revealing that the inter‐cage C—C single bond length of (C₅₉N)₂ is comparable with that of an ordinary C(sp³)‐C(sp³) single bond, and that the most stable conformer of (C₅₉N)₂ is gauche‐conformer with a dihedral angle of 66°. To amend the structural deviations, geometrical structure of (C₅₉N)₂ is optimized by a B3LYP‐D3BJ function, which is proved to be more consistent with its single crystal structure than those by the commonly used B3LYP function. Moreover, the calculation method is also suitable for other representative fullerene dimers, such as (C₆₀)₂ and its divalent anion. Additionally, the dissociation of (C₅₉N)₂ at 473 K under mass spectrometric conditions suggests the inter‐cage C—C bond is relatively weaker than an ordinary C—C single bond, which can be explained by the interaction energies of inter‐cages.     

Synthesis,Structure, and DFT Analysis of the THF Solvate of 2-Picolyllithium: A 2-Picolyllithium Solvate with Significant Carbanionic Character

Previous studies of different solvates of 2-methylpyridyllithium (2-picolyllithium) have uncovered electronic structures corresponding to aza-allyl and enamido resonance forms of the metallated pyridine-based compounds. Here, we report the synthesis and characterization of [2-CH₂Li(THF)₂C₅H₄N], a new THF solvate. X-ray crystallographic studies reveal a dimeric arrangement featuring a non-planar eight-membered [NCCLi]₂ ring, in which the primary cation-anion interaction is between the central Li atom and the C atom of the deprotonated methyl group [length, 2.285(2) Å], suggesting a new carbanionic resonance structure for this 2-picolyllithium series. The significant carbanionic character of [2-CH₂Li(THF)₂C₅H₄N] was confirmed by gas-phase DFT calculations [B3LYP/6-311+G(d)] with the calculated electron density interrogated by means of quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. For comparison these computational analyses were also performed on the literature structures of [2-CH₂Li(2-Picoline)C₅H₄N] and [2-CH₂Li(PMDETA)C₅H₄N]. In a reactivity study, [2-CH₂Li(THF)₂C₅H₄N] was found to undergo nucleophilic addition to pyridine to generate dipyridylmethane in a good yield.     

A theoretical study of the influence of BF3 on the reaction path of the [4+2] cycloaddition of vinylketene with formaldimine

A comprehensive B3LYP/6-31+G^∗ study of the influence of BF₃ on the [4+2] cycloaddition of vinylketene with formaldimine was conducted. For this purpose, the complete pathway was determined and changes in different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χ_anis, and the nucleus-independent chemical shifts, NICS) were monitored along the reaction profile with a view to estimate the aromatization associated to the process. We have also applied the ACID (anisotropy of the current-induced density) method with the same intention.     

A Silatetragallane—Classical Heterobicyclopentane or closo-Polyhedron?

Classical and nonclassical can be used to describe the bonding in the polyhedral Ga₄Si framework of the silagallanate ion [Me₃SiSi{GaSi(SiMe₃)₃}₃GaSiMe₃]⁻ (the GaSi framework is depicted in the picture). This is the result of density functional calculations that were carried out on model compounds. The cluster was obtained by ultrasonication of gallium and iodine and subsequent reaction with (Me₃Si)₃Li(thf)₃.     

The Use of Sustainable Transition Metals for the Cycloaddition of Epoxides and CO2 under Mild Reaction Conditions

Following green chemistry principles, we present a one pot synthesis of zinc curcumin complex as a homogeneous, sustainable catalyst for cyclic carbonate (CC) synthesis from CO₂ and a variety of terminal and internal epoxides under 1 bar CO₂ at 60 °C using DMSO as a solvent. Zinc curcumin ( Zn-Cur ) complex was identified via ¹H/¹³C NMR and ATR-FTIR spectroscopies, elemental analysis, ionic conductivity, and quantitative silver nitrate test to confirm a 1 : 1 molar ratio of metal to the ligand. Interestingly, Zn-Cur showed an outstanding performance in catalysing the synthesis of renewable CCs including dimeric pinene and limonene carbonates. In this context, other metal complexes, including magnesium (Mg^II), calcium (Ca^II), and nickel (Ni^II) complexes showed good to excellent catalytic activity. Furthermore, a plausible reaction mechanism was investigated by density functional theory (DFT) calculations. The reaction was found to be overall exergonic by 39 kJ/mol and the rate determining step was CO₂ insertion, which is in good agreement with the experimental findings.     

Theoretical study of the walk rearrangement in perfluorotetramethyl (Dewar thiophene) exo-S-oxide

A theoretical study of the ‘walk’ rearrangement in bicyclo[2.1.0]pentene and perfluorotetramethyl (Dewar thiophene) exo-S-oxide has been carried out. Despite the differences between them, the results for both reactions show an enhancement of aromaticity in the transition state, which is consistent with a pericyclic behavior. NBO calculations show that the small activation energy for the second reaction can be interpreted in terms of a strong stabilization of the transition state by the exo-oxide substituent. So, the mechanism proposed in the past should be revised.     

Formation and Unimolecular Dehydrogenation of Gaseous Alkaline‐earth Metal Amidoboranes M(NH2BH3)2 (M = Be – Ba): Comparative Computational Study

Formation of alkaline‐earth metal amidoboranes M(NH₂BH₃)₂ (M = Be, Mg, Ca, Sr, Ba) and unimolecular dehydrogenation reactions were computationally studied at the B3LYP/def2‐TZVPPD level of theory. Formation of M(NH₂BH₃)₂ from ammonia borane and MH₂ is exergonic, but subsequent unimolecular dehydrogenation reactions are endergonic at room temperature. In contrast to alkali metal amidoboranes, for M(NH₂BH₃)₂ the nature of M significantly affects their reactivity. Activation energies for the dehydrogenation of first and second hydrogen molecules decrease from Be to Ba. In case of Be compounds, intramolecular M ··· H–B contacts play an important role, whereas for heavier analogs such contacts are much less pronounced.     

Comparative Computational Studies of Gaseous Alkali Metal Amidoboranes MNH2BH3 and their Carbon Analogs MC2H5 (M = Li – Cs): Formation and Unimolecular Hydrogen Evolution

Comparative computational studies of reaction mechanisms of formation and unimolecular hydrogen evolution from alkali metal amidoboranes MNH₂BH₃ and their carbon analogs MC₂H₅ (M = Li – Cs) were performed at the B3LYP/def2‐TZVPPD level of theory. Transition states (TS) for the consecutive dehydrogenation reactions were optimized. In contrast to endergonic dehydrogenation of carbon analogs, dehydrogenation reactions of alkali metal amidoboranes are exergonic at room temperature. The nature of the alkali metal does not significantly affect the thermodynamic characteristics and activation energies of unimolecular gas phase dehydrogenation reactions. The influence of the alkali metal is qualitatively similar for amidoboranes and their carbon analogs.     

A DFT study of the [4+2] cycloadditions of conjugated ketenes (vinylketene, imidoylketene and formylketene) with formaldimine. The pericyclic or pseudopericyclic character from magnetic properties

A comprehensive B3LYP/6-31+G^∗ study of the nature of the [4+2] cycloadditions of conjugated ketenes, vinylketene, imidoylketene and formylketene, with formaldimine was conducted. For each reaction, the complete pathway was determined and changes in different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χ_anis, and the nucleus-independent chemical shift, NICS) were monitored along the reaction profile with a view to estimate the aromatization associated to the process. We have also applied the ACID (anisotropy of the current-induced density) method with the same purpose. The deep analysis of the results indicates the existence of both disrotatory and conrotatory pericyclic paths for the cyclization step of the cycloaddition of vinylketene with formaldimine and the pseudopericyclic character of reactions with imidoylketene and formylketene.     

Thermal isomerization in cyclopenta[<Emphasis Type="Italic">fg</Emphasis>]aceanthrylene

Abstract  Two mechanisms for the isomerization of cyclopenta[fg]aceanthrylene to acefluoranthene were revealed. The first pathway occurs via a cyclobutyl intermediate, whereas the second pathway involves a transition state that contains an sp ³-hybridized carbon atom. Both patterns show that the Stone-Wales rearrangement requires extremely high activation energy and indicate that the isomerization process can occur only under a drastic temperature regime. Graphical abstract        

Dimensions of the Ozonide Anion in M([18]crown‐6)O3·x NH3 with M = K (x = 2), Rb (x = 1) and Cs (x = 8)

Reaction of alkali metal ozonides (KO₃, RbO₃ and CsO₃) with [18]crown‐6 in liquid ammonia yields compounds of the composition M([18]crown‐6)O₃·x NH₃ with M = K (x = 2), Rb (x = 1) and Cs (x = 8). The large intermolecular distance between adjacent radical anions in these compounds leads to almost ideal paramagnetic behavior according to Curie's law. Discrepancies concerning the structure of the ozonide anions in the K and Cs compound compared to a former investigation on Rb([18]crown‐6)O₃·NH₃ have been resolved by means of DFT calculations and a single‐crystal structure redetermination.     

The Structures of Methylenebis(dichloroarsane) and Methylenebisarsonic Acid – A Combined Theoretical and Experimental Study

Methylenebisarsonic acid ( 3 ) was synthesized according to a published procedure. Its molecular structure and its spectroscopic characteristics were determined by single‐crystal X‐ray diffraction. The first intermediate, methylenebis(dichloroarsane) ( 1 ), was structurally and spectroscopically characterized as well. Both molecules were investigated on the B3LYP/6‐31+G(2d,p) level of theory and subsequent NBO analysis.     

离子液体BmmimOAc催化2-芳氨基乙醇与二硫化碳一步缩合合成3-芳基-2-噻唑硫酮

噻唑硫酮因具有独特的生物活性,使其在医学和杂环化学等领域有着广泛的应用,从而引起了科研工作者的研究兴趣。本文以离子液体1-丁基-2, 3-二甲基咪唑鎓醋酸盐(BmmimOAc)为催化剂,2-芳氨基乙醇和二硫化碳为起始原料,一步缩合合成3-芳基-2-噻唑硫酮。以2-苯氨基乙醇和二硫化碳的反应为模型,考察了一系列离子液体的催化活性。发现只有阴离子为醋酸根的离子液体才具有催化活性,这可能是由醋酸根的碱性所导致的。在这些阴离子为醋酸根的离子液体中,BmmimOAc的催化活性最高。以其为催化剂,系统考察了反应时间、反应温度、催化剂用量以及二硫化碳和2-苯氨基乙醇摩尔比对该反应的影响。得到最优的反应条件：反应时间6 h、反应温度130 ℃、10%的BmmimOAc用量以及5 : 1的二硫化碳和2-苯氨基乙醇摩尔比。在该反应条件下,目标产物3-苯基-2-噻唑硫酮的收率达到了97%。以不同的2-芳氨基乙醇为原料,考察了该反应的普适性。结果表明无论是具有给电子基团、吸电子基团或较大空间位阻的2-芳氨基乙醇均可顺利地与二硫化碳反应生成相应的3-芳基-2-噻唑硫酮,且分离收率高达83%–95%。核磁共振波谱和质谱分析表明反应过程中BmmimOAc的醋酸根阴离子可以自发地与二硫化碳反应生成硫代醋酸根阴离子,因此离子液体1-丁基-2, 3-二甲基咪唑鎓硫代醋酸盐(BmmimCOS)可能是2-芳氨基乙醇和二硫化碳反应的催化剂。通过核磁共振波谱研究了BmmimCOS与反应底物2-苯氨基乙醇和二硫化碳之间的相互作用,发现BmmimCOS与2-苯氨基乙醇之间存在氢键相互作用。在反应过程中硫代醋酸根阴离子通过氢键作用活化2-苯氨基乙醇,从而促进反应高效进行。基于表征结果,提出了一个可能的反应机理。首先,BmmimOAc自发地与二硫化碳反应生成BmmimCOS。然后,BmmimCOS中的硫代醋酸根阴离子通过氢键作用活化2-苯氨基乙醇。随后,活化的2-苯氨基乙醇与二硫化碳反应生成中间体。最后,中间体分子内环化生成目标产物3-苯基-2-噻唑硫酮。     

Tetrachlorophenyl‐λ5‐arsane and Tetramethoxyphenyl‐λ5‐arsane: Crystal Structures,NMR Spectra and Bonding Situation

Two phenyl‐substituted λ⁵‐arsanes were prepared from phenylarsonic acid in two‐step procedures. Their molecular structures were determined by single‐crystal X‐ray diffraction. NBO analyses for the title compounds were conducted.