2-Acylmethyl-1H-benzimidazoles in the Biginelli Reaction

By cyclocondensation of 2-acylmethyl-1H-benzimidazoles with aromatic aldehydes and urea according to the Biginelli reaction, we have obtained previously unknown 6-substituted 4-aryl-5-(2-benzimidazolyl)-2-oxo-1,2,3,4-tetrahydropyrimidines. We have developed an efficient procedure for conducting the three-component reaction at fairly low temperatures. We have analyzed the structural features of the synthesized compounds based on ¹H NMR spectra and IR spectroscopy.     

Activation of 1-halonaphthalenes by electrogenerated [Co-salen]

We report in this paper an electroanalytical study of the reaction of 1-halonaphthalenes with electrogenerated [Co^I-salen]. With 1-iodonaphthalene, the reaction observed is a substitution, with a release of the iodide ion. Conversely, the reaction is much slower with 1-bromonaphthalene, and the intermediate adduct is observed at the time scale of cyclic voltammetry. The corresponding rate constants have been determined.     

1-Methylimidazole 3-N-oxide as a new promoter for the Morita-Baylis-Hillman reaction

The Morita-Baylis-Hillman reaction of aldehydes with α,β-unsaturated ketones can be affected by the Lewis bases. We have found that 1-methylimidazole 3-N-oxide promoted the Morita-Baylis-Hillman reaction of various activated aldehyde compounds in non-solvent system. This is a mild reaction condition and requires no special equipment to give the Morita-Baylis-Hillman adducts.     

Copper-catalyzed addition of water affording highly substituted furan and unusual formation of naphthofuran ring from 3-(1-alkenyl)-2-alkene-1-al

We have developed a novel one-pot reaction to generate highly substituted furan through the addition of water followed by oxidation and unusual cyclization to naphthofuran ring under the same reaction condition.     

1,2-Dicarba-closo-dodecaboran-1-yl naphthalene derivatives

1,2-Dicarba-closo-dodecaboranes (o-carboranes) and naphthalenes have potential value as components or building blocks for supramolecular systems. We have efficiently synthesized 1-(1,2-dicarba-closo-dodecaboran-1-yl)naphthalene and 2-(1,2-dicarba-closo-dodecaboran-1-yl)naphthalene derivatives by employing three preparative methods: cyclization of the corresponding acetylenes with decaborane(14), an Ullmann-type coupling reaction of carboranes with aryl halide, and the aromatic nucleophilic substitution (S(N)Ar) reaction of aryl-o-carboranes with nitrophenyl halide. The optimum conditions of each method for synthesis of the title compounds were also investigated.     

Synthesis and some properties of 1-amino-3-nitroindazole

By treating 3-nitroindazole with hydroxylamine-O-sulfonic acid in basis medium, we have obtained its 1-amino derivative. We have observed that in chloroform solution in the presence of triethylamine, it is slowly converted to 1-ethylideneamino-3-nitroindazole. We discuss a possible mechanism for this unexpected reaction.Scientific-Research Institute of Physical and Organic Chemistry, Rostov State University. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1343–1346, October, 1996.     

Diastereoselective Total Synthesis of (±)‐Schindilactone A,Part 1: Construction of the ABC and FGH Ring Systems and Initial Attempts to Construct the CDEF Ring System

First‐generation synthetic strategies for the diastereoselective total synthesis of schindilactone A ( 1 ) are presented and methods for the synthesis of the ABC, FGH, and CDEF moieties are explored. We have established a method for the synthesis of the ABC moiety, which included both a Diels–Alder reaction and a ring‐closing metathesis as the key steps. We have also developed a method for the synthesis of the FGH moiety, which involved the use of a Pauson–Khand reaction and a carbonylative annulation reaction as the key steps. Furthermore, we have achieved the construction of the central 7–8 bicyclic ring system by using a [3,3]‐rearrangement as the key step. However, unfortunately, when this rearrangement reaction was applied to the construction of the more advanced CDEF moiety, the anticipated annulation reaction did not occur and the development of an alternative synthetic strategy would be required for the construction of this central core.     

Kinetics of Hydroperoxide Epoxidation of 1-Octene in the Presence of MoB2

We have studied the kinetics of the process of epoxidation of 1-octene by tert-butyl hydroperoxide in the presence of molybdenum boride MoB₂. We have studied the effect of the concentrations of starting materials and reaction products on the process. We suggest a kinetic scheme and we calculate the kinetic parameters of the process.     

Thiadiazolidine 1-oxide systems for phosphine-free palladium-mediated catalysis

We herein report several highly active catalyst systems with thiadiazolidine 1-oxides as ligands for palladium in the Mizoroki-Heck reaction. Excellent yields of stilbenes derived from aryl iodides and bromides have been achieved using as little as 0.00002 mol % catalyst. The ligand/palladium system can be stored as a stock solution open to air at room temperature with no observable loss of activity for a period of several months.     

Utilization of 1-oxa-2,2-(dimesityl)silacyclopentane acetals in the stereoselective synthesis of polyols

We have developed a route for the stereoselective synthesis of 1-oxa-2,2-(dimesityl)silacyclopentane acetals, intermediates in the synthesis of highly functionalized 1,3-diols. This route involves a diastereoselective conjugate addition reaction of a hydrosilyl anion, a subsequent diastereoselective enolate alkylation, and a fluoride-catalyzed intramolecular hydrosilylation reaction to afford the oxasilacyclopentane acetal. A highly selective nucleophilic substitution reaction, followed by oxidation of the C-Si bond, leads to the desired polyol.     

Theoretical study of the human DNA repair protein HOGG1 activity

We have examined the role of the catalytic lysine (Lys 249) in breaking the glycosidic bond of 8-oxoguanine in the enzyme human 8-oxoguanine DNA glycosylase. Until quite recently it has been assumed that this lysine acts as a nucleophile in an S(N)2 type of reaction after being activated through a donation of a proton to a strictly conserved aspartate, also located in the active site. However, evidence from crystallographic, as well as biochemical studies, questions this assumption mainly because the lysine is not ideally positioned for such an attack. In addition, the catalytic activity is preserved even after that aspartate is mutated to a residue not accepting protons, but still keeping the interactions in the active site. In this study, we have investigated several different reaction mechanisms to discover plausible ways where the lysine could assist in breaking the glycosidic bond. We use hybrid density functional theory to characterize both associative and dissociative pathways. We find that the smallest energetical barrier involves an S(N)1 type of mechanism where the lysine electrostatically stabilizes the dissociating base and then donates a proton with a very small barrier and then finally attacks the sugar ring to create the covalently bound protein-DNA intermediate complex. The S(N)2 mechanism also has a lower barrier than the "spontaneous" bond breaking but considerably above that of the S(N)1 reaction. However, in current conditions, the reactants placed in a conformation posed for an S(N)2 reaction is substantially more stable than if posed for the S(N)1 reaction, indicating that the active site has to bind stronger to the latter in order to achieve a full catalytic effect. An analysis of the polarization of the transition states shows that the polarization is largest for the S(N)1 reaction, indicating that this path will gain most by being placed in a prepolarized active site. These findings give further support to the hypothesis that a dissociative mechanism may be the preferred mode of action for this type of enzymes.     

Chemical reaction of nitric oxides with the 5-1DB defect of the single-walled carbon nanotube

In this work, we applied a two-layered ONIOM (B3LYP/6-31G(d):UFF) method to study the reaction of nitric oxides with a 5-1DB defect on the sidewall of the single-walled carbon nanotube (SWCNT). We have chosen a suitable ONIOM model for the calculation of the SWCNT based on the analyses of the frontier molecular orbitals, local density of states, and natural bond orbitals. Our calculations clearly indicate that the 5-1DB defect is the chemically active center of the SWCNT. In the reaction of nitric oxides with the defected SWCNT, the 5-1DB defect site can capture a nitrogen atom from nitric oxides, yielding the N-substitutionally doped SWCNT. We have explored the reaction pathway in detail. Our work verifies the chemical reactivity of the 5-1DB defects of the SWCNTs, indicates that the 5-1DB defect is a possible site for the functionalization of the SWCNTs, and demonstrates a possible way to fabricate position controllable substitutionally doped SWCNTs with a low doping concentration under mild conditions via some simple chemical reactions.     

Regioselective synthesis of 1,5-diaryl-1H-imidazoles by palladium-catalyzed direct arylation of 1-aryl-1H-imidazoles

[reaction: see text] A variety of 1,5-diaryl-1H-imidazoles have been regioselectively synthesized by direct coupling of 1-aryl-1H-imidazoles with aryl iodides or bromides in DMF in the presence of CsF as the base and a catalyst precursor consisting of a mixture of Pd(OAc)2 and AsPh3. The data obtained in this synthetic study support a reaction mechanism involving an electrophilic attack of an arylpalladium(II) halide species onto the imidazole ring. Interestingly, some imidazole derivatives synthesized in this study have been found to exhibit significant cytotoxic activity against human tumor cell lines.     

1-Phenyl-1-halo-1-silacyclohexanes

The approaches to synthesis of 1-phenyl-1-halo-1-silacyclohexanes C₅H₁₀Si(Ph)X (X = F, Cl, Br) have been examined. 1-Phenyl-1-chloro-1-silacyclohexane has been prepared via the known reaction of phenyltrichlorosilane with dimagnesium derivative of 1,5-dibromopentane; up to 20% of 1-bromo-1-phenyl-1-silacyclohexane admixture is formed along with the target product. The minor product formation has been prevented using an alternative method of chlorination of 1-phenyl-1-silacyclohexane with N-chlorosuccinimide. 1-Phenyl-1-fluoro-1-silacyclohexane has been obtained in close to quantitative yield via the reaction of 1-phenyl-1-chloro-1-silacyclohexane with SbF₃ and in 70% yield via its reaction with HF. The synthesis of 1-phenyl-1-bromo-1-silacyclohexane via bromination of 1-phenyl-1-chloro-1-silacyclohexane with N-bromosuccinimide has given the target product as a minor one, the major product being disiloxane formed due to hydrolysis of the Si–Br bond.     

New derivatives of N-vinyltriazoles: 1,3-diaryl-3-(1H-1,2,4-triazol-1-yl)-2-propen-1-ones

We have synthesized previously unknown N-vinyltriazoles:1,3-diaryl-3-(1H-1,2,4-triazol-1-yl)-2 propen-1-ones. We discuss a hypothesis for a probable reaction mechanism. Institute of Chemistry, Academy of Sciences of the Moldavian Republic, Kishinev 277028. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 910–914, July, 1995. Original article submitted March 24, 1995.     

Radical additions of xenon difluoride to cis- and trans-1-phenylpropenes: comparison with trichloramine and iodobenzene dichloride

We would like to report data which support a free radical pathway for reaction of xenon difluoride (XeF₂) with alkenes in organic solvent. Radical intermediates have been proposed for reaction of XeF₂ to double bonds. For example, a radical pathway was suggested for the gas phase reaction of XeF₂ to ethylene and propene [1]. Zupan speculated on a radical cation pathway for the acid catalyzed reaction of XeF₂ with alkenes but gave no experimental evidence for this mechanism [2,3]. Radical cation intermediates were demonstrated for the reaction of XeF₂ to aromatics by Filler [4]. Acid catalyzed ionic reactions to unsaturated hydrocarbons have been reviewed [5].Zupan and Pollak have shown that alkenes do not react in aprotic solvent with XeF₂ at low concentrations of alkene unless acid catalyst is present [3]. However, we observed that illumination of a dilute solution of $\text{cis-}$ or $\text{trans}$-1-phenylpropenes (I) or (II) in methylene chloride at 0° with a 270 watt sunlamp produced IIIa and IIIb in less then two hours (Table). Furthermore, at high concentration of (I) and (II), a spontaneous reaction occurred in the dark between XeF₂ and these styrenes. The reaction conditions for both of these reactions imply a radical mechanism — the latter a molecule-induced pathway.     

CO2 in 1-butyl-3-methylimidazolium acetate. 2. NMR investigation of chemical reactions

The solvation of CO(2) in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been investigated by (1)H, (13)C, and (15)N NMR spectroscopy at low CO(2) molar fraction (mf) (x(CO(2)) ca. 0.27) corresponding to the reactive regime described in part 1 of this study. It is shown that a carboxylation reaction occurs between CO(2) and Bmim Ac, leading to the formation of a non-negligible amount (~16%) of 1-butyl-3-methylimidazolium-2-carboxylate. It is also found that acetic acid molecules are produced during this reaction and tend to form with elapsed time stable cyclic dimers existing in pure acid. A further series of experiments has been dedicated to characterize the influence of water traces on the carboxylation reaction. It is found that water, even at high ratio (0.15 mf), does not hamper the formation of the carboxylate species but lead to the formation of byproduct involving CO(2). The evolution with temperature of the resonance lines associated with the products of the reactions confirms that they have a different origin. The main byproduct has been assigned to bicarbonate. All these results confirm the existence of a reactive regime in the CO(2)-Bmim Ac system but different from that reported in the literature on the formation of a reversible molecular complex possibly accompanied by a minor chemical reaction. Finally, the reactive scheme interpreting the carboxylation reaction and the formation of acetic acid proposed in the literature is discussed. We found that the triggering of the carboxylation reaction is necessarily connected with the introduction of carbon dioxide in the IL. We argue that a more refined scheme is still needed to understand in details the different steps of the chemical reaction in the dense phase.     

The aging of living α-methylstyryl oligomers. II. The mechanism of aging

The living anions of oligomeric α-methalystyrene in THF transform to a new anion in the presence of excess monomer and UV light. Kinetic results have demonstrated that one step in this process is the second-order disappearance of monomer to form a dimeric intermediate. We have attempted to prepare this intermediate. Contrary to other reports, no hydrogen was liberated on terminating the reactions mixture with water, and an oily liquid which was identified as 1-methyl-1,3-diphenyl-cyclopentane was isolated. However, this is not the intermediate; the true intermediate is 2,5-diphenylhex-1-ene and under the conditions of the reaction the former compound is formed from this by a cyclization reaction.     

M(HSO4)n-Promoted Synthesis of 2-Aryl-1-arylmethyl-1H-1,3-benzimidazole Derivatives

We have developed a highly selective synthesis of 2-aryl-1-arylmethyl-1H-1,3-benzimidazoles from the reaction of o-phenylenediamines and aromatic aldehydes in the presence of metal hydrogen sulfates [M(HSO₄)_n] in water and also under solvent-free conditions in good to excellent yields.     

A DFT investigation on aromatic nucleophilic substitution (SNAr) reaction between 4-fluoro-1-naphthaldehyde/4-fluoro-2-naphthaldehyde/1-fluoro-2-naphthaldehyde/1-fluoronaphthalene and methylthiolate ion in gas phase and in protic/aprotic solvents

Structural Chemistry - We have investigated the mechanism of aromatic nucleophilic substitution (SNAr) reaction between...