Quaternization of electron-deficient pyridines containing two electron-withdrawing substituents

Methyl triflate is an efficient agent for the quaternization of nitropyridines containing an additional electron-withdrawing substituent. When triethyloxonium hexachloroantimonate is used as the quaternizing agent, -elimination occurs with formation of protic pyridinium salt and ethylene.M. V. Lomonosov Moscow State University, 119899 Moscow, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 53–54, January, 2000.     

Synthesis and photolysis of N-phthalimidoaziridines with electron-withdrawing substituents

Mono-, bi-, tetra-, and pentacyclic N-phthalimidoaziridines with electron-withdrawing substituents in the three-membered ring have been obtained by the oxidative addition of N-aminophthalimide to dimethyl fumarate, ethyl cinnamate, N-phenyl-and N-benzylmaleimide, and endotricyclo[6.2.1.0^2,7]undeca-4,9-diene-3,6-dione. Photolysis of 3-benzyl-6-phthalimido-3,6-diazabicyclo-[3.1.0]hexane-2,4-dione obtained in this way in the presence of dimethyl acetylenedicarboxylic acid (DMAD) gives in low yield the dimethyl ester of 3-benzyl-2,4-dioxo-8-phthalimido-3,8-diazabicyclo[3.2.1]oct-6-ene-6,7-dicarboxylic acid, the product of 1,3-dipolar cycloaddition to the N-phthalimidoazomethinylide formed as intermediate. However photolysis of this phthalimidoaziridine in the presence of other 1,3-dipolarophiles, like photolysis in the presence of DMAD of the remaining phalimidoaziridines, does not lead to a 1,3-dipolar cycloaddition product. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1320–1328, September, 2006.     

A novel method for the oxidation of thiophenes. Synthesis of thiophene 1,1-dioxides containing electron-withdrawing substituents

A novel method for the synthesis of thiophene 1,1-dioxides by oxidation of substituted thiophenes with trifluoroperoxyacetic acid was developed. The effect of the solvent nature on the course of the reaction was studied and optimum conditions for the oxidation of thiophenes containing various functional groups were found. Previously unknown thiophene dioxides were obtained.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2144–2150, October, 2004.     

Effect of electron-withdrawing substituents on the electrophilicity of carbonyl carbons

The substituent effects on the carbonyl carbon atom for a series of twelve substituted phenyl acetates have been rationalized using a global electrophilicity index. This index is linearly correlated with the experimental reaction rate coefficients. We found that, in contrast to the proposed interpretation based on experimental ¹³C NMR chemical shifts and ground state destabilization calculations, the electrophilicity of carbonyl compounds increases due to the effect promoted by electron-withdrawing groups in these systems.     

The influence of electron-withdrawing substituents on the adsorption of CO on copper

The chemisorption of carbon monoxide on Cu(100) in the presence of either methyl chloride or formic acid results in an increase in the the C---O stretching frequency to above the gas-phase value and a simultaneous increase in the heat of adsorption of CO. We explain this behavior qualitatively in terms of the simple Lewis acid/base character of both the surface and the adsorbate.     

Ethylene oligomerisation and polymerisation with nickel phosphanylenolates bearing electron-withdrawing substituents: Structure-reactivity relationships

Three SHOP-type catalysts, in which the C=C(O) double bond was substituted by electron-withdrawing substituents, [Ni{Ph2PC(R1)=C(R2)O}Ph(PPh3)] (2: R1,R2 = -C(Me)=NN(Ph)-; 3: R1 = CO2Et, R2 = Ph; 4: R1 = CO2Et, R2 = CF3), were assessed as ethylene-oligomerisation and -polymerisation catalysts and compared to Keim's complex, [Ni{Ph2PCH=C(Ph)O}Ph(PPh3)] (1). A rationale for the influence of the double-bond substituents of the P,O-chelate unit on the catalytic properties is proposed, on the basis of X-ray diffraction studies, spectroscopic data and DFT-B3 LYP calculations. Whatever their relative electron-withdrawing strength, the R1 and R2 substituents induce an increase in activity with respect to catalyst 1. For those systems in which the basicity of the oxygen atom is decreased relative to that of the phosphorus atom, the chain-propagation rate increases with respect to that for catalyst 1. Reduction of the basicity of the P relative to that of the O, however, induces higher chain-termination rates.     

Anionic living polymerization of styrenes containing electron-withdrawing groups

Six styrene derivatives containing electron-withdrawing groups were synthesized and polymerized with anionic initiators in THF to afford stable anionic living polymers. The electron-withdrawing substituents are N,N-dialkylamide(1), N-alkylimino(2), oxazoline(3), tert-butyl ester(4), N,N-dialkylsulfonamide(5) and cyano(6) moieties. The polymers obtained have predictable molecular weights and narrow molecular weight distributions. The respective postpolymerizations proceeded with quantitative efficiency indicating that each polymer chain end retained the propagating reactivity. However, the resulting living polymers could not initiate the polymerizations of styrene and isoprene. On the other hand, the styrene derivatives(5 and 6) were polymerized with weak nucleophilic initiators, such as living polymer of tert-butyl methacrylate. These results suggest that the electron-withdrawing groups stabilize the living ends and also activate the respective monomers for anionic polymerization. The substitution effect reflects on the ¹³C NMR chemical shift of β-carbon of each vinyl group. The signal of the β-carbon appeared at lower magnetic field than that of styrene indicating electron deficiency on the carbon-carbon double bond of these monomers.     

The influence of electron-withdrawing substituents on the geometries and barriers to inversion of vinyl anions

Whereas $\text{ab}$$\text{initio}$ calculations predict that the vinyl anion is bent and has a high barrier to inversion, substitution of cyano, methoxycarbonyl, and formyl substituents at C-1 lower this barrier. Nevertheless, the first two substituents produce significantly bent anions, while the bent and linear 1-formylvinyl anions are essentially isoenergetic.     

The effect of electron-withdrawing properties of substituents on the hydrolysis of some Schiff bases

The dissociation kinetics of the Schiff bases investigated in the present paper [N,N-bis(X-benzylidenes)ethylenediamine], have been examined under basic and acidic conditions, in aqueous medium 25% acetone in water (wt-wt). The base hydrolysis reaction of these compounds was found to follow second-order kinetics, first-order with respect to each of the Schiff base and the hydroxide ions. The rate-determining step is suggested to be the hydroxide ions attack on the free base. The effect of acetone ratio, in hydrolysis medium, has been studied under alkaline conditions. It is deduced that both the hydrogen bonding formation and solvent-solvent interaction have a pronounced role in such hydrolysis reactions. The acid hydrolysis reaction is strictly second-order kinetics, first-order with respect to the Schiff base and also to the hydrogen ions, and the attack of water molecules on the protonated substrate becomes the rate-determining step. A slower rate of the base hydrolysis was observed through the Schiff base II (p-NO₂), on the other hand, a fast acid hydrolysis rate was detected in the case of compound III (p-COOH). Furthermore, from the effect of temperature on the reaction rate, the various thermodynamic parameters have been also calculated and discussed.     

Expanded dipyrrins with electron-withdrawing substituents: broad range of absorption in the visible region

Reaction of meso-aryl-substituted dipyrromethanes with tetracyanoethylene led to generation of a mono-tricyanovinyl-substituted species as well as an expanded dipyrrin analogue bearing both a dicyanomethylene and a tricyanovinyl substituent at the α-positions. These novel compounds exhibit absorption spectral features perturbed by the electron-withdrawing substituents. Unique protonation-induced spectral changes were also disclosed.     

Asymmetric methoxyselenenylations and cyclizations with 3-camphorseleno electrophiles containing oxime substituents at C-2. Formation of an unusual oxaselenazole from an oxime-substituted selenenyl bromide.

Di[(1R)-2-Oximo-endo-3-bornyl] diselenide (4) and its benzoate derivative 5 were prepared from the corresponding known 2-keto diselenide 1. Treatment of 4 and 5 with bromine, followed by silver triflate in methanol-dichloromethane, generated the corresponding selenenyl triflates 6b and 7b. The latter reagents reacted with a variety of mono-, di-, and trisubstituted alkenes to afford the corresponding 1,2-addition products (beta-methoxy selenides) in a highly diastereoselective manner. The free oxime 6b was particularly effective in such methoxyselenenylations, giving diastereomeric ratios (d.r.s) ranging from 86:14 to > 98:2. Even cis-disubstituted alkenes, which typically give poor d.r.s in similar additions with other chiral selenium electrophiles, underwent highly stereoselective additions with this reagent. Reductive deselenizations of the adducts obtained from styrene and cis- and trans-stilbene provided the corresponding methyl ethers, whose absolute configurations were determined by comparison with authentic samples. As expected, the dominant enantiomers thus obtained from cis- and trans-stilbene, using either 6b or 7b, had opposite configurations. Moreover, each geometrical isomer of stilbene produced methyl ethers with the same configuration when treated with either the oxime 6b or the benzoate 7b. Coordination effects between the substituents at the 2-position of the camphor molecule and the positive selenium atoms in the intermediate seleniranium ions are believed to play an important role in determining the stereochemical outcome of methoxyselenenylations. Selenenyl triflate 6b and selenenyl chloride 7c were also investigated in the electrophilic cyclizations of several unsaturated alcohols and carboxylic acids. However, diastereoselectivities were typically much lower than in the methoxyselenenylations. When the selenenyl bromide 6a, derived from the addition of bromine to the corresponding diselenide 4, was allowed to stand in the absence of an alkene, it underwent intramolecular cyclization with the oxime hydroxyl group, followed by further bromination, to afford the unusual oxaselenazole 11, whose structure was determined by spectroscopic means as well as by X-ray crystallography.     

On the reaction of fused benzodiazepines with alkynes containing electron-withdrawing groups

Fused benzodiazepines were found to react with activated alkynes to effect either vinylation of unsubstituted nitrogen atom or dealkylation of nitrogen and its further vinylation. For benzodiazepinones bearing lactam fragment, the reactions with alkynes proceed by several pathways: formation of vinyl-substituted benzodiazepines, the Stevens rearangement products, and expansion of the diazepine ring: benzodiazonine and diazecine.     

Synthesis and reactivity of homogeneous and heterogeneous ruthenium-based metathesis catalysts containing electron-withdrawing ligands

The synthesis and heterogenization of new Grubbs-Hoveyda type metathesis catalysts by chlorine exchange is described. Substitution of one or two chlorine ligands with trifluoroacetate and trifluoromethanesulfonate was accomplished by reaction of [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (IMesH(2) = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) with the silver salts CF(3)COOAg and CF(3)SO(3)Ag, respectively. The resulting compounds, [Ru(CF(3)SO(3))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (1), [RuCl(CF(3)SO(3))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (2), and [Ru(CF(3)CO(2))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (3) were found to be highly active catalysts for ring-closing metathesis (RCM) at elevated temperature (45 degrees C), exceeding known ruthenium-based catalysts in catalytic activity. Turn-over numbers (TONs) up to 1800 were achieved in RCM. Excellent yields were also achieved in enyne metathesis and ring-opening cross metathesis using norborn-5-ene and 7-oxanorborn-5-ene-derivatives. Even more important, 3 was found to be highly active in RCM at room temperature (20 degrees C), allowing TONs up to 1400. Heterogeneous catalysts were synthesized by immobilizing [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] on a perfluoroglutaric acid derivatized polystyrene-divinylbenzene (PS-DVB) support (silver form). The resulting supported catalyst [RuCl(polymer-CH(2)-O- CO-CF(2)-CF(2)-CF(2)-COO)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (5) showed significantly reduced activities in RCM (TONs = 380) compared with the heterogeneous analogue of 3. The immobilized catalyst, [Ru(polymer-CH(2)-O-CO-CF(2)-CF(2)-CF(2)-COO)(CF(3)CO(2))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (4) was obtained by substitution of both Cl ligands of the parent Grubbs-Hoveyda catalyst by addition of CF(3)COOAg to 5. Compound 4 can be prepared in high loadings (160 mg catalyst g(-1) PS-DVB) and possesses excellent activity in RCM with TONs up to 1100 in stirred-batch RCM experiments. Leaching of ruthenium into the reaction mixture was unprecedentedly low, resulting in a ruthenium content <70 ppb (ng g(-1)) in the final RCM-derived products.     

Cross-metathesis of vinylsilanes carrying electron-withdrawing substituents with olefins in the presence of the second-generation Grubbs catalyst

The efficient cross-metathesis of vinylsilanes carrying electron-withdrawing substituents with various olefins is described. High yields and selectivities were obtained when styrene, 1-hexene, and selective functional allyl derivatives were used as the olefins.     

Synthesis of macrocyclic acetals containing lipophilic substituents

A series of new macrocyclic acetals all containing lipophilic substituents were prepared by reacting the appropriate diols and lipophilic acetal-containing dichlorides or ditosylates. The reactions using the ditosylates gave the best yields. Several of the macrocycles contained pyridine subcyclic units. The lipophilic acetals were obtained by reacting a long-chain aldehyde with 2-hydroxyethyl chloride or tosylate and 3-hydroxypropyl chloride or tosylate. At least two of the new pyridino ligands complexed with metal ions as shown by the use of these materials as carriers for silver nitrate through a water-methylene chloride-water bulk liquid membrane system.     

The electronic effects of substituents containing phosphorus

Dissociation constants are reported for p-phosphorophenols, p-RC₆H₄OH, in aqueous alcohol (1:1 by volume), and the nucleophilic constants ^– of the R are found to be as follows: (C₆H₅)₂P 0.26, (C₆H₅)P(O) 0.68, (C₆H₅)₂P(S) 0. 63, and (C₆H₅)₂(CH₃)P⁺ 1.28.See [1–3] for previous communications in this series.