Formation Of Cyclic Products Research Articles

A Comparative Study of Homolytic Reactions of Fullerenes with Aldehydes in a Mass Spectrometer under Electron Impact and in Solution under UV Irradiation

C(60) was reacted in the ionization chamber of a mass spectrometer under electron impact (EI) with aldehydes, RCHO (R = Ph, p-FC(6)H(4), F(5)C(6), p-MeOC(6)H(4), α-thienyl, o-HOC(6)H(4), o-BrC(6)H(4), m-BrC(6)H(4) and t-Bu), with the transfer of R• radicals and with Me•-transfer from i-PrCHO and t-BuCHO. Paramagnetic fullerene derivatives were stabilized by the addition of the next R• radical or a hydrogen atom, or hydrogen or bromine atom loss. A detailed study showed that the reaction between C(60) and PhCHO occurred via a homolytic mechanism that matches one reported earlier for the reaction with acetone. This suggests the generality of the mechanism for the reactions of fullerenes with other species in ionization chambers under EI at ca 300°C. All aldehydes, except one, had radicals at the carbonyl group which were different from those in the ketones examined earlier in the reactions. This expanded the variety of radicals which can be transferred to fullerenes during reactions in ionization chambers under EI. Due to this and the hydrogen atom at the CO group of aldehydes, some reactions occurred that were not found for the ketones: the formation of cyclic products C(60)COC(6)H(4) and C(60)OC(6)H(4) for PhCHO, o-BrC(6)H(4)CHO and o-HOC(6)H(4)CHO, respectively, and HC(60)Ph for o- and m-BrC(6)H(4)CHO. The reaction with α- formylthiophen gives the first example of transferring an aromatic heterocyclic radical to C(60) in an ionization chamber under EI. C(70) reacted with PhCHO, p-FC(6)H(4)CHO and i- PrCHO similarly to C(60). The results for the reactions of C(60) with PhCHO and with i- PrCHO were compared with those in solution under UV irradiation. Incomplete but reasonable coincidence was found; in both modes, the addition of Ph•, PhCO• and Me• radicals to C(60) occurred, whereas some other products were formed in solution, and the explanation is given as to why this occurred. This conformity supports the hypothesis based on the results of kindred reactions with ketones and organomercurials: the results of EI-initiated homolytic reactions between fullerenes and other compounds in an ionization chamber can predict the reactivity of the fullerenes toward them in solution.

The Combination of Liquid Chromatography and Mass Spectrometry Techniques for the Characterization of Aliphatic Polyesters

AbstractAliphatic polyesters are industrially implemented in high performance coatings, paints and varnishes, however it is typically difficult to correlate the resulting properties with the synthesis parameters as these polymers vary in reactivity and application properties. Due to the stepwise polymerization mechanism, it is often assumed that copolyester synthesis by direct polyesterification will lead to randomized products. The formation of cyclic products by transesterification allows even further randomization, enabling a highly complex system. The different methods of polymer chromatography in combination with sophisticated spectroscopic techniques are useful tools for enabling the full description of the molecular heterogeneity of these complex polyesters. Through the use of SEC, HPLC, MALDI‐TOF and ESI‐MS information was obtained on the extent of heterogeneity found during the synthesis of model polyesters based on maleic anhydride and phthalic anhydride with propylene glycol which serve as building blocks for the more complex industrial variety.

Characterization of Alkali Induced Formation of Lanthionine, Trisulfides, and Tetrasulfides from Peptide Disulfides using Negative Ion Mass Spectrometry

Peptide disulfides are unstable under alkaline conditions, resulting in the formation of products containing lanthionine and polysulfide linkages. Electrospray ionization mass spectrometry has been used to characterize major species obtained when cyclic and acyclic peptide disulfides are exposed to alkaline media. Studies on a model cyclic peptide disulfide (Boc-Cys-Pro-Leu-Cys-NHMe) and an acyclic peptide, oxidized glutathione, bis ((gamma)Glu - Cys - Gly - COOH), are described. Disulfide cleavage reactions are initiated by the abstraction of C(alpha)H or C(beta)H protons of Cys residues, with subsequent elimination of H(2)S or H(2)S(2). The buildup of reactive thiol species which act on intermediates containing dehydroalanine residues, rationalizes the formation of lanthionine and polysulfide products. In the case of the cyclic peptide disulfide, the formation of cyclic products is facilitated by the intramolecular nature of the Michael addition reaction of thiols to the dehydroalanine residue. Mass spectral evidence for the intermediate species is presented by using alkylation of thiol groups as a trapping method. Mass spectral fragmentation in the negative ion mode of the peptides derived from trisulfides and tetrasulfides results in elimination of S(2).

The study of the reaction of terminated oligomerization in the synthesis of oligo-(β1-6)-glucosamines

The applicability of terminated oligomerization to the synthesis of oligo-(beta1-6)-glycosamines, fragments of the intercellular polysaccharide adhesin of staphylococci, was studied. The reactions of terminated oligomerization were carried out with mono-, di-, and trisaccharide monomers and N-protected aminopropanol; and spacered mono- and disaccharides as terminating molecules were also attempted. The primary formation of cyclic products of monomer intramolecular glycosylation was observed in almost all the reactions. Only the experiments with the monomer based on the disaccharide bromide under the conditions of the Helferich reaction led to reduced yields (30%) of the cyclic products. However, even in this case, the desired terminated oligosaccharides were generated in approximately 10% yield and mainly were the products of single glycosylation of the terminator by the monomer. These experiments allow the conclusion that, under the examined conditions, the reaction of terminated oligomerization could not result in the synthesis of oligoglucosamines with a high molecular mass.

Computational study of metathesis degradation of rubber, 1. Distribution of cyclic oligomers via intramolecular metathesis degradation ofcis-polybutadiene

The results of the molecular modelling of the intramolecular metathesis degradation of cis-polybutadiene (cis-PB) into cyclic oligomers at PM3 level of theory showed that the chain-ring equilibrium is completely shifted towards the all-trans cyclic isomers. The formation of cyclic products, containing from three to six butadiene units, from larger rings is thermodynamically favoured with cyclic butadiene tetramers and pentamers being the main products. These results are in reasonable agreement with most of the available experimental data. The discrepancy observed in some cases between found and calculated ring distributions for the intramolecular metathesis degradation of cis-PB suggests that the reaction is kinetically controlled under certain conditions.

Novel nonviral vectors for gene delivery: Synthesis and applications

We have synthesized novel cationiclipids for gene delivery bearing an ester bond betweenthe lipid moiety and the polyamine head. We have foundthat an intramolecular rearrangement occurs duringpurification of one of the products. The rearrangementled to a cyclic lipopolyamine which was active for DNAgene transfer. The formation ofcyclization products depends on the spacer foundbetween the lipid and the polyamine. The introduction ofarginine in the linker position prevents the formation ofcyclic products. Linear as well as cyclicanalogues showed high-efficiency gene transfer whentested in vitro for luciferase gene expressionas compared to dioctadecylamidoglycyl spermineor lipofectamine and also in vivo in the Lewislung carcinoma model. The introduction of arginine in thelinker position promoted increased transfectionactivity, demonstrating that a diversity of linkers,such as short peptides or glycosides, can beintroduced into cationic lipids for targeted gene transfer.

A remarkable tendency of o-lithio- N-(2-lithiooxyethyl)- N-methyl-aniline to form heterocyclic derivatives by its reaction with dichlorodialkylsilanes or silicon tetrachloride. Synthesis of 2,5,1-benzoxazasilepines and of the silaspiro analogue

The synthesis of 2,5,1-benzoxazasilepines 3 or the benzoxazasilaspiro compound 4, has been achieved by the reaction of o-lithio- N-(2-lithiooxyethyl)- N-methyl-aniline ( 2) with R 2SiCl 2 (R = Me, Et, Ph) or SiCl 4, respectively. The reaction led to the formation of cyclic products, even under conditions favorable for the formation of polymeric materials.

Formation and X-ray Structures of Eight- and Sixteen-Membered Rings (ArC)(n)()N(2)(n)()(SPh)(n)() [n = 2, Ar = 4-XC(6)H(4) (X = Br, CF(3)); n = 4, Ar = 4-BrC(6)H(4)] and the Electronic Structures of (HC)(2)N(4)(SH)(2) and (HC)(2)N(4)(SH)(2)(2)(-).

Optimum yields of heterocyclic products are obtained when the reaction of 4-XC(6)H(4)CN(2)(SiMe(3))(3) (X = Br, CF(3)) with PhSCl in a 1:3 molar ratio in CH(2)Cl(2) is carried out at -100 degrees C followed by the mixture being warmed to -70 degrees C for 16 h. Under these conditions the eight-membered rings (4-XC(6)H(4))(2)C(2)N(4)S(2)Ph(2) (1b, X = Br; 1c, X = CF(3)) are obtained in 64 and 80% yields, respectively, in addition to the purple diazenes Z,E,Z-PhSN(4-XC(6)H(4))CN=NC(C(6)H(4)X-4)NSPh (2b, 8%; 2c, 19%) and, in the case of X = Br, the sixteen-membered ring (4-BrC(6)H(4))(4)C(4)N(8)S(4)Ph(4) (3) (8%). With a reaction time of 40 h the yield of 3 is increased to 25%. By contrast, the reaction of 3-BrC(6)H(4)CN(2)(SiMe(3))(3) with 3 equiv of PhSCl at -70 degrees C gives Z,E,Z-PhSN(3-BrC(6)H(4))CN=NC(3-BrC(6)H(4))NSPh in 75% yield. A possible pathway for the formation of cyclic products is proposed. The solid-state structures of 1b, 1c, and 3 were determined by X-ray crystallography. The eight-membered rings 1b and 1c adopt long boat conformations with the phenyl groups (attached to S) in equatorial positions. Density functional theory (DFT) calculations for the model ring system (HC)(2)N(4)(SH)(2) reveal that the observed C(2)(v)() geometry is the result of a second-order Jahn-Teller distortion of the planar (D(2)(h)()) structure. The chair conformer (C(2)(h)()) is only ca. 10 kJ mol(-)(1) higher in energy than the boat conformer. The hypothetical dianion (HC)(2)N(4)(SH)(2)(2)(-) is predicted to have a transannular S.S contact of about 2.5 Å. The sixteen-membered ring 3 has a cradle-like structure with S(4) symmetry.

ChemInform Abstract: The SNAr Reaction of 2,3,5,6‐Tetrachloronitrobenzene with Diamines under High Pressure: Formation of Cyclization Products.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

SO3-Mediated reaction of phenylselenenylamide with 1,2-alkadienylphosphonates

SO3-Mediated reaction ofN,N-diethylphenyiselenenylamide with 1,2-alkadienyl phosphonates under conditions of generation of weak electrophilic species results in the formation of cyclization products involving phosphoryl oxygen.

Electrospray Ionization Mass Spectrometry Investigation of Oligomers Prepared by Ring-Opening Metathesis Polymerization of Methyl N-(1-Phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate

Electrospray ionization mass spectrometry (ESI-MS) was used for the characterization of oligomers which were prepared by ring-opening metathesis polymerization (ROMP) of methyl N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate (1), employing molybdenum alkylidene initiators of the type Mo(CH(t-Bu))(NAr)(OR)2 (Ar = 2,6-di(isopropyl)phenyl, R = C(CH3)3 (I), C10H17 (II), and CCH3(CF3)2 (III)). ROMP was terminated with acetone/water (99/1, v/v), the solvent also used for ESI-MS. The oligomers (2) had different alkylidene end groups derived from the active species: neopentylidene (from the catalyst), isopropylidene (reaction with acetone) and (2-(methoxycarbonyl)-5-methyl-N-(1-phenylethyl)pyrrolid-3-yl)methylidene (reaction with water, hydrogenation product). Metathesis equilibration and intramolecular reactions of the active species with ester groups, resulting in the formation of cyclic products, were found. The influence of the initiator structure and the reaction time tR is discussed.

Polyacrylate Effects on Tetraethoxysilane Polycondensation

The 29Si NMR spectroscopy was employed in the assessment of polyacrylate effects on the course of acid-catalyzed polycondensation of tetraethoxysilane. The DEPT pulse sequence was used to achieve the sensitivity enhancement required for obtaining qualitatively and quantitatively interpreted 29Si NMR spectra. Assessment of changes in concentration of reaction products during polycondensation and comparison of mole distribution of chain molecules of reaction systems, which contain different amounts of polyacrylate, has shown that polyacrylate affects polycondensation reactions considerably. The presence of polyacrylate slows up hydrolysis and condensation reactions significantly, and it enhances formation of cyclic products. By this method oligomer distribution changes in the reaction system significantly and the degree of condensation in siloxane gel increases. It is clear that polyacrylate does not act as a single filler, but it changes a structure of siloxane network as well.

The SNAr Reaction of 2,3,5,6-Tetrachloronitrobenzene with Diamines under High Pressure: Formation of Cyclization Products

Abstract The reaction of 2,3,5,6-tetrachloronitrobenzene with ethylenediamine under high pressure gave mainly a 1 : 1-product and a bridged 2 : 1-product by the substitution of a nitro group and/or an o-chlorine atom. The ratio of the products varied depending upon the amount of amine used. Other diamines, such as 1,4-butanediamine cis-and trans-1,2-cyclohexanediamines, m-xylylenediamine, and o-phenylenediamine, gave similar results. On the other hand, N,N′-dimethylethylenediamine and N,N′-dimethyl-1,3-propanediamine gave cyclization products through successive substitutions of an ortho-chlorine atom and a nitro group by the two methylamino groups of a molecule of diamine. N-Methylethylenediamine afforded a 1 : 1-product through the substitution of a nitro group by a primary amino group together with a cyclic 1 : 1-product through substitutions of an o-chlorine atom and a nitro group by secondary and primary amino groups, respectively.

Nucleophilic Substitution of Dinitroolefins with 1,2-Difunctional Ethanes

Reactions of α,β-dinitroolefins with 1,2-ethanedithiol form five-membered ring products. Similarly, reactions of α,β-dinitroolefins with 2-mercaptoethanol give five-membered ring products along with monosubstituted olefins and products disubstituted on one carbon. The formation of cyclic products from α,β-dinitroolefins and 1,2-difunctional nucleophiles is explained in terms of a stepwise addition-substitution mechanism in which a carbanion intermediate must be assumed. A Michael-type reaction seems to occur, and the addition intermediate loses a nitro group by intramolecular substitution. The reaction of 1,2-dinitrocyclohexene with 2-mercaptoethanol unexpectedly forms a β'-substituted α-nitroolefin by means of another reaction mechanism

Formation of cyclic products from the diepoxide of long-chain fatty esters by cytosolic epoxide hydrolase

Since diepoxides are known metabolites of polyunsaturated fatty acids, the action of the cytosolic epoxide hydrolase purified from liver tissue was examined on these diepoxides. Diepoxymethylstearate was metabolized to the corresponding tetraol by high concentrations of affinity-purified cytosolic epoxide hydrolase. When the enzyme was diluted (1000- to 2000-fold), disappearance of the tetraol metabolite occurred simultaneously with formation of other hydration products with GC retention times and chromatographic mobilities different from those of the tetraol. The hydration products were identified as tetrahydrofuran diols based on comparison of chromatographic properties and mass spectral information with the properties and spectra of chemically generated products. Also, a mixture of diepoxymethylarachidonates was hydrated to tetraols using concentrated enzyme. As the enzyme was diluted (1000- to 2000-fold), a decrease in tetraol formation occurred along with the elevation of other hydration products whose mass spectra were consistent with tetrahydrofuran diol structures. These data are consistent with the epoxide hydrolase at low concentrations acting to open one epoxide followed by nonenzymatic cyclization to the tetrahydrofuran diols. The data also suggest that oxygenated lipids may be endogenous substrates for the cytosolic epoxide hydrolase. Since some oxylipins are known chemical mediators, the in vivo presence and role of these novel diols and tetrahydrofuran diols should be examined.

Conformation Dependent Cyclizations of 1,3,3,5-Tetraphenylpentane-1,5-dione

The molecular and crystal structure of 1,3,3,5-tetraphenylpentane-1,5-dione (I) obtained from direct methods and anisotropically refined by the least-squares method shows that the two 3,3-phenyl groups force the molecule into a conformation suitable for formation of cyclic products and intermediates. Compound I crystallizes in P1 group with lattice parameters a = 8.444(1), b = 10.195(2), c = 14.618(2) Å, α = 75.52(2)°, β = 73.22(1)°, γ = 65.47(1)°. Photochemically and thermally found was the system I ↔ II. The reaction of 1,5-dione I with phenylmagnesium bromide gives the 2,3-dihydropyran derivative III, whereas complex hydrides give a mixture of IV and VI. On treatment with magnesium, the diketone I gives diol VIII. Chlorine (Cl2) reacts with compound I to give the mono-, di-, and tetrachloro derivatives XII, XIII, and XIV, respectively. Bromine (Br2) produces 3,5-dibromo-4H-pyran derivative XVIII, whereas I2 only catalyzes the formation of 4H-pyran V. The formylation of dione I with dimethylformamide and POCl3 gives the 4H-pyran-3-carbaldehyde XX. Probable mechanisms of the reactions investigated and the stereochemistry of compounds VI, VIII, XIII, and XIV are discussed.

Improved computer simulation of metathesis reactions

The oligomerization of α,ω-dienes and the polymer degradation by olefln metathesis have been investigated by Monte Carlo simulation assuming a carbene mechanism. The structure of the computer program is described. In the simulation model different stabilities of cyclic products, different reactivities of linear molecules and different probabilities for back-biting reactions can be taken into account. Experimental examples in the literature are compared with simulation data with respect to kinetics and frequency distribution of products at equilibrium. In general, the assumptions in simulation are confirmed by experiment in the cases under consideration. Deviations, as in the formation of cyclic products in polymer degradation, are discussed.

Organotitanium chemistry: Part 17. Substituent effects on the isomerization of 1,5-hexadiene catalyzed by ring-substituted titanocene hydride

The cyclic and linear selectivities of the isomerization of 1,5-hexadiene catalyzed by a substituted titanocene hydride largely depend upon the characteristics of the substituents. Substituents such as methoxyethyl and vinyl favour the formation of cyclic products, whereas allyl and 3-butenyl exhibit high linear selectivities towards the isomerization of 1,5-hexadiene. Factors affecting the reaction process are discussed and the chelation of some substituents on the Cp rings to titanium is proposed.

Acid-catalyzed condensation of model hydroxyl-terminated dimethylsiloxane oligomers - cyclization vs. linear condensation: intra-inter catalysis

pentamethyldisiloxan-1-01 (3) were studied in dioxane and in methylene chloride solutions. The reaction is accompanied by some processes involving siloxane bond cleavage. The condensation of 1 in dioxane shows classical kinetics of ring formation with competing linear growth, complying with the dilution rule of cyclization enhancement. In contrast, this rule does not work for the process in methylene chloride since cyclization in this solvent exhibits the same second-order kinetics in the substrate as the intermolecular condensation. This is explained by the base autocatalysis of the process with the substrate, which picks up a proton from the silanol group exerting nucleophilic attack. This catalysis is intramolecular for linear growth and intermolecular for cyclic product formation (intra-inter catalysis). In dioxane solution this autocatalysis is not observed since it is dominated by the assistance of the solvent molecule. This mechanism was confirmed by comparison of kinetic results of the condensation of reactants 1,2, and 3 and by hydrogen bonding studies of these model oligomers.

Evidence for the ionization steps in monoterpene cyclization reactions using 2-fluorogeranyl and 2-fluorolinalyl pyrophosphates as substrates

Conversion of geranyl pyrophosphate to cyclic monoterpenes is considered to involve the preliminary isomerization of this acyclic precursor to enzyme-bound linalyl pyrophosphate and the cyclization of this tertiary intermediate. 2-Fluorogeranyl pyrophosphate and 2-fluorolinalyl pyrophosphate are effective competitive inhibitors of the cyclization of geranyl pyrophosphate by several different monoterpene cyclases, and the electron withdrawing α-fluorine substituent was shown to suppress the rate of cyclic product formation from both tritium-labeled analogs by at least two orders of magnitude. These results indicate that both steps of the coupled isomerization-cyclization sequence are initiated by ionization of an allylic pyrophosphate, and they confirm the electrophilic nature of this enzymatic reaction type and its similarity to the prenyltransferase reaction.