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Abstract: ¹H NMR studies in [²[H.sub.6]-DMSO] show that the carbanion 4 from bis(phenylsulfonyl)methane reacts with 4,6-dinitrobenzofuroxan to yield a σ-adduct that undergoes base-catalysed elimination to yield an alkene derivative. Rate [...]

Abstract: A useful, unexpected β,γ-unsaturated-α-keto ester (ethyl (E)-5-acetamido-3,4,5- trideoxy6,7:8,9-di-OisopropylideneD-manno-non-3-en-2-ulosonate 5) was isolated in 91% yield following ozonolysis and chromatographic purification of its enoate ester precursor ethyl 5-acetamido-2,3,4, 5-tetradeoxy-6,7:8,9-di-O-isopropylidene-2methylene 4-nitro-D-glycero-D-galacto-nononate (6). [...]

Elimination reactions of N-alkyl-N-chlorothenylamines with MeONa-MeOH and Et2NH-MeCN are studied kinetically. The reactions are second order and exhibit substantial values of Hammett rho and k(sub H)/k(sub D), and an E2 mechanism is evident.

Research has been conducted on the elimination reactions. Results indicate that these reactions proceed via the E2 mechanism and that this mechanism gradually changes from E2 to E1cb due to a systematic change of the reactant structure.

Research was conducted to examine the (C2H5O-) potential energy surface viva a modified Gaussian-2 methodology, the G2++ approximation. Eight stable isomers were found on the surface whose calculated heats of formation are in very good agreement with available experimental data. CH3CH2O- is the most stable among the isomers. Results are in total agreement with the experimental collision activated dissociation and infrared multiple photon induced elimination studies of the ethoxide anion.

Research was conducted to examine the oxidative addition/reductive elimination of H2 and D2 to fulvaleneCr2(CO)6. The objective was to determine the chromium-chromium bond strength in FvCr2(CO)6 and to compare its values for the complexes (C5R5Cr(CO)3)2. The enthalpy of dissociation of FvCr2(CO)6 was observed to be equal to or slightly higher than those of its cyclopentadienyl analogues. This result is attributable to the special electronic property of the fulvalene ligand.

The effect of the beta-aryl group on the nitrile-forming anti transition state was investigated by analyzing the elimination reactions of (Z)-thiophene- and (Z)-furan-2-carbaldehyde O-benzoyloximes with 1,8-diazabicyclo(5.4.0)undec-7-ene in MeCN. It was found that the nitrile-forming anti eliminations from (Z)-thiophene- and (Z)-furan-2-carbaldehyde O-benzoyloximes occur through the E2 mechanism via symmetrical transition states. The structures of the transition states change slightly toward product-like with the change of the beta-aryl group.

The steric interaction of the intermediate and/or transition state, as well as the preparation conditions of the catalyst and reaction conditions determine the dehydration of alcohols over metal oxides. This was gleaned from results of studies of alcohols with proper beta-substituents. Results showed that the anti elimination with cis preference is not true for all catalytic eliminations but depends on the mode of elimination, temperature and the catalyst.

Research was conducted to examine H2 elimination products from neutral Zr + alkene reactions in the gas phase. One-photon ionization at 157 nm and time-of-flight mass spectrometry were used for the identification of the metal-containing products of reactions of the neutral transition metal atom Zr(4d25s2,3F) with ethylene and propylene. Results demonstrate the feasibility and utility of 157 nm photoionization in determining the identity of metal-containing products of reactions of neutral transition-metal species.

Research was conducted to examine the usefulness of the hard and soft acids and bases principle (HSAB) and density functional theory reactivity descriptors as tools in the study of the reactivity of para-substituted phenolates and p-nitrophenethyl bromide. The elimination-substitution ratio for p-nitrophenethy bromide can be explained from a local-local HSAB viewpoint. Results indicate that para-substituted phenolates with higher basicity have a lower attraction to an alkyl carbon atom than to a hydrogen atom from p-nitrophenethyl bromide.

A study was conducted to analyze the elimination of H2 from C2H5+, with emphasis on the associated mechanism and electronic rearrangements. The Gaussian 94 series of programs was utilized to carry out ab initio computations. Intrinsic Reaction Coordinate computations were utilized to analyze the reaction paths. Results indicated that H2 loss from C2H5+ is an endoergic process supporting an energy barrier greater than endoergicity.

Direct dynamics calculations were used in the investigation of the dynamics of the two unimolecular reactions that initiate the thermal decomposition of methyl nitrite. The ab initio measurements were performed with the standard 6-311++G(d,p) basis set. Calculated rate constants and experimental results are in reasonably good agreement with each other. They suggest that the dissociation is remarkably speedier than the elimination since the former method is entropically favored.

Kinetic investigations of the elimination reactions of (E)- and (Z)-benzaldehyde O-benzoyloximes with 1,8-diazabicyclo[5.4.0]undec-7-ene in MeCN were conducted. A mapping of the transition state for the reactions on the More-O'Ferral-Jencks reaction coordinate energy diagram can be undertaken using the resulting structure-reactivity parameters. Results of the investigation offer additional information on transition state differences for the syn- and anti-eliminations forming nitriles.

Efficient algorithms for the parallel implementation of the Gaussian elimination method on message-passing architectures are presented. All the proposed algorithms consider the architecture parameters to perform the appropriate mapping of the tasks onto the processors. Their performances are compared with those of the general-purpose scheduling heuristic, DSC. Results indicate that both the generalized column-oriented scheduling and block scheduling perform better than DSC.

Research was conducted to study the mechanism and structure of an antibody-catalyzed elimination reaction. The antibody, 43D4-3D12, was produced through processes of cloning and sequencing which yielded the recombinant antibody in Escherichia coli as chimeric Fab possessing murine variable regions fused to human constant regions C(sub H)1 and C(sub k)1. Results suggest that related reactions can be utilized as mechanistic probes of biological catalysis.

A new benzotriazole-mediated route to beta-substituted alpha,beta-enones is presented using the corresponding diarylmethanols or diarylmethyl halides and alpha-bromoacetophenone. The preparation of N-(diarylmethyl)benzotriazoles was conducted through the reaction of the corresponding secondary alcohols and benzotriazole under acid conditions. The reaction of N-(diarylmethyl)benzotriazoles with alpha-bromoacetophenone was followed by the elimination of benzotriazole as a tandem reaction which afforded beta,beta-diarylvinyl phenyl ketones in good to excellent yields.

The kinetics of the elimination reactions of (E)-2,4-dinitrobenzaldehyde O-aryloximes promoted by EtO-, PhC(CH3)=NO-/PhC(CH3)=NOH and CF3CH2O-/CF3CH2OH buffers in ethanol were investigated. The only products of the reactions were 2,4-dinitrobenzonitrile and aryloxides. The second-order kinetics were in agreement with the E2 mechanism. The Bronsted beta decreased as the leaving group was made more nucleofugic and the /beta(sub lg)/ increased with a weaker base.

A study was conducted on the reactions of four (E)-Beta-alkylvinyl(phenyl)iodonium salts with chloride ion in acetonitrile and in other solvents at 25 degrees C. The findings indicate that most of the substitution and elimination products form from reaction of the lambda3-iodane. Moreover, the substitution reaction occurs by a concerted bimolecular SN2 mechanism while the elimination reaction proceeds by a unimolecular reaction mechanism.

The existence of double minima in the potential energy surfaces for HF-elimination reactions of SiF(sub x)(OH)(sub y)(super +) with H2O (x = 1-3, y = 0-2) via intramolecular H-atom transfer was investigated. The reaction was induced by SiF(super +), SiF(sub 2)(super *+) and SiF(sub 3)(super +) in H2O using the selected-ion flow tube method. Experimental results showed that the hydrogen fluoride elimination route proceeds through a hydrated reactant ion and an HF-solvated product ion, each at local minima, separated by a transition structure for H-atom transfer.

The intramolecular sequential ketyl-olefin coupling/beta-elimination reaction was mediated by samarium(II) iodide. A novel radical-based protocol was discovered that resulted in the net addition of an alkenyl moiety to a carbonyl group. The SmI2-promoted cyclization of the keto enol ether was anticipated to afford the oxabicyclo(3.3.0)octane. However, the reaction provided 2-(hydroxymethyl)-1-ethenylcyclopentan-1-ol in high yield diastereoselectivity despite the presence of an added proton source.

A study was conducted to describe the selectivities of the 1,2-RH-elimination and -addition reactions and the trapping of (silox)2Ti=NSitBu3 by Lewis bases and alkynes. Elimination reactions happened via a four-center transition state in which the amide/imide nitrogen, the transferring hydrogen and the alpha-carbon of R were relatively linear. Similarities in the activation trends of concerted activations of primary alkanes and cycloalkanes were also observed.

Sixteen-electron d2 niobium alpha-agostic alkyl (4e)-alkyne complexes of the type Tp*Nb(CH2R)(Cl)(alkyne) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, R not = H), isoelectronic with Cp' complexes, were found to undergo reversible migratory alkyne insertion/beta-alkyl elimination reductions in a single system. Solution and solid state data indicate that an alpha-agostic interaction might aid these fundamentally significant reactions.

The transition-state differences for the syn and anti elimination reactions of (E)- and (Z)-benzaldehyde omicron-pivaloyloximes were analyzed during reactions with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in MeCN. Benzonitrile and pivaloate were synthesized by the reaction of (E)- and (Z)-benzaldehyde omicron-pivaloyloximes with DBU. Furthermore, the anti elimination reaction was more facile and proceeded via a more symmetrical transition state compared to the syn elimination reaction.

The solvolytic elimination and substitution reactions of 1-(1-methyl-1-phenylethyl)pyridinium cation were investigated. The reactions produced the substitution product 2-hydroxy-2-phenylpropane and the elimination product 2-phenylpropene. The results showed that the total rate of reaction is dependent on the basicity of the leaving group.

Solvolysis of 9-(N-chloro-N-methylamino)fluorene (1-Cl) in 25 vol % acetonitrile in water produced the imine fluorenylidenemethylamine (3) as the only product. The solvent- and base-promoted reactions of 1-Cl were found to be of E2 type. The corresponding substrates 9-(N-4-Y-benzenesulfonyl-N-methylamino)fluorene (2-Y, Y = OMe,Me, or Br), with very poor leaving groups indicated reversible E1cB reactions with added bases. The strongly activated substrate 9-(N-4-nitrobenzenesulfonyl-N-methylamino)fluorene (2-NO2) does not give any elimination but exclusively undergoes intramolecular nucleophilic aromatic substitution involving rate-limiting hydron transfer.

Solvolysis of the R,R and R,S isomers 2a-X and 2b-X, respectively, (X = I,Br,OBs) in 25 vol % acetonitrile in water produced the elimination products 4, 5a and 5b along with the substitution products 2a-OH, 2b-OH, 2a-NHCOM3 and 2b-NHCOMe. The rates of elimination rise when the acidity of the beta-hydrogen of the substrate as expressed by a Bronsted parameter of alpha = 0.08 and 0.07 for the iodides and the bromides, respectively. On the other hand, the brosylates showed a negative Bronsted parameter for the elimination, alpha = -0.10. This indicated that the brosylates do not give elimination solely by a solvent-promoted E1cB reaction or an E2 reaction with a large component of hydron transfer in the transition state.

The kinetics underlying the elimination reactions of aryl esters of arylacetic acids with R2NH-MeCN were determined to understand the relationship between the reactant structure and the E2 and E1cb transition states during the ketene-forming reactions. The reactions, which exhibited second-order kinetics, showed a reduction in Bronsted beta and beta(sub lg) in direct proportion to the electron-withdrawing ability of beta-withdrawing ability of the beta-aryl substituent. Likewise, concurrent E2 and E1cb mechanisms were found to be present during R2NH/R2NH+2-catalyzed eliminations from p-nitrophenyl p-nitrophenylacetate in aqueous MeCN.

The influence of alpha-thiocarbonyl and alpha-carbonyl substituents on the kinetics of nucleophilic solvent addition to R-1-Y and R-2-Y where R = CH3,Me2NC(S),Me2NC(O),EtC(O) and deprotonation of R-2-Y to produce alpha-substituted 4-methoxystyrene was studied. The results indicate the rate-determining role of thermodynamic stabilities of the reactions' neutral products in partitioning the alpha-substituted 1-phenylethyl carbocations.

Cyclopropanes were synthesized via the highly stereoselective 1,3-elimination or ring closure of (gamma-hydroxypropyl)stannanes derived from the aldol reaction of methyl bis(tributylstannyl)propionate with an aldehyde. The cyclopropanation, which proceeds through a W-shape transition state, affords products with a stannyl group which can undergo transmetalation for incorporation of an electrophile into the propane ring to yield stereocontrolled 1,2,3-trisubstituted cyclopropanes.

The conversion of the Pt(II) dinuclear derivative Pt2(mu-P(t-Bu)2)2(H)2(p(t-BU)2H)2 by carbon monoxide into the new Pt(super I)(sub 2)Pt(super II) triangulo cluster Pt3(mu-P(t-BU)2)3(H)(CO)2 in a stepwise reaction is reported. The triangulo cluster is formed through the slow CO-induced reductive elimination of P(t-BU)2H from the dinuclear derivative, affording an intermediate equilibrium mixture of the mononuclear Pt(0) carbonyl derivative Pt(P(t-Bu)2H)2(CO)2 and the carbonyl-bridged triangulo derivative Pt3(P(t-BU)2H)3(mu-CO)3.

Hydrolysis of 2'-O-(tert-butyldimethylsilyl)uridyl(3'-5')uridine with aqueous acetic acid solution at 30 degrees Centigrade cleaved the 2'-silyl ether linkage at a concentration-dependent rate to form the 2'-tert-butyldimethylsilyl (TBDMS) group. The reaction rate was faster when either formic acid or diluted HCl were used. In contrast, cleavage of the 2'-TBDMS group in the methylphosphonate derivative occurred at a slower rate when catalyzed by any of the three acids. It was suggested that acid-catalyzed desilylation of the 2'-TBDMS group is affected by a neighboring 3'-5' phosphodiester group.

Ab initio molecular orbital calculations were used to examine the relevant parts of the C3H8*+ ground-state potential energy surface. Results show that partial bond dissociation to an ion-neutral complex comprised of the methyl radical coordinated to the H-bridged ethyl cation and methane elimination therefrom take place, at internal energies about 15 kJ/mol below the thermochemical threshold for methyl radical loss. A transition structure composed of the methyl radical coordinated to the nonclassical H-bridged ethyl action mediates the carbon skeletal rearrangement of the propane radical cation.

Mono- and disubstituted derivatives are achieved by sequential elimination reactions of 1,3-dicyanotetrafluorobenzene with various (trimethylsilyl)iminophosphoranes. However, only monosubstituted derivatives are readily produced from the reaction of 1,2- and 1,4-dicyanotetrafluorobenzene. Ligands from substitution reactions of iminophosphoranes on the cyano-fluoroaromatic rings also afford Rh(I) complexes. Polymeric complexes may also be formed by ligands having a CN moiety that is para to the central iminophosphorane.

Serum albumins, off-the-shelf proteins, catalyze the eliminative ring-opening of a benzisoxazole at the same rate as other catalytic antibodies. The albumins use a lysine side-chain amino group as the catalytic general base. Enzyme catalysis requires specific conditions, as the active-site catalytic groups and the substrate need to be positioned precisely in a well-structured environment. A nonspecific medium effect enhances the antibody catalysis in both systems.

An efficient route to chiral ansa-metallocenes of the type rac-(EBI)ZrX2 where (EBI = ethylene-1,2-bis 1-indenyl) and (X = NMe2,Cl,Me) was developed. The procedure is stereoselective because it involves a reversible amine elimination reaction in toluene between the amide Ze(NMe2)4 and (EBI)H2, otherwise known as 1,2-bis 3-indenyl(ethane). Moreover, the ratio of the rac-(EBI)Zr(NMe2)2 to the meso-(EBI)Zr(NMe2)2 products may be controlled by modifying the reaction conditions.

Halogenated ethylenes undergo reductive beta-elimination to alkynes under environmental conditions. To test this hypothesis, zero-valent metals such as iron and zinc were used to degrade contaminants such as dichloroethylenes and chlorinated ethylenes, respectively, under controlled conditions. The results confirmed previous findings that reductive beta-elimination pathways are involved in the reaction of chloroethylenes with zero-valent metals.

An analysis of the reactions of 1,4-pentadiene and 3-methyl-1,4-pentadiene with [Pd(C6F5)Br(CH3CN)2] at low temperature revealed that these yield two types of eta1-eta2-pentenylpalladium derivatives, following insertion of one double bond into the Pd-C6F5 bond. These are the 4.5-membered palladacycles [Pd2(mu-Br)2(5-Pf-3-R-1,2,4-eta1-eta2-pentenyl)2] (Pf = C6F5; R = H, Me) and the 5.5-membered metallacycles [Pd2(mu-Br)2(5-Pf-3-R-1,2,5-eta1-eta2-pentenyl)2] (R = H, Me). Two competitive processes are involved in evolution to give eta3-allyls, namely, Pd migration and cyclopropane formation from 4.5-membered eta1-eta2-palladacycles and reopening.

Hydrogen atom abstraction involves geometric determination of the oxygen-hydrogen atomic distance, the gamma-hydrogen angle, the C=O...H angle and the C-H...O angle. The Norrish/Yang type II photochemistry of a homologous series of medium-sized ring and macrocyclic diketones reveals stereoselective cyclobutanol formation by crystalline diketones. The distance and angular parameters of the abstraction of reactive gamma-hydrogen atoms is determined from crystallographic data. Geometric parameters are also obtained for the ring closure reactions of the intermediate 1,4-hydroxy biradicals.

A Streptomyces lividans enzyme inactivates the peptidolactone antibiotic etamycin, by an elimination reaction involving ring opening. The enzyme catalyzes lactone ring cleavage to form a linear dehydrobutyrine peptide. The peptide does not incorporate water and its mass is the same as that of etamycin. The reaction of etamycin in NaOH gives a product formed by lactone bond hydrolysis and another product similar to that formed by the enzyme reaction. Spectroscopic studies show that the inactivation is due to an elimination rather than a hydrolysis reaction.

The beta-elimination reactions of N-2-(p-nitrophenyl)ethyl alkylammonium ions with different leaving groups result in the formation of p-nitrostyrene. Acid-base catalysis, H/D exchange and solvent isotope studies showed that the structure of the leaving group causes a shift from partially reversible E1cb mechanism to an irreversible E1cb mechanism. The results showed that the shift in rate-determining step is caused by the increased steric requirement of the leaving group.

The solvolysis of 9-(1-X-ethyl)fluorene (1-X, X = I, Br, Cl, OTs or OBs) leads to the elimination products 9-(1-ethylidene)fluorene (3) and 9-vinylfluorene and the substitution products 9-(1-hydroxyethyl)fluorene and 9-(1-acetamidoethyl)fluorene. A solvent promoted concerted E2 reaction which predominantly gives 3 from 1-I and 1-Br. A bimolecular substitution pathway competes when strong nucleophiles are added. A change in the leaving group X in 1-X or an alternation in structure from tertiary to secondary are responsible for the transition from stepwise to concerted elimination.

The intramolecular aldol condensation sequence constituting four separate reaction steps, starting with a keto aldehyde and resulting to 2-benzyl-2- cyclohexenone, is catalyzed by antibody 78H6. A single transition state analog motif induces this multistep catalysis. The aldol condensation is catalytically selective for the disfavored trans-elimination with a single enantiomer of stereoisomer of 2-benzyl-3-hydroxy-cyclohexanone. In the reaction sequence a carboxyl group is the general base for catalysis.

The reverse Cope elimination reaction of N-4-pentenyl- and N-5-hexenyl-N-methylhydroxylamine under mild conditions gives 1,2-dimethylpyrrolidine N-oxide and 1,2-dimethylpiperidine N-oxide respectively. This novel reaction is thermodynamically regulated and concerted. The cyclization process is analyzed and its potential is discussed. Comparisons of the process are made with the cyclization of monosubstituted alkenylhydroxylamines giving cyclic hydroxylamines.

The delta-elimination reaction of the enzymology of endonuclease V from bacteriophage T4 using an oligonucleotide containing a site-specific cis-syn cyclobutane thymine dimer showed that delta-elimination occurs during a separate enzyme encounter with the incised DNA. The reaction requires Glu-23 at the N-terminus when examined with T2P, E23Q and E23D mutants.

The thermolysis of dppePtMe3I (1, dppe = Ph2PCH2CH2PPh2) in solid state and solution follows a competitive reaction resulting in reductive elimination of ethane and methyl iodide and simultaneous formation of the Pt(II) products, dppePtMe2 and dppePtMeI. The carbon-carbon bond is reduced when iodide is added, leading to an equilibrium between (1) and the products dppePtMe22/MeI. A five-coordinate cationic intermediate is common for the carbon-iodide and carbon-carbon elimination products.

Trifluoroacetylation of electron-rich olefins with acid anhydride undergoes an addition-elimination reaction. In this study, addition products were formed when electron rich olefins such as vinyl ether and vinyl sulfide were reacted with trifluoroacetic anhydride in CCl4 at room temperature. The products were identified as stable intermediates, which eventually gave the corresponding trifluoroacetylated olefins as substitution products.

The decomposition of the octahedral alkoxo complexes mer-cis-HIr(OCH3)Cl(PR3)3 (R = Me, Et) yields the dihydrido products mer-cis-H2IrCl(PR3)3 by elimination of a beta-hydride. The formation of a pentacoordinate dissociation product is the initial step, and the transition state before the formation as well as the formation are most likely stabilized by pi-donation from the coordinating methoxide. The alkyl substituent of the alkoxide, the phosphine nature and the medium determine the rate of the reaction. In the iridium complex, the reaction rate is first order but it is of 1.33 order in the alcohol.

Kinetic analysis of debromination reactions of erythro-dl-1-aryl-1,2-dibromo-2-nitropropanes with secondary amines in MeCN shows that these reactions progress through an E2 mechanism initiated by the attack of the base at the C-2-Br bond. The attack occurs by an E1cb-like transition with C(sub beta)-Br bond cleavage, negative charge development at beta-carbon and restricted C(sub alpha)-Br bond cleavage.

Cyclic voltammetric analysis of electrochemical debromination reactions of erythro-dl-aryl-1,2-nitropropanes at a platinum electrode shows that the debromination occurs via an EC mechanism, during which the dibromides accept an electron from cathode to form the anion radical in the rate determining step. The reaction results in the formation of (E)-1-aryl-2-nitropropenes in excellent yield. The peak potentials for the reduction waves are between -0.51 and -0.56 volts. The relative rates of reaction are not consistent with Hammett substitutent constants.

Theoretical and experimental analyses of the regioselective deprotonation of anti-alkylthiirane S-oxides or anti-silylthiirane S-oxides under reaction conditions of LiHMDS THF -78 degrees Celsius indicate the reaction products to be (E)-2-alkylethenesulfenate and 1-silylethenesulfenate anions. A stereoselective ring opening accompanies the regioselective deprotonation. Anti-substitutions such as the coordination of lithium anti to the methyl and gem to the silyl are highly stable. Ring-opening occurs on these stable intermediates with lithium syn to sulfoxide, generating the reaction products.