Formal Elimination Research Articles

Meisenheimer and Other Rearrangements of N-Oxides Derived from 2-Azabicyclo[2.2.1]hept-5-enes; the Influence of Reaction Conditions and Stereochemistry at Nitrogen

N-Benzyl-2-azabicyclo[2.2. 1]hept-5-ene reacts rapidly with m-CPBA and, on basification, a single N-oxide is released which rapidly forms N-benzyl-2-oxa-3-azabicyclo[3.2.1]oct-6-ene via a Meisenheimer rearrangement at room temperature. In addition, competition from a formal Cope elimination in a non-planar system leads to novel substituted cyclopentadienes; these show unusual VT NMR behavior and an unusually high J g e m value of 23.8 Hz is observed in one isomer at low temperature as a result of diastereotopicity induced by slow inversion at nitrogen in the side chain. N-Benzyl-2-azabicyclo[2.2.1]heptane forms two stable N-oxides with m-CPBA. Invertomer preferences are measured in the starting amines and the relationship between invertomer ratios, N-oxide stereochemistry, and rearrangement pathways is explored.

Heck self-condensation of polycyclic haloalkenes: the case of (1 R)-2-iodobornene

The unusual reactivity of a haloalkene undergoing Heck reaction behaving both as reagent and substrate (Heck donor and acceptor) is studied and discussed in detail in the case of (1 R)-2-iodo-1,7,7-trimethyl-bicyclo[2.2.1]hept-2-ene (2-iodobornene). This enantiopure substrate allows for a rational description of the mechanism which takes into account the nature of the products and the substitution of one of the substituents (iodine and proton) at carbons 2 and 3 of the bornene skeleton. Under catalytic conditions the main products are the syn and anti-cyclotrimers, a head-to-tail dimer and an arene derived from the latter. The products of the stoichiometric reaction between palladium(0) tetrakis(triphenylphosphine) and 2-iodobornene are principally trans-Pd(PPh 3) 2PhI and various dimeric species. The results are rationalized in terms of a catalytic reaction which takes into account the Pd(II)–Pd(IV) oxidation state sequence. The major products in both the catalytic and stoichiometric reactions are dimeric species with formal elimination of an iodine molecule that are unprecedented in the literature for the Heck reaction.

Reactivity of Silyl-Substituted Heterobimetallic Iron–Platinum Hydride Complexes towards Unsaturated Molecules, I Alkyne Insertions into the Platinum-Hydride Bond, Phosphane-Induced σ-Alkenyl–μ-Vinylidene Rearrangements and Formation of μ-Isonitrile Complexes

The heterobimetallic hydride complexes [(OC)3Fe{Si(OMe)3}(μ-Ph2PXPPh2)Pt(H)(PR3)] (1a: X = CH2, PR3 = PPh3; 1b: X = NH, PR3 = PPh3; 1c: X = CH2, PR3 = PMePh2) have been prepared by the oxidative addition of [(OC)3Fe(H){Si(OMe)3}(η1-Ph2PXPPh2)] to [Pt(H2CCH2)(PPh3)2] or by reaction of K[(OC)3Fe{Si(OMe)3}(η1-dppm)] with trans-[Pt(Cl)(H)(PPh3)2]. The solid-state structure of compound 1b has been determined by single-crystal X-ray diffraction. 1-Alkynes such as methylpropiolate or phenylacetylene insert in a regiospecific manner into the Pt–H bond of 1 to yield the σ-alkenyl complexes [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-Ph2PXPPh2)Pt{C(R)=CH2}] (2a: X = CH2, R = CO2Me; 2b: X = NH, R = CO2Me; 3a: X = CH2, R = Ph). Addition of the Pt–H bond of 3a across the triple bond of [D1]phenylacetylene affords [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-dppm)Pt{C(Ph)=C(D)H}] (3a*) having the deuteron trans to platinum (cis addition). This insertion reaction is accompanied by dissociation of the platinum-bonded PR3 ligand and saturation of the vacant coordination site by a dative μ-η2-Si–OPt interaction. When 3 is treated with PR3 again, a subsequent phosphane-induced rearrangement leading to vinylidene-bridged complexes [(OC)3Fe{μ-CC(H)R′}(μ-Ph2PXPPh2)Pt(PR3)] (4a: X = CH2, R′ = Ph, PR3 = PPh3; 4b: X = NH, R′ = Ph, PR3 = PPh3; 4c: X = CH2, R′ = Ph, PR3 = PMePh2; 4d: X = CH2, R′ = p-tolyl, PR3 = PPh3) occurs. Upon purging a solution of 3a with carbon monoxide, the labile CO adduct [(OC)3Fe{Si(OMe)3}(μ-dppm)-Pt(CO){C(Ph)=CH2}] 5a is formed, addition of 2,6-xylyl isocyanide to 2a and 3a affords the isonitrile adducts [(OC)3Fe{Si(OMe)3}(μ-dppm)Pt(CNxylyl){C(R)=CH2}] (5b: R = CO2Me; 5c: R = Ph), respectively. When hydride complex 1a is allowed to react with stoichiometric amounts of aromatic isonitriles, formal elimination of HSi(OMe)3 occurs, yielding the heterodinuclear isonitrile-bridged complexes [(OC)3Fe(μ-C=N-R)(μ-dppm)Pt(PPh3)] (6a: R = 2,6-xylyl; 6b: R = o-anisyl; 6c: R = p-anisyl; 6d: R = p-C6H4NH2) and the bis(isonitrile) complexes [(OC)2(RN≡C)Fe(μ-C=N–R)(μ-dppm)Pt(PPh3)] (7a: R = 2,6-xylyl; 7b: R = p-anisyl). Single-crystal X-ray diffraction studies perfomed on 6a and 6b reveal that the molecular structures of these μ-isonitrile complexes closely resemble the μ-vinylidene complexes 4. The two metal centers are bridged in a symmetric manner by strongly bent CNR ligands, the aromatic groups R being oriented towards the Fe(CO)3 moiety. Electrophilic addition of HBF4 to the basic nitrogen atom of the μ-CNR ligand transforms 6 to the cationic μ-aminocarbyne complexes [(OC)3Fe{μ-CN(H)R}(μ-dppm)Pt(PPh3)][BF4] (8a: R = 2,6-xylyl; 8b: R = p-anisyl; 8c: R = p-C6H4NH2).

Addition of the [(tBuP)3As]− anion to the cyclopentadienyl ring of [(C5H5)M(CO)3Cl] (M = Mo, W)

Reactions of the [(tBuP)3As]− anion with [(C5H5)M(CO)3Cl] (M = Mo, W) gives [(C5H4{As(PtBu)3})M(CO)3Cl] (M = Mo 1; M = W 2) as a result of addition to the C5H5 ring (with formal elimination of LiH), rather than the expected product resulting from substitution of the metal-bonded Cl ligand.

Charge-remote fragmentation characteristics of functionalized alkanes in high-energy collision-induced dissociation

In this study we report on high-energy, collision-induced dissociation processes leading to charge-remote fragmentations, using three alkyl cations, namely n-hexadecylpyridinium, n-hexadecyltriphenylphosphonium and n-hexadecyltriethylammonium, each with and without (2)H(2)-labelling at the C(9) position of the hexadecyl chain. The characteristic patterns corresponding to the formal elimination of alkane elements were observed, and the (2)H(2)-labelling at C(9) clearly affected only one charge-remote fragment ion of the homologous series. However, in addition to the expected fragment ion containing only one deuterium atom, a significant ion retaining two deuterium atoms was observed. MS/MS/MS experiments demonstrated clearly that the latter ion showed partial deuteration around the charge site, the level of deuteration depending on the structure of the original precursor cation. These results can be interpreted in terms of two novel, distinct mechanisms, one of which involves an excited state in an aromatic ring. Mixed-site fragmentation (MSF) ions were also observed from the phosphonium and ammonium ion precursors. We believe that the observation of the MSF process occurring at an sp(2)-hybridized center in the phosphonium series has not been reported previously. It thus becomes apparent that high-energy collisions leading to charge-remote reactions in fact lead to a broad range of pathways. Copyright 2000 John Wiley & Sons, Ltd.

SYNTHESIS AND X-RAY CRYSTAL STRUCTURE OF THE DILITHIUM COPPER SILOXIDE Cu(μ-OSiPh2OSiPh2O)2 [Li(THF)2

CuCl2 reacts with four equivalents of Ph2SiO2Li2 in THF to form Cu(μ-OSiPh2OSiPh2O)2 [Li(THF)2]2 in 80% yield by formal elimination of Li2O and LiCl. CuBr2 reacts analogously. The product of these reactions has a spirocyclic metallasiloxane structure containing two and two rings.

Reactions of the Lithium Salts of the Tribenzylidenemethane Dianion, Diphenylacetone Dianion, and Related Compounds

Potentially synthetically useful reactions of the dilithium salts of the title dianions have been investigated. Electrophilic quenching with a variety of reagents usually leads to the expected products in good yield. Quenching the diphenylacetone dianion with 1 equiv of trimethylchlorosilane, however, gives a good yield of 1,3-diphenylallene obtained by formal elimination of a trimethylsiloxy anion from an intermediate monoquenched monoanion salt. NMR studies, however, do not reveal the intermediacy of the 1,3-diphenyl-2-(trimethylsiloxy)allyl anion but rather suggest that the initial reaction site is at carbon, rather than oxygen. Oxidation of the dianions leads either to ring closure or dimerization for the tribenzylidenemethane dianion and to dimerization for the diphenylacetone dianion. The dimerization reactions are stereospecific, both with respect to the two new stereocenters produced and for the double bonds of the bis-silyl enol ether products if the dimeric bis-enolate dianion products are quenc...

Reaction between Dinitroamide Ion and the Radical Cation of N-tert-Butyl-alpha-phenylnitrone. Formal Elimination of Nitrous Acid from a Spin Adduct.

Reaction between Dinitroamide Ion and the Radical Cation of N-tert-Butyl-alpha-phenylnitrone. Formal Elimination of Nitrous Acid from a Spin Adduct.

Preparation and NMR Spectra of Difluoromethylated Silver(I) and Silver(III) Compounds. Structure of [PNP][Ag(CF(2)H)(4)

The thermally unstable [Ag(CF(2)H)(2)](-) moiety is obtained in solution by reaction of silver(I) salts with Cd(CF(2)H)(2) in DMF/diglyme at -80 degrees C. Oxidation with I(2) leads to the argentate(III) [Ag(CF(2)H)(4)](-), which has been isolated as its PNP salt. According to DSC/TG analysis, the exothermic decomposition of this air-stable salt proceeds in two steps at 121 and 150 degrees C with formal elimination of one and three CFH units, respectively. Difluoromethylation of [Ag(CN)(2)](-) in the presence of acetyl chloride leads to the argentate(I) [Ag(CF(2)H)(CN)](-), which is oxidized by bromine at low temperatures to the thermally labile [trans-Ag(CF(2)H)(2)(CN)(2)](-) anion. Stable argentates(III) containing both difluoromethyl and trifluoromethyl groups are obtained by reaction of [Ag(CF(3))(n)()(CN)(4)(-)(n)()](-) (n = 1, 2-cis, 2-trans, and 3) with Cd(CF(2)H)(2)-the cis and trans configurations of the reactants being retained in their products for n = 2. The compounds are identified and characterized by multinuclear NMR spectroscopy. Crystals of [PNP][Ag(CF(2)H)(4)] belong to the tetragonal space group P4(3) with a = 9.475(1) Å, c = 42.159(6) Å, and Z = 4. The coordination of the silver atom is approximately square-planar with an average Ag-C bond length of 2.083(14) Å. The ligands are so oriented that each C-H bond is geared between the C-F bonds of a neighboring CF(2)H group-the overall symmetry being approximately C(4)(h)().

Cluster chemistry: LXXI. Isomerisation of a pentanuclear ruthenium cluster by elimination of phenylphosphinidene from a tertiary phosphine. X-Ray structure of Ru 5(μ 5-C 2Ph)(μ 4-PPh)(μ-PPh 2)(CO) 13

Reactions of Ru 5(μ 5-C 2PPh 2)(μ-PPh 2)(CO) 13( 1 in oxirane gave an isomer of 1, Ru 5(μ 5-C 2Ph)(μ 4- PPh)(μ-PPh 2)(CO) 13, which has been formed by formal elimination of PPh from the C 2PPh 2 ligand in 1 to the cluster, with concomitant cleavage of an RuRu bond. The rhomboidal Ru 4 core interacts with a C 2Ph ligand to give a trigonal prismatic C 2Ru 4 arrangement, of which a triangular face is capped by the fifth Ru atom and a square face by the PPh group; the Ru 5 skeleton has an envelope conformation. Notable is the short bond (1.965(6) Å) from the acetylide C α to the edgebridging Ru atom, indicating some carbenic character for this carbon.

Thermal reactions of aryl azides with trans-1,2-dibenzoyl- and trans-1,2-diacetyl-ethylene. Reactivity of 4,5-dibenzoyl- and 4,5-diacetyl-1-aryltriazolines

Thermal reactions of 4-substituted phenyl azides (1) with trans-1,2-dibenzoyl-(DBE) and trans-1,2-diacetyl-ethylene (DAE) have been investigated in benzene solution at room temperature and at 110 °C. These reactions lead to decomposition products of unstable 4,5-diacyl-1-aryltriazolines (14A and B) which have generally escaped isolation except in one case. At room temperature triazolines (14A and B) undergo formal elimination of an aldehyde moiety to give 4-acyltriazoles (3A and B), isomerization to diazo diones (15A and B) from which 1-arylamino-1,2-diacylethylenes (2A and B) are eventually formed, and oxidation to diacyltriazoles (10A and B). At 110 °C 1-arylamino-2,2diacylethylenes (12A and B) and N-aryl-N-vinylamides (13A and B), the rearrangement products occurring via aryl-group migration, are preferentially produced. Under these conditions varying amounts of pyrrolidines (11A and B) also occur. These compounds (11A and B) are ascribed to cycloaddition reactions of azomethine glides resulting from ring opening of intermediate aziridines (16A and B) with DBE or DAE. However, decomposition of triazolines (14A and B) in the presence of triethylamine leads exclusively to the enamines (2A and B). The possible reaction mechanisms involved in the formation of the observed products are discussed.

Soviets and the Organs of People's Control

Important conditions for improving the productiveness of the overall activity of the soviets, for monitoring the observance of laws, government resolutions, for the soviets' own decisions, and for consolidating links with the masses are the observance by each and every soviet of people's deputies of party decisions aimed at strengthening the leadership of the bodies of people's control, the full and proper use of their powers to this effect, and the elimination of flaws and formalism in their work.

Spontane bildung von selenobenzaldehyde-verbrückten zweikernkomplexen [(CO) 5W] 2(μ 2,η 2-SeC(H)C 6H 4R) aus (CO) 5W[SeC(H)C 6H 4R

The selenobenzaldehyde complexes (CO) 5W[SeC(H)C 6H 4R- p] (R = CF 3, H, Me) react in solution with formal elimination of one “SeC(H)C 6H 4R” molecule per two molecules of the complex giving the binuclear selenobenzaldehyde-bridged complexes [(CO) 5W] 2(μ 2,η 2-SeC(H)C 6H 4R- p). The reaction is inhibited by free carbon monoxide.

Systematic Design of Automation, Protection, and Control in Substations

A design tool is proposed for the subsequent development steps of a substation control system, viz. task specification, system design, software production, and hardware implementation. Process control is characterized by properties like causality, determinism, asynchronity, stochastic events, and real-time control. All control tasks can directly be expressed in terms of a subclass of Petri nets with the above mentioned properties. The formal Petri net properties guarantee well defined interfaces (supporting task sharing), limit consequences of changes (in technology or by extension) to local alterations (i.e. reusability of the unaffected parts), permit concurrent task formulation (supporting availability and response time respectively) and facilitate formal error elimination. Moreover, the system design can be mapped via software to hardware by formal procedures.

Two-nucleon processes in a coupled-channel approach to pion-nucleus single-charge-exchange reactions

A momentum space coupled-channel formalism is proposed for the study of pion-nucleus single-charge-exchange reactions at medium energies. Formal elimination of certain reaction channels leads to a reduced set of coupled equations with a complex and energy-dependent interaction. A nonperturbative method based upon unitarity considerations is then used to construct each order of this effective pion-nucleus interaction. Our analysis thus leads to a second-order pion-nucleus interaction with analytical properties very different from those obtained from multiple-scattering theory. The theory is applied to the study of pion-$^{13}\mathrm{C}$ elastic scattering and the single-charge-exchange reaction $^{13}\mathrm{C}({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{0})^{13}\mathrm{N}(\mathrm{g}.\mathrm{s})$. Included in our calculations are the first- and second-order pion-nucleus strong interactions, and the pion-nucleus Coulomb interaction. We have calculated the first-order interaction using a covariant, nonstatic theory and have evaluated contributions to the second-order interaction arising from two-nucleon processes related to true pion absorption and to the scattering of pions from a nucleon pair. We present a general relation connecting the second-order pion-nucleus strong interaction potentials of nuclei whose structure do not differ appreciably. Theoretical results for $\ensuremath{\pi}^{13}\mathrm{C}$ elastic scattering predicted by our theory are found to be in good agreement with the data. The calculated excitation function of the single-charge-exchange reaction exhibits a high sensitivity to the type of two-nucleon processes considered. Pion-nucleus single-charge-exchange reactions therefore have promise as a tool for investigating pion-nucleus reaction mechanisms.NUCLEAR REACTIONS Coupled-channel theory, pion-nucleus single-charge-exchange reactions, pion absorption, nucleon-nucleon correlations, $\ensuremath{\pi}^{13}\mathrm{C}$ elastic cross sections at 50 and 180 MeV, excitation function of $^{13}\mathrm{C}({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{0})^{13}\mathrm{N}(\mathrm{g}.\mathrm{s})$ between 30 and 260 MeV.

Aldol Reaction of Aluminium Enolate Resulting from 1,4-Addition of R2AlX to α,β-Unsaturated Carbonyl Compound. A 1-Acylethenyl Anion Equivalent

Abstract Organoaluminium reagents R2AlX (X=SPh, SeMe) easily add to α,β-unsaturated carbonyl compounds in 1,4-fashion. The resulting aluminium enolates react with aldehydes to give aldol adducts in fair to good yields. Formal elimination of HX from the adducts provides α-substituted α,β-unsaturated carbonyl compounds. The overall transformation is an addition of aldehydes to 1-acylethenyl anion equivalent. Diethylaluminium iodide also is found to be an efficient reagent for the same type transformation.

Biological activities and protracted action of carba-analogues of deamino-oxytocin with O-methyltyrosine in position 2

The biological potency and the duration of the effect of two analogues of deamino-oxytocin, having the disulfide bond substituted by a thioether group and the tyrosine residue replaced by O-methyltyrosine, were compared in the uterotonic and galactogogic assay in vivo. [2-O-Methyltyrosine]deamino-6-carba-oxytocin had a very low formal elimination constant (i.e. strongly protracted action) in the uterotonic assay.

Slow chemical reactions and perfectly mobile complexation equilibria in electrode processes

A rigorous formulation of the diffusional problem relative to an electrode process complicated with slow homogeneous chemical reactions and perfectly mobile complexation equilibria is given on the basis of the law of conservation of mass. A general procedure allowing the formal elimination of the mobile complexation equilibria from the diffusional problem is described.

Determination of antidiuretic activity in the rat for structural analogues of the neurohypophysial hormones.

ABSTRACT A procedure for measuring the antidiuretic activity of the neurohypophysial hormones and their synthetic structural analogues in the hydrated rat in the dose range of 5–100 antidiuretic microunits is described. The technique of measurement allows the determination of diuresis over one-minute intervals, as well as the total amount of urine excreted over longer periods. The precision of the measurement is greatly increased by the use of a drop divider. The electrical conductivity of the urine is continuously recorded, and the conductivity and creatinine clearance are correlated with the urine flow. These techniques allow the precise determination of parameters such as the half-life of the antidiuretic effect, formal elimination constants, etc.; they can therefore serve for the comparison even of analogues showing qualitative differences in their antidiuretic effects from the chosen standard (arginine or lysine vasopressin), e. g. analogues of the hormonogen type with prolonged effects.

We Must Fully Relieve Schoolchildren of Excessive Homework

It is now clear to everybody that the school reform is unthinkable without a detailed revision of every aspect of educational work and a decisive elimination of formalism and cliches in the organization and methods of education and upbringing of our schoolchildren. But not enough is being done in this respect.