Vinylic Carbon Atom Research Articles

Stereoselective synthesis of (Z)-enethiols and their derivatives: vinylic S(N)2 reaction of (E)-alkenyl(phenyl)-lambda3-iodanes with thioamides.

[reaction: see text]. Exposure of (E)-beta-alkylvinyl(phenyl)-lambda3-iodanes to thioamides in dichloromethane at room temperature was found to result in a bimolecular nucleophilic substitution (S(N)2) at the vinylic carbon atom to give inverted (Z)-enethiols and/or (Z)-S-vinylthioimidonium salts. Vinylic S(N)2 reactions with thioureas are also discussed.

Molecular weight distributions in terpolymerization of α‐methylstyrene/styrene/acrylic acid in continuous stirred tank reactor

Free-radical terpolymerization of α-methylstyrene/styrene/acrylic acid (AMS/ST/AA) in a continuous stirred tank reactor (CSTR) was studied theoretically and experimentally. A series of reactions were conducted to investigate the effect of the reaction temperature, residence time, solvent contents, initiator concentration, chain-transfer agent level, and different monomer compositions on the molecular weight distribution (MWD). The mathematical model based on “the instantaneous property method (IPM)” and the pseudokinetic rate constant method was introduced and modified to predict the MWD of the bulk terpolymer produced in a CSTR. The effects of process variables were included in the mathematical model. Extensive comparisons were made between the theoretical results and experimental values. The rate of the free-radical terpolymerization of AMS/ST/AA was comparatively slow and it was found that the concentration of α-methylstyrene had a strong influence on the molecular weight and polydispersity of the MWD. This presumably reflected the existence of a normal bimolecular termination rate and a slow propagation rate due to steric hindrances at the doubly substituted vinyl carbon atom or transfer of the allylic hydrogen from the α-methyl group. Good agreement was obtained between calculated MWD and the experimental one by assuming that the disproportionation termination of free radicals was the dominant chain-stoppage mechanism. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 479–487, 2001

Regiochemistry in aryl radical cyclisations (5-exo versus 6-endo) of N-vinylic 2-iodobenzamides

Bu3SnH-mediated aryl radical cyclisations of a range of N-vinylic 2-iodobenzamides 10 were examined. The enamides 10a–d gave exclusively the 5-exo cyclisation products 11a–d, whereas the enamides 10e,f having a phenyl substituent on the vinylic carbon atom α to the nitrogen atom gave predominantly the 6-endo cyclisation products 14 and 18, respectively. The experiments on the effect of concentration of Bu3SnH or temperature on the products distribution showed that the formation of the 6-endo cyclisation products 14 and 18 was a result of a 5-exo cyclisation of the aryl radicals formed from 10e,f followed by neophyl rearrangement of the intermediate radicals.

Molecular weight distributions in terpolymerization of ?-methylstyrene/styrene/acrylic acid in continuous stirred tank reactor

Free-radical terpolymerization of α-methylstyrene/styrene/acrylic acid (AMS/ST/AA) in a continuous stirred tank reactor (CSTR) was studied theoretically and experimentally. A series of reactions were conducted to investigate the effect of the reaction temperature, residence time, solvent contents, initiator concentration, chain-transfer agent level, and different monomer compositions on the molecular weight distribution (MWD). The mathematical model based on “the instantaneous property method (IPM)” and the pseudokinetic rate constant method was introduced and modified to predict the MWD of the bulk terpolymer produced in a CSTR. The effects of process variables were included in the mathematical model. Extensive comparisons were made between the theoretical results and experimental values. The rate of the free-radical terpolymerization of AMS/ST/AA was comparatively slow and it was found that the concentration of α-methylstyrene had a strong influence on the molecular weight and polydispersity of the MWD. This presumably reflected the existence of a normal bimolecular termination rate and a slow propagation rate due to steric hindrances at the doubly substituted vinyl carbon atom or transfer of the allylic hydrogen from the α-methyl group. Good agreement was obtained between calculated MWD and the experimental one by assuming that the disproportionation termination of free radicals was the dominant chain-stoppage mechanism. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 479–487, 2001

Formation of fluorosulfatodimerization products in reactions of perfluoroaliphatic α,β-unsaturated carbonyl compounds and conjugated dienes with electrochemically generated peroxydisulfuryldifluoride

Reactions of fluoroaliphatic α,β-unsaturated carbonyl compounds and perfluoro-2,7-dimethylocta-3,5-diene with electrochemically generated peroxydisulfuryldifluoride proceed to give both 1∶1 adducts and fluorosulfatodimerization products, whose formation is explained by generation of heteroallyl and allyl radicals due to the addition of a fluorosulfonyloxy radical to the sterically hindered vinyl carbon atom.

1,4-Silyl migration from oxygen to carbon in silyl allyl ethers: Kinetic and thermodynamic factors

The lithium amide-induced rearrangement reactions of silyl allyl ethers bearing two organometal(loid) residues on the vinylic carbon atoms have been studied as a function of various parameters: metal(loid) groups, base, silyl moiety, base concentration, reaction time and temperature. Kinetic and thermodynamic effects are discussed. It is often possible using the appropriate conditions to select either one of the two possible reaction processes (1,4-silyl migration and 1,3-hydrogen migration).

13C and19F NMR study of α,β-difluorostyryl derivatives of transition metal carbonylates. A method of signal assignment based on the carbon—fluorine spin-spin coupling constants

The13C and19F NMR spectra ofZ- andE-isomers of β-X-substituted α,β-difluorostyrenes (X=F, Cl, CpFe(CO)2, Re(CO)5, Re2(CO)9Na) were studied. Direct and long-range (across 1–5 bonds) spin-spin coupling constants and the (13C−12C) isotope shifts in the19F NMR spectra were determined. The study of the13C satellites in the19F NMR spectra of substituted difluorostyrenes permitted assignment of the13C NMR signals of the vinylic carbon atoms. Similarly, the signals in19F NMR spectra were assigned based on coupling constants of fluorine withipso-carbon. These assignments were found to be in good agreement with the data available from the literature (X=F, Cl). The developed approach was applied to the elucidation of the structure ofZ−PhCF=CClFe(CO)2Cp.

ChemInform Abstract: Synthesis and Structure of Aromatic and Heterocyclic Tellurium Compounds. Part 33. Synthesis of (2‐(Aryltelluro)vinyl)aldehydes and ‐ ketones and Stereochemistry of Nucleophilic Substitution at the Vinylic Carbon Atom.

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.

Nucleophilic additions to palladium(II)-activated CC bonds: Synthesis of cyclopalladated 8-substituted quinoline derivatives

8-Vinylquinoline and α-methyl-8-vinylquinoline have been prepared in 40–67% overall yield from 8-methyl- and 8-ethyl quinoline, respectively. These unsaturated compounds undergo nucleophilic addition with carbon and oxygen nucleophiles at the terminal vinyl carbon atom in the presence of Pd 11 compounds affording, exclusively, five-membered metallacyclic rings.

Selective hetero- and carbo-cycle syntheses via masked cyclopalladated secondary amine and ketone functions

The iodo-bridged or cationic cyclopalladated complexes 1b and 1c derived from N-phenyl-2-pyridylamine and 4b derived from phenyl-2-pyridylketone reacted with internal alkynes to yield five-membered heterocyclic 3 and carbocyclic products 6 with high chemoselectivity. The indoles 3b– 3f, formed from 1b or 1c and disymmetric alkynes, were obtained regioselectively, suggesting that this reaction might be under both electronic and steric control. Analysis of the regiochemistry of this reaction has led us to propose a pathway involving a nucleophilic addition of the secondary amine function to an alkyne activated by η 2- coordination to palladium. The indenol derivatives 6, obtained as stable bis( O, N)-palladated chelates, result from the insertion of the alkyne into the Pd-C bond of 4b followed by attack of the palladated vinyl carbon atom on the electrophilic carbonyl function. In so far as their reactivities towards alkynes are concerned, 1b and 1c behave as masked cyclopalladated secondary amine functions and 4b as masked cyclopalladated ketone functions.

Nucleophilicity towards a vinylic carbon atom: rate constants for the addition of amines to the 1-methyl-4-vinylpyridinium cation in aqueous solution

Second-order rate constants (KNu) have been measured for the addition of 44 primary amines (including five α-effect amines), 28 secondary amines, 19 tertiary amines, ammonia and hydroxide ion to the vinyl group of the 1-methyl-4-vinylpyridinium cation (1) in aqueous solution at 25° C (ionic strength 0.1 mol dm–3). Nucleophilic attack is shown to be rate-determining for primary and secondary amines, with secondary amines being generally more reactive than primary amines of the same basicity. After classification of these species in terms of structure, they describe a number of Bronsted-type correlations having βnuc in the range 0.35–0.54 for six structural classes of primary amine, βnuc= 0.48 for α-effect amines, and βnuc in the range 0.23–0.34 for four structural classes of secondary amine. Substitution upon the α-carbon atom reduces amine nucleophilicity of both primary and secondary amines. The presence of an unsaturated carbon atom (either sp2- or sp-hybridized) as the β-carbon atom leads to an enhanced reactivity relative to the corresponding β-sp3 species in all cases. Tertiary amines are in general less reactive than other amines of the same basicity. Bronsted-type plots for tertiary amines present the appearance of random scatter which is not readily decipherable in terms of structure. β-Hydroxy and β-amino tertiary amines are unusually reactive relative to their basicity. All of these phenomena suggest that protonation of the carbanionic intermediate by a molecule of water is the rate-determining step for the addition of tertiary amines to 1.Rate constants for the attack of primary and secondary amines on 1 are shown to correlate with literature data for a variety of other reactions involving rate-determining nucleophilic attack of amines upon electrophilic carbon. These kNu for primary and secondary amines reacting with 1 are also shown to correlate with Ritchie's N+ parameters for nucleophilic attack at electrophilic sp2-carbon. N+ parameters for amine nucleophiles have not been widely available previously; the parameters that have been available for selected amines are known to be sensitive to the nature of the defining electrophile. The minimal steric hindrance at the electrophilic centre in nucleophilic attack upon 1 suggests that this species is an appropriate electrophile for the definition of N+ parameters for amine nucleophiles; these parameters are evaluated for 70 primary and secondary amines and ammonia and are suggested to provide an appropriate data base for future investigations of the reactivity and selectivity of amine attack upon sp2-carbon electrophiles in aqueous solution.

Structural chemistry of polymerizable monomers, 4. Crystal and molecular structure of N‐methyldimethacrylamide and its effects on the initial stage of solid‐state cyclopolymerization

AbstractThe structure of N‐methyldimethacrylamide was solved by direct methods and refined to a discrepancy index (reliability factor) R = 0,055 and weighted discrepancy index Rw = 0,068. C9H13NO2, relative molecular mass Mr = 167,21, monoclinic, C 2/c, a = 11,882 (1), b = 8,130 (1), c = 10,079 (1) Å, β = 94,21 (1)°, V = 971,0 (1) Å3, Dcal (Z = 4) = 1,143, D obs = 1,16 Mg · m−3, μ(MOKa) = 0,087 mm−1, mp 364 K, colourless needle crystal by sublimation. The molecule has a crystallographic C2 symmetry. The shortest spacing between vinyl carbon atoms in the molecule is 2,908 (2) Å (C(3)…C(3′)). Planes of two intramolecular vinyl groups assume a dihedral angle of 40,6 (4)°. It seems that the location of the vinyl carbon atoms allows an intramolecular closure in the initiation process, that is, tail‐to‐tail cyclization as observed. The subsequent solid‐state reaction probably proceeds through dimerization predominantly along a plane near the (101) plane in the lattice.

Copolymerization reactivities, electron structure and nuclear magnetic resonance spectra of vinylazoles

AbstractData obtained on the electronic structure of a series of C‐ and N‐vinylazoles using the SCF MO method in MNDO approximation and analysis of the 13C and 1H NMR data as well as their copolymerization reactivity ratios in the copolymerization with styrene have shown individual correlations between the relative activity 1/r (r is the copolymerization reactivity ratio of styrene) and the chemical shifts of the terminal vinyl carbon atoms in 13 C NMR spectra, between 1/r and chemical shifts of the protons in trans‐position towards the substituent in 1H NMR spectra, and between 1/r and the net effective charges on the terminal vinyl carbon atoms for each type of monomers considered. The correlations obtained and the analyses obtained from the monomers studied within the modified Alfrey‐Price scheme indicate that the reactivity of vinylazoles in copolymerization is mainly influenced by two factors: the acceptor inductive effect of a substituent in the vinyl bond and the conjugation effect. These factors operate in a different manner for C‐ and N‐vinylazoles and determine their different reactivity in radical copolymerization with styrene.

The influence of intermediate carbenium ion stabilization on the mechanism of the acid-catalysed hydrolysis of α-acetoxystyrenes

The hydrolysis of α-acetoxystyrenes 1a-f in 37% sulfuric acid and 1e at different acid strengths to the corresponding acetophenone 2a-f exhibits pseudo-first-order kinetics. Apparent rate constants ( k h) have been measured spectroscopically at 23 °C by following the change in absorbance with time at a wavelength of 280 nm. Good linearity has been found for the log ( k h) versus log [H +] plot, but not for the plot against H 0. A linear relationship also exists between log ( k h) and the electron density of the terminal vinylic carbon atom. The mechanistic implications of the data are discussed.

Nucleophilic vinylic substitutions on unactivated substrates. : The behaviour of styryl alkyl sulphides and selenides towards sulphur and selenium nucleophiles.

Sodium alkanethiolates or lithium methyl selenide react with styryl alkyl sulphides and selenides, in DMF at 100°C, to give the products of vinylic or aliphatic substitution. The two nucleophilic reagents are extremely selective. In the case of RSNa the attack at the vinylic carbon atom is much faster than that at the aliphatic carbon atom and the (Z)- or (E)- styryl alkyl sulphides are obtained as the result of a stereospecific vinylic substitution which occurs with retention of configuration. On the contrary, in the case of MeSeLi, under the same experimental conditions, the only reaction occurring is the aliphatic substitution which affords the vinyl thiolate anions, as an equilibrium mixture of the (E)- and (Z)- isomers, or the vinyl selenide anions which retain the configuration of the starting styryl alkyl selenides.

Nucleophilic reactions of fluoroolefins. II. Regioselectivity and elimination-addition competition in the reaction of 1-phenylpentafluoropropenes with sodium ethoxide

1-Phenylpentafluoropropene and its para-substituted analogs 1 are susceptible to nucleophilic attack at both vinylic carbon atoms C-1 and C-2. They react with ethanolio sodium ethoxide to give predominantly substitution products, 1-ethoxy-1-phenyltetrafluoropropenes 2 and 2-ethoxy-1-phenyltetrafluoropropenes 3 , with only little formation of adducts, viz . 2-ethoxy-1H-1-phenylpentafluoropropanes 4 . Alkenes 1 , where the para-substituent X  H,Cl,and CF 3 give additionally 1,2-diethoxy-1-phenyltrifluoropropenes 5 and, where X = CF 3 also 2,2-diethoxy-1H-1-phenyltetrafluoropropane 6 . Overall regioselectivity of nucleophilic attack of the ethoxide ion on alkenes 1 exhibits the Hammett type correlation with Ó p values of substituents X: CH 3O and CH 3 groups favour the attack on the vinylic carbon C-1, while CF 3 and Cl substituents direct the attack on the C-2 carbon of alkenes 1 . The E and Z isomers of 1-ethoxy and 1,2-diethoxy substituted alkenes 2 and 5 were formed in comparable amounts, while the E isomers of 2-ethoxy substituted alkenes 3 were always formed with a 93 – 97 % selectivity.

Rearrangements and fragmentations of phenyl styryl sulfides: 2—labelling studies

AbstractMetastable molecular ions of phenyl styryl sulfides may decompose by loss of CH3˙, SH˙, CHS˙, C6H5˙, C6H6 or C7H7˙. Labelling with carbon‐13 and deuterium gave information about the mechanisms of these reactions. It appears that extensive rearrangements occur prior to most of these fragmentations. In the case of phenyl β‐styryl sulfide both phenyl groups and both vinyl carbon atoms are found in the C7H7 fragment in comparable amounts. For phenyl α‐styryl sulfide this fragmentation leads more specifically to the loss of the S‐phenyl group and the β‐vinyl carbon atom. It was concluded that rearrangements occur, partly via symmetric diphenyl ethene sulfide structures, to benzyl phenyl thione ions, from which the fragmentation occurs. For the loss of CHS˙ an earlier proposed mechanism was confirmed. From both compounds the S‐phenyl ring can be lost as C6H5˙ or C6H6 as well as the C‐phenyl ring. Fragmentation occurs from one of the initial structures as well as from benzyl phenyl thione. Loss of CH3˙ is thought to occur after ring closure with formation of dihydrobenzo[b]thiophenes followed by ring opening by rupture of a CS bond. While phenyl β‐styryl sulfide shows a strong tendency towards isomerization to a symmetric structure like 1,2‐diphenylethene sulfide, phenyl α‐styryl sulfide easily rearranges in an electrocyclic reaction with formation of benzyl phenyl thione.

Unusual lithium transfer reactions in lithium-substituted organo-silicon compounds. Reinvestigation of the reaction of 1,8-di-lithionaphthalene with trimethylchlorosilane

The product of the reaction of 1,8-dilithionaphthalene with trimethylchlorosilane is 2-(1-naphthyl)-2,4,4-trimethyl-2,4-disilapentane rather than 1,8-bis(trimethylsilyl)naphthalene as previously reported. A novel, presumably intramolecular, metalation process transfers the organolithium function in 1-trimethylsilyl-8-lithionaphthalene to a methyl substituent on the trimethylsilyl group, and it is this new organolithium reagent which reacts with the second mole of trimethylchlorosilane. Ring-opening of 1,1-dimethyl-2,3-bis(trimethylsilyl)-1-silirene by methyllithium is followed by a similar transfer of the organolithium function from the vinylic carbon atom to a methyl group on silicon.

Organometallic compounds of group III : XXXIV. Steric factors in the carbalumination of olefins. The question of the anomalous, reduced reactivity of olefins versus acetylenes.

In order to understand the reasons for the anomalous, reduced reactivity of olefins toward electrophilic carbalumination, compared with that of acetylenes, the reactivity, stereochemistry and regiochemistry of a series of acyclic and cyclic olefins in carbalumination with triphenylaluminum were investigated. The following substrates underwent reaction between 80 and 225°C with decreasing ease in the order: norbornadiene > cis-β-methylstyrene > trans-β-methylstyrene ∼ 1,2-dihydronaphthalene ∼ 1,1-dimethylindene > cis-1,2-diphenylethylene > 3,3,3-triphenylpropene > trans-1,2-diaryethylenes ∼ phenylcyclopropanes. The stereochemistry of the mono- and bis-carbaluminations of norbornadiene was shown to be syn, exo. The regiochemistry observed with unsymmetrical olefins could readily be rationalized by a steric effect operative in the preferential collapse of an olefin—(C 6H 5) 3Al π-complex. Besides carbalumination, several other reactions were observed with these olefins: (1) cis, trans-isomerization of acyclic olefins; (2) metallation of vinylic carbon atoms by (C 6H 5) 3Al; (3) elimination of (C 6H 5) 2AlH from carbalumination adducts; (4) by inference from the foregoing reaction with certain systems, epimerization at sp 3-hybridized carbon-aluminum bonds; and (5) decarbalumination with carbon-carbon bond scission. These side reactions were considered together with relative reactivities, stereochemistry and regiochemistry in developing energy profiles for the carbalumination of olefins and acetylenes. The reduced reactivity of olefins is thought to arise from steric factors that destabilize a π-complex-with (C 6H 5) 3Al and that cause a trapezoidal-like transition state to be of higher energy and rate-determining. The higher reactivity of acetylenes is ascribed to less steric hindrance both to π-complexation with (C 6H 5) 3Al, and to the collapse of the complex via a trapezoidal configuration. For acetylenes, it is judged that the formation of an intimate π-complex is rate-determining.

The mechanism of isomerization and exchange of olefins over metal catalysts: IV. Reactions of some C 5, C 6 and C 7 alkenes in the presence of perdeuteropropene on iron films

The exchange and isomerization of pent-1-ene, cis-pentene, cis-hept-2-ene, trans-hept-3-ene, 2-methylbut-2-ene and 2,3-dimethylbut-2-ene have been investigated on iron films in the presence of a large excess of perdeuteropropene. Further evidence has been given for the occurrence of a direct intramolecular hydrogen shift in double bond migration, and, in cis-trans isomerization, for a direct process without the formation or the breaking of any CH bond. The classical Horiuti-Polanyi mechanism seems to be restricted to cis-trans isomerization and involves only two consecutive steps. The pronounced maxima for d 8, d 5 and d 4 deutero-isomers in the distributions of but-1-ene, pent-1-ene and 3-methylbut-1-ene obtained from the corresponding alk-2-enes show that the isomerization mechanisms involve a dissociative adsorption at a vinylic carbon atom, accompanied by a complete exchange of all the adjacent primary allylic hydrogen atoms. It is suggested that interconversions between σ-π-binuclear surface complexes are responsible for this process.