Cross-metathesis of vinyl aromatic heterocycles: comparison of Grubbs catalyst and Schrock catalyst

Metathesis of 2-vinyl aromatic heterocycles such as furan and thiophene has been investigated in the presence of a ruthenium-based Grubbs catalyst from a synthetic standpoint. The self-metathesis of 2-vinyl aromatic heterocycles was not successful. However, the cross-metathesis of these aromatic heterocycles with 1-octene occurred efficiently, but the selectivity of cross-metathesis product was very low, below 50%. The origin of the low selectivity of heterodimer formation was elucidated through metallacyclobutane intermediate mechanism, observations of carbenes by in situ ¹H NMR, and the reaction products. The effect of oxygen on the reaction behavior was also examined. Furthermore, the data obtained on the Grubbs catalyst were compared with those on a molybdenum-based Schrock catalyst.     

Chiral phosphinothiourea organocatalyst in the enantioselective Morita-Baylis-Hillman reactions of aromatic aldehydes with methyl vinyl ketone

A new class of chiral phosphinothioureas has been developed as efficient organocatalyst for the enantioselective Morita-Baylis-Hillman reaction of aromatic aldehydes with methyl vinyl ketone. The reaction proceeds under very mild conditions to afford the desired product in a short time period in good to excellent yields with up to 94% ee.     

Photophysics of vinyl aromatic polymers

The experimental approaches required to characterize energy migration and excimer formation in vinyl aromatic polymers are considered. As an example the photophysical processes occurring in poly(acenaphthylene) (PACE) and water soluble acenaphthylene copolymers have been investigated using steady state and time resolved fluorescence spectroscopy. Excimer formation in these polymers is determined by both structural and dynamic factors. The difficulties in the application of fluorescence decay analyses to examine energy migration in polymers are discussed. For PACE with a 9-methylanthryl (9MA) end-group and the copolymers containing solubilized 9MA, energy migration and transfer can be demonstrated.     

Rhodium-catalyzed ring opening of vinyl epoxides with alcohols and aromatic amines

[Rh(CO)(2)Cl](2) is an effective catalyst for the ring opening of vinyl epoxides with alcohols and aromatic amines under neutral conditions at room temperature. The reaction occurs with excellent diastereo- and regioselectivity (>20:1) giving the trans-1,2-amino alcohols or alkoxy alcohols for a wide range of substrates. The regio- and stereochemistry of these reactions is complementary to that typically obtained with palladium-catalyzed ring openings of vinyl epoxides.     

Cross-metathesis of vinyl aromatic heterocycles with 1-octene in the presence of a Schrock catalyst

Metathesis of 2-vinyl aromatic heterocycles such as furan, thiophene, pyrrole and pyridine in the presence of a molybdenum-based Schrock catalyst has been investigated from a synthetic point of view. The self-metathesis of 2-vinyl aromatic heterocycles was not successful. However, in cross-metathesis of thiophene, furan and styrene with 1-octene, the cross-metathesis product, heterodimer, was readily obtained selectively, together with only small amounts of the two corresponding self-metathesis products. The origin of the surprisingly high selectivity of heterodimer formation was elucidated through metallacyclobutane intermediate mechanism, observations of carbenes by in situ ¹H NMR, and reaction products.     

Photostabilisation of wood using aromatic vinyl esters

Thin wood veneers were esterified to different weight gains with vinyl benzoate, vinyl cinnamate or vinyl-4-T-butylbenzoate to graft aromatic groups to wood's molecular components. We hypothesised that such modification would increase the resistance of wood to photodegradation. There was a linear relationship between the level of esterification of wood with vinyl benzoate and the photostability of the modified veneers exposed to natural weathering. Vinyl benzoate protected lignin and cellulose in wood from photodegradation at high weight gains (>30%) whereas modification of wood with vinyl-4-T-butylbenzoate provided no such protection and vinyl cinnamate increased the photodegradation of wood. We provide an explanation for why these effects occurred and discuss the implications of our findings for the development of weather-resistant wood materials.     

Synthesis and characterization of macrocyclic vinyl aromatic polymers

The synthesis and characterization by size exclusion chromatography, liquid chromatography, NMR, matrix‐assisted laser desorption/ionization, thermal analysis, and other techniques of well‐defined and narrow molecular weight distribution macrocyclic polystyrene (PS), poly(2‐vinylpyridine), poly(α‐methylstyrene), poly (2‐vinyl‐naphthalene) (P2VN), and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene, methylidene, or 9,10‐anthracenylidene unit are reviewed. The absorption and emission spectroscopy of PS, P2VN, and PDMVF is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2139–2155, 2006     

An unexpected highly diastereoselective double Baylis-Hillman reaction of per- (or poly)fluorophenyl aromatic aldimines with methyl vinyl ketone

Aza-Baylis-Hillman reaction of per- (or poly)fluorophenyl aromatic aldimines 1 with methyl vinyl ketone (MVK) was studied. It was found that both the used Lewis base and solvent can significantly affect the reaction. Using triphenylphosphine as a Lewis base, the reaction of 1 with MVK proceeded smoothly to give the normal Baylis-Hillman adduct 2 along with the double Baylis-Hillman adduct 3 as by-product in THF. When 1,4-diazabicyclo[2.2.2]octane was used as a Lewis base in DMF, the aza-Baylis-Hillman reaction of 1 with MVK gave the double aza-Baylis-Hillman adduct 3 exclusively in moderate to good yields with excellent diastereoselectivities. The double Baylis-Hillman adduct 3 was conveniently converted to fluorine-containing 4-alkylidene-2-cyclohexen-1-ones under mild reaction conditions in good yields.     

Direct synthesis of aromatic polyamides

The synthesis of aromatic polyamides, namely poly(p-phenylenetere-phthalamide) and poly(p-benzamide), via phosphorylation reaction has been thoroughly investigated. The effect of reaction temperature, concentration of monomers and reactants, type and concentration of salts, amount of the activator and its stepwise addition have been considered and the optimum reaction conditions found. The resultant synthesis of the above polymers, also in connection with the high purification techniques of all components of the reaction mixture, allowed to reach the highest molecular weights obtained so far by this synthetic way.     

Synthesis and thermal and spectroscopic properties of macrocyclic vinyl aromatic polymers

Well‐defined and narrow molecular weight distribution macrocyclic poly(2‐vinylnaphthalene) (P2VN) and poly(2‐vinyl‐9,9‐dimethylfluorene) (PDMVF) containing a single 1,4‐benzylidene or 9,10‐anthracenylidene unit have been synthesized via the potassium naphthalide initiated polymerization of the monomers followed by the end‐to‐end coupling of the resulting P2VN dianions under high‐dilution conditions with 1,4‐bis(bromomethyl)benzene or 9,10‐bis(chloromethyl)anthracene. Molecular characterization has been carried out by size exclusion chromatography, nuclear magnetic resonance, differential scanning calorimetry, ultraviolet–visible spectroscopy, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The thermal properties show distinct differences between the cyclic and matching linear polymers, with the macrocycles showing much higher glass‐transition and decomposition temperatures. The absorption bands are both hyperchromic and hypochromic with respect to the model aromatic compounds, and this is consistent with intensity borrowing. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5488–5503, 2004     

Reaction of aromatic amines with vinyl alkyl ethers

Summary Aromatic amines such as aniline, p-anisidine, and p-bromoaniline in the presence of BF₃ etherate react with vinyl alkyl ethers to form 1-alkoxy-tetrahydroquinaldine derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12 p. 2221–2222, December, 1964     

A highly selective cascade approach to diverse aromatic ring systems from simple aromatic aldehydes and propiolates

[reaction: see text] A new triethylamine-catalyzed cascade reaction of aromatic aldehydes with propiolates has been developed. This serial multi-bond-forming process furnishes diverse polycyclic aromatic hydrocarbons, including naphthalenes, phenanthrenes, benzofurans, and 2,3,9,9a-tetrahydronaphtha[2,3-b]furans. The chemical outcome of the process depends on the reaction temperature and can be tailored selectively by an appropriate choice of experimental conditions.     

Emulsion polymerization of vinyl stearate

The polymerization of vinyl stearate in aqueous emulsions with a non-ionic emulsifying agent and potassium peroxydisulfate as initiator has been investigated by use of a dilatometric method to follow the reaction. In general, the reaction kinetics do not follow the pattern established for styrene. Variation of initiator concentration produced latices containing approximately equal numbers of latex particles, even though the rate of reaction was almost directly proportional to the peroxydisulfate concentration. For a given initiator and monomer concentration polymerization occurs very slowly when the monomer is completely solubilized but as the number of micelles is reduced and the number of emulsion droplets increased, the rate increases to an optimum value, whereafter it decreases. A mechanism is proposed by which the sparsely soluble vinyl stearate reacts and redistributes itself into latex particles of a different size range from the micelles and emulsion droplets originally present.     

Anionic graft polymerization of vinyl monomers initiated by metallized aromatic rings of graphite powder

Anionic graft polymerizations of methyl methacrylate (MMA) and styrene from graphite powder initiated by metallized aromatic rings on the surface were investigated. Metalation of the surface was achieved by the reaction of polycondensed aromatic rings of graphite withn-butyllithium (BuLi) in N,N,N,N-tetramethylethylenediamine (TMEDA) or hexamethylphosphorous triamide (HMPT) at 0 °C., Anionic polymerizations of MMA and styrene were initiated by metallized graphite, and these polymers were grafted onto the surface. The conversion and percentage of grafting increased by increasing the amount of BuLi used for metalation. When 0.20 g of graphite was treated with 0.4–0.5 mmol of BuLi in TMEDA, the percentage of grafting of PMMA and polystyrene reached the maximum value: PMMA 52.8% (PMMA/graphite =0.528 g/1.0 g) and polystyrene 37.2% (polystyrene/graphite=0.372 g/1.0 g). Grafting of polymers was also confirmed by infrared spectra. Although no metalation of graphite proceeded in toluene, graphite could be metallized even in toluene by the addition of crown ether as a complexing cation agent. The stability of graphite powder in organic solvent dispersion was found to be improved remarkably by grafting of polymer onto the surface.     

Syntheses of aromatic polyketones and aromatic polyamide

High molecular weight aromatic polyketones were prepared from p- and m-phenoxybenzoic acid in polyphosphoric acid by heating the reaction mixture at 100°C. High molecular weight aromatic polyamide was derived from the polyketone obtained through Schmidt reaction or Beckmann rearrangement. The polyamide obtained by Schmidt reaction was found to have some regularity in an arrangement of its repeating units. The thermal stability of the polyketone and the polyamide were good.     

Pyrolysis-gas chromatography of polymers obtained by Friedel-Crafts reactions of poly(vinyl chloride) with aromatic compounds

Pyrolysis, in combination with gas-chromatography technique, was used in the determination of the structure and study of the thermal degradation mechanism of the condensation polymers obtained by Friedel-Crafts reactions of poly(vinyl chloride) with benzene, toluene, and naphthalene. The separation of the pyrolysis products was made using a column packed with chromosorb W (80–100 mesh) coated with 15% silicone SE-52. The identification of the pyrolysis products resulted as a consequence of the thermal decomposition of condensation polymers and their semiquantitative estimation led to the final conclusion that the initial normal chlorine substitution in the macromolecular chain of poly(vinyl chloride) is followed by an important intramolecular cyclization reaction yielding 1,3-methyleneindan units.     

Soap-free emulsion polymerization of aromatic vinyl monomer using AIBN

Soap-free emulsion polymerizations of aromatic vinyl monomers using 2,2′-azobis(2-methylpropionitrile) (AIBN) were investigated to clarify the origin of the negative charge of the synthesized particles. It was found that the zeta potential and size of the particles synthesized by soap-free emulsion polymerization using AIBN had a strong relationship with the pi electron cloud density in the aromatic vinyl monomer used in the polymerization. The effect of the position of the substituent atom in the phenyl ring on the synthesized particle properties was small.     

Pyridines and pyridine derivatives from vinyl allenes and imines

The Lewis acid mediated reaction of acyclic vinyl allenes and imines, yielding tetrahydropyridines has been carried out. Only one cycloadduct was observed in each case, and thus, the reaction progressed in all cases with total regio-, face- and endo/exo selectivities. The cycloadducts were transformed into polysubstituted pyridines, including bipyridines, by catalytic transfer hydrogenation using cyclohexene as hydrogen donor in good yield. The reaction was extended to the aromatization of the bicyclic cycloadducts prepared in previous works from the reaction of semicyclic vinyl allenes and imines, yielding tetrahydropyridines.     

Palladium-catalyzed cyclization of vinyl iodide-tethered allensulfonamide

This Letter describes a palladium-catalyzed cyclization of vinyl iodide-tethered allensulfonamide in the presence of alkylol, which provides a facile access to 2-alkoxy-3-methylene-tetrahydropyridine. The asymmetric version of this reaction has also been preliminarily realized with up to 81% enantioselectivity when chiral bisphosphine ligands were used.     

Development of a catalytic aromatic decarboxylation reaction

A palladium-catalyzed aromatic decarboxylation reaction has been developed. With electron-rich aromatic acids, the reaction proceeds efficiently under fairly mild conditions in good yields. The method was useful with complex functionalized substrates containing hindered carboxylic acids.