Synthesis of para-substituted styrenes

Using double Stille cross-coupling reaction bromo (or chloro)benzylbromide is easily transformed into substituted styrene monomers bearing a wide range of substituents in para position     

Photolysis and emission spectra of substituted polyacrylophenones

Poly-[3′,4′-dimethoxyacrylophenone], poly-4′-phenylacrylophenone, poly-2′-acrylonaphthone and copolymers of acrylophenone monomers with styrene and methyl methacrylate were prepared. Quantum yields of main chain scission in chlorobenzene by 313 nm radiation were 10³ times lower for all homopolymers and copolymers studied than for polyacrylophenone. The emission spectra of the polymers, copolymers and model compounds were taken for films at 77 K. The 3′,4′-dimethoxyacrylophenone, 4′-phenylacrylophenone and 2′-acrylonaphthone structural units exhibited poorly resolved emission spectra in homopolymer, copolymer and model compound. No difference in the emission spectra of films and dispersed homopolymer or copolymer in a poly(methyl methacrylate) matrix was observed. The decay of the emission of all homopolymers and copolymers under study was exponential, the life-time exceeding 0.20 sec.     

Carbon-13 NMR substituent effects in para-substituted benzophenones

The carbon-13 NMR spectra for a series of benzophenones was obtained and analyzed, using the dual substituent parameter (DSP) equation. The DSP analysis indicates that transmission of the substituent effect to the substituted ring is primarily resonance controlled while the transmission to the second phenyl ring involves a π-bond polarization mechanism. The DSP analysis of the C'₄ chemical shifts (para carbon in ring B) was found to compare very favorably with the fluorine “tag” data for analogous systems. Data for some para-para' benzophenones is also given.     

Solvent effect on thermal degradation of plasticized para-substituted polystyrenes

The thermal effect on stability of a series of para-substituted polystyrenes with methyl, methoxy and α-methyl substituents in various solvents was studied in the temperature range of 298-363 K. They gave a monomer fluorescence as a minor part and excimer fluorescence as a major part. Thermal heating of para-substituted polystyrenes shows a decrease in both monomer and excimer fluorescences in all used solvents. Thermal heating causes a small fluorescence quenching effect at lower temperatures in solution but becomes very dominant at higher temperatures. Added terephthalate and phthalate plasticizers to these para-substituted polystyrenes caused a quenching of both monomer and excimer fluorescences without the formation of exciplex emission. The thermal quenching processes of the plasticized polymers were accompanied by a change in the structure of the fluorescence spectra at high heating temperatures. This may indicate that thermodestruction of these polymers starts from a random chain scission. The change in solvent polarity has considerable effect on fluorescence quenching but it has a minor effect on the thermal degradation of these polymers. The binding energies for excimer formation were calculated in the used solvents.     

Photodegradation kinetics of poly(para-substituted styrene) in solution

The UV irradiation effects on stability of polystyrene, poly(4-methoxystyrene), poly(4-methylstyrene), poly(α-methylstyrene), poly(4-tert-butylstyrene), poly(4-chlorostyrene), and poly(4-bromostyrene) in dichloromethane, dichloromethane, tetrahydrofuran, and N,N-dimethylformamide solutions were studied in the presence of oxygen at different intervals of irradiation time. The photodegradation was studied at 293 K using fluorescence spectroscopy. Solutions of these polymers were accompanied by quenching of monomer and excimer emissions during the exposure of their solutions to UV light, and by a change in the structure of the fluorescence spectrum. Irradiation of poly(4-methylstyrene) and poly(α-methylstyrene) at excitation wavelength of 265 nm showed an increase of fluorescence intensity of a broad band, at longer wavelength without clear maxima. This may indicate that photodestruction of these polymers by irradiation with light of frequency absorbed by the polymer, may start from a random chain scission, with the possibility of formation of polyene and carbonyl compounds.     

Larvicidal and structural studies of some triphenyl- and tricyclohexyltin para-substituted benzoates

Several new triphenyl- and tricyclohexyltin para-substituted benzoates were synthesized. Their structures were characterized by IR and Mössbauer spectroscopies. The structures were determined to be four-coordinated monomers. Larvicidal activities of the new compounds as well as other benzoates were evaluated against the 2nd larval instar of the Anopheles stephensi and Aedes aegypti mosquitoes. Results from the screening studies indicated that the triphenyltin benzoates were more toxic towards the Ae. aegypti larvae. A quantitative-structure activity relationship was also developed for the An. stephensi larvae.     

Triadic analysis of substituent effects—gas-phase acidity of para-substituted phenols

A large variety of para-substituted phenols was examined and their acidities in the gas-phase were rationalized by a triadic formula, which is capable of delineating the initial, intermediate and final state effects in the deprotonation process. It is shown that triadic analysis is equivalent to the homodesmotic reactions approach, while being much more informative at the same time. The applied MP2(fc)/6-311+G(d,p)//B3LYP/6-31G(d) theoretical method gives acidities in very good agreement with available measured values, meaning that calculations can safely replace the missing experimental data for compounds not easily amenable to laboratory examinations. It is found that the underlying principle leading to enhanced acidity of para-substituted phenols containing strong π-electron acceptor groups is the final state effect. It reflects a more pronounced ability to accommodate the excess negative charge. Particular attention has been focused on superacidifying NO₂, SO₂CF₃ and S(O)(NSO₂CF₃)CF₃ and C(CN)C(CN)₂ moieties. It is shown that their influence on acidity is strong and that the deprotonation ability increases along the sequence of substituents NO₂<SO₂CF₃<S(O)(NSO₂CF₃)CF₃<C(CN)C(CN)₂. On the contrary, the electron releasing substituents NH₂, OCH₃, OH and CH₃ decrease acidity of phenol albeit to a small extent. Finally, it is demonstrated that pentacyano derivative of phenol is a powerful OH superacid as evidenced by ΔH_acid value of 287.5 kcal mol⁻¹.     

Synthesis and kinetic investigation of the selective acidolysis of para-substituted N-benzyl- or N-phenyl-N-phenylacetyl-α,α-dialkylglycine cyclohexylamides

Several derivatives of N-phenylacetyl-N-benzyl-α,α-dimethylglycine cyclohexylamide and their α,α-dibenzylglycine analogues were synthesised by a Ugi-Passerini reaction. In addition, a few analogues of the former but having an N-phenyl instead of a benzyl group at the nitrogen atom were synthesised. The compounds in each of these three sets differed from each other at position 4 of the N-benzyl (and N-phenyl) group. These adducts were submitted to acidolysis with TFA to obtain the corresponding free acids, the reactions being monitored by HPLC and data collected for kinetic purposes. The kinetic data were submitted to Hammett uni- and biparametric relationships and the results were analysed in terms of structure-reactivity in connection with the sensitivity of the reaction rates to the electronic contributions of the various substituents at position 4 of the aromatic rings. The results allowed comparison with information obtained in previous investigations and rationalise the contribution of the substituent at the nitrogen atom to the lability of the C-terminal amide bond.     

Thermal and photochemical reactions of allylcobaloximes with para-substituted benzenesulphonyl chloride under aerobic and anaerobic conditions

The compounds p-XC₆H₄SO₂Cl (X = Cl, Br, I, OMe) react regiospecifically with allyl-, 2-methylallyl-, 3-methylallyl- and 3,3-dimethylallyl-cobaloximes under thermal and photochernical conditions. A rearranged organic product is obtained in each case. The yields are much better in photochemical reactions. A chain mechanism is involved in which the organosulphonyl radical and cobaloxime(II) are the chain propagating species. Yields of the sulphones are drastically reduced when the reactions are carried out in the presence of oxygen.     

Tri-n-butyltin carboxylate derivatives of para-substituted phenyl-ethanoic acids: synthesis, characterization and X-ray structure determination

The tributyltin esters of 4-(ethyl)-phenyl-ethanoic acid and 4-(isopropyl)-phenyl-ethanoic acid have been prepared as model compounds of the repeating unit of the related stannylated polystyrenic derivatives. Both the products were fully characterized by proton and carbon NMR two-dimensional techniques. FT-IR spectra show in the solid state carboxylated moieties bridging R₃Sn groups with the metal atom expanding its coordination number, this structure being destroyed in solution. The supramolecular arrangement of the products in the solid state has been investigated by X-ray diffraction, which confirms the pentacoordination at tin in both the products, and indicates a different spatial arrangement of the alkylated aryl groups, as evidenced also by the slightly different thermal properties.     

Electronic effect on the regioselectivity in the ring opening of para-substituted phenyloxiranes by acetylides

The electronic effect on the regioselectivity in the alkynylation of phenyloxiranes was investigated using three kinds of metal acetylides. BF₃ mediated lithium acetylide provided either the α- or β-alkynylated products by controlling the effect of the para-substituents of the phenyloxiranes. LiClO₄ mediated lithium acetylide and titanium acetylide, on the other hand, afforded predominantly the β- and α-products, respectively.     

Restricted rotation in a tetrakis(para-substituted phenyl) porphyrin bearing four porphyrin-fullerene substituents

A porphyrin substituted with four porphyrin-fullerene moieties has been prepared and variable-temperature NMR studies revealed a high barrier to free rotation about the four para-substituted phenyl groups of the central porphyrin core.     

Synthesis and thermal study of poly-N-p-substituted phenylmaleimides

Poly-N-p-bromomethylphenylmaleimide was synthesized from poly-N-p-methylphenylmalcimide at 80°C in benzene solution using N-bromosuccinimide as a brominating agent with a trace amount of benzoyl peroxide. The alcoholysis, aminolysis and Wurtz reaction of poly-N-p-bromomethylphenylmaleimide were carried out using various alcohols, amines and sodium metal, respectively. The polymers obtained were characterized on the basis of elemental analysis. IR spectra and molecular weight measurements. The thermal behaviour of these polymers was studied by DTA and TG methods and the probable mechanism of degradation and crosslinking reactions are proposed.     

Synthesis of meso-substituted dipyrromethanes using iodine-catalysis

This Letter presents a non-conventional synthesis of meso-substituted dipyrromethanes, using molecular iodine as the catalyst. Various aromatic dipyrromethanes were obtained in good yields after a preliminary study using nitrobenzaldehyde. The reactants and reagents were used as such, without prior distillation.     

Highly stereoselective synthesis of para-substituted (E)-N-styrylcarbazoles via sequential silylative coupling-Hiyama coupling reaction

A series of new para-substituted (E)-(N)-styrylcarbazoles, i.e., eight (E)-9-[2-(aryl)ethenyl]-9H-carbazoles (5-12) and 1,4-bis[(E)-2-(9H-carbazol-9-yl)vinyl]benzene (13), have been synthesized in high yield and stereoselectively by a sequential silylative coupling-Hiyama coupling reaction, i.e., coupling of commercially available 9-vinylcarbazole with vinyltriethoxysilane or divinyltetramethyldisiloxane in the presence of [RuHCl(CO)(PCy₃)₂] (I), followed by Pd (II) catalyzed cross-coupling with para-substituted iodobenzenes.The tandem procedure has facilitated the synthesis of 13. X-ray structures of the intermediate silylvinylcarbazole (4), as well as products 12 and 13 have been obtained.     

Synthesis and electrochemical properties of substituted para-benzoquinone derivatives

A facile transformation of pentasubstituted tribromophenol derivatives to the corresponding alkyl-substituted dibromo-p-benzoquinones has been achieved using PbO₂ as oxidizing agent in combination with 60% aq HClO₄ in acetone in 70-72% yields. The electrochemical properties of these quinones were studied by means of cyclic voltammetry and compared with p-benzoquinone (BQ) and 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) recorded under identical experimental conditions.     

Synthesis of lupiwighteone via a para-Claisen-Cope rearrangement

The lanthanide catalysed para-Claisen-Cope rearrangement has been used as the key step in a short synthesis of the prenylated isoflavone, lupiwighteone. The Mitsunobu reaction was employed for the 5-O-prenylation of the acid/base sensitive acetylated isoflavone to afford the allyl aryl ether precursor, which was then rearranged under mild conditions in good yield. Rearrangement of the isoflavone gave the 8-prenylisoflavone as a single product, in good yield.     

Synthesis of N-substituted 2,4-thiazolidinediones from oxazolidinethiones

A novel reaction has been found between oxazolidinethione and bromoacetyl bromide to afford N-substituted 2,4-thiazolidinediones through an intramolecular nucleophilic substitution reaction. Interestingly a step of elimination was carried out in trisubstituted oxazolidinethiones forming a double bond.     

Synthesis and self-assembly properties of para-acyl-calix[8]arenes

The synthesis of a series of novel para-acyl-calix[8]arenes is described, while for acyl chain lengths of greater than eight carbon atoms total substitution at the para position occurs, in contrast to the para-acyl-calix[4]arenes, some esterification at the phenolic face may also occur, particularly for shorter acyl chain lengths. Simple saponification with potassium hydroxide in ethanol allows the pure compounds to be obtained in good yields. All the derivatives show amphiphilic behaviour with formation of stable monolayers at the air-water interface and apparent molecular areas between 150 and 275 Å².     

Synthesis and fluorescence emission of neutral and anionic di- and tetra-carboranyl compounds

A new family of photoluminescent neutral and anionic di-carboranyl and tetra-carboranyl derivatives have been synthesized and characterized. The reaction of α,α'-bis(3,5-bis(bromomethyl)phenoxy-m-xylene with 4 equiv. of the monolithium salt of 1-Ph-1,2-C(2)B(10)H(11) or 1-Me-1,2-C(2)B(10)H(11) gives the neutral tetracarboranyl-functionalized aryl ether derivatives closo-1 and closo-2, respectively. The addition of the monolithium salt of 1-Ph-1,2-closo-C(2)B(10)H(11) to α,α,'-dibromo-m-xylene or 2,6-dibromomethyl-pyridine gives the corresponding di-carboranyl derivatives closo-3 and closo-4. These compounds, which contain four or two closo clusters, were degraded using the classical method, KOH in EtOH, affording the corresponding nido species, which were isolated as potassium or tetramethylammonium salts. All the compounds were characterized by IR, (1)H, (11)B and (13)C NMR spectroscopy, and the crystal structure of closo-3 was analysed by X-ray diffraction. The carboranyl fragments are bonded through CH(2) units to different organic moieties, and their influence on the photoluminescent properties of the final molecules has been studied. All the closo- and nido-carborane derivatives exhibit a blue emission under ultraviolet excitation at room temperature in different solvents. The fluorescence properties of these closo and nido-derivatives depend on the substituent (Ph or Me) bonded to the C(cluster), the solvent polarity, and the organic unit bearing the carborane clusters (benzene or pyridine). In the case of nido-derivatives, an important effect of the cation is also observed.