Synthesis and emission spectra of anionic para-substituted polyacrylophenones

Polyacrylophenone (aPAP), poly-4′-ethylacrylophenone (aP4EAP), poly-4′-methoxyacrylophenone (aP4MAP) and poly-4′-phenylacrylophenone (aP4PAP) were prepared by anionic polymerization initiated by lithium tert-butoxide. ¹H NMR analysis revealed higher content of isotactic dyads for aPAP (86%) and aP4MAP (88%) compared with polymers rPAP (60%) and rP4MAP (60%) prepared by radical polymerization. ¹H NMR spectra of a aP4EAP and a P4PAP were too complicated for analysis and ¹³C NMR spectra were not sensitive to stereostructure. The molecular weights of anionic polyacrylophenones were about 5000. In emission spectra, a bathochromic shift was observed in going from model compound to anionic and radical polymer doped in poly(methyl methacrylate) film at 77°K. The emission decay of rP4PAP and aP4PAP is non-exponential in comparison with model 4′-phenyl-3-chloropropiophenone. The bathochromic shift in the emission spectra and the non-exponential emission decay of polymers depends on molecular weight suggesting that the number of structural perturbations (triplet excimers) increases with molecular weight.     

Novel anti-Markovnikov regioselectivity in the Wacker reaction of styrenes

The Wacker reaction is one of the longest known palladium-catalysed organic transformations, and in the vast majority of cases proceeds with Markovnikov regioselectivity. Palladium(II)-mediated oxidation of styrenes was examined and in the absence of reoxidants was found to proceed in an anti-Markovnikov sense, giving aldehydes. Studies on the mechanism of this unusual transformation were carried out, and indicate the possible involvement of a eta(4)-palladium-styrene complex. With a heteropolyacid as the terminal oxidant, oxidation of styrene to give the anti-Markovnikov aldehyde as the major product was found to be catalytic.     

Copper-catalyzed efficient dithiocyanation of styrenes: Synthesis of dithiocyanates

A novel Cu-catalyzed intermolecular chemoselectivity dithiocyanation of styrenes with ammonium thiocyanate has been developed under mild conditions. This reaction exhibits a wide range of functional-group tolerance in styrenes to afford various dithiocyanates. The reaction mechanism was primarily investigated and a radical process was proposed.     

Synthesis of alkenylsilanes via palladium(0)-catalyzed silylation of alkenyl iodides with hydrosilane

Various alkenyl iodides were silylated with hydrosilanes in the presence of KOAc and a catalytic amount of Pd₂(dba)₃·CHCl₃ to afford the corresponding regio- and stereodefined (E)-alkenylsilanes in high yields.     

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.     

Regio- and selective synthesis of 4,6-disubstituted-2-pyridones

Palladium catalysed regio- and stereoselective annulation of allenyl stannanes by β-iodo vinylic amides gives good yields of the corresponding 2-pyridones. This annulation probably occurs via a Stille reaction/cyclisation sequence.     

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.     

A Novel Domino Synthesis of Quinazolinediones by Palladium‐Catalyzed Double Carbonylation

Combining commercially available bromoanilines and bromobenzonitriles in a novel double carbonylation process allows for a straightforward synthesis of isoindolo[1,2‐b]quinazoline‐10,12‐diones. At least five different C?C and/or C?N bonds are selectively formed in this 3‐component reaction, which likely proceeds through sequential carbonylation–cyclization–isomerisation–carbonylation steps. Notably, two molecules of CO are inserted in this highly efficient palladium‐catalyzed process.     

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.     

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.     

Regioselective hydroboration-oxidation and -amination of fluoro-substituted styrenes

Hydroboration of fluorinated styrenes with common hydroborating agents results in polymerization. However, regioselective hydroboration has been achieved by utilizing iodoborane-dimethyl sulfide. A series of fluorinated β-phenethyl alcohols and amines were synthesized via this methodology.     

N-Bromosuccinimide-mediated reaction of cyclic styrenes with chloramine-T

A facile route toward substituted allylic sulfonamides 3 is developed from the N-bromosuccinimide (NBS)-mediated allylic amination of cyclic styrenes 2 with chloramine-T (1a). Skeleton 2 is prepared by Grignard addition of cyclic ketones with different arylmagnesium bromides in THF followed by dehydration of the resulting tertiary alcohols with BF₃·OEt₂ in CH₂Cl₂. The synthetic route obtained moderate yields from the one-step operation and the key structures of skeleton 3 were confirmed by X-ray crystallographic analysis.     

Selective double Suzuki cross-coupling reactions. Synthesis of unsymmetrical diaryl (or heteroaryl) methanes

Using a double Suzuki cross-coupling reaction ortho- or para-bromobenzyl bromides are easily transformed into unsymmetrical diaryl (or heteroaryl) methanes     

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.     

Synergistic copper-TEMPO catalysis of intermolecular vicinal diamination of styrenes

A copper-catalyzed, 2,2,6,6-tetramethyl piperidine N-oxy radical-assisted intermolecular diamination of styrenes with N-fluorobenzenesulfonimide has been developed. The current protocol proved amenable to a diverse array of styrenes via cascade radical addition to readily afford synthetically useful aromatic vicinal diamines with exclusive diastereoselectivity.     

Photoredox-copper catalyzed Meerwein cyanoarylation of styrenes

A new procedure for the cyanoarylation of styrenes with arenediazonium salts and Bu₄NCN employs double catalytic system Eosyn Y/Cu(OAc)₂ under the irradiation with green light (530 nm). In the case of diazonium salts bearing electron withdrawing substituents, the products are formed in 40–65% yields. The relative thiocyanatoarylation proceeds only in the presence of photocatalyst, but the Cu(OAc)₂ additive allows for the product yield improvement     

功能化MCM-41负载双齿氮钯催化剂的制备及其在Suzuki偶联中的应用

首先胺功能化修饰介孔材料MCM-41,再与二-(吡啶-2-基-)甲酮缩合成席夫碱,最后通过Pd(OAc)2配位制备了MCM-41负载双齿氮钯配合物,采用X射线衍射(XRD)以及X射线光电子能谱(XPS)对其结构表征.该负载催化剂在以二甲苯为溶剂,K2CO3为碱以及n-Bu4NF用作添加剂的Suzuki偶联中表现出优越的催化性能.