Density functional study on the effect of substituent group for the monomer of donor‐acceptor copolymer

The effect of the substituent groups (alkyl or aryl) on the structure, electronic, optical properties, ionization potentials (IPs), electron affinities (EAs), and reorganization energy of the donor–acceptor monomers 5,8‐di‐2‐thienyl‐quinoxaline (T[Q]T), 4,9‐di‐2‐thienylpyrazine[2,3‐g]quinoxaline (T[PQ]T) were studied theoretically. The lowest‐lying absorption in assigned to π→π* transition, and the fluorescence can be described as originating from the ¹[ππ*] excited state. The lowest‐lying absorption and emission spectrum of T[Q]T and T[PQ]T with alkyl groups exhibit blue‐shifted, while T[Q]T and T[PQ]T with aryl groups exhibit the opposite result. The extra absorption bond at 400 nm of T[Q]T‐Bph is contributed by the π‐π* transitions between the biphenyl and acceptor fragment. Orbital compositions transfer coefficient (χ) of the donor in LUMOs is reduced with the aryl groups on the acceptor, which illuminates that the aryl contributes to intramolecular charge transfer, and the result is in accord with the analysis of reorganization energy. IPs is brought down by both of the alkyl and aryl groups, but EAs is raised only by aryl, therefore, aryl is conductive to forming excitons for D‐A‐D molecule. Consequently, T[Q]T and T[PQ]T with aryl groups are more reasonable monomers of donor–acceptor copolymers as a solar cell materials comparing with the alkyl‐introduced ones. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Direct atom-efficient esterification between carboxylic acids and alcohols catalyzed by amphoteric, water-tolerant TiO(acac)2

A diverse array of oxometallic species were examined as catalysts for a test direct condensation of benzoic acid and 2-phenylethanol in 1:1 stoichiometry. Besides group IVB MOCl2-xH2O and TiOX2-xH2O, group VB VOCl2-xTHF and group IVB TiO(acac)2 were found to be the most efficient and water-tolerant catalysts for the test reaction. The new neutral catalytic protocol with the optimal TiO(acac)2 tolerates many stereo/electronic structural variations in both (di)acid (1 degree -3 degrees alkyl and aryl) and (di)alcohol (1 degree, 2 degrees alkyl, and aryl) components with high chemoselectivity.     

Facile photochemical transformation of alkyl aryl selenides to the corresponding carbonyl compounds by molecular oxygen: use of selenides as masked carbonyl groups

Alkyl aryl selenides with and without functional groups on the alkyl group were transformed efficiently into the corresponding carbonyl compounds, particularly primary alkyl aryl selenides in good yields, by a simple photolysis in the presence of air or oxygen. This transformation can be conducted without protection of functional groups. The yield of carbonyl compounds was much affected by the solvent viscosity, reaction temperature, concentration of dissolved oxygen in the solvents, wavelength of light, and structure of the aryl substituents. The present study indicates that aryl selenides can be considered as a masked carbonyl group that can be easily converted to a carbonyl group by very mild reaction conditions even in the presence of various unprotected functional groups. Therefore, this functional group transformation can be used as an important tool in organic synthesis due to its simplicity and mild reaction condition.     

Scope and Limitations of the s-Block Metal-Mediated Pudovik Reaction

The hydrophosphorylation of phenylacetylene with di(aryl)phosphane oxides Ar₂P(O)H (Pudovik reaction) yields E/Z-isomer mixtures of phenylethenyl-di(aryl)phosphane oxides ( 1 ). Alkali and alkaline-earth metal di(aryl)phosphinites have been studied as catalysts for this reaction with increasing activity for the heavier s-block metals. The Pudovik reaction can only be mediated for di(aryl)phosphane oxides whereas P-bound alkyl and alcoholate substituents impede the P−H addition across alkynes. The demanding mesityl group favors the single-hydrophosphorylated products 1-Ar whereas smaller aryl substituents lead to the double-hydrophosphorylated products 2-Ar . Polar solvents are beneficial for an effective addition. Increasing concentration of the reactants and the catalyst accelerates the Pudovik reaction. Whereas Mes₂P(O)H does not form the bis-phosphorylated product 2-Mes , activation of an ortho-methyl group and cyclization occurs yielding 2-benzyl-1-mesityl-5,7-dimethyl-2,3-dihydrophosphindole 1-oxide ( 3 ).     

Mechanistic study of thermal behavior and combustion performance of epoxy resins: I homopolymerized TGDDM

Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior.     

Trapping silicon surface-based radicals

The spontaneous one-electron reduction of diazonium salts on hydride-terminated porous silicon (pSi) and flat silicon produces surface radicals that can be trapped chemically. These silicon radicals react with reagents such as alkyl/arylselenoethers, alkenes, alkynes, and alkylbromide groups to generate covalently bound functionalities in a manner analogous to the chemistry of molecular-based silicon radical species, prepared via different methods. When pSi is exposed to an acetonitrile solution of any of the three diazonium salts examined in this study, aryl groups from the diazonium precursor become covalently bound and significant oxidation is noted; if, however, a reactive trapping agent is added, such as an alkyl/arylselenoether or a carbon-carbon unsaturated bond, no aryl group attachment is observed and oxidation is circumvented due to the efficiency of the trapping chemistry. The reactions proceed rapidly, in less than 3 h to maximum coverage, at room temperature. The diazonium salt-initiated radical reaction with alpha,omega-alkenes and alkynes tolerates various functional groups including aryl, diene, diyne, carboxylic acid, and hydroxyl, reacting exclusively via the carbon-carbon unsaturated bond; alpha,omega-bromoalkenes are not, however, compatible with this chemistry. A silicon-based molecule, tris(trimethylsilyl)silane, in the presence of a diazonium salt initiator and a primary alkyne does not lead to the hydrosilylation product but to tris(trimethylsilyl)silylbromide and the hydrogenated arene, derived from the diazonium. The difference in reactivity between the molecule and the surface is due to the fact that the silicon surface is a source of electrons to reduce the diazonium salts to aryl radicals, whereas a heterolytic pathway is followed in the molecular silane case.     

Dendrimers as photochemical reaction media. Photochemical behavior of unimolecular and bimolecular reactions in water-soluble dendrimers

Synthesis and studies of poly(alkyl aryl ether) dendrimers, possessing carboxylic acid functionalities at their peripheries, are reported. 5-Bromopentyloxy methylisophthalate was utilized as the monomer to O-alkylate the phenolic hydroxyl groups of poly(alkyl aryl ether) dendrimers. Dendrimers of first, second, and third generations, possessing 6, 12, and 24 carboxylic acids, respectively, were thus prepared. These dendrimers were soluble in alkaline aqueous solutions, and the ensuing microenvironmental properties of the aqueous solutions were assessed by pyrene solubilization studies. Upon establishing the presence of nonpolar microenvironments within the dendritic structures, solubilizations of few organic substrates were conducted and their photochemical behaviors were assessed. Specifically, the photolysis of 1-phenyl-3-p-tolyl-propan-2-one and benzoin ethyl ether and photodimerization of acenaphthylene were conducted. These studies revealed that the product distribution and the "cage effect" were more distinct and efficient for the third generation dendrimer, than for the first and second generation dendrimers. The photochemical studies of carboxylic acid functionalized dendrimers were compared to that of hydroxyl group terminated poly(alkyl aryl ether) dendrimers.     

Colloidal systems containing free radical‐forming particles and composites on their basis

Controlled surface activity and reactivity of new carbon‐chain functional surface‐active oligoperoxides (FSAP) and derived metal complexes (OMC) with side and end di‐tertiary and tert‐alkyl (aryl) peroxidic, respectively, and other active functional groups cause the possibility of their tailored utilization as emulsifiers, surface‐active initiators and modifiers of the phase boundaries of liquid, solid and mixed phases in different colloidal systems in a wide temperature range. New materials can be developed such as water and hydrocarbon polymer dispersions, artificial water dispersions of unsaturated polyesters and alkyd resins, polymer/polymeric blends, active glass and carbon fibers, dispersed fillers, reinfourced and filled polymer composites with the definite special properties. Methods for the obtaining and the application of these materials are described.     

Synthesis of 4,4‐Disubstituted‐4H‐benzo[d][1,3]oxathiin‐2‐ones,a New Class of Compounds

4,4‐Dialkyl and 4,4‐diaryl‐4H‐benzo[d][1,3]oxathiin‐2‐ones were synthesized by the reaction of 2‐(mercapto‐phenyl)‐dialkyl‐ (or diaryl)‐methanol with CDI in excellent yield. The 2‐(mercaptophenyl)‐dialkyl‐ (or diaryl)‐methanols were prepared by the reaction of commercially available methylthiosalicylate with an appropriate alkyl or aryl Grignard reagent.     

Enantioselective synthesis of aminobenzazepinones

Enantioselective synthesis of constrained trans-aminobenzazepinone utilizing palladium-mediated Jeffery-Heck reaction and rhodium(II) catalyzed asymmetric hydrogenation as key steps are described. Diverse functional groups such as alkyl, aryl, basic or amino acid moieties were introduced with minimal racemization.     

Palladium-catalyzed alkylation-hydride reduction sequence: synthesis of meta-substituted arenes

A new three-component, palladium-catalyzed domino reaction which gives access to meta-substituted arenes using aryl iodides and primary alkyl halides is reported. Various functional groups are tolerated on both the aryl iodide and alkyl halide. In addition, isotopic labeling studies provide insight into the mechanism of this Catellani-type reaction. [reaction: see text]     

First synthesis of cyclic organogermanium peroxides, 1,2,4,5,7,8-hexaoxa-3-germonanes

First, previously unknown, cyclic organogermanium peroxides, 1,2,4,5,7,8-hexaoxa-3-germonanes, were synthesized by the reaction of 1,1′-dihydroperoxydi(cyclododecyl)peroxide with (di)alkyl(aryl)dihalogengermanes. The new compounds have a higher tendency to undergo hydrolysis compared to silicon-containing analogs.     

A rapid and efficient method for the reduction of quinoxalines

Mono and di‐substituted alkyl and aryl quinoxalines are rapidly reduced in high yield to their respective 1,2,3,4‐tetrahydro‐derivatives by borane in THF solution. In the case of the 2,3‐di‐substituted compounds, reduction is stereoselective yielding exclusively the cis‐isomers. Sodium borohydride in acetic acid also reduces alkyl and aryl quinoxalines, but proceeds with lower yields and often produces side products. Sodium borohydride in ethanol reduces quinoxaline and 2‐methylquinoxaline in high yield; however, the reaction is very slow, whereas 2,3‐dialkyl and 2‐aryl quinoxalines are not efficiently reduced by sodium borohydride in ethanol.     

Cesium carbonate‐catalyzed indium insertion into alkyl iodides and their synthetic utilities in cross‐coupling reactions

A catalytic amount of cesium carbonate (10 mol%) was found to be capable of effectively catalyzing the insertion of indium powder into alkyl iodides. The thus‐generated alkyl indium reagents could readily undergo palladium‐catalyzed cross‐coupling reactions with a wide variety of aryl halides, showing compatibility to a range of important functional groups.     

Catalytic Hydroalkylation of Allenes

We have developed a catalytic method for the hydroalkylation of allenes using alkyl triflates as electrophiles and silane as a hydride source. The reaction has an excellent substrate scope and is compatible with a wide range of functional groups, including esters, aryl halides, aryl boronic esters, sulfonamides, alkyl tosylates, and alkyl bromides. We found evidence for a reaction mechanism that involves unusual dinuclear copper ally complexes as catalytic intermediates. The unusual structure of these complexes provides a rationale for their unexpected reactivity.     

Synthesis of some derivatives of 2-benzimidazolemethanethiol

Summary Ten new S-derivatives of 2-benzimidazolemethanethiol were synthesized by the reaction of the sodium or potassium salt of 2-benzimidazolemethanethiol with alkyl or aryl halides containing, in some cases, functional groups.     

结肠位点药物传载凝胶的溶胀动力学研究

合成了带不同疏水侧基的甲基丙烯酸酯、甲基丙烯酰胺及丙烯酸与 4,4′ 二 (甲基丙烯酰胺基 )偶氮苯交联共聚的凝胶 .主要研究了这类凝胶在pH =2 .2至pH =7.4的缓冲溶液的溶胀特性 .其溶胀过程遵循二级溶胀动力学 ,影响这类凝胶溶胀行为的因素包括交联程度、疏水基链的长度、pH值等 .通过调节这些因素是完全可以控制凝胶在小肠内的溶胀程度 ,进而避免凝胶内部的药物被提前释放     

Abstraction of iodine from aromatic iodides by alkyl radicals: steric and electronic effects

Abstraction of the iodine atom from aryl iodides by alkyl radicals takes place in some cases very efficiently despite the unfavorable difference in bond dissociation energies of C-I bonds in alkyl and aryl iodides. The abstraction is most efficient in iodobenzenes, ortho-substituted with bulky groups. The ease of abstraction can be explained by the release of steric strain during the elimination of the iodine atom. The rate of abstraction correlates fairly well with the strain energy, calculated by density functional theory (DFT) and Hartree-Fock (HF) methods as a difference in the total energy of ortho and para isomers. However, besides the steric bulk, the presence of some other functional groups in an ortho substituent also influences the rate. The stabilization of the transition state, resembling a 9-I-2 iodanyl radical, by electron-withdrawing groups seems to explain a positive sign of the Hammett rho value in the radical abstraction of halogen atoms.     

Solvent‐free synthesis of new 2,4,6‐triarylpyridines catalyzed by a Brønsted acidic ionic liquid as a green and reusable catalyst

Some new 4‐(aryl)‐2,6‐di‐2‐naphthylpyridines and 4‐(aryl)‐2,6‐di‐2‐thienylpyridines have been prepared through three‐component condensation of 2‐acetylnaphthalene or 2‐acetylthiophene, aromatic aldehydes, and ammonium acetate in presence of 1‐(4‐sulfonylbutyl) pyridinium hydrogensulfate [(CH₂)₄SO₃HPy][HSO₄], a Brønsted acidic ionic liquid as a green and reusable catalyst in solvent‐free conditions. Also some new 4,4'‐(1,4‐phenylene)‐bis‐(2,6‐di‐aryl pyridine) was prepared. J. Heterocyclic Chem., (2011).     

Reactions of 1,2-dialkyl-3-pyrazolidinones

The condensation of 1,2-dialkyl-3-pyrazoIidinones (1) with a series of aldehydes, ketones and esters in the presence of sodium hydride is described. Alkylation of I with several alkyl bromides gave 4-alkyl substitution products in modest yield and reaction of 1,2,4-trimethyl-3-pyrazolidinone with n-butyl bromide gave a 4,4-dialkylation product. Compound 1 reacted with aryl Grignard reagents to form 3-aryl-3-pyrazoIines whereas the corresponding products were not realized in the case of alkyl Grignards. The reduction of a single example of 1 as well as the reduction of two 3-pyrazolines to pyrazolidines is also reported.