Search results for "ALK"
showing 10 items of 4314 documents
A theoretical study of the selectivity for the domino [5+2]/[4+2] cycloadditions of γ-pyrones bearing tethered alkenes with substituted 1,3-butadienes
2001
Abstract Selectivity of the domino [5+2]/[4+2] cycloaddition reactions of a β-silyloxy-γ-pyrone bearing a tethered alkene with two substituted 1,3-butadienes have been theoretically studied at the B3LYP/6-31G∗//AM1 and B3LYP/6-31G∗ computational levels. Analysis of these results allow explaining the regio, stereo and chemoselectivity observed experimentally at these domino reactions. Selectivity outcome is reproduced by these calculations.
ChemInform Abstract: A Theoretical Study of the Selectivity for the Domino [5 + 2]/[4 + 2] Cycloadditions of γ-Pyrones Bearing Tethered Alkenes with …
2010
Abstract Selectivity of the domino [5+2]/[4+2] cycloaddition reactions of a β-silyloxy-γ-pyrone bearing a tethered alkene with two substituted 1,3-butadienes have been theoretically studied at the B3LYP/6-31G∗//AM1 and B3LYP/6-31G∗ computational levels. Analysis of these results allow explaining the regio, stereo and chemoselectivity observed experimentally at these domino reactions. Selectivity outcome is reproduced by these calculations.
ChemInform Abstract: Phosphido- and Amidozirconocene Cation-Based Frustrated Lewis Pair Chemistry.
2016
Methyl abstraction from neutral [Cp2ZrMe(ERR′)] complexes 1 (E = N, P; R, R′ = alkyl, aryl) with either B(C6F5)3 or [Ph3C][B(C6F5)4] results in the formation of [Cp2Zr(ERR′)][X] complexes 2 (X– = MeB(C6F5)3–, B(C6F5)4–). The X-ray structure of amido complexes [Cp2Zr(NPh2)][MeB(C6F5)3] (2d) and [Cp2Zr(NtBuAr)][B(C6F5)4] (2e′, Ar = 3,5-C6H3(CH3)2) is reported, showing a sterically dependent Zr/N−π interaction. Complexes 2 catalyze the hydrogenation of electron-rich olefins and alkynes under mild conditions (room temperature, 1.5 bar H2). Complex 2e binds CO2, giving [Cp2Zr(CO2)(NtBuAr)]2[MeB(C6F5)3]2 (3e). Amido complex 2d reacts with benzaldehyde yielding [Cp2Zr(OCH2Ph)((OC)PhNPh2)][MeB(C6F5…
ChemInform Abstract: 1-Alkyl- and Azeto[1,2-a][1,5]benzodiazepine Derivatives in the Reaction of o-Phenylenediamine with 3-(Dimethylamino)propiopheno…
2001
The reaction of o-phenylenediamine (4) with one, two or three equivalents of p-substituted 3-dimethylaminopropiophenone hydrochlorides 5a−e was studied. 4-Aryl-2,3-dihydro-1H-1,5-benzodiazepine derivatives 6a−e were obtained in good yields, along with the 1:2-adducts 7c−e and the unexpected 1:3-adducts rac-8c−e. The type of adduct formed is determined by the molar ratio of the reactants 4 and 5 and by the nature of the substituent in the para position of the propiophenone 5.
Straightforward synthesis of bioconjugatable azo dyes. Part 2: Black Hole Quencher-2 (BHQ-2) and BlackBerry Quencher 650 (BBQ-650) scaffolds
2014
Abstract A further extension of the efficient synthetic methodology described in Part 1, to the aromatic bis-diazo scaffold of Black Hole Quencher-2 dye is presented. Bioconjugatable derivatives bearing either azido, terminal alkyne, or maleimide reactive group were easily obtained as well as the free-phenol form of BlackBerry® Quencher 650 (BBQ-650®) initially developed by Berry & Associates, Inc. Company. The efficient conjugation ability of azido- and maleimide-quenchers was demonstrated through the facile preparation of the first water-soluble and formylated BHQ-2 dyes and a FRET-based probe suitable for the in vitro/in cellulo detection of a cancer-associated protease namely urokinase-…
Nickel‐Catalyzed C(sp2)−C(sp3) Kumada Cross‐Coupling of Aryl Tosylates with Alkyl Grignard Reagents
2019
Aryl tosylates are an attractive class of electrophiles for cross‐coupling reactions due to ease of synthesis, low price, and the employment of C−O electrophiles, however, the reactivity of aryl tosylates is low. Herein, we report the Ni‐catalyzed C(sp2)−C(sp3) Kumada cross‐coupling of aryl tosylates with primary and secondary alkyl Grignard reagents. The method delivers valuable alkyl arenes by cross‐coupling with challenging alkyl organometallics possessing β‐hydrogens that are prone to β‐hydride elimination and homo‐coupling. The reaction is catalyzed by an air‐ and moisture stable‐Ni(II) precatalyst. A broad range of electronically‐varied aryl tosylates, including bis‐tosylates, underwe…
Synthesis of cyanoacetic acid by carbon dioxide and electrogenerated acetonitrile anion in undivided cells equipped with sacrificial anodes
2008
The electrochemical synthesis of cyanoacetic acid was performed by cathodic reduction of tetraalkylammonium salts (R4NX) in acetonitrile in undivided cells equipped with sacrificial anodes with concomitant or subsequent addition of carbon dioxide. These syntheses avoid the use of dangerous reagents, yield cyanoacetic acid in moderate faradic yields and confirm that the cathodic reduction of tetraalkylammonium salts in the presence of acetonitrile leads to the formation of the anion CNCH2-.
Poly(ethylene glycol) diacrylate based monolithic capillary columns for the analysis of polar small solutes by capillary electrochromatography
2018
Monolithic stationary phases based on poly(ethylene glycol) diacrylates for capillary electrochromatography were developed. Several poly(ethylene glycol) diacrylates (Mn 250, 575, and 700) were used as single monomers and the resulting columns were carefully compared. Methanol and ethyl ether were selected as porogenic solvents, and in all cases ultraviolet radiation was selected as initiation method to prepare polymeric monoliths. The influence of the monomer chain length and ratio monomer/porogen on the morphological and electrochromatographic properties of the resulting monoliths was investigated. Several families of compounds with different polarity (alkyl benzenes, organophosphorous pe…
Life-time studies with capillary electrochromatography columns operated under different conditions.
2000
A test system has been established to permit the monitoring of the life-time performance of several reversed- phase capillary electrochromatography (CEC) columns. The retention factors, k(cec), peak symmetry coefficients, lambda(sym), and column efficiencies, N, of three neutral n-alkylbenzene analytes, namely ethyl-, n-butyl- and n-pentylbenzenes, were determined for Hypersil 3 microm n-octylsilica and n-octadecylsilica packed into CEC capillary columns of 100 microm I.D., with a packed length of 250 mm, and a total length of 335 mm. The performances of these CEC capillary columns were examined for a variety of eluents with pH values ranging between pH 2.0 - 8.0, similar to those employed …
Hybrid methacrylate monolithic columns containing magnetic nanoparticles for capillary electrochromatography
2015
Abstract Vinylized iron oxide magnetic nanoparticles (VMNPs) were incorporated into polymethacrylate monolithic columns to develop novel stationary phases with enhanced separation performance. The VMNPs were dispersed in a polymerization mixture containing gycidyl methacrylate and ethylene glycol dimethacrylate as monomers, cyclohexanol and 1-dodecanol as porogens and azobisisobutyronitrile as initiator. The stability of the VMNPs in the polymerization mixture was investigated at several VMNP contents. Using short UV-polymerization times, polymeric beds with homogenously dispersed VMNPs were obtained. The novel stationary phases were characterized by scanning electron microscopy. The chroma…