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21.
A systematic investigation into the Lewis base catalyzed, asymmetric, intramolecular selenoetherification of olefins is described. A critical challenge for the development of this process was the identification and suppression of racemization pathways available to arylseleniranium ion intermediates. This report details a thorough study of the influences of the steric and electronic modulation of the arylselenenyl group on the configurational stability of enantioenriched seleniranium ions. These studies show that the 2-nitrophenyl group attached to the selenium atom significantly attenuates the racemization of seleniranium ions. A variety of achiral Lewis bases catalyze the intramolecular selenoetherification of alkenes using N-(2-nitrophenylselenenyl)succinimide as the electrophile along with a Br?nsted acid. Preliminary mechanistic studies suggest the intermediacy of ionic Lewis base-selenium(II) adducts. Most importantly, a broad survey of chiral Lewis bases revealed that 1,1'-binaphthalene-2,2'-diamine (BINAM)-derived thiophosphoramides catalyze the cyclization of unsaturated alcohols in the presence of N-(2-nitrophenylselenenyl)succinimide and methanesulfonic acid. A variety of cyclic seleno ethers were produced in good chemical yields and in moderate to good enantioselectivities, which constitutes the first catalytic, enantioselective selenofunctionalization of unactivated olefins. 相似文献
22.
We have investigated the effect of nitrogen protecting groups in radical addition trapping experiments leading to beta(2)-amino acids. Of the three N-protecting groups examined, the phthalimido group was optimal with respect to both yields and enantioselectivity. Additionally, radical additions to more complex acrylates were also investigated, which provided access to functionalized beta(2)-amino acids in modest selectivity. 相似文献
23.
Novel red emitting organic luminescent complexes, namely Eu0.5Ln0.5(TTA)3 Phen (Eu: europium, Ln: Y/Tb, Y: yttrium, Tb: terbium, TTA: thenoyl tri fluoro acetone, Phen: phenanthroline) were synthesized by solution technique, maintaining stoichiometric ratio. These complexes were characterized by various techniques such as XRD, optical absorption and photoluminescence (PL) spectra. Electroluminescence cells were designed by sandwiching Eu0.5Ln0.5(TTA)3Phen between indium tin oxide (ITO) and aluminum (Al). Voltage?current characteristics and voltage?brightness characteristics of the developed electroluminescent cell were carried out. Turn on voltage of both the devices was found to be 9 V. These devices emit intense red emission at 611 nm, proving their potential applications as organic light emitting diodes and displays. 相似文献
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Catalytic aminolysis of oxalates by simple and substituted ureas has been shown to give carbamates, oxamates and derivatives of imidazolidine trione. Various substituted ureas and oxalates were screened to verify the applicability of the protocol. The role of dibutyltin oxide as catalyst, effect of solvent and reaction conditions on product distribution pattern has been discussed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
26.
Separation of enzymes by sequential macroaffinity ligand-facilitated three-phase partitioning 总被引:1,自引:0,他引:1
Pectinase and cellulase were separated from a commercial enzyme preparation called Pectinex Ultra SP-L. This was carried out using a process called macroaffinity ligand-facilitated three-phase partitioning (MLFTPP). In this method, a water-soluble polymer is floated as an interfacial precipitate by adding ammonium sulfate and tert.-butanol. The polymer (appropriately chosen) in the presence of an enzyme for which it shows affinity, selectively binds to the enzyme and floats as a polymer-enzyme complex. In the first step, pectinase was purified (with alginate as the polymer) 13-fold with 96% activity recovery. In the second MLFTPP step, using chitosan, cellulase was purified 16-fold with 92% activity recovery. Both preparations showed a single band on sodium dodecylsulfate-polyacrylamide gel electrophoresis. This illustrative example shows that the strategy of sequential MLFTPP can be used to separate important biological activities from a crude broth. 相似文献
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Kalyani D McMurtrey KB Neufeldt SR Sanford MS 《Journal of the American Chemical Society》2011,133(46):18566-18569
This communication describes the development of a room-temperature ligand-directed C-H arylation reaction using aryldiazonium salts. This was achieved by the successful merger of palladium-catalyzed C-H functionalization and visible-light photoredox catalysis. The new method is general for a variety of directing groups and tolerates many common functional groups. 相似文献
29.
Cellulose - In situ modification of bacterial cellulose (BC) allows structural and morphological tuning which determines the crucial properties such as water absorption/retention and rheological... 相似文献
30.
Pramana - This work concerns the modelling of the dynamics of polarisation of a centrosymmetric material subjected to an amplitude-modulated excitation (AME). The dynamic equation obtained for the... 相似文献