1,721,050 research outputs found
Recent Advances in Recoverable Systems for the Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction (CuAAC)
Full text linkThe explosively-growing applications of the Cu-catalyzed Huisgen 1,3-dipolar
cycloaddition reaction between organic azides and alkynes (CuAAC) have stimulated an impressive
number of reports, in the last years, focusing on recoverable variants of the homogeneous or quasihomogeneous
catalysts. Recent advances in the field are reviewed, with particular emphasis on
systems immobilized onto polymeric organic or inorganic supports
Homogeneous and heterogeneous asymmetric transformations in batch and in flow with a focus on 2-oxindole substrates
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Separation of Enantiomers by Inclusion Gas Chromatography: On the Influence of Water in the Molecular Complexation of Methyl 2-Chloropropanoate Enantiomers and the Modified γ-Cyclodextrin Lipodex-E
Full text linkA profound influence of water has previously been detected in the complexation of the enantiomers of methyl 2-chloropropanoate (MCP) and the chiral selector octakis(3-O-butanoyl-2,6-di-O-pentyl)-γ-cyclodextrin (Lipodex-E) in NMR and sensor experiments. We therefore investigated the retention behavior of MCP enantiomers on Lipodex-E by gas chromatography (GC) under hydrous conditions. Addition of water to the N2 carrier gas modestly reduced the retention factors k of the enantiomers, notably for the second eluted enantiomer (S)-MCP. This resulted in an overall decrease of enantioselectivity -ΔS,R(ΔG) in the presence of water. The effect was fully reversible. Consequently, for a conditioned column in the absence of residual water, the determined thermodynamic data, i.e. ΔS,R(ΔH) = -12.64 ± 0.08 kJ mol-1 and ΔS,R(ΔS) = -28.18 ± 0.23 J K-1 mol-1, refer to a true 1:1 complexation process devoid of hydrophobic hydration. Chirality 28:124-131, 2015
Insoluble polystyrene-bound bis(oxazoline): batch and continuous-flow heterogeneous enantioselective glyoxylate–ene reaction
No full textThe use of a new, insoluble polymer-bound bis(oxazoline) ligand (IPB-box) for the copper-catalyzed heterogeneous enantioselective glyoxylate-ene reaction is described. Good activity and ee values in the range 85-95% have been obtained during five to seven recycles, either in batch mode or under flow conditions, demonstrating also the recovery and reuse of the whole catalytically active copper complex
Asymmetric dihydroxylation (AD) with recoverable Cinchona alkaloid derivatives: a warning note and an improved insoluble polymer-bound (IPB) ligands architecture
No full textEnantioselective Synthesis and CD Assignement of Absolute Configuration of (-)-1,3-diphenylpropane-1,3-diol
No full textHighly stereoselective hydrogenation of dibenzoylmethane in the presence of [RuCl2 {(R)-biphemp}] [biphemp = 2,2′-bis(diphenylphosphino)-6,6′-dimethyl-1,1′-biphenyl], in ethanol-dichloromethane, gives enantiomerically pure (−)-1,3-diphenylpropane-1,3-diol (2) (70% yield); analysis of the CD spectra of the corresponding acetonide allows the absolute configuration of the diol to be established as (S,S). The direct HPLC separation of the enantiomers of (2) is also reported
New Polymer-Supported Mono- and Bis-Cinchona Alkaloid Derivatives: Synthesis and Use in Asymmetric Organocatalyzed Reactions
Full text linkThe straightforward synthesis of polystyrene-supported Chinchona alkaloids and their application in the asymmetric dimerization of ketenes is reported. Six different immobilized derivatives, consisting of three dimeric and two monomeric 9-O ethers, were prepared by “click” anchoring of soluble alkaloid precursors on to azidomethyl resins. The resulting insoluble polymer-bound (IPB) organocatalysts were employed for promoting the dimerization of in-situ generated ketenes. After opening of the ketene dimer intermediates with N,O-dimethylhydroxylamine, valuable Weinreb amides were eventually obtained in good yield (up to 81 %) and excellent enantiomeric purity (up to 96 % ee). All of the IPB catalysts could be recycled effectively without significant loss of activity and enantioselectivity. The extension to other asymmetric transformations (meso-anhydride desymmetrization and α-amination of 2-oxindoles) is also briefly discussed
CLICK IN FLOW: IMMOBILIZED Cu NANOPARTICLES FOR HUISGEN AZIDE-ALKYNE CYCLOADDITION
No full textHere we report the use of Cu nanoparticles obtained by metal vapour synthesis (MVS) supported on
commercial 3-aminopropyl functionalized silica (APSiO2) as a novel catalyst for CuAAC reactions under
continuous-flow conditions
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