Afewerki S.,Mid Sweden University |
Ibrahem I.,Mid Sweden University |
Rydfjord J.,Mid Sweden University |
Breistein P.,Mid Sweden University |
And 2 more authors.
Chemistry - A European Journal | Year: 2012
The first direct intermolecular regiospecific and highly enantioselective α-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd 0 complexes and simple chiral amines as co-catalysts is disclosed. The co-catalytic asymmetric chemoselective and regiospecific α-allylic alkylation reaction is linked in tandem with in situ reduction to give the corresponding 2-alkyl alcohols with high enantiomeric ratios (up to 98:2 e.r.; e.r.=enantiomeric ratio). It is also an expeditious entry to valuable 2-alkyl substituted hemiacetals, 2-alkyl-butane-1,4-diols, and amines. The concise co-catalytic asymmetric total syntheses of biologically active natural products (e.g., Arundic acid) are disclosed. Go organic! Direct intermolecular regiospecific and highly enantioselective α-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd 0 complexes and simple chiral amines as co-catalysts is disclosed (see scheme). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Goncalves S.,French National Center for Scientific Research |
Santoro S.,Arrhenius Laboratory |
Nicolas M.,Pierre Fabre |
Wagner A.,French National Center for Scientific Research |
And 3 more authors.
Journal of Organic Chemistry | Year: 2011
An unprecedented and highly diastereoselective 6-endo-trig cyclization of 2-alkenyl-1,3-dithiolanes has been developed yielding trans-decalins, an important scaffold present in numerous di- and triterpenes. The novelty of this 6-endo-trig cyclization stands in the stepwise mechanism involving 2-alkenyl-1,3-dithiolane, acting as a novel latent initiator. It is suggested that the thioketal opens temporarily under the influence of TMSOTf, triggering the cationic 6-endo-trig cyclization, and closes after C-C bond formation and diastereoselective protonation to terminate the process. DFT calculations confirm this mechanistic proposal and provide a rationale for the observed diastereoselectivity. The reaction tolerates a wide range of functionalities and nucleophilic partners within the substrate. We have also shown that the one-pot 6-endo-trig cyclization followed by in situ 1,3-dithiolane deprotection afford directly the corresponding ketone. This improvement allowed the achievement of the shortest total synthesis of triptophenolide and the shortest formal synthesis of triptolide. © 2011 American Chemical Society.
Eden M.,Arrhenius Laboratory
Journal of Magnetic Resonance | Year: 2010
Three two-dimensional (2D) NMR homonuclear correlation techniques invoking double-quantum (2Q) filtration of the central transitions of half-integer spins are evaluated numerically and experimentally. They correlate directly detected single-quantum (1Q) coherences in the t2 domain with either of 1Q, two-spin 2Q or single-spin multiple-quantum coherence-evolutions in the indirect (t1) dimension. We employ experimental 23Na and 27Al NMR on sodium sulfite and the natural mineral sillimanite (SiAl2 O5), in conjunction with simulated 2D spectra from pairs of dipolar-recoupled spins-3/2 and 5/2 at different external magnetic fields, to compare the correlation strategies from the viewpoints of 2D spectral resolution, signal sensitivity, implementational aspects and their relative merits for establishing internuclear proximities and quadrupolar tensor orientations. © 2010 Elsevier Inc. All rights reserved.
Garcia-Bennett A.E.,Uppsala University |
Xiao C.,Arrhenius Laboratory |
Zhou C.,Nanologica AB |
Castle T.,Arrhenius Laboratory |
And 3 more authors.
Chemistry - A European Journal | Year: 2011
The replication of amphiphilic systems within an inorganic silica matrix allows the study of the fundamental properties of mesostructural changes, that is, kinetic and structural parameters. Herein we report a detailed study of the transition between cubic bicontinuous mesostructure with space groups Ia3̄d and Pn3̄m symmetry, which are associated with the minimal G and D surfaces, respectively. The transition may be induced through micellar swelling of the anionic amphiphilic surfactant N-lauroyl alanine by trimethylbenzene. Rich kinetic behaviour is observed and has been exploited to prepare particles with biphasic structures. Transmission electron microscopy evidence indicates that there is epitaxial growth from one mesostructure to the other involving the  and  orientations of the Ia3̄d and Pn3̄m symmetry structures, respectively. From kinetic studies, we show that the formation of the Ia3̄d mesophase is preceded by a hexagonal phase (plane group p6mm) and an epitaxial relationship has been observed involving the sixfold or 3̄ axis orientations of both structures. Our data suggests that the Pn3̄m mesostructure is kinetically stable at low temperatures whereas the Ia3̄d mesostructure is the more stable structure after prolonged periods of hydrothermal treatment. We present evidence from transmission electron microscopy and small-angle X-ray diffractograms and also electron crystallography modelling of the unit cells at particular points in the structural change. Expect the unexpected! The unexpected happens at the interface. Mesoporous particles with biphasic cubic bicontinuous structures have been prepared through micellar swelling and studied by using electron crystallography and imaging (see figure). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Iftekhar S.,Arrhenius Laboratory |
Grins J.,Arrhenius Laboratory |
Eden M.,Arrhenius Laboratory
Journal of Non-Crystalline Solids | Year: 2010
We report physical properties of density, glass transition temperature, Vickers hardness and refractive index for 15 La-Al-Si-O glasses within the compositional region 10-28 mol% La2O3, 11-30% Al2O3 and 45-78% SiO2. The glass transition temperature varies only slightly between 871 and 883 °C. Both the density (3.25-4.33 g cm-3) and refractive index (1.59-1.70) display similar compositional dependencies and are primarily dictated by the La2O3 content. The hardness (6.4-9.0 GPa) increases with decreasing SiO2 content and to a minor extent also with the amount of La2O3 of the glass. The physical properties, in particular the hardness, are discussed with reference to glass structure. The similarity in the observed properties between the present oxide-based glasses and those of analogous rare-earth (RE) element-containing RE-Si-(Al)-O-N oxynitride glasses is highlighted and discussed in relation to the apparent, but hitherto largely neglected, role of RE-ions to primarily control many enhanced physical properties of oxynitride glasses. © 2010 Elsevier B.V. All rights reserved.