- Direct Organocatalytic Asymmetric α-Chlorination of Aldehydes
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The direct organocatalytic enantioselective α-chlorination of aldehydes has been developed. The reaction proceeds for a series of different aldehydes with NCS as the chlorine source using easily available catalysts such as L-proline amide and (2R,5R)-diphenylpyrrolidine. The α-chloro aldehydes are obtained in up to 99% yield and up to 95% ee. The synthetic utility of the enantioselective α-chlorination of aldehydes is demonstrated by transformation of the α-chloro aldehydes to the corresponding α-chloro alcohols (>90% yield) by standard reduction and further transformation to both a terminal epoxide and amino alcohol, both obtained without loss of optical purity. Oxidation of the α-chloro aldehydes followed by esterification gave optically active α-chloro esters without loss of optical purity. It is demonstrated that these optically active α-chloro esters can be converted into nonproteinogenic amino acids in overall high yields, maintaining the enantiomeric excess obtained in the catalytic enantioselective α-chlorination step. Copyright
- Halland, Nis,Braunton, Alan,Bachmann, Stephan,Marigo, Mauro,Jorgensen, Karl Anker
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p. 4790 - 4791
(2007/10/03)
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- Oxidation of olefins by palladium(II): Part 17. An asymmetric chlorohydrin synthesis catalyzed by a bimetallic palladium(II) complex
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Previous studies showed that oxidation of α-olefins with monometallic catalysts containing chiral diphosphines and diamines gave chlorohydrins with poor to good enantioselectivites (28-82% ee). The present studies demonstrate that bimetallic catalysts containing a β-triketone and bridging chiral diphosphine and diamines are excellent catalysts for this reaction giving enantioselectivites considerably higher than the monometallic catalysts. Enantioselectivities were more than 50% for most olefins tested. The highest optical purities were 94% ee for propene and 93% ee for allylphenyl ether. A useful feature of this asymmetric synthesis is the fact it is a net air oxidation.
- El-Qisairi, Arab,Henry, Patrick M.
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- SYNTHESIS OF LIQUID CRYSTALS CONTAINING CHLORINE ON THE CHIRAL CENTER
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A synthetic pathway is described for the preparation of the homologous series of (R)-(2-chloropropyl)-4-benzoates with high optical purity.The liquid crystalline members of the series exhibit smectic A phase and can be used as chiral dopants in ferroelectric mixtures.The n=8 member was used in a mixture exhibiting monotropic and the n=9 member enantiotropic smectic C* phase around room temperature.
- Fodor-Csorba, K.,Vajda, A.,Bata, L.,Holly, S.,Gacs-Baitz, E.,et al.
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- Molecular properties of the WB4101 enantiomers and of its chiral methyl derivatives for α1-adrenoceptor recognition
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The optical isomers of the well known α1-antagonist WB4101 and of its derivatives with a methyl group in the oxyethyl moiety were prepared for the evaluation of their α-adrenoceptors binding affinity. By means of a detailed computational analysis, the present work shows that the introduction of a methyl group affects the behaviour of WB4101 in different ways. A limitation of the conformational freedom in certain regions of the torsional subspace of the potential energy function, differences in the reactivity of the protonated species towards a model proton acceptor and the quality of the superposition with the rigid template for α1 antagonists, corynanthine, are examined and discussed in order to select a candidate bioactive form and possible features which act as modulators of the recognition process at the α1-adrenoceptors.
- Villa,Valoti,Villa,Pallavicini,Ferri,Iuliano,Brunello
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p. 587 - 606
(2007/10/02)
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- Chiral Mesogenic Compounds: Carbocyclic and Heterocyclic Schiff Bases
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Five different chiral p-substituted anilines derived from 4-aminobenzoic acid and from 4-aminophenol were condensed with four carbocyclic and heterocyclic aldehydes in order to obtain chiral Schiff bases resembling DOBAMBC and HOBACPC.With the exception of the pyridine-3-carboxaldehyde derivatives, the compounds are mesomorphic.Some of the compounds exhibit ferroelectric SC* phases, and all exhibit SA or Ch mesophases on heating.Benzaldehyde and pyridine-2-carboxaldehyde derivatives show similar mesomorphic behavior, as was to be expected from MNDO semiempirical calculations.Values of the spontaneous polarization of certain compounds were measured.
- Barbera, J.,Melendez, E.,Serrano, J. L.,Sierra, M. T.,Ezcurra, A.,Jubindo, M. A. Perez
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p. 151 - 158
(2007/10/02)
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- Synthesis of Some Chiral Smectics with Chloroalkoxy Side Chains
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We have synthesized two new series of chiral esters, the (R)-4'-(2-chloropropoxy)phenyl 4-alkoxybenzoates (3) and the (R)-4'-(2-chloropropoxy)phenyl 4-alkoxycinnamates (4).Compounds belonging to the former series mainly exhibit smectic A phases at moderate temperatures (about 50 deg C) while the compounds of the latter series show A phases at somewhat higher temperatures.Some members of both series show, in addition, a cholesteric or a smectic B phase but tilted are not found at all.Keywords: chiral smectics, phenyl benzoates, phenyl cinnamates.
- Alstermark, Christer,Nilsson, Martin,Otterholm, Bengt
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p. 277 - 288
(2007/10/02)
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- New Chiral Polar Smectic C Liquid Crystals
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Applicability of ferroelectric liquid crystals to large screens handling high density information has been demonstrated.High speed and bistable effect are the greater advantages of these materials.The chemical problems to be solved were to synthesize broad-band room temperature substances with high polarisation, negative dielectric anisotropy, large pith and adequate tilt angle.A number of compounds having in their structure the R-(-) 2 chloro propyl group have been synthesized. The smectic stability for these series has been examined.Some compounds exhibit the chiral smectic C phase.All of them can be used as chiral dopants in broad-band room temperatures mixtures.Some examples of these mixtures will be presented.Keywords: liquid crystal, ferroelectric, smectic C, display, material, chiral
- Decobert, Guy,Dubois, Jean-Claude
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p. 199 - 210
(2007/10/02)
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