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Single Isomer (single + isomer)
Selected AbstractsSeparation of propranolol enantiomers by CE using sulfated ,-CD derivatives in aqueous and non-aqueous electrolytes: Comparative CE and NMR study,ELECTROPHORESIS, Issue 9 2010Anne-Catherine Servais Abstract Separations using CE employing non-aqueous BGE are already as well established as separations in aqueous buffers. The separation mechanisms in achiral CE with non-aqueous BGEs are most likely similar to those in aqueous buffers. However, for the separation of enantiomers involving their interaction with chiral buffer additives, the interaction mechanisms might be very different in aqueous and non-aqueous BGEs. While the hypothesis regarding distinct mechanisms of enantiomer separations in aqueous and non-aqueous BGEs has been mentioned in several papers, no direct proof of this hypothesis has been reported to date. In the present study, the enantiomers of propranolol were resolved using CE in aqueous and non-aqueous methanolic BGEs with two single isomer sulfated derivatives of ,-CD, namely heptakis (2,3-diacetyl-6-sulfo)-,-CD and heptakis (2,3-dimethyl-6-sulfo)-,-CD. The enantiomer migration order of propranolol was inverted when an aqueous BGE was replaced with non-aqueous BGE in the case of heptakis (2,3-dimethyl-6-sulfo)-,-CD but remained the same in the case of heptakis (2,3-diacetyl-6-sulfo)-,-CD. The possible molecular mechanisms leading to this reversal of enantiomer migration order were studied by using nuclear overhauser effect spectroscopy in both aqueous and non-aqueous BGEs. [source] Highly Efficient Rhodium Catalysts for the Asymmetric Hydroformylation of Vinyl and Allyl Ethers using C1 -Symmetrical Diphosphite LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Aitor Gual Abstract Here, we describe the successful application of novel glucofuranose-derived 1,3-diphosphites in the rhodium-catalysed asymmetric hydroformylation of vinyl acetate, 2,5-dihydrofuran and 2,3-dihydrofuran. In the hydroformylation of vinyl acetate, total regioselectivity and high ee (up to 73%) were obtained. When 2,3- and 2,5-dihydrofuran were the substrates, total chemo- and regioselectivities were achieved together with ees up to 88%. These results correspond to the highest ee values reported to date in the asymmetric hydroformylation of these substrates. The HP-NMR studies of the [RhH(CO)2(L)] species (L=15 and 17) demonstrated that both ligands coordinate to the Rh centre in an eq-eq fashion. The complex [RhH(CO)2(15)] was detected as a single isomer with characteristic features of eq-eq coordination. However, the broadening of the corresponding signals indicated that this species is rapidly interchanging in solution. In contrast, complex [RhH(CO)2(17)] was detected as a mixture of two conformational isomers at low temperature due to the greater flexibility of the monocyclic backbone of this ligand. [source] Indazaboles,synthesis and molecular structureAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2010Bernd Wrackmeyer Abstract The reaction of 1-trimethylsilyl-indazole with boranes affords indazaboles accompanied by elimination of trimethysilane. Thus, the two isomers of parent indazabole are formed in a 1:1 ratio using borane in THF (BH3/THF), characterized by NMR spectroscopy in solution (1H, 11B and 13C NMR). In contrast, the analogous reaction with 1,2-bis(tetramethylene)diborane(6) proceeds to give a single isomer of the B-alkylated indazabole via symmetric ring cleavage of the diborane(6), as shown by NMR in solution and X-ray structural analysis in the solid state. The molecular structure is fluxional in solution. In the solid state, the central B2N4 ring adopts a distorted boat conformation. Calculated gas phase geometries of the parent indazaboles and of the B-alkylated indazabole were optimized by DFT methods at the B3LYP/6-311 + G(d,p) level of theory. Copyright © 2010 John Wiley & Sons, Ltd. [source] Silver-Catalyzed Incorporation of Carbon Dioxide into Propargylic Alcohols,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2007Wataru Yamada Abstract The combined use of a catalytic amount of silver acetate and a stoichiometric amount of DBU efficiently catalyzed the incorporation of CO2 under mild reaction conditions into a wide range of propargylic alcohols bearing a terminal or an internal triple bond to afford the corresponding cyclic carbonates in high-to-excellent yields. All the cyclic carbonates obtained from the reaction were found to be single isomers. The geometries were determined to be (Z) by X-ray crystal structure analysis and NOE experiments.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] | ||||||||||