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Chiral Products (chiral + products)

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Chemistry100%

Selected Abstracts

A Lewis Acid Promoted Asymmetric Umpolung Reaction with ChiralN -Sulfinyl Imines as the Electrophiles

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2005
Xin Xu
Abstract An new asymmetric umpolung reaction has been developed by reacting N -sulfinyl imines with 2-lithio-2-phenyl-1,3-dithiane. The reaction was conducted at between ,20 and,25 °C in THF in the presence of Et2AlCl as the Lewis acid promoter. Excellent diastereoselectivities (up to >95,% de) and chemical yields (64,95,%) have been achieved for nine substrates with all individual isomers separated and characterized. The absolute structure of the chiral products has been unambiguously determined by synthetic conversions to a known sample. 2-Lithio-2-phenyl-1,3-dithiane was found to be much less reactive than its 2-methyl counterpart, which was reported very recently. All individual isomers have been readily separated by column chromatography. The absolute structure of the chiral products has been unambiguously determined by conversion into a known compound. This method provides an easy access to enantiomerically pure ,-amino ketones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Highly Enantioselective Iridium-Catalyzed Hydrogenation of Trisubstituted Olefins, ,,,-Unsaturated Ketones and Imines with Chiral Benzylic Substituted P,N Ligands

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010
Wei-Jing Lu
Abstract The benzylic substituted P,N ligands, diphosphinobenzyloxazolines, showed their high catalytic activity as well as asymmetric induction in the iridium-catalyzed asymmetric hydrogenation of unfunctionalized alkenes, ,,,-unsaturated esters, allyl alcohols, ,,,-unsaturated ketones, and imines, providing the corresponding chiral products in high ee with high conversion. [source]

Autocatalytic Enantiomerisation at the Crystal Surface in Deracemisation of Scalemic Conglomerates

CHEMISTRY - A EUROPEAN JOURNAL, Issue 39 2009
Shengwei Wei Dr.
Abstract Deracemisation of racemic or scalemic conglomerates of intrinsically chiral compounds appears to be a promising method of chiral resolution. By combining the established methods of asymmetric synthesis and the physical process of crystal growth, we were able to achieve a complete deracemisation (with 100,%,ee) of an asymmetric Mannich product conglomerate,vigorously stirred in its saturated solution,from a starting enantiomeric excess value of 15.8,% in the presence of pyrrolidine (8,mol,%) as an achiral catalyst for the CC bond-forming reaction. Strong activation of this deracemisation process was observed on mild isothermal heating to only 40,°C, resulting in dramatic acceleration by a factor of about 20 with respect to the results obtained at room temperature. Despite the fact that the racemisation half-life time of the nearly enantiopure Mannich product (with 99,%,ee) in the homogenous solution at the reaction temperature is eight days, the deracemisation process took only hours in a small-scale experiment. This apparent paradox is explained by a proposed rapid enantiomerisation at the crystal/solution interface, which was corroborated by a 13C labelling experiment that confirmed the involvement of rapid enantiomerisation. Frequent monitoring of the solution-phase ee of the slowly racemising compound further revealed that the minor enantiomer dominated in solution, supporting an explanation based on a kinetic model. A generalisation of the process of "aymmetric autocatalysis" (resulting in automultiplication of chiral products in homogenous media) to encompass heterogeneous systems is also suggested. [source]

TiIV -Catalyzed Asymmetric Sulfenylation of 1,3-Dicarbonyl Compounds

CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2007
Marjan Jereb Dr.
Abstract The electrophilic enantioselective sulfenylation of 1,3-dicarbonyl compounds with phenylsulfenyl chloride is effectively catalyzed by [Ti(TADDOLato)] complexes. The corresponding products are obtained in moderate to high yields. The highest ee values (up to 97,%) are obtained in toluene at room temperature and with a typical catalyst loading of 5,mol,%. Bulky ester groups and sterically undemanding substituents at the ,-position were found to be crucial structural features of the starting materials in order to assure high enantioselectivity. The absolute configuration of one of the chiral products has been determined. The stereochemical course of the reaction is similar to that of analogous [Ti(TADDOLato)]-catalyzed atom-transfer reactions. A common side-reaction the sulfenylated products undergo is a deacylation leading to racemic ,-sulfenylated esters. [source]