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One Diastereomer (one + diastereomer)

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Chemistry100%

Selected Abstracts

Cationic Iridium Complexes with Chiral Dithioether Ligands: Synthesis, Characterisation and Reactivity under Hydrogenation Conditions

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005
Leticia Flores-Santos
Abstract A series of cationic IrI complexes containing chiral dithioether ligands have been prepared in order to study the influence of the sulfur substituents and the metallacycle size on the acetamidoacrylate hydrogenation reaction. In the case of complexes 6, 7 and 10, a mixture of diastereomers is observed in solution due to the sulfur inversion processes. In contrast, this fluxional behaviour is efficiently controlled by using bicyclic ligands which inhibit the S-inversion in complexes 8 and 9. The solid-state structure of complex 10b shows only one diastereomer with the sulfur substituents in a relative anti disposition and in an overall configuration of SCSCSSSS at the coordinated dithioether ligand. Iridium complexes containing seven- and six-membered metallacycles (6b,d, 7b,c, 10a,b) react with the substrate through S-ligand substitution, and the rate of this substitution is related to the position of the fluorine atom on the aromatic ring. On the contrary, complexes containing a bismetallacycle (8 and 9) are not displaced by the substrate. The catalytic hydrogenation activity of complexes 8 and 9 is analysed in terms of the high stability of the corresponding dihydride complexes (13 and 14). In both cases, only two of the four possible diastereomeric dihydride species are formed in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Complete Chiral Induction from Enantiopure 1,2-Diamines to Benzophenone-Based Achiral Bisphosphane Ligands in Noyori-Type RuII Catalysts

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2006
Qing Jing
Abstract We report the design and synthesis of a novel class of RuII catalysts (3) composed of achiral benzophenone-based bisphosphane ligands and enantiopure 1,2-diamines for the asymmetric hydrogenation of aryl ketones. The developed catalysts show excellent enantioselectivities (up to 97,% ee) and activities (up to S/C = 10,000) in the hydrogenation of a variety of aromatic ketones.Complete chiral induction from the enantiopure 1,2-diamine to the achiral bisphosphane ligand was observed. The coordination of the C=O moiety in 3 to the cationic RuII center is considered to be of key importance in providing a higher thermodynamic and kinetic rotation barrier for the flexible bisphosphane ligand, resulting in the preferential formation of only one diastereomer, and thus explaining the high enantioselectivity of the catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

New P-ligands: The aromaticity and reactivity of 2,4,6-trialkylphenylphospholes

HETEROATOM CHEMISTRY, Issue 2 2005
György Keglevich
A further member of 2,4,6-trialkyl-phenyl-phos-pholes, the ditertbutylmethylphenyl derivative (1c) was characterized by Bird index and by the sum of angles at the phosphorus atom to describe the flattening of the P-pyramid. Both numbers suggested a slight aromaticity. The reaction of arylphospholes with phosphorus tribromide was extended to phosphole 1c leading this occasion, after further steps, to the mixture of 3- and 2-substituted products (3c-1 and 3c-2, respectively). A triisopropylphenyl-2H -phosphole (4) formed by sigmatropic rearrangement was utilized in the preparation of new 1-phosphanorbornene derivatives, such as sulfide 6 and hemi-oxides 8-1 and 8-2. Further oxidation of the latter species (8-1 and 8-2) led to the decomposition of the dimeric structure (11). 4 could also be trapped by benzaldehyde to afford the oxaphosphanorbornene (10) as one diastereomer. Finally, the reversible formation of 2H -phosphole 4 from 1H -phosphole 1a at 150°C was proved. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:104,222, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20077 [source]

Addition, elimination, exchange, and epimerization in nitro sulfones

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2007
Charles A. Kingsbury
Abstract Three reactions were studied in the diastereomers of 1-(benzenesulfonyl)-2-nitro-1-phenylpropane (1A and 1B) and briefly in related compounds: elimination of the benzenesulfonyl group, epimerization of one diastereomer to the other, and deuterium/hydrogen exchange at the methine group next to nitro in starting material. The two diastereomers showed quite different reactivity. The high melting diasteromer showed rapid elimination and some exchange. The low melting diastereomer (at approximately a half-life) showed extensive epimerization, and elimination to the alkene, but little exchange. There is little effect of aromatic substituents on reaction course. The situation is complicated by re-addition of benzenesulfinate to the alkene. The addition reaction was similar to elimination in agreement with the Principle of Microscopic Reversibility expectations. An electron transfer mechanism for addition is calculated to be comparatively favorable. Copyright © 2007 John Wiley & Sons, Ltd. [source]