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Sulfur Ylides (sulfur + ylide)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

ChemInform Abstract: A Highly Efficient Methodology of Asymmetric Epoxidation Based on a Novel Chiral Sulfur Ylide.

CHEMINFORM, Issue 7 2010
Francisco Sarabia
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Reactivity parameters for rationalizing iminium-catalyzed reactions,

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010
Sami Lakhdar
Abstract The correlation equation (1), lg k(20,°C),=,s(E,+,N), where electrophiles are characterized by one (E) and nucleophiles are characterized by two parameters (N, s) was used to rationalize the scope of iminium-catalyzed reactions. Kinetics of the reactions of iminium triflates, pregenerated from cinnamaldehyde and secondary amines, with cyclic ketene acetals were studied by UV,Vis spectroscopy. From the second-order rate constants, electrophilicity parameters ,10,<,E,<,,7 have been derived for these iminium ions. Eqn (1) was found to correctly predict the rate constants for the reactions of the cinnamaldehyde-derived iminium ions with pyrroles, indoles, and sulfur ylides. The zwitterion obtained from cinnamaldehyde and indoline-2-carboxylic acid reacts more than 105 times faster with a sulfur ylide than predicted by Eqn (1), which is explained by MacMillan's ,electrostatic activation'. The failure of imidazolidinones to catalyze cyclopropanations of ,,,-unsaturated carbonyl compounds by sulfur ylides is not due to the low nucleophilic reactivity of sulfur ylides but due to their high Brønsted basicity which inhibits the formation of the iminium ions. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Computational Investigations on the General Reaction Profile and Diastereoselectivity in Sulfur Ylide Promoted Aziridination

CHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2007
Deepa Janardanan
Abstract Mechanism and diastereoselectivity of sulfur ylide promoted aziridination reactions were studied by density functional theory with inclusion of solvent effects through the continuum solvation model. The general reaction pathway was modeled for the addition of substituted sulfur ylides (Me2S+CH,R) to an aldimine ((E)-methyl ethylidenecarbamate, MeHCNCO2Me). The nature of the substituents on the ylidic carbon atom substantially affects the reaction profile. The stabilized (R=COMe) and semistabilized (R=Ph) ylides follow a cisoid addition mode leading to trans aziridines via anti betaine intermediates. The simplest model ylide (unstabilized, R=H) underwent cisoid addition in a similar fashion. In the case of stabilized ylides product diastereoselectivity is controlled by the barriers of the elimination step leading to the 2,3- trans aziridine, whereas it is decided in the addition step in the case of semistabilized ylides. The importance of steric and electronic factors in diastereoselective addition (2 and 5) and elimination (5) transition states was established. Comparison of results obtained with the gas-phase optimized geometries and with the fully optimized solvent-phase geometries reveals that the inclusion of solvent effects does not bring about any dramatic changes in the reaction profiles for all three kinds of ylides. In particular, diastereoselectivity for both kinds of ylides was found to be nearly the same in both these approaches. [source]

Asymmetric Cyclopropanation of Optically Active (1-Diethoxyphosphoryl)vinyl p -Tolyl Sulfoxide with Sulfur Ylides: A Rationale for Diastereoselectivity

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2005
Wanda H. Midura
Abstract The title sulfoxide (S)-(+)- 1a was found to react with sulfur ylides affording the corresponding cyclopropanes in high yields. With fully deuterated dimethyl(oxo)sulfonium methylide, (CD3)2S(O)CD2, the cyclopropanation reaction occurred in a highly diastereoselective manner producing the cyclopropane 4a - d2 as a major diastereomer in which the newly formed quaternary ,-carbon atom is chiral due to isotopic substitution (CH2 vs. CD2). The diastereomer 4b - d2, having the opposite configuration at the ,-carbon atom, was obtained starting form the 2,2-dideuterio substituted vinyl sulfoxide, (S)-(+)- 1a - d2, and the nondeuterated ylide. The diastereomeric ratio in both reactions was found to be ca. 10:1. The reaction of (S)-(+)- 1a with diphenylsulfonium isopropylide yielded the cyclopropane (+)- 7 as a single diastereomer. X-ray structural studies of the crystalline 1-phosphorylvinyl sulfoxide 9 as well as density functional calculations (B3LYP/6-31G*) on (1-phosphoryl)vinyl sulfoxides revealed the origin of the experimentally observed diastereoselectivities and allowed us to propose a transition state model for the cyclopropanation reaction of chiral 1-phosphorylvinyl sulfoxides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Indolizines, triazolo[4,3- a]pyridines, benzimidazo[1,2- d]oxadiazoles, and pyrazolo[1,5- c]triazoles via nitrogen and sulfur ylides

HETEROATOM CHEMISTRY, Issue 6 2004
Kamal M. Dawood
The pyridinium salts 2a,b reacted with dimethyl acetylenedicarboxylate (DMAD) to give the indolizine derivatives 6a,b. Pyridinium salts 2a,b also reacted with pyrazole-5-diazonium salt to afford the hydrazonoyl bromides 8a,b, which on treatment with aqueous ethanolic sodium carbonate furnished the 8aH -1,2,4-triazolo[4,3- a]pyridine 10. When sulfonium bromide 11 was treated with nitrous acid and with pyrazole-5-diazonium salt, it afforded the new hydroximoyl and hydrazonoyl halides 12 and 17, respectively. Compound 12 reacted with 2-methylthiobenzimidazole to furnish benzimidazo[1,2- d]-1,2,4-oxadiazole derivative 14. Treatment of either 12 with 3-phenyl-5-aminopyrazole or 17 with triethylamine resulted in the formation of the same product: pyrazolo[1,5- c]-1,2,4-triazole derivative 16. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:432,436, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20037 [source]

Reactivity parameters for rationalizing iminium-catalyzed reactions,

Concise Asymmetric Synthesis of Fully Substituted Isoxazoline- N -Oxide through Lewis Base Catalyzed Nitroalkene Activation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2010
Cheng Zhong Dr.
Transforming isoxazoline- N -oxides: A concise asymmetric synthesis of isoxazoline- N -oxides is reported through secondary amine Lewis base catalyzed nitroalkene activation and sequential intermolecular condensation with aldehydes and ylides. Application of camphor-derived chiral sulfur ylides gave the enantiomeric-enriched isoxazoline- N -oxides in excellent yields and stereoselectivity. Simple transformations of isoxazoline- N -oxide led to the gram-scale synthesis of a (,)-clausenamide analogue in four steps, with excellent stereochemistry control (see scheme). [source]