Home About us Contact
|
Home About us Contact | ||
|
|
||
Efficient Organocatalysts (efficient + organocatalyst)
Selected AbstractsChemInform Abstract: A Designer Axially Chiral Amino Sulfonamide as an Efficient Organocatalyst for Direct Asymmetric anti-Selective Mannich Reactions and syn-Selective Cross-Aldol Reactions.CHEMINFORM, Issue 46 2009Taichi Kano Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] Water versus Solvent-Free Conditions for the Enantioselective Inter- and Intramolecular Aldol Reaction Employing L -Prolinamides and L -Prolinethioamides as OrganocatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Diana Alma Abstract Organocatalysts 1, derived from L -proline and (1S,2R)- cis -1-aminoindan-2-ol or (R)-1-aminoindane, are evaluated as promoters in the direct asymmetric aldol reaction between ketones and aromatic aldehydes in the presence of water and under solvent-free reaction conditions. L -Prolinethioamides 1c and 1d exhibited higher enantioselectivity than the corresponding prolinamides 1a and 1b in the model aldol reaction between cyclohexanone and 4-nitrobenzaldehyde in the presence of 4-nitrobenzoic acid as cocatalyst. In particular, L -prolinethioamide 1d (5,mol%), derived from L -proline and (R)-1-aminoindane, is shown as the most efficient organocatalyst studied promoting the direct aldol reaction of cycloalkyl, alkyl, and ,-functionalized ketones with aromatic aldehydes in the presence of water and under solvent-free reaction conditions employing only 2 equivalents of nucleophile. Generally, anti -aldol products are obtained in high yields and excellent diastereo- and enantioselectivities (up to >98/2 anti/syn, up to 98% ee). Solvent-free conditions give slightly higher dr and ee than using water as solvent. In addition, organocatalyst 1d can be easily recovered by extractive work-up and reused. Prolinethioamide 1d (5 mol%) in combination with 4-NO2C6H4CO2H (5 mol%) is also a very effective organocatalytic system for the asymmetric solvent-free intramolecular Hajos,Parrish,Eder,Sauer,Wiechert reaction with comparable or higher levels of enantioselectivity (up to 88% ee) to other reported catalysts in organic solvents. [source] Organocatalytic synthesis of cyanohydrin trimethylsilyl ethers by potassium 4-benzylpiperidinedithiocarbamate under solvent-free conditionsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010Mohammad G. Dekamin Abstract Potassium 4-benzylpiperidinedithiocarbamate was found to be an efficient organocatalyst for facile addition of trimethylsilyl cyanide to a wide variety of aldehydes and ketones to afford corresponding cyanohydrin trimethylsilyl ethers in high to quantitative yields. The reaction proceeded smoothly by employing 2.0 mol% PBPDC loading under mild conditions at room temperature within a very short reaction time. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis of Binaphthyl Sulfonimides and Their Application in the Enantioselective Michael Addition of Ketones to NitroalkenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010Shurong Ban Abstract Novel types of L -proline-based binaphthyl sulfonimides and sulfonamides were found to be efficient organocatalysts for the asymmetric Michael addition of ketones to nitroalkenes to provide optically active ,-nitroketone derivatives of synthetic and biological importance. After the fine optimization of solvents, temperature, and additive, good to excellent enantioselectivities and diastereoselectivities (71,96,%,ee, up to >99:1,dr) can be achieved. [source] Highly Enantioselective Conjugate Addition of Ketones to Alkylidene Malonates Catalyzed by a Pyrrolidinyl,Camphor-Derived OrganocatalystEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2010Dhananjay R. Magar Abstract Pyrrolidinyl,camphor derivatives have been proven to be efficient organocatalysts for enantioselective conjugate addition of ketones to alkylidene malonates, affording high chemical yields (up to 95,%) of the corresponding products with high to excellent levels of diastereoselectivity (up to >99:1,dr) and enantioselectivity (up to 96,%,ee) under solvent-free reaction conditions at ambient temperature. [source] Highly Efficient Asymmetric Michael Reaction of Aldehydes to Nitroalkenes with Diphenylperhydroindolinol Silyl Ethers as OrganocatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Ren-Shi Luo Abstract New dihydroindole and perhydroindole derivatives were synthesized in good yields and evaluated as chiral catalysts in the asymmetric Michael reaction of aldehydes to nitroalkenes. (2S,3aS,7aS)-Diphenylperhydroindolinol silyl ether 10 facilitated the reaction of a wide range of aldehyde and nitroalkene substrates, providing Michael adducts in nearly optically pure form (99% ee), good yields and high diastereoselectivities (syn/anti up to 99:1). These results show for the first time that perhydroindole derivatives can also be highly efficient organocatalysts for the asymmetric Michael reaction, exhibiting comparable or even better enantioselectivities than proline derivatives. [source] Highly Enantioselective Transfer Hydrogenation of ,-Imino Esters by a Phosphoric AcidADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2007Qiang Kang Abstract Chiral phosphoric acids have been identified as highly efficient organocatalysts for the asymmetric transfer hydrogenation of ,-imino esters and amide. Utilizing Hantzsch esters as the hydrogen donor, versatile highly enantioenriched ,-amino esters and their derivatives were obtained with up to 98,% ee. [source] | ||||||||||