Home About us Contact
|
Home About us Contact | ||
|
|
||
Aldol Products (aldol + products)
Selected AbstractsSynthesis of Novel Oxime Functionalized Aldol Products via Michael Addition of Oximes onto Baylis,Hillman Adducts.CHEMINFORM, Issue 23 2006Debnath Bhuniya 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, please click on HTML or PDF. [source] A Temporary Stereocentre Approach for the Stereodivergent Synthesis of Either Enantiomer of ,-MethyloctanalEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2007D. Gangani Niyadurupola Abstract The aldol reaction of a chiral N -(acyl)oxazolidin-2-one with 2-methyleneoctanal or (E)-2-methyloct-2-enal affords chiral aldol products whose alkene functionalities were hydrogenated using Brown's or Wilkinson's catalyst to afford syn - or anti -selective products with excellent levels of diastereocontrol. Subsequent retro -aldol cleavage of these syn - or anti -adducts resulted in the formation of either (R)- or (S)-enantiomer of ,-methyloctanal with no racemisation occurring, which could be derivatised in-situ to afford chiral dithiane, alcohol or ,,,-unsaturated ester products in enantiopure form.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Hydrophobically Directed Aldol Reactions: Polystyrene-Supported L -Proline as a Recyclable Catalyst for Direct Asymmetric Aldol Reactions in the Presence of Water,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2007Michelangelo Gruttadauria Abstract A simple synthetic methodology for the preparation of a polystyrene-supported L -proline material is reported, and this material has been used as catalyst in direct asymmetric aldol reactions between several ketones and arylaldehydes to furnish aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water or methanol, at lower levels of conversion in the latter case. This solvent effect, coupled with the observed high stereoselectivities, has been explained in terms of the formation of a hydrophobic core in the inner surface of the resin, whereas the hydrophilic proline moiety lies at the resin/water interface. Such a microenvironment both promotes the aldol reaction and increases the stereoselectivity. Recycling investigations have shown that this material can be reused, without loss in levels of conversion and stereoselectivity, for at least five cycles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Asymmetric Aldol Reaction of Ketones with Alkenyl Trichloroacetates Catalyzed by Dibutyltin Dimethoxide and BINAP,Silver(I) Complex: Construction of a Chiral Tertiary Carbon CenterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Akira Yanagisawa Abstract A novel aldol reaction of alkenyl trichloroacetates with ,-keto esters was realized by using dibutyltin dimethoxide as a catalyst, which was regenerated by the addition of methanol. The reaction was found to be remarkably accelerated by the addition of a catalytic amount of a bidentate phosphine,silver(I) complex. Use of the BINAP,silver triflate (AgOTf) complex as the chiral co-catalyst resulted in the formation of optically active aldol products possessing a chiral tertiary carbon with up to 93% ee. This catalytic method was further applied to the asymmetric reaction of diketene with methyl benzoylformate. [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] New Simple Hydrophobic Proline Derivatives as Highly Active and Stereoselective Catalysts for the Direct Asymmetric Aldol Reaction in Aqueous MediumADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2008Francesco Giacalone Abstract New 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl chains [4-phenylbutanoate and 4-(pyren-1-yl)butanoate] provided better results. The latter catalysts were successfully used in only 2 mol% at room temperature without additives to give aldol products in excellent stereoselectivities. These results demonstrate that derivatization of the proline moiety with the proper simple hydrophobic substituent in the 4-position can furnish highly active and stereoselective catalysts without the need of additional chiral backbones in the molecule. Finally, an explanation of the observed stereoselectivities in the presence of water is provided. [source] Catalytic Asymmetric Aldol Reactions of Enolizable Carbon Pronucleophiles with Formaldehyde and Ethyl GlyoxylateADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007Isao Fukuchi Abstract We herein describe novel catalytic asymmetric aldol reactions of acidic carbon pronucleophiles including ,-keto esters and specific ketones with reactive electrophiles such as formaldehyde and ethyl glyoxylate. In the presence of a catalytic amount of chiral Pd(II)-BINAP complexes, the hydroxymethylation of ,-keto esters with paraformaldehyde or formalin was examined, and the corresponding adducts were obtained in good yields with good to high enantioselectivity (ca. 86,% ee). In some cases, the similar Pt(II) complex also worked well to give the products with better enantioselectivity. Furthermore, these complexes were found to promote the aldol reactions of less acidic ketones, and ethyl glyoxylate underwent reaction with 3-coumaranone and ,-tetralone, affording the aldol products with a significant level of enantioselectivity of up to 83,% ee. [source] A Highly Efficient Asymmetric Organocatalytic Aldol Reaction in a Ball MillCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2007Belén Rodríguez Dr. Abstract Anti -aldol products with up to >99,% enantiomeric excess (ee) have been obtained by proline catalysis in excellent yields under experimentally simple solvent-free conditions. Efficient mixing of all the components is accomplished by applying a mechanochemical technique (ball milling). The catalysis is air and moisture tolerant and can be performed with non-purified starting materials. Even mixtures of solely solid compounds react, giving (mostly solid) products through a partially homogeneous (honey-like) intermediate melt. Since the reactant ratio is almost 1:1 (avoiding the common excess of ketone), the product isolation is easy leading to high aldol product yields. [source] | ||||||||||