Organocatalytic Asymmetric Aldol Reaction Research Articles

Asymmetric organocatalytic direct aldol reactions of cyclohexanone with aldehydes in brine

Organocatalytic asymmetric direct aldol reactions in brine with high diastereo- and enantioselectivities, using a readily available bifunctional amide catalyst, were developed.Key words: aldol reaction, organocatalyst, asymmetric catalysis, water.

Regiospecific Organocatalytic Asymmetric Aldol Reaction of Methyl Ketones and α,β-Unsaturated Trifluoromethyl Ketones

[structure: see text]. The aldol reaction of methyl ketones and alpha,beta-unsaturated trifluoromethyl ketones occurred under mild conditions with the combination of proline-derived N-sulfonylamide and trifluoroacetic acid as the catalyst to give the corresponding unsaturated alpha-trifluoromethyl tertiary alcohols in high yields with good enatioselectivities.

Organocatalytic asymmetric aldol reaction in the presence of water

Water was found to be a suitable solvent for the l-prolinethioamide catalysed aldol reaction of various cyclic ketones with aromatic aldehydes. Treatment of 4-nitrobenzaldehyde with as little as 1.2 equiv. of cyclohexanone in the presence of the protonated catalyst 1-TFA, afforded aldol products in high yields (up to 97%) with high diastereo- and enantioselectivity (up to >5 : 95 dr and 98% ee). The use of a high excess of ketone was avoided by conducting the aldol addition in the presence of water. Furthermore, different 'salting-out' and 'salting-in' salts were investigated and it was proven that the rate of acceleration and the stereochemical outcome of the reaction are affected by hydrophobic aggregation. Scope and limitation studies revealed that electron deficient aldehydes afforded aldol products with high stereoselectivity in the presence of 1-Cl(2)CHCO(2)H. It was shown that various cyclic ketones, under the conditions found, gave aldol products with fair yields, even if they are used in substoichiometric amounts (1.2 to 2.0 equiv.).

Enantioselective Organocatalytic Aldol Reaction of Ynones and Its Synthetic Applications

[Structure: see text] For the first time, unmodified ynones were used in organocatalytic asymmetric aldol reactions delivering monoprotected anti-alpha,beta-dihydroxyynones in high yields, dr's up to 19:1, and ee's up to 95%. These products can be either reduced to afford enantioenriched unsaturated anti,anti-triol or cyclized using a novel intramolecular phosphine-catalyzed alpha-addition to the ynone. This organocatalytic sequential aldol-cyclization process provides a concise entry to unusual enantioenriched oxygenated heterocycles, which can be used for subsequent structural manipulations.

Direct Organocatalytic Asymmetric Aldol Reactions of α‐Amino Aldehydes: Expedient Syntheses of Highly Enantiomerically Enriched anti‐β‐Hydroxy‐α‐amino Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of β‐Hydroxyaldehydes with Stereogenic Quaternary Carbon Centers by Direct Organocatalytic Asymmetric Aldol Reactions.

Synthesis of β‐Hydroxyaldehydes with Stereogenic Quaternary Carbon Centers by Direct Organocatalytic Asymmetric Aldol Reactions.

Synthesis of β‐Hydroxyaldehydes with Stereogenic Quaternary Carbon Centers by Direct Organocatalytic Asymmetric Aldol Reactions

Mit einem Fluoreszenzdetektor wurden Katalysatorsysteme aus chiralen Aminen und Säuren für asymmetrische direkte Aldolreaktionen von α,α-Dialkylaldehyden mit Arylaldehyden identifiziert (siehe Schema). Der optimierte Katalysator lieferte das α,α-Dimethyl-Aldolprodukt aus Isobutyraldehyd und p-Nitrobenzaldehyd mit 92 % Ausbeute und 96 % ee. (R1, R2= Alkyl; X=NO2, CN, Br, Cl, OMe, H)

Synthesis of beta-hydroxyaldehydes with stereogenic quaternary carbon centers by direct organocatalytic asymmetric aldol reactions.

A fluorescence detection system was used to identify effective chiral-amine/acid combinations as bifunctional catalysts for asymmetric direct catalytic aldol reactions of α,α-dialkyl aldehydes with aryl aldehydes (see scheme). With the optimized catalyst system, the reaction of isobutyraldehyde with p-nitrobenzaldehyde provided the α,α-dimethyl aldol product in 92 % yield with 96 % ee. R1, R2=alkyl; X=NO2, CN, Br, Cl, OMe, H. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2004/z53546_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.