Search results for "aldol"

Hydrophobically Directed Aldol Reactions: Polystyrene-SupportedL-Proline as a Recyclable Catalyst for Direct Asymmetric Aldol Reactions in the Presen…

2007

The cover picture shows the aldol reaction between ketones and arylaldehydes carried out by using a polystyrene-supported L-proline catalyst. This material furnishes aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water. This solvent effect, coupled with the high stereoselectivities observed, has been explained by the formation of a hydrophobic core in the inner surface of the resin with the hydrophilic proline moiety in the resin/water interface. Such a microenvironment promotes the aldol reaction and increases the stereoselectivity. Recycling investigations have shown that this material can be reus…

Zur frage: Psoriasis vulgaris und Leber

1964

Der wiederholt geauserten Meinung einer Krankheitskorrelation zwischen Psoriasis vulgaris und Leber wird durch Bestimmung fur die Leberdiagnostik besonders geeigneter Enzyme (Glutaminsaure-Oxalessigsaure-Transaminase, Glutaminsaure-Brenztraubensaure-Transaminase, Aldolase) und des Zweifarbstofftests sowie wiederholt auch des Serumgesamtbilirubins nachgegangen. In der uberwiegenden Zahl der Psoriasis vulgaris-Kranken konnten normale Befunde erhoben werden. Von 14 Psoriatikern mit vorwiegend nur gering von der Norm abweichenden Befunden konnte anamnestisch und klinisch zumeist die Ursache fur die pathologischen Serum veranderungen ermittelt werden, ohne das sich jedoch hieraus der Nachweis fu…

Stereoselective synthesis of oligosaccharides by de novo saccharide welding

2012

Asymmetric Synthesis of Functionalized Tricyclic Chromanes via an Organocatalytic Triple Domino Reaction

2017

A highly stereoselective triple domino reaction for the synthesis of functionalized tricyclic chromane scaffolds has been developed. A secondary amine-catalyzed domino Michael/Michael/aldol condensation reaction between aliphatic aldehydes, nitro-chromenes, and α,β-unsaturated aldehydes leads to the formation of synthetically important tricyclic chromanes bearing four contiguous stereogenic centers including a tetrasubstituted carbon in good yields (20–66%) and excellent stereoselectivities (>20:1 dr and >99% ee).

ChemInform Abstract: Stereoselective Synthesis of syn-α-Methyl-β-hydroxy Esters.

2000

Abstract Boron enolates of an ethyl ketone structurally related to erythrulose react with achiral aldehydes in a highly stereoselective fashion to yield 1,2- syn /1,3- syn stereoisomers. Oxidative cleavage of the aldol adducts yields enantiopure O -formylated syn -α-methyl-β-hydroxy esters, easily cleaved to the corresponding hydroxyl-free compounds. The aforementioned ketone behaves therefore as a chiral propionate enolate equivalent.

ChemInform Abstract: The Construction of Quaternary Stereocenters by the Henry Reaction: Circumventing the Usual Reactivity of Substituted Glyoxals.

2011

The enantioselective Henry reaction between alkyl- and arylglyoxal hydrates and nitromethane catalyzed by Cu(II)-iminopyridine complexes takes place regioselectively on the ketone carbonyl group to give chiral tertiary nitroaldols with high functional group density and enantiomeric excesses of up to 96 %. Both aromatic and aliphatic glyoxals are suitable substrates for this reaction.

Stereoselective Synthesis of the Glycosidase Inhibitor Australine through a One-Pot, Double-Cyclization Strategy

2006

[reaction: see text] A stereocontrolled, convergent synthesis of the alkaloid australine, a glycosidase inhibitor of the pyrrolizidine class, is described. The chiral starting materials were ketone 3, derived from L-erythrulose, and alpha-alkoxy aldehyde 4, prepared from L-malic acid. A key step of the synthesis was the highly stereoselective aldol reaction between 4 and a Z boron enolate derived from 3. Another key step was the one-pot construction of the bicyclic pyrrolizidine system by means of a three-step sequence of SN2 displacements induced by benzylamine on a trimesylate precursor.

ChemInform Abstract: Facile Synthesis of 2-Nitroalkanols by Tetramethylguanidine (TMG)- Catalyzed Addition of Primary Nitroalkanes to Aldehydes and A…

2010

Abstract Tetramethylguanidine-catalyzed addition of primary nitroalkanes to aldehydes and alicyclic ketones constitutes a practical means to perform the nitro-aldol reaction (Henry reaction). The very mild conditions employed, together with the short reaction times, make the procedure tolerant of a range of functionalities and highly versatile for the synthesis of a variety of 2-nitroalkanols.

Facile synthesis of 2-nitroalkanols by tetramethylguanidine (TMG)-catalyzed addition of primary nitroalkanes to aldehydes and alicyclic ketones

1997

Abstract Tetramethylguanidine-catalyzed addition of primary nitroalkanes to aldehydes and alicyclic ketones constitutes a practical means to perform the nitro-aldol reaction (Henry reaction). The very mild conditions employed, together with the short reaction times, make the procedure tolerant of a range of functionalities and highly versatile for the synthesis of a variety of 2-nitroalkanols.

Counterion's Effect on the Catalytic Activity of Zn-Prolinamide Complexes in Aldol Condensations

2012

The catalytic activity of complexes involving organic ligands and Lewis acids can be modulated by changing any of their components. In this work we have studied the influence on the stereoselectivity and catalytic activity exerted by the counterion of zinc salts employed as cocatalysts of L-prolinamide in aldol condensations. The structures of the complexes have been determined both in solution and in the solid state.