Search results for "aldol"

Enantioselective Synthesis of Unsymmetrical Benzoins from (S)-Mandelic Acid Enolate and Aromatic Aldehydes.

2004

The reaction of the lithium enolate of the 1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with aromatic aldehydes proceeds readily to give the corresponding aldol products in good yields and diastereoselectivities. Subsequent hydroxyl protection, basic hydrolysis of the dioxolanone, oxidative decarboxylation of the α-hydroxyacid moiety, and hydroxyl deprotection provides chiral unsymmetrical benzoins with high enantiomeric excesses.

Cationic mono- and bi-nuclear iron complexes as Lewis acid catalysts in Mukaiyama reactions

1992

Organometallic Lewis acids derived from photolysis of mono- and bi-nuclear cationic iron carbonyl complexes function as excellent catalysts for the Mukaiyama aldol reaction.

Synthesis of a New Fluorinated Oxazolidinone and Its Reactivity as a Chiral Auxiliary in Aldol Reactions.

2007

A new enantiomerically pure fluorinated oxazolidinone has been prepared from a fluorinated imidoyl chloride and an optically pure sulfoxide. The diastereoselective reduction of the β-iminosulfoxide thus formed followed by elimination of the sulfoxide and cyclization of the created aminoalcohol furnishes the desired product. The fluorinated oxazolidinone was subsequently used as a chiral auxiliary in Aldol reactions. We also found that the selective formation of the syn-Evans and syn-non-Evans diastereoisomer can be controlled by adjusting the Lewis acid/base ratio.

2.14 Selected Diastereoselective Reactions: Enolate Alkylation

2012

This chapter discusses processes in which enolates are subjected to reaction with alkylating reagents. In all the processes examined here, at least one of the two reaction components is chiral and the reaction gives rise to one or more diastereomeric compounds. In most cases, the enolate is generated through deprotonation of the corresponding carbonyl precursor with a suitable base, but in several cases, the enolate is generated differently, for example, through Michael addition of a nucleophile to a conjugated carbonyl compound. The various factors that have been found to influence the stereochemical outcome of the alkylation reaction in a measurable way are also discussed. The material ha…

A Convenient Generation of Acetic Acid Dianion

2003

The lithium enediolate of acetic acid can be generated efficiently, as a 0.5 M solution in THF, using lithium amides prepared from n-butyllithium in THF and either diethylamine or 1,3,3-trimethyl-6-azabicyclo-(3.2.1)-octane (AZA). Its reaction with carbonyl compounds leads to the corresponding β-hydroxy acids in good to moderate yields. Better yields are usually obtained when these amines are added in sub-stoichiometric amounts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Novel supported dipeptides as recyclable catalysts for asymmetric aldol reaction

2009

Enantioselective synthesis and absolute configurations of aculeatins A, B, D, and 6-epi-aculeatin D

2006

The three naturally occurring, bioactive spiroacetals aculeatins A, B, and D, as well as the non-natural 6-epi-aculeatin D have been synthesized for the first time in enantiopure form using an asymmetric allylation as the only chirality source. A further key step was a stereoselective aldol reaction with remote induction. The absolute configurations of the natural products have been established and an erroneous structural assignment has been corrected.

Fructose-1,6-Bisphosphate Protects Hippocampal Rat Slices from NMDA Excitotoxicity

2019

Effects of fructose 1,6-bisphosphate (F-1,6-P2) towards N-methyl-d-aspartate NMDA excitotoxicity were evaluated in rat organotypic hippocampal brain slice cultures (OHSC) challenged for 3 h with 30 &mu

Stereoselective synthesis of the naturally occurring styryllactones (+)-goniofufurone and (+)-cardiobutanolide.

2004

The naturally occurring gamma-lactones (+)-goniofufurone 1 and (+)-cardiobutanolide 2, two pharmacologically active products from Goniothalamus species (Annonaceae), have been synthesized in enantiopure form using l-erythrulose as the chiral starting material. Key steps of these syntheses were a stereoselective anti boron aldol reaction and an asymmetric allylboration.

Sequential Suzuki/Asymmetric Aldol and Suzuki/Knoevenagel Reactions Under Aqueous Conditions

2012

Here we describe for the first time a sequential Suzuki/asymmetric aldol reaction. Such sequential approach was achieved through the combined use of an ionic liquid supported palladium catalyst and the organocatalyst trans-4-(2,2-diphenylacetoxy)proline. Suzuki and asymmetric aldol reactions were performed under aqueous conditions. The use of a palladium catalyst under basic conditions allowed also the first example of sequential Suzuki/Knoevenagel reaction. Reactions were carried out under aqueous conditions and products were isolated in good to high yields and, in the case of the Suzuki/aldol reaction, with diastereoselectivities up to 91:9 and enantioselectivities up to at least 99 %.