Search results for "aldol"
showing 10 items of 134 documents
Stereospecific CC-bond formation with rabbit muscle aldolase - A chemoenzymatic synthesis of (+)-exo-brevicomin
1990
Abstract (+)-(1S,5R,7S)-Exo-brevicomin 9, a sex pheromone of the western pine bark beetle, is synthesized using an aldol reaction catalyzed by fructose-1,6-diphosphate aldolase (EC 4.1.2.13) from rabbit muscle as the key step by which the absolute configuration of the target is established.
Stereoselective Synthesis of (+)-Boronolide
2002
The delta-lactone boronolide (+)-1, a pharmacologically active, naturally occurring product, has been synthesized in enantiopure form with L-erythrulose as the chiral starting material. The key steps of the synthesis were a highly stereoselective aldol-reduction one-pot sequence, an indium-mediated diastereoselective aldehyde allylation, and a ring-closing metathesis.
Synthesis of (S)-(+)-sotalol and (R)-(−)-isoproterenol via a catalytic enantioselective Henry reaction
2010
Abstract A unified approach for the synthesis of ( S )-(+)-sotalol and ( R )-(−)-isoproterenol has been developed. The enantioselective Henry reaction of the appropriate aldehyde in the presence of a camphor-derived amino pyridine–Cu(II) complex was the key step of the synthesis. The reduction of the nitro group to give the corresponding amino alcohols followed by reductive alkylation of the amine provided the target products with high enantiomeric excesses.
The role of Zn2+ in enhancing the rate and stereoselectivity of the aldol reactions catalyzed by the simple prolinamide model
2011
Abstract The aldol reaction between acetone and 4-nitrobenzaldehyde catalyzed by single l -prolinamide and its zinc complexes has been studied. An increase in the rate and the stereoselectivity of the reaction has been shown by using zinc derivatives. A mechanistic proposal, based on NMR and ESI studies, has been put forward to explain the experimental data: zinc–prolinamide complexes catalyze the reaction following the general mechanism of stereoselective enamine nucleophilic addition to the acceptor aldehyde. Zn2+ prevents the nonspecific base-catalyzed reaction by diminishing the basicity of the amine nitrogen of prolinamide.
Dienediolates of unsaturated carboxylic acids in synthesis. Aldehydes and ketones from alkyl halides, by ozonolysis of β,γ-unsaturated α-alkyl carbox…
1997
Abstract A convenient two-step procedure for a two carbon homologative conversion of alkyl halides into aldehydes and methyl ketones by α-alkylation of unsaturated carboxylic acids, followed by ozonolysis is developed and applied to the synthesis of ω-chloro aldehydes. Triethylamine is superior to dimethyl sulfide or triphenylphosphine for cleavage of the ozonides, except when aldol condensation side reactions require use of protic solvents and iodide salts. Cleavage of the ozonides by triethylamine is shown to occur mainly through a reductive process.
Zur C-17-Oxidation von Clavinalkaloiden mit primärer alkoholischer Hydroxylgruppe
1975
Die Oppenauer-Oxidation von 1 mit Cyclohexanon fuhrt zu dem Aldolkondensationsprodukt 4 und der Carbonsaure 3. Analog konnte Lysergsaure (8) in geringer Menge aus 6 gewonnen und im Reaktionsgemisch von 7 nachgewiesen werden. Damit wurden erstmals Clavinalkaloide mit primarer alkoholischer Hydroxylgruppe chemisch zu den entsprechenden Carbonsauren oxidiert. C-17-Oxidation of Clavine Alkaloids with a Primary Alcoholic Hydroxyl Group. 1 is converted by Oppenauer oxidation with cyclohexanone to the aldol condensation product 4 and to the carboxylic acid 3. Lysergic acid (8) was obtained in a small yield by the analogous reaction of 6 and was found in the reaction mixture of 7. Thus clavine alka…
Double diastereoselection in aldol reactions mediated by dicyclohexylchloroborane between L-erythrulose derivatives and chiral aldehydes. The Felkin-…
2003
Both matched and mismatched diastereoselections have been observed in aldol reactions of the B,B-dicyclohexylboron enolate of a protected l-erythrulose derivative with a range of chiral aldehydes. The stereochemical outcome of reactions with alpha-methyl aldehydes can be adequately explained within the Felkin-Anh paradigm. In the case of alpha-oxygenated aldehydes, however, strict adherence to this model does not allow for a satisfactory account of the observed results. In such cases, the Cornforth model provides a much better explanation.
Asymmetric Synthesis of Spiro Tetrahydrothiophene-indan-1,3-diones via a Squaramide-Catalyzed Sulfa-Michael/Aldol Domino Reaction
2016
Synthesis 48(08), 1131-1138(2016). doi:10.1055/s-0035-1560412
Density functional theory study of the 5-pyrrolidin-2-yltetrazole-catalyzed aldol reaction
2005
Abstract The replacement of the carboxylic acid functionality with a tetrazolic acid in the proline-catalyzed asymmetric aldol reaction between acetone and trimethylacetaldehyde has been studied using DFT methods at the B3LYP/6-31G** computational level. For the C–C bond-formation step, four reactive channels corresponding to the syn and anti arrangement of the enamine and the re and si attack modes have been analyzed. The B3LYP/6-31G** results allowed us to explain the stereoselectivity and the increase in reactivity relative to the proline-catalyzed process in DMSO.
Bioactivation of the Fungal Phytotoxin 2,5-Anhydro-D-glucitol by Glycolytic Enzymesisan Essential Component of itsMechanism of Action
2002
An isolate of Fusarium solani, NRRL 18883, produces the natural phytotoxin 2,5-anhydro-ᴅ-glucitol (AhG). This fungal metabolite inhibited the growth of roots (I50 of 1.6 mᴍ), butit did nothave any in vitro inhibitory activity. The mechanism of action of AhG requires enzymatic phosphorylation by plant glycolytic kinases to yield AhG-1,6-bisphosphate (AhG-1,6- bisP), an inhibitor of Fru-1,6-bisP aldolase. AhG-1,6-bisP had an I50 value of 570 μᴍ on aldolase activity, and it competed with Fru-1,6-bisP for the catalytic site on the enzyme, with a Ki value of 103 μᴍ. The hydroxyl group on the anomeric carbon of Fru-1,6-bisP is required for the formation of an essential covalent bond to ζ amino fu…