Home About us Contact
|
Home About us Contact | ||
|
|
||
Enolate
Kinds of Enolate Terms modified by Enolate Selected AbstractsDomino Aza-Claisen/Mannich Cyclization Reaction from a Chiral ,-Alkoxy Enamine or Sequential Alkylation of an ,-Alkoxy Ester Enolate or Nitrile Anion, Followed by an Intramolecular Wittig Reaction: Two (3+2) Annulation Routes to Homochiral 4-Alkyl-4-hydroxy-2-cyclopentenone SynthesisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2003Cyrille Kuhn Abstract A study on the enantioselective synthesis of 4-alkyl-4-hydroxyalkylidene-cyclopentenone prostaglandins is reported. Two (3+2) annulation processes allow the synthesis of homochiral 4-alkyl-4-hydroxy-2-cyclopentenones 4,5, 10,11, and 17. The first process involves a domino aza-Claisen/Mannich cyclization reaction, resulting from the alkylation of an ,-alkoxy-enamine, derived from chiral ,-alkoxy aldehydes 1, 9, or 16 with 3-iodo-2-(methoxymethoxy)prop-1-ene (3) as the acetonyl equivalent. The second process is based on the sequential alkylation of esters 21, 39, or nitrile 20 with acetonyl equivalents 3 or 25, followed by an intramolecular Wittig reaction. As an application, the synthesis of the naturally occurring alkylidene-cyclopentenone prostaglandin clavulone II from the spiro[cyclopentene-furan]one 5 and the formal total synthesis of (+/-)-untenone 19 has been carried out. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Oxidation von Catecholborenolaten mit TEMPO,ANGEWANDTE CHEMIE, Issue 33 2009Martin Pouliot Dr. Persistente Radikale treffen auf Enolate: Milde und effiziente Oxidationen von Catecholbor-Ketonenolaten lassen sich durch Behandlung mit dem persistenten Radikal TEMPO erzielen. Die Catecholborenolate sind leicht durch 1,4-Reduktion von ,,,-ungesättigten Ketonen oder Transmetallierung von Silylenolethern oder Zinkenolaten mit Chlorcatecholboran erhältlich. Enolatbildung und Oxidation lassen sich als ,Eintopf-Prozess" hoch regio- und stereoselektiv ausführen. [source] ChemInform Abstract: Asymmetric Aldol Additions with a Titanium Enolate of N-Thioglycolyl Oxazolidinethione.CHEMINFORM, Issue 9 2008Aurelio Ortiz 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 of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Dicationic ((-)-Sparteine)palladium-Catalyzed Enantioselective Aldol Reaction of Aldehydes with 1-Phenyl-1-trimethylsilyloxyethene, Proceeding via a Palladium Enolate.CHEMINFORM, Issue 40 2006Syun-ichi Kiyooka 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] Lithium Benzocyclobuteneoxide as a Precursor of a Vinylogous Enolate: Solvent-Controlled Synthesis of Highly Functionalized Seven-Membered Benzocarbocycles.CHEMINFORM, Issue 50 2005Jose Barluenga Abstract For Abstract see ChemInform Abstract in Full Text. [source] Novel 2-Pyrone Synthesis via Michael Addition of Mandelic Acid Enolate to trans-1,2-Diaroylethenes.CHEMINFORM, Issue 7 2005Santiago Barroso No abstract is available for this article. [source] Enantioselective Synthesis of Unsymmetrical Benzoins from (S)-Mandelic Acid Enolate and Aromatic Aldehydes.CHEMINFORM, Issue 6 2005Gonzalo Blay Abstract For Abstract see ChemInform Abstract in Full Text. [source] Highly Diastereoselective Arylation of (S)-Mandelic Acid Enolate: Enantioselective Synthesis of Substituted (R)-3-Hydroxy-3-phenyloxindoles and (R)-Benzylic Acids and Synthesis of Nitrobenzophenones.CHEMINFORM, Issue 5 2005Santiago Barroso Abstract For Abstract see ChemInform Abstract in Full Text. [source] Catalytic Enantio- and Diastereoselective Aldol Reactions of Glycine-Derived Silicon Enolate with Aldehydes: An Efficient Approach to the Asymmetric Synthesis of anti-,-Hydroxy-,-Amino Acid Derivatives.CHEMINFORM, Issue 47 2004Jun Kobayashi No abstract is available for this article. [source] Diastereoselective Michael Addition of (S)-Mandelic Acid Enolate to Nitroalkenes.CHEMINFORM, Issue 20 2004-Hydroxy-, -diaryl-, -lactams., Enantioselective Synthesis of Abstract For Abstract see ChemInform Abstract in Full Text. [source] Highly Diastereoselective anti-Aldol Reactions Utilizing the Titanium Enolate of cis-2-Arylsulfonamido-1-acenaphthenyl Propionate.CHEMINFORM, Issue 31 2003Arun K. Ghosh Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Transmetalation of Palladium Enolate and Its Application in Palladium-Catalyzed Homocoupling of Alkynes: A Room-Temperature, Highly Efficient Route to Make Diynes.CHEMINFORM, Issue 33 2002Aiwen Lei Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Copper(I) Iodide Promoted Hydroxylation onto the Lithium or Potassium Enolate of Lactones and Lactams.CHEMINFORM, Issue 11 2002Norio Nakazawa Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Highly Diastereoselective Aldol Additions of a Chiral Ethyl Ketone Enolate under Lewis Base Catalysis.CHEMINFORM, Issue 44 2001Scott E. Denmark Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A New Reaction of Cyclohexanone Enolate with Nitroarenes.CHEMINFORM, Issue 44 2001Nikolai Moskalev Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Asymmetric Synthesis of ,-Substituted ,-Methyl-,-amino Esters by Mannich Reaction of (S,S)-(+)-Pseudoephedrine Acetamide Derived Enolate with Imines.CHEMINFORM, Issue 27 2001Jose L. Vicario Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Amphoteric Character of 2-Vinyloxiranes: Synthetic Equivalents of ,,,-Unsaturated Aldehydes and a Vinylogous Enolate.CHEMINFORM, Issue 13 2001Mark Lautens Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Controlling Factors in Chiral Bisoxazoline-Catalyzed Asymmetric Lithium Ester Enolate,Imine Condensation Producing a ,-Lactam.CHEMINFORM, Issue 11 2001Takeshi Kambara Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Generation of Cationic [Zr-{tert -Butyl Enolate}] Reactive Species: Methyl Abstraction versus Hydride AbstractionCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Bing Lian Dr. Abstract Treatment of the neutral methyl,Zr,enolate [Cp2Zr(Me){O(tBuO)CCMe2}] (1) with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] as a methyl abstractor in THF at 0,°C leads to the selective formation of the free ion pair complex [Cp2Zr(THF){O(tBuO)CCMe2}]+,[anion], (2) (anion=MeB(C6F5)3,, B(C6F5)4,), which is relevant to the controlled polymerization of methacrylates. Cation 2 rapidly decomposes at 20,°C in THF with release of one equivalent of isobutene to form the cationic Zr,carboxylate species [Cp2Zr(THF)(O2CiPr)]+ (3), through a proposed intramolecular proton transfer process from the tert -butoxy group to the enolate. The reaction of 1 with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] in CH2Cl2 leads to the direct, rapid formation of the dimeric ,-isobutyrato,Zr dicationic species [{Cp2Zr[,-(O2CiPr)]}2]2+ (4), which gives 3 upon dissolution in THF. Contrastingly, when [Ph3C][B(C6F5)4] is used to generate the cationic Zr,enolate species from 1 in CD2Cl2, a 15:85 mixture of dicationic complexes 4 and [{Cp2Zr[, -(O2CC(Me)CH2)]}2]2+[B(C6F5)4] (5 -[B(C6F5)4]2) is obtained quantitatively. The formation of 5 is proposed to arise from initial hydride abstraction from a methyl enolate group by Ph3C+, as supported by the parallel production of Ph3CH, and subsequent elimination of methane and isobutene. In addition to standard spectroscopic and analytical characterizations for the isolated complexes 2,5, complexes 4 and 5 have also been structurally characterized by X-ray diffraction studies. [source] The First Mimetic of the Transketolase ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2006Mark E. B. Smith Abstract Although the biocatalytic formation of acyclic ,,,,-dihydroxy ketones by transketolase is well documented in the literature, there is currently no one-pot chemical synthesis of these dihydroxy ketones available. Here, we report preliminary results of an atom-efficient one-pot synthesis of ,,,,-dihydroxy ketones in water by a mimic of the transketolase reaction. The formation of a quaternary ammonium enolate is postulated in this tertiary-amine-mediated carbon,carbon bond-forming reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Lactone Kinetic Resolution by Acylation , Application to the Enantioselective Synthesis of Estrane DerivativesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2005Serge Wilmouth Abstract The acylation of an excess of racemic spirolactone 1 (6,9-divinyl-1-oxaspiro[4.4]nonan-2-one) enolate by protected methyl (S)-lactate or (,)-bornyl carbonate occurs with a kinetic resolution. The resulting lactones were alkylated with 1-iodobenzocyclobutenes to afford compounds that serve as precursors to nonracemic steroids such as 11,-alkyloxycarbonyl-11,,13,-(,-carbolactone)-17,-vinylgonatri-1,3,5(10)-enes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The Biosynthesis of 3-(trans -2-Nitrocyclopropyl)alanine, a Constituent of the Signal Metabolite HormaomycinEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2005Melanie Brandl Abstract Feeding experiments with Streptomyces griseoflavus using deuterium-labeled racemic 3,3-[D2]- (6b), 4,4-[D2]- (6c), 5,5-[D2]- (6d), and 6,6-[D2]-lysine (6e), and 3-amino-5-(2-amino-1,1-dideuterioethyl)-4,5-dihydrofuran-2-one dihydrochloride (34·2HCl) were carried out in order to obtain detailed information about the hitherto unknown biosynthetic pathway from lysine to the unusual amino acid 3-(trans -2,-nitrocyclopropyl)alanine [(3-Ncp)Ala] (2), which is a building block of hormaomycin 1a. The corresponding lysine dihydrochlorides were prepared in 33, 24, 19, and 30% overall yield, respectively, along a new efficient general synthetic route applying an alkylation of the lithium enolate of O,Donnel's glycine equivalent 7 as a key step. In the attempted preparation of 5,5-[D2]-4-hydroxylysine (29), the respective ,-lactone (34·2 HCl) was obtained in five steps with 10% overall yield. The distribution of isotope labels in hormaomycins 1b,d led to the formulation of a reasonable cyclization mechanism of 2-amino-4-hydroxy-6-(hydroxyimino)hexanoic acid, an ,-oxime analogue of 4-hydroxylysine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Studies on the Origin of 1,5- anti Induction in Boron-Mediated Aldol ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2004Bridget L. Stocker Abstract A model for the origin of selectivity in boron-mediated 1,5- anti -aldols is presented. This model involves ,-stacking between the boron enolate and a remote aromatic ring. A short, facile method for the synthesis of the C-12 to C-22 segment of peloruside A and its 1,5- anti -aldol coupling using the proposed model is also presented. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of Monocyclic and Bicyclic Imino SugarsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2003Markus Kummeter Abstract A diastereoselective aldol reaction between the chelated alanine ester enolate 5 and the protected threose derivative 6, followed by cyclization under Mitsunobu conditions, gave the pipecolinic acid derivative 9. This compound could easily be converted into the versatile protected derivative 11, which could be transformed in excellent yields either into the corresponding piperidine imino sugar 14 or into the unnatural amino acid 17. The imino alcohol 13, an intermediate in the synthesis of imino sugar 14, was also used in a straightforward approach to indolizidinone 19, involving an intramolecular Horner,Emmons reaction for ring-closure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Formation of a living anionic oligomer of ethylphenylketene on polystyrene beads and its application to the solid-supported synthesis of poly(methyl methacrylate)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Atsushi Sudo The anionic oligomerization of ethylphenylketene (EPK) by lithium benzyl alkoxide on a polystyrene resin readily afforded the corresponding lithium enolate immobilized on beads through a benzyl ester linker. The lithium enolate so prepared was applied as a solid-supported initiator for the anionic synthesis of poly(methyl methacrylate), which was readily isolated from the resin by selective cleavage of the benzyl ester linker. [source] Organocatalytic Asymmetric Mannich Reactions with N -Boc and N -Cbz Protected ,-Amido Sulfones (Boc: tert -Butoxycarbonyl, Cbz: Benzyloxycarbonyl)CHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2007Olindo Marianacci Abstract Different malonates and ,-ketoesters can react with N - tert -butoxycarbonyl- (N -Boc) and N -benzyloxycarbonyl- (N -Cbz) protected ,-amido sulfones in an organocatalytic asymmetric Mannich-type reaction. The reaction makes use of a simple and easily obtained phase-transfer catalyst and proceeds under very mild and user-friendly conditions. The optimised protocol avoids the preparation and the isolation of the relatively unstable N -Boc and N- Cbz imines that are generated in situ from the bench-stable ,-amido sulfones. The corresponding Mannich bases are generally obtained in good yields and enantioselectivities, and can be readily transformed into key compounds, such as optically active ,3 -amino acids in one easy step. Enantioenriched N -Boc and N -Cbz protected ,-amino acids that are suitable for peptide synthesis are also available from the Mannich adducts through simple manipulations. Control experiments showed the dual role of the enolate,catalyst ion pair in this reaction, as well as the crucial role of the presence of water to achieve high enantioselectivities. [source] Diastereoselective Synthesis of Five- and Seven-Membered Rings by [2+2+1], [3+2], [3+2+2], and [4+3] Carbocyclization Reactions of ,-Substituted (Alkenyl)(methoxy)carbene Complexes with Methyl Ketone Lithium EnolatesCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2005José Barluenga Prof. Dr. Abstract ,-Substituted alkenylcarbene complexes react with methyl ketone lithium enolates to give different carbocyclization products depending on the structure of the lithium enolate, on the metal of the carbene complex, and on the reaction media. Thus, the reactions of aryl and alkyl methyl ketone lithium enolates with ,-substituted alkenyl chromium and tungsten carbene complexes in diethyl ether afford 1,3-cyclopentanediol derivatives derived from a formal [2+2+1] carbocyclization reaction. However, the lithium enolates of acetone and tungsten complexes furnish formal [3+2+2] carbocyclization products. In the case of alkynyl methyl ketone lithium enolates, competitive formal [2+2+1] and [3+2] carbocyclization reactions occur and 1,3-cyclopentanediol and 3-cyclopentenol derivatives are formed. Conversely, alkenyl methyl ketone lithium enolates react with alkenylcarbene complexes under the same reaction conditions to form 2-cycloheptenone derivatives by a formal [4+3] carbocyclization reaction. Finally, when the reaction was performed in the presence of a coordinating medium, the [3+2] carbocyclization pattern was observed independently of the nature of the methyl ketone lithium enolate used. Los complejos alquenilcarbeno , -sustituidos reaccionan con enolatos de litio de metil cetonas para dar diferentes productos de carbociclación dependiendo de la estructura del enolato de litio, del metal del complejo carbeno y del medio de reacción. Así, la reacción de enolatos de litio de aril y alquil metil cetonas con complejos alquenilcarbeno de cromo y wolframio , -sustituidos en dietil eter origina derivados de 1,3-ciclopentanodiol, derivados de una reacción de carbociclación formal [2+2+1]. Sin embargo, el enolato de litio de la acetona y complejos de wolframio dan lugar a productos de carbociclación formal [3+2+2]. En el caso de enolatos de litio de alquinil metil cetonas, se observa la formación de una mezcla de derivados de 1,3-ciclopentanodiol y 3-ciclopentenol derivados de reacciones de carbociclación formal [2+2+1] y [3+2] competitivas. Por el contrario, los enolatos de litio de alquenil metil cetonas reaccionan con complejos alquenilcarbeno en las mismas condiciones de reacción para generar derivados de 2-cicloheptenona a través de una reacción de carbociclación formal [4+3] Finalmente, cuando la reacción se lleva a cabo en presencia de PMDTA, un medio coordinante, se observa el modelo de carbociclación formal [3+2], independientemente de la naturaleza del enolato de litio utilizado. [source] The Zirconium Alkoxide-Catalyzed Aldol-Tishchenko Reaction of Ketone AldolsCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2005Christoph Schneider Prof. Dr. Abstract The aldol-Tishchenko reaction of ketone aldols as enol equivalents has been developed as an efficient strategy to furnish differentiated 1,3- anti -diol monoesters in one step. The thermodynamically unstable ketone aldols undergo a facile retro-aldolization to yield a presumed zirconium enolate in situ, which then undergoes the aldol-Tishchenko reaction in typically high yields and with complete 1,3- anti diastereocontrol. Evaluation of a broad range of metal alkoxides as catalysts and optimization of the reaction protocol led to a modified zirconium alkoxide catalyst with attenuated Lewis acidity and dichloromethane as solvent, which resulted in suppression of the undesired acyl migration to a large extent. Various ketone aldols have been prepared and subjected to the general process, giving rise to a broad range of differently substituted 1,3- anti -diol monoesters, which may be hydrolyzed to the corresponding 1,3- anti -diols. [source] Novel Hypervalent Complexes of Main-Group Metals by Intramolecular Ligand,Metal Electron Transfer*CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004Matthias Driess Prof. Dr. Abstract New fascinating electronic features of the simple diketoamine chelate ligand HN[CH2C(tBu)O]2 (1) are described. Unexpectedly, the corresponding trianionic amido-dienolate form of 1 is capable of reducing main-group metal atoms M after initial coordination and intramolecular L,M two-electron transfer and of stabilizing main-group elements in unusual low oxidation states. This is impressively shown by the synthesis and structural characterization of the novel Ge and Sn complexes 4,6 by redox reactions of lithiated 1 with the corresponding metal halides GeCl4 and MCl2 (M=Ge, Sn). Surprisingly, conversion of tris-lithiated 1 with GeCl4 readily consumes two molar equivalents of GeCl4 and results in the formation of the neutral GeCl3 complex 4 and GeCl2. The former represents the second example of a structurally characterized neutral octahedrally coordinated germanium compound. Reaction of dilithiated 1 with GeCl2 does not lead to the expected ClGe(+2) complex but affords the novel dimeric germylene 5, whereas similar reaction using SnCl2 furnishes the monomeric stannylene (ClSn(+2) complex) 2 and elemental tin due to the higher oxidation potential of Sn(+2). Unexpectedly, a similar redox reaction of dilithiated 1 with PbCl2 furnishes the first air- and water-stable lithium 1,2-diketoimine,enolate 7 and elemental lead. Compound 7 is tetrameric in the solid state and consists of a strongly distorted Li4O4 cubic core with trigonal-bipyramidal coordinated Li+ ions. [source] Generation of Cationic [Zr-{tert -Butyl Enolate}] Reactive Species: Methyl Abstraction versus Hydride AbstractionCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Bing Lian Dr. Abstract Treatment of the neutral methyl,Zr,enolate [Cp2Zr(Me){O(tBuO)CCMe2}] (1) with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] as a methyl abstractor in THF at 0,°C leads to the selective formation of the free ion pair complex [Cp2Zr(THF){O(tBuO)CCMe2}]+,[anion], (2) (anion=MeB(C6F5)3,, B(C6F5)4,), which is relevant to the controlled polymerization of methacrylates. Cation 2 rapidly decomposes at 20,°C in THF with release of one equivalent of isobutene to form the cationic Zr,carboxylate species [Cp2Zr(THF)(O2CiPr)]+ (3), through a proposed intramolecular proton transfer process from the tert -butoxy group to the enolate. The reaction of 1 with one equivalent of B(C6F5)3 or [HNMe2Ph][B(C6F5)4] in CH2Cl2 leads to the direct, rapid formation of the dimeric ,-isobutyrato,Zr dicationic species [{Cp2Zr[,-(O2CiPr)]}2]2+ (4), which gives 3 upon dissolution in THF. Contrastingly, when [Ph3C][B(C6F5)4] is used to generate the cationic Zr,enolate species from 1 in CD2Cl2, a 15:85 mixture of dicationic complexes 4 and [{Cp2Zr[, -(O2CC(Me)CH2)]}2]2+[B(C6F5)4] (5 -[B(C6F5)4]2) is obtained quantitatively. The formation of 5 is proposed to arise from initial hydride abstraction from a methyl enolate group by Ph3C+, as supported by the parallel production of Ph3CH, and subsequent elimination of methane and isobutene. In addition to standard spectroscopic and analytical characterizations for the isolated complexes 2,5, complexes 4 and 5 have also been structurally characterized by X-ray diffraction studies. [source] | |||||||||||||||||||||||||