Aldol Reactions Of Enolates Research Articles

Asymmetric total synthesis of spongistatins 1 and 2.

The total synthesis of spongistatin 1 (1) and spongistatin 2 (2) has been achieved through an advanced-stage intermediate. The synthesis is highlighted by a highly convergent assembly of the four key fragments (the C1-C15 AB fragment 2, the C16-C28 CD fragment 3, the C29-C43 EF fragment 4, and the C44-C51 side chain 5) at a very advanced stage of the synthesis with minimal functional group interconversion. The CD fragment 3 functions as the central building block to which the other fragments are attached. The synthesis of the AB and CD spiroketal fragments is accomplished through the addition of a metalated gamma-pyrone to a beta-alkoxy aldehyde followed by spiroketalization. The EF subunit was assembled with high diastereoselectivity relying on asymmetric aldol reactions of chlorotitanium enolates of N-propionyl oxazolidinethiones and a double diastereoselective boron aldol to join the E and F fragments. Wittig coupling of the CD and EF fragments followed by a diastereoselective aldol reaction between the CDEF ketone and an AB aldehyde set the stage for attachment of the C44-C51 side chains and final macrolactonization and deprotection.

Synthesis of stereo-defined α-trifluoromethyl (Tfm)-malic units

Aldol reactions of titanium enolates of N-acyl-1,3-oxazolidin-2-ones with ethyl trifluoropyruvate occurred with low to good stereoselectivity depending on the steric properties of the N-acyl group. Attempts to transform the resulting aldols into peptidomimetics incorporating stereo-defined α-trifluoromethyl (Tfm)-malic units are described.

Lewis base-promoted aldol reaction of dimethylsilyl enolates in aqueous dimethylformamide: use of calcium chloride as a Lewis base catalyst.

In the presence of CaCl2, dimethylsilyl (DMS) enolates smoothly reacted with aldehydes under mild conditions to give aldol adducts in good to high yields. The catalytic activities of various metal and tetrabutylammonium salts have revealed that CaCl2 works as a Lewis base catalyst to activate DMS enolates. The CaCl2-promoted reaction proceeded even in the presence of water or in pure water. This catalytic system was applicable to the aldol reaction with aqueous aldehydes such as formalin.

Highly diastereoselective lithium enolate aldol reactions of butane-2,3-diacetal desymmetrized glycolic acid and deprotection to enantiopure anti-2,3-dihydroxy esters.

[reaction--see text] The butane-2,3-diacetal (BDA) desymmetrized glycolic acid building block 1 undergoes efficient and highly diastereoselective lithium enolate aldol reactions with both aromatic and aliphatic aldehydes to afford, after an acidic methanolysis deprotection step, the enantiopure anti-2,3-dihydroxy esters in good yield.

ChemInform Abstract: Ester Derived Titanium Enolate Aldol Reaction: Chelation Controlled Diastereoselective Synthesis of syn‐Aldols.

AbstractChemInform 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.

Ester derived titanium enolate aldol reaction: chelation controlled diastereoselective synthesis of syn-aldols

A chelation controlled and highly diastereoselective synthesis of syn-aldols is described. Aldol reaction of commercially available l-phenylalaninol derived esters with a variety of bidentate oxyaldehydes proceeded with excellent syn-diastereoselectivities and isolated yields.

ChemInform Abstract: High Stereocontrol in Aldol Reaction with Ketones: Enantioselective Synthesis of β‐Hydroxy γ‐Ketoesters by Ester Enolate Aldol Reactions with 2‐Acyl‐2‐alkyl‐1,3‐dithiane 1‐Oxides.

AbstractChemInform 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.

ChemInform Abstract: Aldol Addition of Lithium and Boron Enolates of 1,3-Dioxan-5-ones to Aldehydes. A New Entry into Monosaccharide Derivatives.

Methods allowing control of stereoselectivity in aldol reactions of enolates derived from 1,3-dioxan-5-ones (4) are described. Boron enolates, generated in situ, react with benzaldehyde to give the corresponding anti aldol selectively (the anti:syn ratio of up to 96:4) and in high yield. Lithium enolates give high anti selectivity only with aldehydes branched at the α-position. Enantioselective deprotonation of CS symmetrical dioxanones (e.g., 4b) can be accomplished efficiently, with enantiomeric excess of up to 90%, with chiral lithium amide bases of general structure PhCH(Me)N(Li)R (9, 10) if the R group is sufficiently bulky (e.g, R = adamantyl) or is fluorinated (e.g., R = CH2CF3). Dioxanone boron and lithium enolates react readily with glyceraldehyde derivatives (19), yielding protected ketohexoses (20 and 21).

High stereocontrol in aldol reaction with ketones: enantioselective synthesis of beta-hydroxy gamma-ketoesters by ester enolate aldol reactions with 2-acyl-2-alkyl-1,3-dithiane 1-oxides

The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lactones, proceeds with a high degree of stereocontrol at both carbonyl and enolate prochiral centers, the stereocontrol mainly determined by the configuration of the sulfoxide sulfur atom. The sense of induced stereochemistry observed for ester enolates is different from that seen for lactone enolates. Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substituted beta-hydroxy-gamma-ketoesters.

Aldol addition of lithium and boron enolates of 1,3-dioxan-5-ones to aldehydes. A new entry into monosaccharide derivatives

Methods allowing control of stereoselectivity in aldol reactions of enolates derived from 1,3-dioxan-5-ones (4) are described. Boron enolates, generated in situ, react with benzaldehyde to give the corresponding anti aldol selectively (the anti:syn ratio of up to 96:4) and in high yield. Lithium enolates give high anti selectivity only with aldehydes branched at the alpha-position. Enantioselective deprotonation of C(S) symmetrical dioxanones (e.g., 4b) can be accomplished efficiently, with enantiomeric excess of up to 90%, with chiral lithium amide bases of general structure PhCH(Me)N(Li)R (9, 10) if the R group is sufficiently bulky (e.g, R = adamantyl) or is fluorinated (e.g., R = CH2CF3). Dioxanone boron and lithium enolates react readily with glyceraldehyde derivatives (19), yielding protected ketohexoses (20 and 21).

The synthesis and evaluation of a solution phase indexed combinatorial library of non-natural polyenes for reversal of P-glycoprotein mediated multidrug resistance.

A combinatorial library of polyenes, based on (-)-stipiamide, has been constructed and evaluated for the discovery of new multidrug resistance reversal agents. A palladium coupling was used to react each individual vinyl iodide with a mixture of the seven acetylenes at near 1:1 stoichiometry. The coupling was also used to react each individual acetylene with the mixture of six vinyl iodides to create 13 pools indexed in two dimensions for a total of 42 compounds. Individual compounds were detected at equimolar concentration. The vinyl iodides, made initially using a crotylborane addition to generate the anti1,2-hydroxylmethyl products, were now made using a more efficient norephedrine propionate boron enolate aldol reaction. The indexed approach, ideally suited for cellular assays that involve membrane-bound targets, allowed for the rapid identification of reversal agents using assays with drug-resistant human breast cancer MCF7-adrR cells. Intersections of potent pools identified new compounds with promising activity. Aryl dimension pools showed R = ph and naphthyl as the most potent. The acetylene dimension had R' = phenylalaninol and alaninol as the most potent. Isolated individual compounds, both active and nonpotent, were assayed to confirm the library results. The most potent new compound was 4ek (R = naphthyl, R' = phenylaninol) at 1.45 microM. Other nonnatural individual naphthyl-amide compounds showed potent MDR reversal including the morpholino-amide 4ej (1.69 microM). Synergistic activities attributed to the two ends of the molecule were also identified. Direct interaction with Pgp was established by ATPase and photoaffinity displacement assays. The results indicate that both ends of the polyene reversal agent are involved in Pgp interaction and can be further modified for increased potency.

Transition-State Mimetics for HIV Protease Inhibitors: Stereocontrolled Synthesis of Hydroxyethylene and Hydroxyethylamine Isosteres by Ester-Derived Titanium Enolate Syn and Anti-Aldol Reactions.

Stereocontrolled syntheses of hydroxyethylene dipeptide isostere and aminoalkyl epoxides for hydroxyethylamine isosteres are described. The stereochemistry of both stereogenic centers of the aminoalkyl epoxides 10 and 15 as well as the gamma-lactone 17 was assembled by our recently developed highly selective ester-derived titanium enolate aldol reactions. The Ti-enolate of 6 reacted with (benzyloxy)acetaldehyde and cinnamaldehyde to provide the syn-aldol product 7 and anti-aldol product 12, respectively. Removal of the chiral template followed by Curtius rearrangement of the resulting acid provided the desired amine functionality. The present syntheses represent practical and enantioselective entry to a range of other dipeptide isosteres, which are not limited to amino acid derived substituents.

ChemInform Abstract: Ester Derived Titanium Enolate Aldol Reaction: Highly Diastereoselective Synthesis of syn‐ and anti‐Aldols.

AbstractChemInform 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.

Ester derived titanium enolate aldol reaction: Highly diastereoselective synthesis of syn- and anti-aldols

Aldol reactions of bidentate aldehydes and cis-1-arylsulfonamido-2-indanyl ester derived titanium enolates proceed with excellent syn-diastereoselectivities and good to excellent isolated yields.

Effect of Calcium Reagents on Aldol Reactions of Phenolic Enolates with Aldehydes in Alcohol

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTEffect of Calcium Reagents on Aldol Reactions of Phenolic Enolates with Aldehydes in AlcoholHiroyuki Saimoto, Koji Yoshida, Tetsuya Murakami, Minoru Morimoto, Hitoshi Sashiwa, and Yoshihiro ShigemasaCite this: J. Org. Chem. 1997, 62, 5, 1564Publication Date (Web):March 7, 1997Publication History Published online7 March 1997Published inissue 1 March 1997https://doi.org/10.1021/jo9640332Copyright © 1997 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views879Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Get e-Alerts Get e-Alerts

ChemInform Abstract: Effect of Calcium Reagents on Aldol Reactions of Phenolic Enolates with Aldehydes in Alcohol.

AbstractChemInform 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.

ChemInform Abstract: anti‐Selective Aldol Reactions of Amino Acid Ester Enolates. Application to the Synthesis of α‐Alkylated β‐Hydroxy Amino Acids.

AbstractChemInform 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.

ChemInform Abstract: Synthesis of Enantiomerically Pure Anti‐Aldols: A Highly Stereoselective Ester‐Derived Titanium Enolate Aldol Reaction.

AbstractChemInform 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.

Anti‐Selective Aldol Reactions of Amino Acid Ester Enolates. Application to the Synthesis of α‐Alkylated β‐Hydroxy Amino Acids

AbstractDeprotonation of N‐protected esters of the amino acids alanine 1, ethylglycin 6, valine 7, and phenylalanine 8 with LDA and subsequent addition of various metal salts result in the formation of a probably chelated metal enolate. Aldol reactions of these enolates with aldehydes afford the anti isomers of α‐alkylated α‐amino‐β‐hydroxy acids in a highly diastereoselective fashion. Best results are obtained with titanium enolates, bulky aliphatic aldehydes, and sterically demanding amino acids.

ChemInform Abstract: Highly Stereoselective Aldol Reaction of Metal Enolates of α‐ Fluoropropanethioates with Aldehydes Affording erythro‐α‐Fluoro‐. alpha.‐methyl‐β‐hydroxy Alkanethioates.

AbstractChemInform 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.