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Acyl Migration (acyl + migration)
Selected AbstractsDynamic Kinetic Asymmetric Allylic Amination and Acyl Migration of Vinyl Aziridines with Imido Carboxylates.CHEMINFORM, Issue 48 2007Barry M. Trost 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] A Highly Efficient Preparative Method of ,-Ylidene-,-diketones via AuII -Catalyzed Acyl Migration of Propargylic Esters.CHEMINFORM, Issue 45 2006Shaozhong Wang 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] Synthesis of 1,3,5-Trisubstituted Hydantoins by Regiospecific Domino Condensation/Aza-Michael/O,N Acyl Migration of Carbodiimides with Activated ,,,-Unsaturated Carboxylic Acids.CHEMINFORM, Issue 32 2005Alessandro Volonterio Abstract For Abstract see ChemInform Abstract in Full Text. [source] Regioselective C-6 Hydrolysis of Methyl O -Benzoyl-pyranosides Catalysed by Candida Rugosa LipaseEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2009Aslan Esmurziev Abstract Hydrolysis of six methyl O -benzoyl-pyranosides has been investigated using Candida rugosa lipase in dioxane/buffer mixtures. The lipase catalysed the hydrolysis of all substrates in a regiospecific manner at C-6. The rate of reaction was dependent on pyranoside structure, reaction temperature and scale, dioxane concentration and agitation speed. Starting from their C-6 O -benzoyl precursors, the methyl 2,3,4-tri- O -benzoyl-pyranosides of ,- D -galactose, ,- D -galactose, ,- D -glucose, and methyl 2,3-di- O -benzoyl-,- D -galactopyranoside could be isolated in 85,96,% yield. In hydrolysis of methyl 2,3,4,6-tetra- O -benzoyl-,- D -glucopyranoside and methyl 2,3,4,6-tetra- O -benzoyl-,- D -galactopyranoside substrate inhibition were observed, which in part could be overcome by increasing the reaction volume. Methyl 2,3,4,6-tetra- O -benzoyl-,- D -glucopyranoside and methyl 2,3,4,6-tetra- O -benzoyl-,- D -mannopyranoside were poor substrates for Candida rugosa lipase and low degree of conversion towards products were obtained under all conditions. No acyl migration was detected in any of the products.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Reaction of Carboxylic Acids with Isocyanides: A Mechanistic DFT StudyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2008Tommaso Marcelli Abstract We present a computational investigation of the reaction between isocyanides and carboxylic acids. Our results indicate that this reaction begins with a stereoselective concerted ,-addition of the acid to the isocyanide, leading exclusively to a Z -acyl imidate. Isomerization to the E isomer and successive rate-limiting 1,3 O,N acyl migration yields an N -formyl imide. The calculated barriers are in good agreement with the experimental reaction conditions. Our results might provide an explanation for the peculiar reactivity observed when this reaction is carried out in a self-assembled capsule. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Chemistry of ,-hydroxymethylserine: problems and solutions,JOURNAL OF PEPTIDE SCIENCE, Issue 11 2008Marcin Stasiak Abstract Further improvements related to the synthesis of peptides containing HmS are presented. Efficient synthetic protocols have been developed to synthesize "difficult" sequences containing a C -terminal HmS residue, MeA,HmS or consecutive HmS. Preparative methods for orthogonal N - and/or C -protected HmS(Ipr) derivatives are described. Their compatibility with standard solution or solid-phase peptide chemistry protocols allows synthetic flexibility toward HmS-containing peptides. In the synthesis of the sterically hindered dipeptides with the C -terminal HmS(Ipr) residue, HATU proves the highest efficiency, as compared with the fluoride and PyBroP/DMAP coupling methods. The HATU method also outperforms the fluoride activation in the solid-phase assembly of HmS homosequence. Specific protocols are described to overcome an undesired cyclization to diketopiperazines that occurs during the removal of Fmoc from dipeptides with the C -terminal HmS(Ipr) or HmS residues, thus precluding their C , N elongation. The successful protocols involve: (i) the 2 + 1 condensation using mixed anhydride activation yielding the desired product with the highest optical integrity or (ii) use of the 2-chlorotrityl resin as a solid support sterically suppressing the undesired cleavage due to diketopiperazine formation. The latter approach allows the mild conditions of peptide cleavage from solid support, preserving the isopropylidene protection and minimizing the undesired N , O -acyl migration that was observed under prolonged acid treatment used for cleaving the HmS peptide from the Wang resin. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Synthesis of (,)-Cubebol by Face-Selective Platinum-, Gold-, or Copper-Catalyzed Cycloisomerization: Evidence of Chirality Transfer and Mechanistic InsightsCHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2009Charles Fehr Dr. Abstract We describe in detail a direct, stereoselective synthesis of (,)-cubebol based on a Pt-, Au-, or Cu-catalyzed cycloisomerization in which control of the configuration of the propargylic center is essential for the facial selectivity. In addition, we show that cycloisomerization reactions of enantioenriched propargyl pivalates occur with substantial chirality transfer. We confirm a mechanism by means of cyclization followed by an [1,2]-acyl migration for the Pt- and the Au-catalyzed cycloisomerization. So far, no evidence supports that the Cu-catalyzed cycloisomerization follows the same reaction course. [source] The Laulimalide Family: Total Synthesis and Biological Evaluation of Neolaulimalide, Isolaulimalide, Laulimalide and a Nonnatural AnalogueCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2009Andreas Gollner Dipl.-Ing. Abstract A sensitive family: The first total synthesis of the antitumor agents neolaulimalide and isolaulimalide as well as a highly efficient route to laulimalide is described. A Kulinkovich reaction followed by a cyclopropyl,allyl rearrangement is used to install the exo -methylene group. The cytotoxicity of neolaulimalide could be confirmed for the first time since its original isolation and it could be shown that it induces tubulin polymerization as efficiently as laulimalide. We herein describe in full detail the first total synthesis of the antitumor agents neolaulimalide and isolaulimalide as well as a highly efficient route to laulimalide. A Kulinkovich reaction followed by a cyclopropyl,allyl rearrangement is used to install the exo -methylene group. The C2,C16 aldehyde fragment is coupled with the C17,C28 sulfone fragments by a highly (E)-selective Julia,Lythgoe,Kocienski olefination to deliver the key intermediates of all three syntheses. Various conditions for the Yamaguchi macrolactonization are applied to close the individual macrocycles. Finally a carefully elaborated endgame was developed to solve the problem of acyl migration in the case of neolaulimalide. All compounds were tested against several cell lines. The cytotoxicity of neolaulimalide could be confirmed for the first time since its original isolation and it could be shown that it induces tubulin polymerization as efficiently as laulimalide. [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] Electronic structure calculations as a tool for investigating acyl migrations in ester aponinsPHYTOCHEMICAL ANALYSIS, Issue 5 2002Sandra Apers Abstract The possibility of acyl migrations in ester saponins from Maesa lanceolata was investigated by molecular mechanics and electronic structure calculations carried out on the major constituent maesasaponin IV3 (3,-O-{[,- L -rhamnopyranosyl-(1,2)-,- D -galactopyranosyl-(1,3)]-[,- D -galactopyranosyl-(1,2)]-,- D -glucopyranuronyl}-21,-angeloyloxy-22,-propanoyloxy-13,,28-oxido-olean-16,, 28,-diol). It was confirmed that acyl migrations could occur in rings D and E of maesasaponins. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||