135,962 research outputs found
Improving backward stability of Sakurai-Sugiura method with balancing technique in polynomial eigenvalue problem
No full textsummary:One of the most efficient methods for solving the polynomial eigenvalue problem (PEP) is the Sakurai-Sugiura method with Rayleigh-Ritz projection (SS-RR), which finds the eigenvalues contained in a certain domain using the contour integral. The SS-RR method converts the original PEP to a small projected PEP using the Rayleigh-Ritz projection. However, the SS-RR method suffers from backward instability when the norms of the coefficient matrices of the projected PEP vary widely. To improve the backward stability of the SS-RR method, we combine it with a balancing technique for solving a small projected PEP. We then analyze the backward stability of the SS-RR method. Several numerical examples demonstrate that the SS-RR method with the balancing technique reduces the backward error of eigenpairs of PEP
GENERALIZED VECTOR DOMINANCE AND INELASTIC ELECTRON-PROTON SCATTERING
No full textSAKURAI JJ, Schildknecht D. GENERALIZED VECTOR DOMINANCE AND INELASTIC ELECTRON-PROTON SCATTERING. Physics Letters B. 1972;40(1):121-126
GENERALIZED VECTOR DOMINANCE AND INELASTIC ELECTRON NUCLEON-SCATTERING - SMALL OMEGA-' REGION
No full textSAKURAI JJ, Schildknecht D. GENERALIZED VECTOR DOMINANCE AND INELASTIC ELECTRON NUCLEON-SCATTERING - SMALL OMEGA-' REGION. Physics Letters B. 1972;42(2):216-220
GENERALIZED VECTOR DOMINANCE AND INELASTIC ELECTRON-NUCLEON SCATTERING - NEUTRON-TO-PROTON RATIO
No full textSAKURAI JJ, Schildknecht D. GENERALIZED VECTOR DOMINANCE AND INELASTIC ELECTRON-NUCLEON SCATTERING - NEUTRON-TO-PROTON RATIO. Physics Letters B. 1972;41(4):489-494
Hosomi—Sakurai Reactions of Silacyclic Allyl Silanes.
No full textSubstituted silacyclohexenes, generated through silene–diene [4 + 2] cycloaddition reactions, undergo Lewis acid promoted Sakurai type reactions with acetals to afford, following oxidation of the resultant fluorosilane, 1,4-diols with four contiguous chiral centres
Asymmetric, <i>anti</i>-Selective Scandium-Catalyzed Sakurai Additions to Glyoxyamide. Applications to the Syntheses of <i>N</i>-Boc d-Alloisoleucine and d-Isoleucine
No full textAn enantio- and diastereoselective Sakurai−Hosomi reaction, catalyzed by chiral scandium pyridyl-bis(oxazoline) (pybox) complexes, has
been developed. Both alkyl- and aryl-substituted allylsilanes are effective coupling partners with N-phenylglyoxamide. Applications of this
reaction to the asymmetric syntheses of N-Boc d-alloisoleucine and d-isoleucine are described
Asymmetric, <i>anti</i>-Selective Scandium-Catalyzed Sakurai Additions to Glyoxyamide. Applications to the Syntheses of <i>N</i>-Boc d-Alloisoleucine and d-Isoleucine
No full textAn enantio- and diastereoselective Sakurai−Hosomi reaction, catalyzed by chiral scandium pyridyl-bis(oxazoline) (pybox) complexes, has
been developed. Both alkyl- and aryl-substituted allylsilanes are effective coupling partners with N-phenylglyoxamide. Applications of this
reaction to the asymmetric syntheses of N-Boc d-alloisoleucine and d-isoleucine are described
Brønsted-Säure-katalysierte Hosomi-Sakurai-Reaktionen und Prolin-katalysierte Mannich-Reaktion von Acetaldehyd
No full textDie vorliegende Arbeit gliedert sich in zwei Teile. Im ersten und größeren Teil wird die Entwicklung von Brønsted-Säure-katalysierten Hosomi-Sakurai-Reaktionen von Acetalen beschrieben. Diese neue organokatalytische Methode erlaubt den direkten Zugang zu Homoallylethern mit sehr guten Ausbeuten und zeichnet sich besonders durch ein breites Substratspektrum, eine hohe Toleranz gegenüber funktionellen Gruppen sowie eine praktische Anwendbarkeit aus. Des Weiteren wurde eine Hosomi-Sakurai-Dreikomponentenreaktion entwickelt. Auch die Sequenz aus Acetalisierung von Aldehyden und Allylierung lieferte die entsprechenden Homoallylether mit guten Ausbeuten. Eine asymmetrische Hosomi-Sakurai-Reaktion unter Einsatz von chiralen Brønsted-Säuren wird ebenfalls beschrieben. Chirale N Triflylphosphoramide katalysieren die Bildung von Homoallylethern mit Enantioselektivitäten von bis zu 53%. Der zweite Teil beinhaltet die Arbeiten zur Prolin-katalysierten Mannich-Reaktion von Acetaldehyd mit N-Boc-Iminen, welche die Nützlichkeit der von Acetaldehyd abgeleiteten Mannich-Produkte für die organische Synthese veranschaulicht
Tandem Sakurai-Aldol Addition Reactions as a Route to Structurally Complex Carbocycles
No full textTandem intramolecular Sakurai-aldol reactions provide a concise and highly diastereoselective route
to substituted cyclohexenone derivatives. The cyclization substrates are readily obtained using olefin
isomerization−Claisen rearrangement (ICR) reactions to prepare the key chiral allyl silane
precursors. The Claisen reaction products are elaborated to the chiral Sakurai-aldol substrates by
an efficient two-step sequence involving vinyl organometallic-aldehyde addition and oxidation of
the resulting alcohol. The reaction of the resulting enones with TiCl4 elicits a highly stereoselective
allyl silane conjugate addition to produce a trichlorotitanium enolate as the reaction intermediate;
intermolecular trapping of the enolate with an aldehyde provides pentasubstituted cyclohexanone
derivatives in which the annulation reaction establishes four stereocenters and two new C−C bonds.
A fully intramolecular variant of the Sakurai-aldol reaction that creates four stereocenters, two
new C−C bonds, and establishes two new carbocyclic rings is also described
Applications of Iridium-Catalyzed Isomerization Claisen Rearrangements (ICR) to Complex Molecule Synthesis
No full textThe iridium-catalyzed isomerization Claisen rearrangement (ICR) methodology developed in theNelson group has provided access to a broad range of diastereomerically enricheddisubstituted unsaturated aldehydes. Allylsilyl aldehydes produced by the ICR reaction havebeen further elaborated into substrates for highly diastereoselective intramolecular Hosomi-Sakurai annulation reactions. The Sakurai annulation has proven to be particularly powerfulwhen carried out in tandem with intramolecular aldol or Mannich reactions to form complexfused ring systems. An attempted strategic application of this methodology to the synthesis ofthe Rauwolfia alkaloids reserpine and yohimbine is detailed.Vinyl boronic esters have been demonstrated to be effective precursors for the ICRreaction providing diastereomerically enriched boronic aldehydes. The potential forintramolecular chelation between the newly formed aldehyde and proximal boronic ester hasbeen investigated. The boron functionality has proven to be useful for accessing alkoxy- andaryl-substituted compounds that are typically unavailable from the ICR reaction. A synthesis ofthe plant growth inhibitor penieone has been explored in order to demonstrate the practicalapplication of this methodology to complex molecule construction
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