The Experts below are selected from a list of 42 Experts worldwide ranked by ideXlab platform

William R. Roush - One of the best experts on this subject based on the ideXlab platform.

  • Total synthesis of formamicin.
    Journal of the American Chemical Society, 2004
    Co-Authors: Timothy B. Durham, Nicolas Blanchard, Brad M. Savall, Noel A. Powell, William R. Roush
    Abstract:

    The enantioselective total synthesis of the cytotoxic plecomacrolide natural product formamicin (1) is described. Key aspects of this synthesis include the efficient transacetalation reactions of MOM ethers 28 and 38 to form the seven-membered formyl acetals 29 and 39, a late-stage Suzuki cross-coupling reaction of the highly functionalized vinyl boronic acid 6 and vinyl iodide 7, a highly beta-selective glycosidation reaction of Beta-Hydroxy Ketone 4 with 2,6-dideoxy-2-iodoglucopyranosyl fluoride 3, and the global desilylation of penultimate intermediate 77 mediated by in situ generated Et(3)N.2HF.

  • An NMR Method for Assigning Relative Stereochemistry to β-Hydroxy Ketones Deriving from Aldol Reactions of Methyl Ketones
    The Journal of organic chemistry, 2002
    Co-Authors: William R. Roush, Thomas D. Bannister, Michael D. Wendt, Michael S. Vannieuwenhze, Darin J. Gustin, Garrett J. Dilley, Gregory C. Lane, Karl A. Scheidt, William Smith
    Abstract:

    We describe a simple 1H NMR analysis that permits the stereochemistry of Beta-Hydroxy Ketones to be assigned by visual inspection of the ABX patterns for the alpha-methylene unit of the Beta-Hydroxy Ketone in the 1H NMR spectra. This method has been verified by application to a wide range of Beta-Hydroxy Ketones deriving from aldol reactions of chiral aldehydes with a variety of chiral and achiral methyl Ketone enolates (see Tables 1 and 2). The stereochemistry of 54 of these compounds have been assigned by rigorous chemical methods.

Marcos N. Eberlin - One of the best experts on this subject based on the ideXlab platform.

  • Structurally diagnostic ion-molecule reactions: acylium ions with α-, β- and γ-hydroxy Ketones
    Journal of mass spectrometry : JMS, 2002
    Co-Authors: Luiz Alberto Beraldo De Moraes, Marcos N. Eberlin
    Abstract:

    Gas-phase reactions of four acylium ions and a thioacylium ion with three isomeric alpha-, beta- and gamma-hydroxy Ketones are performed by pentaquadrupole mass spectrometric experiments. Novel structurally diagnostic reactions are observed, and found to correlate directly with interfunctional group separation. All five ions tested (CH(3)CO(+), CH(2)(double bond)CHCO(+), PhCO(+), (CH(3))(2)NCO(+) and (CH(3))(2)NCS(+)) react with the gamma-hydroxy Ketone (5-hydroxy-2-pentanone) to form nearly exclusively a cyclic oxonium ion of m/z 85 that formally arises from hydroxy anion abstraction. With the Beta-Hydroxy Ketone (4-hydroxy-2-pentanone), CH(2)(double bond)CHCO(+), PhCO(+) and (CH(3))(2)NCO(+) form adducts that undergo fast cyclization via intramolecular water displacement, yielding resonance-stabilized cyclic dioxinylium ions. With the alpha-hydroxy Ketone (3-hydroxy-3-methyl-2-butanone), PhCO(+), (CH(3))(2)NCO(+) and (CH(3))(2)NCS(+) form stable adducts. Evidence that these adducts display cyclic structures is provided by the triple-stage mass spectra of the (CH(3))(2)NCS(+) adduct; it dissociates to (CH(3))(2)NCO(+) via a characteristic reaction-dissociation pathway that promotes sulfur-by-oxygen replacement. If cyclizations are assumed to occur with intramolecular anchimeric assistance, relationships between structure and reactivity are easily recognized.

Bin Chao - One of the best experts on this subject based on the ideXlab platform.

Luiz Alberto Beraldo De Moraes - One of the best experts on this subject based on the ideXlab platform.

  • Structurally diagnostic ion-molecule reactions: acylium ions with α-, β- and γ-hydroxy Ketones
    Journal of mass spectrometry : JMS, 2002
    Co-Authors: Luiz Alberto Beraldo De Moraes, Marcos N. Eberlin
    Abstract:

    Gas-phase reactions of four acylium ions and a thioacylium ion with three isomeric alpha-, beta- and gamma-hydroxy Ketones are performed by pentaquadrupole mass spectrometric experiments. Novel structurally diagnostic reactions are observed, and found to correlate directly with interfunctional group separation. All five ions tested (CH(3)CO(+), CH(2)(double bond)CHCO(+), PhCO(+), (CH(3))(2)NCO(+) and (CH(3))(2)NCS(+)) react with the gamma-hydroxy Ketone (5-hydroxy-2-pentanone) to form nearly exclusively a cyclic oxonium ion of m/z 85 that formally arises from hydroxy anion abstraction. With the Beta-Hydroxy Ketone (4-hydroxy-2-pentanone), CH(2)(double bond)CHCO(+), PhCO(+) and (CH(3))(2)NCO(+) form adducts that undergo fast cyclization via intramolecular water displacement, yielding resonance-stabilized cyclic dioxinylium ions. With the alpha-hydroxy Ketone (3-hydroxy-3-methyl-2-butanone), PhCO(+), (CH(3))(2)NCO(+) and (CH(3))(2)NCS(+) form stable adducts. Evidence that these adducts display cyclic structures is provided by the triple-stage mass spectra of the (CH(3))(2)NCS(+) adduct; it dissociates to (CH(3))(2)NCO(+) via a characteristic reaction-dissociation pathway that promotes sulfur-by-oxygen replacement. If cyclizations are assumed to occur with intramolecular anchimeric assistance, relationships between structure and reactivity are easily recognized.

William Smith - One of the best experts on this subject based on the ideXlab platform.