- Trans-Selective and Switchable Arene Hydrogenation of Phenol Derivatives
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A trans-selective arene hydrogenation of abundant phenol derivatives catalyzed by a commercially available heterogeneous palladium catalyst is reported. The described method tolerates a variety of functional groups and provides access to a broad scope of trans-configurated cyclohexanols as potential building blocks for life sciences and beyond in a one-step procedure. The transformation is strategically important because arene hydrogenation preferentially delivers the opposite cis-isomers. The diastereoselectivity of the phenol hydrogenation can be switched to the cis-isomers by employing rhodium-based catalysts. Moreover, a protocol for the chemoselective hydrogenation of phenols to cyclohexanones was developed.
- Bergander, Klaus,Glorius, Frank,Heusler, Arne,Wollenburg, Marco
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p. 11365 - 11370
(2020/11/24)
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- Porcine pancreas lipase catalysed acetylation of β-cyclodextrin anchored 4-t-butylcyclohexanol
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Porcine pancreas lipase (PPL) catalyzed acetylation of 4-t- butylcyclohexanol gives 10% ester. However, when the latter is included inside hepatakis (2,3,6-tri-O-acetyl)-β-cyclodextrin (β-CD acetate) cavity, this enzymatic reaction affords the highest yield of 86.6%. The enzymatic esterification has been studied as a function of β-CD acetate, PPL and acetic anhydride concentrations. A stoichiometry of 2:1 for 4-t-butylcyclohexanol-β-CD acetate complex is determined. Both trans and cis 4-t-butylcyclohexanol have been found to be acetylated. Gas Chromatographic analysis of the reaction mixtures shows that trans/cis ratios of the esters formed varied from 2.1 to 4.34.
- Manohar, Balaraman,Divakar, Soundar
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p. 2661 - 2665
(2007/10/03)
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- 2-Norbornanediazonium Ions Revisited
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The reactions of 2-norbornanediazonium ions have been reinvestigated with the aid of optically active and deuterium-labeled precursors.Enantiomeric purities were determined by direct VPC methods, and deuterium distributions by 2H NMR spectroscopy.The product pattern is strongly affected by the polarity of the solvent. exo-Diazonium ions 13 in water yield racemic exo alcohol (s,kΔ) of the norbornadiazonium ions.Optically active exo products are typical of nonpolar solvents and originate most probably from assymetric ion pairs.Model studies with optically active bicyclooct-3-en-2-amine (36) provide conclusive evidence that ion-pair colapse may lead to optically active products even in the case of delocalized achiral carbocations.
- Kirmse, Wolfgang,Siegfried, Rainer
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p. 950 - 956
(2007/10/02)
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- A PROCEDURE FOR ALCOHOL INVERSION USING CESIUM ACETATE
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A convenient and efficient procedure for alcohol inversion by means of the reaction of mesylates or alkyl halides with cesium acetate is described.
- Huffman, John W.,Desai, Ranjit C.
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p. 553 - 558
(2007/10/02)
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- Acid-induced 13C Nuclear Magnetic Resonance Chemical Shift Changes of Ether and Ester Carbon Atoms
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13C N.m.r. chemical shifts of ehters dissolved in tetrachloromethane are displaced on addition of trifluoroacetic acid.The displacements result from independent interactions of the acid with the substrate oxygen atoms and alkyl residues.The structure-dependent and stereoselective shift changes are useful for signal assignments, structure determination, conformational analysis, assessment of the distribution of rapidly interconverting conformers of esters, and estimation of the relative basicity of ethers.
- Begtrup, Mikael
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p. 1609 - 1618
(2007/10/02)
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- Solvent and Gas-phase Effects on the Equilibrium between Configurational Isomers of Some 4-t-Butylcyclohexanes
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Through a combination of gas chromatographic head space analysis, gas chromatography retention times, and calorimetrically determined enthalpies of solution, the effect of various solvents, relative to the gas phase, on values of ΔG0, ΔH0, and ΔS0 for the equilibrium between r-1,t-2-dibromo-c-4- and r-1,t-2-dibromo-t-4-t-butylcyclohexane has been determined.It is shown that the more polar diequatorial dibromo-isomer is stabilised relative to the diaxial isomer both in terms of Gibbs energy and enthalpy in polar media.Although values of ΔG0, ΔH0, and ΔS0 for the equilibrium in nonpolar solvents approach the gas-phase values, there are still noticeable differences in these thermodynamic parameters between the gas phase and solvents such as hexane and cyclohexane.The effects of various media on ΔG0 values for the equilibria between cis- and trans-4-t-butylcyclohexyl bromide and cis- and trans-4-t-butylcyclohexyl acetate have also been determined, but values of ΔG0 for these two equilibria are largely independent of the reaction medium.
- Abraham, Michael H.,Xodo, Luigi E.,Cook, Michael J.,Cruz, Raymundo
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p. 1503 - 1510
(2007/10/02)
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