- The Mechanism of Hydrogenation by Aqueous Chromium(II) Ion of the Carbon-Carbon Double Bond of Olefinic Compounds with Polar Substituents
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The kinetics of the reaction of Cr2+ with maleic acid, fumaric acid, methylmaleic acid, chloromaleic acid, dichloromaleic acid, and methylfumaric acid have been investigated over a wide range of chloromaleic > maleic methylmaleic > dichloromaleic > fumaric and maleic > dichloromaleic ligand is in excess.In excess of Cr2+ the rate law is as shown below and k3 follows the trend: chloromaleic > maleic > dichloromaleic > methylmaleic > methylfumaric.With excess ligand, L, the rate law has two terms (below) and the two rate constants, k3' and k2' follow the order: chloromaleic > maleic methylmaleic > dichloromaleic > fumaric and maleic > dichloromaleic methylmaleic > chloromaleic respectively.The kinetic data are supplemented by stoicheiometric data, by determinations of product distribution, and by spectroscopic data, and they are discussed in terms of a model involving at least partial attack by Cr2+ directly on the C=C double bonds.
- Katakis, Dimitris,Vrachnou-Astra, Ersi,Konstantatos, John
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p. 1491 - 1498
(2007/10/02)
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- TOTAL SYNTHESIS OF ANTITUMOR AGENT AT-125, (αS,5S)-α-AMINO-3-CHLORO-4,5-DIHYDRO-5-ISOXAZOLEACETIC ACID
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A short and efficient total synthesis of racemic AT-125 and its racemic threo isomer proceeds via an intramolecular Michael cyclization of a protected α,β-dehydroglutamic acid γ-hydroxamate.Separation of diastereomers and deprotection to racemic AT-125 followed by enzymatic resolution of the N-chloroacetamide with hog-kidney acylase provides the natural αS,5S isomer.
- Baldwin, Jack E.,Cha, Jin K.,Kruse, Lawrence I.
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p. 5241 - 5260
(2007/10/02)
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- Dianions Derived from α-Halo Acids. The Darzens Condensation Revisited
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The dianions of α-halo carboxylic acids are readily generated by the addition of the acids to 2 equiv of lithium diisopropylamide at low temperatures.When the mixture warms to room temperature dimeric products are formed.When aldehydes and ketones were added to the cooled solutions of the dianions and the reaction mixtures were allowed to warm to room temperature, followed by acid quench, glycidic acids were formed.The glycidic acids, per se, were often too unstable to be isolated and purified but could be analyzed by conversion to their methyl esters withdiazomethane.When the reactions were quenched prematurely, α-chloro-β-hydroxy carboxylic acids were isolated.Homologated aldehydes and ketones were obtained from the glycidic acids by catalytic and thermal decarboxylation methods.
- Johnson, Carl R.,Bade, Thomas R.
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p. 1205 - 1212
(2007/10/02)
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