Hydrogenation of α- and β-isocinchonines on Pt-alumina catalyst in acetic acid
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The transformations of a-ICN and b-ICN were studied in the presence of hydrogen in AcOH over Pt-alumina catalyst under the conditions of the enantioselective hydrogenation of EtPy (hydrogen pressure 1-30 bar, temperature 298-323 K). It was established that the quinoline skeleton of the alkaloids is hydrogenated even under mild experimental conditions, whereas hydrogenolysis of the oxazacycloalkane structure only takes place at hydrogen pressures exceeding 1 bar. ESI-MS-MS, HPLC-ESI-ion-trap MS and NMR made possible the identification of several hydrogenated cinchona alkaloid derivatives with so far unknown structures. According to these experimental results, the conformation of isocinchona alkaloids remains unchanged under the conditions of the enantioselective hydrogenation of activated ketones, making them suitable for utilization as chiral modifiers of well-defined conformation.
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