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Hydrogenation of cinchona alkaloids over supported Pt catalyst
György Szöllosi1, Péter Forgó, Mihály Bartók
1Organic Catalysis Research Group of the Hungarian Academy of Sciences, Department of Organic Chemistry, University of Szeged, Szeged, Hungary. szollosi@chem.u-szeged.hu
Abstract:
The heterogeneous catalytic hydrogenation of two isomeric cinchona alkaloids, cinchonidine and cinchonine, was studied over Pt/Al(2)O(3) in 1N H(2)SO(4) solution under 100 bar H(2) at 25 degrees C. Cinchonidine was transformed into two diastereomeric hexahydroderivatives by hydrogenation of ring A (with N) of the quinoline moiety (yield over 95%, diastereomeric ratio 2/3), whereas hydrogenation of cinchonine resulted in the formation of three products, the major one being formed by the hydrogenation of ring B (without N) (yield 60%). The isolated hexahydroderivatives were investigated by (1)H-, (13)C-NMR, (1)H-(1)H COSY, (1)H-(13)C HetCOSY, and NOESY spectroscopy and were used as modifiers in the heterogeneous enantioselective hydrogenation of ethyl pyruvate and as catalysts in the Michael addition of ethyl 2-oxocyclopentanecarboxylate to methyl vinyl ketone.