Reversal of the ee in enantioselective hydrogenation of activated ketones in continuous-flow fixed-bed reactor system

A study on the hydrogenation of ethyl pyruvate, methyl benzoylformate and 2,2,2-trifluoroacetophenone over Pt–cinchona alkaloid chiral catalysts and over the “unmodified” catalysts resulted after a cleaning step at 323 K of the chirally modified surfaces in continuous-flow fixed-bed reactor system is presented. According to these investigations the sense of the residual ee observed in the reactions carried out in the absence of modifiers over the catalysts rinsed after the chiral hydrogenations was influenced by the solvent and the structure of the activated ketone, pointing on the effect of these parameters on the structure of the adsorbed intermediate complexes and implicitly on the chiral induction.

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► Cinchona alkaloid modified Pt/Al2O3 was rinsed with solvent at 323 K.
► The sense of the residual ee was dependent on the solvent and substrate structure.
► Different activated ketones follow different routes during hydrogenation.
► The route followed is affected by the structure of the intermediate complexes.