Modifier–substrate interactions of various types in the Orito reaction: Reversal of the enantioselection in the hydrogenation of ketopantolactone on Pt modified by β-isocinchonine and O-phenylcinchonidine

The enantioselective hydrogenation of ketopantolactone (KPL) on Pt–alumina catalyst modified by β-isocinchonine (β-ICN) and O-phenylcinchonidine (PhOCD) in toluene, acetic acid and their mixtures under otherwise identical experimental conditions was studied. Reversal of the enantioselection was obtained dependent on the concentration of acetic acid (eemax = 17% (S) on Pt–PhOCD and 50% (R) on Pt–β-ICN, respectively). The possible role in enantioselection of adducts forming in the reaction mixture and the stability of PhOCD under the conditions of the hydrogenation was investigated by ESI-MS. The results of the nonlinear phenomenon measurements on β-ICN + PhOCD mixtures suggest that the intermediate surface complexes β-ICN–KPL and PhOCD–KPL responsible for the opposite enantioselection include different types of interactions and the enantioselection is directed by the competition between these interactions.

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► Hydrogenation of KPL over Pt modified β-ICN and PhOCD was studied.
► The reversal of the enantioselection was dependent on the AcOH concentration.
► PhOCD did not suffered C–O bond hydrogenolysis in the presence of AcOH.
► Competing intermediate complexes involving different interactions were suggested.