Asymmetric hydrogenation of racemic 2-fluorocyclohexanone over cinchona modified Pt/Al2O3 catalyst

The first example of enantioselective heterogeneous catalytic hydrogenation of an α-fluoro ketone is reported. The hydrogenation of racemic 2-fluorocyclohexanone over cinchonidine- or methoxycinchonidine-modified Pt/Al2O3 resulted in diastereoselective and enantioselective formation of the cis  -(1R,2S1R,2S)-2-fluorocyclohexanol. Due to the preferential hydrogenation of the S enantiomer, the kinetic resolution of the substrate was possible; the unreacted R enantiomer was accumulated in the reaction mixture. Under our experimental conditions, high diastereoselectivities (up to 85%) and good enantioselectivities (up to 59%) were obtained, demonstrating that activation of a ketone by a single α fluorine atom is efficient for obtaining enantiodiscrimination in this heterogeneous catalytic system.