Asymmetric hydrogenation of cyclohexane-1,2-dione over cinchonidine-modified platinum

摘要

The asymmetric hydrogenation of cyclohexane-1,2-dione over cinchonidine-modified platinum was investigated.Despite the fact that first hydrogenation step is close to nonenantioselective, a high enantiomeric excess is obtained for the (R)-alpha-hydroxyketone due to kinetic resolution. In the second hydrogenation step one out of the fourreactions of the network is substantially accelerated with respect to the others and with respect to the reaction in the absence of modifier, leading to an enantiomeric excess of (1R,2R)-trans-dyclohexane-1,2-diol of over 80%. Comparison with recently reported asymmetric hydrogenation of alpha-hydroxyethers indicates striking similarities, which hint at similar reactant-modifier interaction in both cases. The importance of cis versus trans conformation of the reactant for the reactant-modifier interaction emerges from a comparison of suggested fraction intermediates for cyclohexane-1,2-dione and butane-2,3-dione hydrogenation, respectively.