Asymmetric hydrogenation of diketones catalyzed by magnesium oxide‐supported chitosan–Rh complex

MgO‐supported chitosan–Rh complex (MgO‐CS‐Rh) has been prepared and found to be a highly stereoselective catalyst for the asymmetric hydrogenation of some diketones to corresponding chiral alcohols, such as 2,3‐butanedione to (2S,3S)‐(+)‐2,3‐butanediol and 2,4‐pentanedione to (2S,4S)‐(+)‐2,4‐pentanediol at room temperature and under 1 atm H2. The optical yield was greatly affected by the Rh content in the complex, the solvent and the reaction temperature. The optical yields of (2S,3S)‐(+)‐2,3‐butanediol and (3S,4S)‐(+)‐2,4‐pentanediol obtained were 87% and 81.2%, respectively. The chiral chitosan–Rh complex catalyst was very easy to prepare, and could be reused without noticeable change in its optical catalytic activity.