Ruthenium-Catalyzed Asymmetric Hydrogenation of Aromatic Ketones

3 Ruthenium-Catalyzed Asymmetric Hydrogenation of Aromatic Ketones 

With the chiral diamine (S,S)-20 as a co-catalyst full conversion was obtained in all cases, indicating that the amine has a pronounced influence on reactivity and selectivity (entries 9-14). The combination (R Rc)-4ael/(S,S)-20 afforded 18a as an almost racemic mixture (entry 9). The value of 6% ee (R) obtained in this experiment reflects two opposite contributions. On one hand, the system chiral phosphorous ligand/achiral diamine (R Rc)-4ael/19 led to 18a with 65% ee (S) (entry 1). On the other hand, an ee value of 75% (R) in the hydrogenation of 1-acetonaphthone has been reported for the system achiral phosphine (PPh3)/(S,S)-20 [41] This indicates that two inductions are canceled in an almost additive way in the mixed system. 

With respect to the enantioselectivity, the results obtained with QUINAPHOS compares well with the best catalytic systems known [31] Significantly higher catalyst activity has been found using the Noyori system [42]. 

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