Asymmetric Proline‐Catalyzed Addition of Aldehydes to 3H‐Indol‐3‐ones: Enantioselective Synthesis of 2,3‐Dihydro‐1H‐indol‐3‐ones with Quaternary Stereogenic Centers

The proline‐catalyzed addition of various aliphatic aldehydes to sterically hindered 2‐aryl‐substituted 3 H ‐indol‐3‐ones affords 2,2‐disubstituted 2,3‐dihydro‐1 H ‐indol‐3‐one derivatives with excellent enantioselectivities. In addition, the synthesis of a chiral derivative, ( S )‐2‐(2‐bromophenyl)‐2,3‐dihydro‐2‐(2‐hydroxyethyl)‐1 H ‐indol‐3‐one, which can be used as an intermediate for the preparation of the natural product hinckdentine A was accomplished with a high level of enantioselectivity.