Asymmetric Conjugate Addition of Unmodified Propionaldehyde to β- Nitrostyrenes Catalyzed by Readily Available Proline-Based Dipeptidols

Organocatalytic asymmetric additions of unmodified aldehydes to β-nitrostyrenes are important carbon-carbon bond formation reactions and have become very attractive recently, because they are metal-free and environmentally benign. This work employed a series of L-proline-based diphenyl dipeptidols to catalyze this reaction. The results showed that these dipeptidols were effective organocatalysts with the yield up to 99%. 3a was optimal with the highest enantioselectivity up to 75% and dr (syn/anti) up to 94/6. In addition, the mechanism of this asymmetric reaction is also discussed.