Chiral Lewis Base‐Catalyzed, Enantioselective Reduction of Unprotected β‐Enamino Esters with Trichlorosilane

Catalytic asymmetric reduction of N‐unsubstituted β‐enamino esters represents a major challenge for asymmetric catalysis. In this paper, the first organocatalytic system that could be used for the asymmetric hydrosilylation of N‐unsubstituted β‐enamino esters has been developed. Using N ‐ tert ‐butylsulfinyl‐ L ‐proline‐derived amides and L ‐pipecolinic acid‐derived formamides as catalyst, a broad range of β‐aryl‐ and β‐alkyl‐substituted free β‐amino esters could be prepared with high yields and enantioselectivities. The practicality was illustrated by the gram‐scale asymmetric synthesis of ethyl ( R )‐3‐amino‐3‐phenylpropanoate and isopropyl ( S )‐3‐amino‐4‐(2,3,5‐trifluorophenyl)butanoate. The resulting product can be smoothly transformed to the FDA approved medicines dapoxetine and sitagliptin in a short synthetic route.