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.
Ye, Jianheng,Wang, Chao,Chen, Lin,Wu, Xinjun,Zhou, Li,Sun, Jian
p. 1042 - 1047
(2016/04/19)
A highly enantioselective organocatalytic method for reduction of aromatic N-alkyl ketimines
A study has demonstrated the development of a highly enantioselective catalytic method for the reduction of aromatic N-alkyl ketimines by trichlorosilane under mild conditions using the newly designed Lewis base organocatalyst that incorporates C- and S-chirality. The S-chiral sulfinamide group in these catalysts plays a crucial role similar to the carboxamide groups as Lewis base for the activation of HSiCl3, and also serves as a source of chirality that the carboxamide group lacks for the asymmetric induction. The results of the study showed that excellent enantioselectivities of up to 99.6% ee and high yields were obtained for a wide range of substrates. Further works is also in progress to clarify the mechanism of the transformation and explore the full application scope of the present catalyst system.
Wang, Chao,Wu, Xinjun,Zhou, Li,Sun, Jian
supporting information; experimental part
p. 8789 - 8792
(2009/09/25)
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