Chiral organosilicon compounds, such as α-aminosilanes, are useful in pharmaceutical chemistry. Existing methods for the synthesis of chiral α-aminosilanes usually require stoichiometric chiral reagents or other expensive reactants.

Zhenfeng Zhang, Wanbin Zhang, and colleagues, Shanghai Jiao Tong University, China, have developed the first asymmetric hydrogenation of N-sulfonyl arylsilylimines, which provides access to protected chiral α-aminosilanes (example pictured). The team used Pd(OCOCF₃)₂ as the catalyst, together with the chiral diphosphine ligand QuinoxP* or 2,3-bis(tert-butylmethylphosphino)quinoxaline. This allowed them to convert a range of N-sulfonyl arylsilylimines into the corresponding amines under an H₂ atmosphere.

The reaction proceeds with high yields and excellent enantioselectivities. The sulfonyl protecting group (RO₂S–) can be removed by converting it to a tert-butoxycarbonyl (Boc) group using di-tert-butyl dicarbonate (Boc₂O). The Boc group is then removed using chlorotrimethylsilane (TMSCl) to give the free α-aminosilanes. According to the researchers, these products can act as mimics of natural α-amino acids in biologically active compounds.

• Synthesis of Chiral α-Aminosilanes through Palladium-Catalyzed Asymmetric Hydrogenation of Silylimines,
  Dongyang Fan, Yang Liu, Jia Jia, Zhenfeng Zhang, Yangang Liu, Wanbin Zhang,
  Org. Lett. 2019.
  https://doi.org/10.1021/acs.orglett.8b04073