Facile and Efficient Enantioselective Strecker Reaction of Ketimines by Chiral Sodium Phosphate

A facile and efficient enantioselective Strecker reaction of ketimines catalyzed by a chiral alkali-metal salt has been developed. When 10 mol% BNPNa (BNP=1,1'-binaphthyl-2,2'-diylphosphate) prepared in situ and 10 mol % para-test-butyl-ortho-adamantylphenol (PBAP) were introduced into the reaction, up to 96% yield and up to 95% ee (ee = enantiomeric excess) were obtained. Both aliphatic and aromatic ketimines, especially sterically bulky cyclic ketimines derived from beta-acetonaphthone, alpha-indanone, and a-tetralone were found suitable for this reaction. On the basis of the experimental results and previous reports, trimethylsilyl cyanide (TMSCN) was indicated to be the real reactive nucleophile despite the existence of PBAP, and a possible working model was proposed to explain the origin of the asymmetric induction. The facile availability of 1,1'-binaphthy1-2,2'-diylphosphoric acid (BNPH) and the simplicity of the procedure are beneficial for practical applications.