Masked oxo sulfinimines (N-sulfinyl imines) in the asymmetric synthesis of proline and pipecolic acid derivatives.

[structure: see text]. On addition of Et2AlCN/i-PrOH, masked oxo sulfinimines give alpha-amino nitriles that afford oxo alpha-amino acids on hydrolysis. These amino acids cyclize and are reduced to cis proline and cis pipecolic acids derivatives in high ee and good yield. This new procedure avoids many of the limitations related to the preparation of oxo amino acids from proteinogenic amino acids.