Asymmetric synthesis of pre-protected α,α-disubstituted amino acids from tert-butanesulfinyl ketimines

A method for the asymmetric synthesis of pre-protected α,α-disubstituted amino acids is described. 5-Methylfuryllithium is added into sulfinyl ketimines 1 in the presence of AlMe3 to afford the sulfinamides 2 in 75–97% yields and with diastereoselectivities ranging from 75:25 to 99:1. Subsequent oxidation with RuCl3/NaIO4 affords tert-butanesulfonyl (Bus)-protected α,α-disubstituted amino acids 3 in 62–69% yields. Bus-protected amino acids readily undergo amide bond formation, after which the Bus group can be removed with TfOH/CH2Cl2 to afford the free amine.