Diastereoselective Reductive Amination of Aryl Trifluoromethyl Ketones and α‐Amino Esters

Reductionist art: Careful choice of the reducing agent in the reductive amination of trifluoromethyl ketones with α-amino esters allows stereoselective access, from the imine formed, to either the R,S or S,S diastereomers of the resulting amino acids. Whereas NaBH4 affords the R,S diastereomers, Zn(BH4)2 affords the S,S diastereomers (see scheme), which can be easily converted into potent cathepsin K inhibitors.