Synthesis of enantiopure (S)-(E)-1-haloalk-1-ene-3-amines with total or very high diastereoselectivity by halomethylenation of α-amino aldehydes promoted by CrCl2

Highly diastereoselective synthesis of enantiopure (S)-(E)-1-haloalk-1-ene-3-amines was achieved by reaction of α-amino aldehydes with trihalomethane promoted by chromium dichloride. The absence of racemization in the halomethylenation reaction was checked by chiral HPLC. A mechanism to explain this transformation is proposed.