The invention relates to a novel process for the preparation of (3S,4S)- or (3R,4R)-1-benzyl-4-(halogen-aryl)-pyrrolidine-3-carboxylic acids of formula I or salts thereof, wherein X and Y are each independently hydrogen or a halogen atom, with the proviso that at least one of X or Y is a halogen atom. The compounds of formula I are useful as starting materials or intermediates for the preparation of pharmaceutically active compounds, especially for compounds, which are useful for the treatment of central nervous system disorders.