The Hofmann-Löffler-Freytag reaction, carried out by irradiation in sulphuric acid of N-chloro-l-amino-acids 3a-d, gives δ-chlorinated compounds which can be cyclized to l-prolines 4a-e. This convenient synthesis does not affect the asymmetric centres of the starting material giving prolines in optically-pure form directly without the need for resolution.