Racemization-Free Synthesis of (<i>S</i>)-(+)-Tylophorine from <scp>l</scp>-Proline by Radical Cyclization

Abstract

The phenanthroindolizidine alkaloid (S)-(+)-tylophorine was synthesized from L-proline in nine linear steps including a double bromination and a free-radical cyclization of an N-aziridinylimine as the key steps. The phenanthrene moiety was prepared from homoveratric acid and veratraldehyde and permits the variation of each oxygen-substituted ring.