Total Synthesis of Phenanthroindolizidine Alkaloids by Combining Iodoaminocyclization with Free Radical Cyclization

A concise and modular synthesis of phenanthroindolizidine alkaloids was achieved by combining iodoaminocylization with a free radical cyclization approach. The route described allowed the preparation of (+/-)-tylophorine, (+/-)-antofine, and (+/-)-deoxypergularinine in six steps. When commercially available L-prolinol was used as a chiral building block, (S)-(+)-tylophorine was also synthesized in 49% yield and >99% ee over five linear steps.