Tandem radical cyclizations with iodoaryl azides: formal total synthesis of (+/-)-aspidospermidine.

An iodoazide radical cascade cyclization strategy has been used as the key step in a formal synthesis of aspidospermidine. Specifically, this step generated the alkaloid's B- and E-rings in the ethylidene-functionalized tetracycle 5. In turn, this was converted into pentacycle 25, a known advanced synthetic precursor of aspidospermidine.