Synthetic Study on Tetrapetalones: Stereoselective Cyclization of <i>N</i>-Acyliminium Ion To Construct Substituted 1-Benzazepines

The synthesis of the tetracyclic core of complex antibiotic tetrapetalones has been achieved in three steps starting from the simple intermediate γ-hydroxy amide, which can be accessed through a high-yielding six-step sequence. The successful synthesis relies on a novel strategy based on the N-acyliminium ion cyclization.