Synthetic study on tetrapetalones: stereoselective cyclization of N-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 gamma-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.