Synthesis of Azepinoindoles and Oxepinoindoles through Brønsted-Acid-Catalyzed Cyclization of an Generated Dihydrospiroquinoline Intermediate.

We have developed a straightforward and efficient synthetic protocol to produce 5,6,7,12-tetrahydrobenzo[2,3]azepino[4,5-]indole and 7,12-dihydro-6-benzo[2,3]oxepino[4,5-]indole derivatives under mild conditions. This annulation process involves the intramolecular cyclization of the generated ketimine moiety via the formation of dihydrospiroindolequinoline, which serves as a key intermediate in the reaction pathway. Several control experiments and spectroscopic studies were performed to elucidate the underlying reaction mechanism.