Synthesis of Azepinoindoles and Oxepinoindoles through Brønsted-Acid-Catalyzed Cyclization of an <i>In Situ</i> Generated Dihydrospiroquinoline Intermediate

Abstract

We have developed a straightforward and efficient synthetic protocol to produce 5,6,7,12-tetrahydrobenzo[2,3]azepino[4,5-<i>b</i>]indole and 7,12-dihydro-6<i>H</i>-benzo[2,3]oxepino[4,5-<i>b</i>]indole derivatives under mild conditions. This annulation process involves the intramolecular cyclization of the <i>in situ</i> 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.