Synthesis of Azepinoindoles and Oxepinoindoles through Brønsted-Acid-Catalyzed Cyclization of an In Situ 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-b]indole and 7,12dihydro-6H-benzo[2,3]oxepino[4,5-b]indole derivatives under mild conditions. This annulation process involves the intramolecular cyclization of the in situ 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.

Base-promoted fused β-carboline formation from 2-(1H-indol-3-yl)cyclohexan-1-ones, aldehydes and ammonium salts

“…Besides, it was found that the addition of radical scavengers such as TEMPO and BHT into the systems had no obvious prohibiting effect on the yield, suggesting that the three-component reaction might not proceed through a radical pathway. Based on previous studies and related literature, 4,15 b ,16 a ,18,21 we propose a plausible mechanistic reaction pathway to account for the product formation (Fig. 5b).…”