Diels‐Alder Cycloaddition of Azepino[4,5‐b]indoles Towards Hydrocarbazole Derivatives and Related Heterocycles

Abstract An approach to hydrocarbazoles bearing an all‐carbon quaternary center at C4a position was developed via a Brønsted acid‐initiated Diels‐Alder cycloaddition/retro‐aza‐Michael addition cascade process from azepino[4,5‐ b ]indoles and commercially available dienophiles. The method provided a range of hydrocarbazoles in 63–99% yields. The practicality of this transformation was demonstrated by a scale‐up experiment and various transformations to several hydrocarbazole derivatives and the tetracyclic indoline scaffold. Moreover, hetero‐Diels‐Alder cycloadditions of azepino[4,5‐ b ]indoles were explored with 4‐phenyl‐3 H ‐1,2,4‐triazole‐3,5(4 H )‐dione (PTAD) and 82–99% yields were obtained. magnified image