Green and modular synthesis of azepino[4,3,2-cd]indoles and diazepino[6,5,4-cd]indoles via hydride transfer-involved cascade cyclization in ethanol†

The modular synthesis of high-value azepino[4,3,2-cd]indole and its analogs from versatile synthons and readily available feedstocks has been a challenging area of research. Herein, we report a 1,6-hydride transfer-involved cascade [6 + 1] cyclization of 4-dialkylamino-indole-3-carbaldehydes with diverse 1C,1C- and 1N,1N-bisnucleophiles in ethanol, enabling the green and modular synthesis of azepino[4,3,2-cd]indoles and diazepino[6,5,4-cd]indoles. The key features of this method are: catalyst-free, redox-neutral conditions, excellent substrate compatibility, operational simplicity, gram-scale applicability, and versatile product derivatization.