1,6-Hydride Transfer-Enabled [6 + 1] Annulation to Access Polycyclic 3,4-Fused Azepinoindoles

A [6 + 1] annulation reaction via cascade 1,6-hydride transfer/cyclization is reported to construct a polycyclic 3,4-fused azepinoindole skeleton. The newly designed 4-amino-indole-3-carbaldehyde is applied as a novel six-atom synthon, interacting with arylamines and malononitrile to achieve the [6 + 1] annulation. Notably, the reaction proceeds smoothly under redox-neutral and metal-free conditions, providing a wide range of azepinoindoles in up to 94% yields, with water as the only byproduct. Besides, the advantage of high step- and atom-economy further highlights the practicality of this methodology.