Hydrogen‐Bonding‐Promoted Cascade Rearrangement Involving the Enlargement of Two Rings: Efficient Access to Polycyclic Quinoline Derivatives.

An efficient cascade reaction of tryptamine‐derived isocyanides with C,N‐cyclic azomethine imines is described. The polycyclic pyrrolo[2,3‐c]quinoline derivatives, which benefited from rearrangement process driven by hydrogen bonding, could be directly assembled in moderate to good yields (40–87 %) under metal‐free and mild conditions. This transformation involved four new heterocyclic rings formations and uniquely, ring opening of indole as well as ring expansion of C,N‐cyclic azomethine imine. Both experimental and DFT studies provided guidance on the in‐depth insight into the reaction pathways and hydrogen bonding was identified to lower the free energy barrier in transition states. This work constitutes a rare example of tryptamine‐derived isocyanide‐based cascade reactions, and potentially could be a powerful synthetic strategy for accessing polycyclic analogues involved in natural products. [ABSTRACT FROM AUTHOR]