Indole Annulation via an Internal Redox Cascade

Significance

Seidel and colleagues developed a novel indole annulation reaction, which forms polycyclic azepinoindoles 3 in a one-pot internal redox process. The transformation is thought to proceed via an acid-catalyzed condensation of aminobenzaldehydes 1 and indoles 2 to form a putative intermediate A (in equilibrium with B). A 1,5-hydride shift from the amine moiety at 150 ˚C presumably generates iminium C, which undergoes cyclization to form 3. A range of substituents on the indole and aminoaldehyde partners as well as non-indole nucleophiles were tolerated in the reaction.