Direct Access to Bridged Tetrahydroquinolines and Chromanes via an InCl3-Catalyzed Sequential Three-Component Cascade.

A sequential three-component cascade process was developed for the synthesis of bridged tetrahydroquinolines and chromanes bearing 2,6-methanobenzo[d][1,3]diazocine and 2,6-methanobenzo[g][1,3]oxazocine scaffolds, respectively, in good yields from readily available materials. The InCl3-catalyzed reaction progressed via enamine formation, Michael addition, intramolecular cyclization, and intramolecular iminium ion cyclization steps. Notably, this high atom economic approach (-2H2O) allowed the generation of four new bonds (1 C-C and 3 C-N or 1 C-C, 1 C-O and 2 C-N) and two heterocyclic rings in a single operation.