Rhodium(I)-catalyzed cycloisomerization of nitrogen-tethered indoles and alkylidenecyclopropanes: convenient access to polycyclic indole derivatives.

At the end of its tether: A new synthetic protocol for the preparation of polycyclic indole derivatives has been developed from a rhodium(I)-catalyzed cycloisomerization of a nitrogen-tethered indole and alkylidenecyclopropane, affording the corresponding tetrahydro-β-carboline derivatives in moderate to good yields. Further transformations give a direct and rapid route to tetracyclic compounds through transition-metal catalysis.