Nanoconfinement in a Supramolecular Capsule Promotes the Formation of 5- to 8-Membered Rings in Cycloalkane-[b]-indoles

Challenging cyclization of common- to medium-sized rings is promoted by nanoconfinement inside the cavity of a self-assembled hexameric resorcinarene capsule. While no cyclization occurs outside the capsule, high to excellent yields of cycloalkane-[b]-indoles are obtained inside the capsule irrespective of ring size (5–8 members). Kinetic analysis coupled to NMR investigation of substrate binding shows that the cyclization step under nanoconfinement is not rate-determining, not even for the formation of an 8-membered ring.