Catalyzing the Enantioselective Tail‐to‐Head Terpene Cyclization Inside Optically Active Hexameric Resorcin[4]arene Capsules: A Surprising Odd‐Even Effect of the Catalyst

Abstract Terpenes, created in Nature via tail‐to‐head terpene (THT) cyclizations, have long fascinated chemists due to their complex structures and biological activities. Recreating such THT cyclizations in the laboratory using man‐made catalysts has been challenging. Especially difficult is performing the reaction in an enantioselective fashion, as the substrate is flexible and does not contain much functionality to form strong interactions with the chiral catalyst. This study explores the enantioselective THT cyclization inside hexameric capsules self‐assembled from optically active resorcin[4]arene derivatives. An unexpected odd‐even effect, where the enantioselectivity of the reaction depended on the length of the alkyl chain attached to the resorcin[4]arene capsule was uncovered. To our knowledge, this is the first example of an odd‐even effect in the catalyst itself, and also the first instance in which this effect is related to the enantioselectivity of the reaction.