Diels–Alder Reactions of Inert Aromatic Compounds within a Self‐Assembled Coordination Cage

A self‐assembled coordination cage serves as a nanometer‐sized molecular flask to promote the Diels–Alder reactions of aromatic hydrocarbons with N ‐cyclohexylmaleimide. The coordination cage accelerated the Diels–Alder reaction of anthracene at the electronically unfavorable, terminal benzene ring to give a compact, cavity‐restrained syn ‐adduct. Activation‐parameter measurements for the reactions revealed considerable reduction in the entropy cost, and preorganization of the substrates is a dominant factor in the enhanced reactivity. Owing to this entropy‐cost reduction , otherwise‐unreactive aromatic compounds, such as naphthalenes or triphenylene, also underwent Diels–Alder reactions in a regio‐ and stereocontrolled fashion. In the naphthalene Diels–Alder reaction, X‐ray crystallographic analysis of the guest‐inclusion complex clarified the reinforced orientation and proximity of the substrate pairs before the reaction. A perylene Diels–Alder adduct was stabilized inside the cage and protected from aerial oxidation .