Diels-Alder reactions of inert aromatic compounds within a self-assembled coordination cage.

Shinnosuke Horiuchi, Takashi Murase, Makoto Fujita

Index: Chem. Asian J. 6(7) , 1839-47, (2011)

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Abstract

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.Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.