Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Chem Asian J. 2011 Jul 4;6(7):1839-47. doi: 10.1002/asia.201000842. Epub 2011 Feb 18.
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.
自组装的配位笼可作为纳米级的分子烧瓶，促进芳烃与 N-环己基马来酰亚胺的 Diels-Alder 反应。配位笼加速了蒽的 Diels-Alder 反应，发生在电子不利的末端苯环上，得到了一个紧密的、腔约束的顺式加合物。反应的活化参数测量表明熵成本有相当大的降低，底物的预组织是增强反应性的主要因素。由于这种熵成本的降低，否则不反应的芳香族化合物，如萘或三联苯，也以区域和立体控制的方式进行 Diels-Alder 反应。在萘的 Diels-Alder 反应中，客体包合物的 X 射线晶体学分析阐明了反应前底物对的增强取向和接近。苝的 Diels-Alder 加合物稳定在笼内，防止了空气氧化。
