Department of Applied Chemistry, School of Engineering, The University of Tokyo, and Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
Chem Rec. 2010 Oct;10(5):342-7. doi: 10.1002/tcr.201000027.
A self-assembled molecular flask with a nanometer-sized restricted cavity offers a new reaction environment that is quite different from the bulk solution. The self-assembled cage accommodates a pair of hydrophobic molecules to perform unusual Diels-Alder reactions and [2+2] photoadditions of otherwise unreactive aromatic molecules. In this cage, for example, the Diels-Alder reaction of naphthalene proceeds smoothly under mild conditions, and aceanthrylene shows reactivity for both [2+2] and [2+4] cycloadditions via the identical ternary host-guest complex. The observed greatly enhanced reactivity stems from the increased local concentration and pre-organization of the substrate pair within the cage, which reduces the entropic cost and switches the reaction profile from a bimolecular to a pseudo-intramolecular reaction pathway. The reinforced orientation and arrangement of substrate pairs specify regio- and stereo-selectivities of the subsequent reactions in the cavity. Chiral auxiliaries outside the cage create the inner chiral environment and induce asymmetric reactions inside the cage (up to 50% ee).
一种具有纳米尺寸受限空腔的自组装分子瓶提供了一种全新的反应环境，与体相溶液有很大的不同。自组装的笼容纳一对疏水分子，以进行不寻常的 Diels-Alder 反应和 otherwise unreactive 芳香族分子的[2+2]光加成反应。例如，在这个笼中，萘的 Diels-Alder 反应在温和条件下顺利进行，而 acenaphthylene 通过相同的三元主客体配合物表现出对[2+2]和[2+4]环加成的反应性。观察到的反应活性大大增强源于底物对在笼内的局部浓度和预组织增加，这降低了熵成本，并将反应途径从双分子反应转变为拟分子内反应途径。底物对的强化取向和排列指定了腔体内后续反应的区域和立体选择性。笼外的手性助剂创造了内部手性环境，并诱导笼内的不对称反应（最高可达 50%ee）。
