Highly selective photomediated 1,4-radical addition to o-quinones controlled by a self-assembled cage.
Highly selective photomediated 1,4-radical addition to o-quinones controlled by a self-assembled cage.
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DOI：
10.1002/anie.200705139
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发表时间：
2008-02
影响因子：
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通讯作者：
Takumi Yamaguchi;M. Fujita
中科院分区：
文献类型：
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作者：
Takumi Yamaguchi;M. Fujita
自由基反应中的区域和立体选择性控制通常很困难，反应通常会导致由各种反应途径形成的复杂混合物。选择性自由基反应可以通过使特定途径比所有其他不利途径更快来实现。在酶促反应中通常假定这种反应选择性的控制。固定在酶袋内特定方向的底物在几何上无法沿着常见的反应途径发生反应，从而导致相当不常见的反应产物。通过这种方式，自由基反应受到酶的严格控制，正如光合作用反应中通常观察到的那样。我们之前报道过，自组装笼 1（方案 1）可以限制封装基板的相对方向，从而导致在热、光化学和自由基条件下产生不寻常的产品。例如，蒽的狄尔斯-阿尔德反应在末端而不是中心苯环进行； α-二酮的光照射产生分子内环化产物，而常见的α-裂解被完全抑制。在此，我们报道了邻醌 2 和取代的甲苯 3，共包在 1 的空腔中，在光照射下选择性转化为不寻常的 1,4-加合物 4（方案 2）。所提出的反应机理
Regioand stereoselective control in radical reactions is generally difficult, with reactions typically resulting in a complex mixture formed by various reaction pathways. Selective radical reactions can be achieved by rendering a specific pathway faster than all the other unfavorable pathways. Such control of reaction selectivity is often postulated in enzymatic reactions. A substrate fixed in a specific orientation within an enzyme pocket is geometrically unable to react along common reaction pathways, thus leading to rather uncommon reaction products. In this way, radical reactions are strictly controlled by enzymes, as typically observed in photosynthetic reactions. We previously reported that self-assembled cage 1 (Scheme 1) can restrict the relative orientation of encapsulated substrates, thus leading to unusual products under thermal, photochemical, and radical conditions. For example, the Diels–Alder reaction of anthracene proceeded at a terminal rather than a central benzene ring; the photoirradiation of an a-diketone gave intramolecular cyclized products, while common a-cleavage was completely suppressed. Herein we report that o-quinone 2 and substituted toluene 3, coenclathrated in the cavity of 1, are selectively transformed into an unusual 1,4-adduct 4 upon photoirradiation (Scheme 2). The proposed reaction mechanism