Zwitterionic Corroles: Regioselective Nucleophilic Pyridination of a Doubly Linked Biscorrole
Zwitterionic Corroles: Regioselective Nucleophilic Pyridination of a Doubly Linked Biscorrole
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DOI：
10.1002/anie.200805674
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发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Osuka, Atsuhiro
中科院分区：
文献类型：
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作者：
Hiroto, Satoru;Aratani, Naoki;Osuka, Atsuhiro
广泛π共轭体系因其在功能材料领域的应用前景而受到广泛关注。我们最近合成了双链双氯咯1，它很容易被氧化成2（方案1）。氧化后的双酚2在基态以稳定的单线态双自由基形式存在然后我们开始探索这种独特的双基双氯的化学反应性。由于2的强烈缺电子性质，2的进一步官能化应该是可能的直接亲核加成反应。虽然迄今为止已经报道了几种具有适度区域选择性的亲电取代反应，但迄今为止还没有报道过中性分子的亲核加成反应。[2 - 4]我们在此报道了一个高度区域选择性的2的亲核加成反应，该反应只发生在湾区的3和3 '位置，以产生稳定的两性离子（方案2）。此外，两性离子双碱还具有独特的光物理性质和对氟离子的选择性感应能力。用吡啶处理2后，溶液的颜色逐渐由绿色变为棕色。在室温下搅拌14h后，原料2完全消失，得到三种产物。这些产物很容易在硅胶柱层析上分离。第一馏分为还原双氯咯1（产率22%），第二馏分为吡啶加成产物3a（产率60%），其质谱在m/z 1664.1350处呈现母离子峰（calcd for （C79H20F30N9） À= 1664.1368 [（MÀH） À]）。3a的1H核磁共振谱显示了与吡啶基取代基的5个质子以2:1（邻位/对位/元）的比例对应的信号，表明它在氮原子上的附着。还观察到β-吡咯质子和三个质子单重态的四对相互耦合的双重态信号。这表明，添加选择性地发生在双氯咯2的最拥挤的β位置，即海湾区域。值得注意的是，在d= 4.57和3.42 ppm处出现了两个NH质子，在d= À3 ppm附近出现了较宽的NH质子信号，而普通粒子的NH质子出现了。[5]NH质子的这种低场位移可以用其中一个环中存在的氢键相互作用来解释。第三组分在质谱m/z= 1743.1810处的母质离子峰(计算为（C84H25F30N10)+= 1743.1779 [(m)+]）
Extensively π-conjugated systems have attracted considerable attention because of their possible applications in the area of functional materials. We have recently synthesized doubly linked biscorrole 1, which is easily oxidized to 2 (Scheme 1). The oxidized biscorrole 2 exists as a stable singlet biradical species in the ground state.[1] We then set out to explore the chemical reactivity of this unique biradical biscorrole 2. Owing to the strongly electron-deficient nature of 2, further functionalization of 2 should be possible by direct nucleophilic addition reactions. Although several electrophilic substitution reactions with modest regioselectivities have been reported so far, no nucleophilic addition reactions to neutral corroles have been reported to date.[2–4] We report herein a highly regioselective nucleophilic addition reaction to 2 that occurs exclusively at the 3 and 3’positions in the bay area to produce stable zwitterions (Scheme 2). Furthermore, the zwitterionic biscorroles have unique photophysical properties and selective sensing ability for the fluoride ion. Upon treatment of 2 with pyridine, the color of the solution gradually changed from green to brown. After stirring at room temperature for 14hours, the starting material 2 completely disappeared to yield three products. These products were easily separated by column chromatography on silica gel. The first fraction was reduced biscorrole 1 (22% yield), the second fraction was the pyridine addition product 3a (60% yield), the mass spectrum of which exhibited the parent ion peak at m/z 1664.1350 (calcd for (C79H20F30N9) À= 1664.1368 [(MÀH) À]). The 1H NMR spectrum of 3a displays signals that correspond to the five protons of the pyridyl substituent in a 2: 1: 2 (ortho/para/meta) ratio, which indicates its attachment at the nitrogen atom. Four pairs of mutually coupled doublet signals for the β-pyrrolic protons and three proton singlets were also observed. This indicates that the addition occurred selectively at the most sterically congested β positions, namely the bay area, of biscorrole 2. It is noteworthy that two NH protons appeared at d= 4.57 and 3.42 ppm along with broad signal of NH protons around d= À3 ppm, where NH protons of ordinary corroles appear.[5] Such low-field shifts of NH protons can be accounted for by the existence of hydrogen-bonding interactions in one of the corrole rings. The third fraction was shown by its parent mass ion peak at m/z= 1743.1810 in the mass spectrum (calcd for (C84H25F30N10)+= 1743.1779 [(M)+])