Tribenzotriquinacene: a versatile synthesis and C3-chiral platforms.
Tribenzotriquinacene: a versatile synthesis and C3-chiral platforms.
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三苯并三醌：多功能合成和 C3 手性平台。
DOI：
10.1002/anie.201207220
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发表时间：
2012
影响因子：
--
通讯作者：
H. Hopf
中科院分区：
文献类型：
--
作者：
Georgios Markopoulos;Lars Henneicke;Jun Shen;Y. Okamoto;P. Jones;H. Hopf
点群C3分子由于在不对称催化和手性识别中的应用而引起了人们的广泛兴趣。尽管如此，与众多的C2-手性体系相比，C3-手性分子的数量仍然有限，并且需要更多的C3-手性分子。获得功能性C3-手性分子的一种方法是将三个对映体纯的柄附加到非手性平台上，这在三脚架配体的合成中是最常见的。第二种方法，这是更常见的超分子化学，是从一开始就与C3-手性平台，并扩展它与非手性识别单元。分子碗三苯并三喹并苯（1;方案1）由于其刚性和构型稳定性而构成第二策略的优良平台。然而，C3手性衍生物的制备由于缺乏区域选择性而受到严重阻碍。在这里，我们希望报告一个C3-特定的进入这类化合物，从而提供了一个新的访问这个新的家庭的C3-手性分子。这项工作是基于一个新的和通用的合成的母体烃1和它以前只有很难接近的邻位衍生物。后者还为扩大的碳网络提供了一个备受期待的入口。我们的三苯并三喹并苯1的合成从亚苄基丙二酮2开始（方案1），其可以通过Knoevenagel缩合容易地获得。Olah等人已经报道了还原为非对映体二醇3（32%产率），我们通过开发优化的Luche方法改进了该步骤（93%产率）。11]Olah获得二醇3的动机是他们在超酸性条件下（FSO 3 H/SO 2ClF，80 ° C）的研究，由此他观察到环脱水中间体，推测为4型。在使用二醇3时，我们发现即使在温和的酸性条件下（在CH 2Cl 2中的催化剂对甲苯磺酸，RT）也会发生异构化和环化脱水，并假设这种环化可能最终导致三苯并三喹并苯（1）。将Kuck环化脱水条件（H3 PO 4，氯苯，130 ℃，20 h）应用于二醇3确实以28%的产率得到三苯并三喹并苯。改用多聚磷酸（PPA）作为脱水剂将产率提高到32%，使1首次以克为单位供应。还测试了其他酸，但未证明有效（乙酸、三氟乙酸、甲磺酸、伊顿试剂、三氟甲磺酸（TfOH）、Tf 2 O、H2SO 4）。该反应可能通过一系列分子内Friedel-Crafts烷基化与碳阳离子中间体进行，这得到了产率不依赖于所使用的3的非对映异构体的事实的支持。在支持信息中提出了一种反应机理，也解释了二氢茚并茚副产物5的形成。该合成比Kuck的母体烃合成产率更高（三步：19%对5%）。此外，正如我们将在下面显示的，它允许通过改变Knoevenagel加合物的容易获得的苯甲醛和二苯甲酰甲烷组分来有计划地引入芳族取代基。三苯并三喹并苯中芳环的官能化在很大程度上限于外缘位置，因为这些位置容易通过亲电芳族取代而接近。13]三苯并三喹并苯的邻位官能化是罕见的，并且范围有限。已知一个实例，其中方案1.三苯并三喹并苯的合成（1）.
Molecules belonging to point group C3 have recently attracted much interest owing to their applications in asymmetric catalysis and chiral recognition. Nonetheless, the number of C3-chiral molecules is still limited compared to the numerous C2-chiral systems, and more entries to C3-chiral molecules are needed. One way to obtain functional C3-chiral molecules, which is the most common in the synthesis of tripodal ligands, is to append three enantiopure handles to an otherwise achiral platform. The second approach, which is much more common in supramolecular chemistry, is to start with a C3-chiral platform from the very beginning and to extend it with achiral recognition units. The molecular bowl tribenzotriquinacene (1; Scheme 1) constitutes an excellent platform for the second strategy owing to its rigidity and configurational stability. However, the preparation of C3chiral derivatives is severely hampered by the lack of regioselectivity. Herein we wish to report a C3-specific entry to this class of compounds, thereby providing a new access to this novel family of C3-chiral molecules. The work is based on a new and versatile synthesis of the parent hydrocarbon 1 and its previously only poorly accessible ortho derivatives. The latter furthermore provide a highly anticipated entry to extended carbon networks. Our synthesis of tribenzotriquinacene 1 starts off with the benzylidene propanedione 2 (Scheme 1), which can be easily obtained by Knoevenagel condensation. Reduction to the diastereomeric diols 3 had already been reported by Olah et al. (32 % yield), and we improved this step by developing an optimized Luche procedure (93% yield). 11] Olah s motivation for accessing diols 3 was their study under superacidic conditions (FSO3H/SO2ClF, 80 8C), whereby he observed a cyclodehydrated intermediate, presumably of form 4. While working with diols 3, we found that isomerizations and cyclodehydrations took place even under mildly acidic conditions (cat. p-toluenesulfonic acid in CH2Cl2, RT) and hypothesized that such cyclizations might eventually lead to tribenzotriquinacene (1). Application of Kuck s cyclodehydration conditions (H3PO4, chlorobenzene, 130 8C, 20 h) to diols 3 indeed gave tribenzotriquinacene in 28% yield. Switching to polyphosphoric acid (PPA) as dehydrating agent increased the yield to 32 %, making 1 available in gram quantities for the first time. Other acids were also tested, but did not prove effective (acetic acid, trifluoroacetic acid, methanesulfonic acid, Eaton s reagent, trifluoromethanesulfonic acid (TfOH), Tf2O, H2SO4). The reaction presumably proceeds through a series of intramolecular Friedel–Crafts alkylations with carbocation intermediates, which is supported by the fact that the yield did not depend on the diastereomer of 3 being used. A reaction mechanism that also explains the formation of the dihydroindenoindene byproduct 5 is proposed in the Supporting Information. The synthesis is higher-yielding than Kuck s synthesis of the parent hydrocarbon (over three steps: 19% vs. 5%). Moreover, as we will show below, it allows the planned introduction of aromatic substituents by varying the easily available benzaldehyde and dibenzoylmethane components of the Knoevenagel adduct. Functionalization of the aromatic rings in tribenzotriquinacene has largely been limited to the outer rim positions, as these are easily accessible by electrophilic aromatic substitution. 13] Ortho functionalization of tribenzotriquinacenes is rare and limited in scope. One example is known in which Scheme 1. The synthesis of tribenzotriquinacene (1).
影响因子：
4.6
作者：
Ronson, Tanya K.;Carruthers, Christopher;Hardie, Michaele J.
通讯作者：
Hardie, Michaele J.
三苯并三醌与六邻六苯并苯合并：Scholl 反应生成的环庚三烯单元
影响因子：
4.9
作者：
E. U. Mughal;D. Kuck
通讯作者：
D. Kuck
基于菲咯啉的受体对碳水化合物的高效识别：α-与β-端基异构体结合偏好
影响因子：
--
作者：
M. Mazik;A. Hartmann;P. G. Jones
通讯作者：
P. G. Jones