Absolute helical arrangement of stacked benzene rings: heterogeneous double-helical interaction comprising a hydrogen-bonding belt and an offset parallel aromatic-aromatic-interaction array.-猫眼课题宝

DOI：

10.1002/anie.200352788

发表时间：

2004-03

期刊：

Angewandte Chemie

影响因子：

通讯作者：

中科院分区：

文献类型：

作者：

I. Azumaya;D. Uchida;Takako Kato;A. Yokoyama;Aya Tanatani;H. Takayanagi;T. Yokozawa

在结晶态或溶液中形成螺旋结构的化合物[1]引起了人们的极大关注，因为生物利用螺旋结构来存储遗传信息，而且具有螺旋有序结构的化合物为固体或液体晶体工程提供了新的材料。[2]螺旋结构有几种类型：由于疏溶剂效应或客体连接而螺旋折叠的单链，[4]由阳离子或阴离子连接而形成的双或多股螺旋，[5]或氢键，[6]以及由构象螺旋或盘状小分子通过氢键支撑的柱状堆积形成的螺旋超结构，[7]其他例子见参考文献[8]。在螺旋结构中，平行的芳香相互作用[9]往往是稳定结构的一个非常重要的驱动力，有时氢键或其他弱的分子间相互作用有助于形成高度有序的螺旋排列。这种螺旋结构本质上是手性的，即它有一个右手螺旋(P-螺旋)或一个左手螺旋(M-螺旋)，这两个螺旋是对映体。不对称合成产生一个对映体螺旋是很重要的，特别是在自组装系统中，在折叠体、[1a]或催化手性引发的具有螺旋结构的聚合物中[5-7]。通常有两种驱动力来决定化合物将采用哪种螺旋性，它们是内部或外部手性来源。例如，DNA的螺旋性是由脱氧核糖链中手性碳原子的内部手性推导出来的。另一方面，Moore和他的同事制备的一种寡苯乙炔在手性配体连接时折叠成单一螺旋形式。[4b，c]在这种情况下，非手性分子的绝对不对称组装特别有趣。在我们的自发光学拆分的研究过程中，我们发现了一种盘状化合物，三(2-羟乙基)-1，3，5-苯三羧酸酯(1)，它以手性晶体的形式结晶，其中几乎是平面的分子螺旋排列在单个单晶中。三酯1的螺旋性来自分子的螺旋排列，由通过单一部分的氢键阵列和相邻分子的偏置芳香族堆积来支撑。以甲醇/氯仿为原料合成了一级结构几乎为平面的高度对称的三酯1，得到了细长的棱柱状单晶。初步的X射线结晶学分析(图1)表明该晶体属于非中心对称空间群P61(或P65)。这一结果令人惊讶，因为大多数无手性有机化合物倾向于填充到中心对称晶体中。最有趣的特征是，平面的盘状分子排列成柱状堆叠，相邻分子之间有渐进的螺旋扭曲，在晶格中形成螺旋超结构。晶体的手性本质上来源于分子的螺旋排列，辅以末端羟基相对于中心苯环平面的扭曲，从而导致构象手性的产生。我们测量了几个晶体的固态CD光谱(以KbR为单位)。[13]科顿效应是发色团的螺旋结构的特征。[14]不出所料，我们发现两个对映体晶体在200-320 nm之间(图2)显示镜像曲线；一个(图2中的红线)在210 nm左右显示负的科顿效应，在224 nm显示一个大的正的，在248 nm显示一个负的，以及…

Compounds that form helical structures in the crystalline state or in solution [1] have attracted much attention because living things utilize helical structures to store genetic information, and because compounds with a helical-ordered structure have provided new materials in solid-or liquidcrystal engineering.[2] There are several types of helical structure: a single strand that folds helically owing to solvophobic effect [3] or guest ligation,[4] a double or multiple helix of strands derived from cation or anion ligation,[5] or hydrogen bonding,[6] and a helical super-structure formed by conformationally helical or discotic small molecules through columnar stacking supported by hydrogen bonds,[7] for other examples see ref.[8]. In helical structures, a parallel aromatic–aromatic interaction [9] is often a very important driving force to stabilize the structure, and sometimes hydrogen bonding or other weak intermolecular interactions assist the formation of the highly ordered helical arrangement. Such a helical structure is intrinsically chiral, that is, it has a righthanded helix (P-helix) or a left-handed helix (M-helix), which are enantiomeric. Asymmetric synthesis to produce one enantiomeric helix is important, especially in self-assembling systems,[5–7] in foldamers,[1a] or in polymers with a helical structure induced by catalytic chiral initiation.[10] There are generally two kinds of driving forces to determine which helicity a compound will adopt, they are, an internal or an external chiral source. For example, the helicity of DNA is derived from the internal chirality of the chiral carbon atom in the deoxyribose chain. On the other hand, one of oligophenylacetylenes prepared by Moore and co-workers folded into a single helical form upon ligation of a chiral ligand.[4b, c] In this context, absolute asymmetric assembly of an achiral molecule is especially intriguing. In the course of our investigation [11] of spontaneous optical resolution,[12] we found a discotic compound, tris (2-hydroxyethyl)-1, 3, 5-benzenetricarboxylate (1), which crystallized as chiral crystals in which the nearly planar molecules were helically arranged within individual single crystals. The helicity of the triester 1 was derived from the helical arrangement of the molecules, supported by an array of hydrogen bonding through a single moiety and offset aromatic stacking of the adjacent molecules. The triester 1, which has an almost planar and highly symmetrical primary structure, was synthesized and crystallized from methanol/chloroform to give slender prismatic single crystals. A preliminary X-ray crystallographic analysis (Figure1) revealed that the crystal belonged to the noncentrosymmetric space group P61 (or P65). This result was surprising, since the majority of achiral organic compounds tend to pack into centrosymmetric crystals. The most interesting feature is that the planar, discotic molecules were arranged in a columnar stack with a progressive helical twist between adjacent molecules to form helical superstructures in the crystal lattice. The chirality of the crystals was intrinsically derived from the helical arrangement of the molecules, assisted by the twist of the terminal hydroxy groups with respect to the plane of the central benzene ring, which leads to the generation of conformational chirality. We measured the solid-state CD spectrum (in KBr) of several crystals of 1.[13] The Cotton effect was characteristic of a helical structure of a chromophore.[14] As expected, we found two enantiomeric crystals which showed mirror-image curves in the region between 200–320 nm (Figure 2); one (red line in Figure 2) showed a negative Cotton effect at around 210 nm, a large positive one at 224 nm, a negative one at 248 nm, and …

Absolute helical arrangement of stacked benzene rings: heterogeneous double-helical interaction comprising a hydrogen-bonding belt and an offset parallel aromatic-aromatic-interaction array.

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