Pure C-H hydrogen bonding to chloride ions: A preorganized and rigid macrocyclic receptor
Pure C-H hydrogen bonding to chloride ions: A preorganized and rigid macrocyclic receptor
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DOI：
10.1002/anie.200704717
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Flood, Amar H.
中科院分区：
文献类型：
--
作者：
Li, Yongjun;Flood, Amar H.
阴离子扮演着重要的化学和生物学角色[1]，涉及它们的超分子化学[2]也相应地发展起来。[3]这些发展的范围从非共价键的基础研究[4]到阴离子受体的设计[2，5，6]和阴离子辅助不对称催化。[7]大量的人工有机阴离子主体结合了强氢键（H-键），通常是NH 4 H···XH 4 H，[8]例如杯吡咯，或者如果使用CH 4 H··XH 4 H键，则碳原子与阳离子中心相邻，例如咪唑。[9]中性环体系中的弱C_2H···X_2H键的强度及其相对重要性最近得到了研究。[10]虽然比以前认为的更强，但这些氢键仅被认为是“宿主腔中的额外结合位点”。[10b]因此，令人惊讶的是，当本文所述的新型大环显示出强的氯离子结合时，发现了与该教条的突破，其中仅存在芳族C1 H2···Cl 1H 2-键。[11]这个例子似乎进一步加强了Cram的想法[12]，即每个结合位点都是预先组织的[13]刚性主体应该显示出最强的客体结合。这种受体的设计最初是出于形状持久性大环化合物的持续合成发展[14]以及铜催化的公认效率[15] 1，末端叠氮化物和乙炔的3-偶极环加成反应生成五元1，2，3-三唑环体系。在最近的研究中，[16]这些三唑与其他环系统的区别在于环系统中sp2氮原子提供的空间应变的缓解。这一观察结果刺激了本文所述的预测，即用苯环对三唑进行1，4-二取代将产生环间共面性，这将为平面大环的制备建立有利的结构单元。为此，我们开发了高效的合成（27%的收率，七个步骤），使用点击化学，形状持久的大环结合亚苯基亚基。正是在这项工作的基础上，
Anions play important chemical and biological roles,[1] and the supramolecular chemistry involving them [2] has grown accordingly.[3] These developments range from fundamental studies on noncovalent bonding [4] to the design of anion receptors [2, 5, 6] and anion assistance to asymmetric catalysis.[7] A substantial number of artificial organic hosts for anions incorporate strong hydrogen bonds (H-bonds), usually NÀ H··· XÀ,[8] eg, calixpyrrole, or if CÀH··· XÀ H bonds are used, the carbon atom is adjacent to a cationic center, eg, imidazolium.[9] The strength and the relative significance of weak CÀH··· XÀ H bonds originating from neutral ring systems has been examined recently.[10] Although stronger than previously thought, these H-bonds were only considered as “additional binding sites within a host cavity.”[10b] It was surprising, therefore, to discover a break from this dogma when strong chloride binding was displayed by a novel macrocycle described herein, in which there are only aromatic CÀH··· ClÀ H-bonds.[11] This example appears to strengthen further Cram s idea [12] that a rigid host in which each binding site is preorganized [13] should show the strongest guest binding.The design for this receptor was originally motivated from the ongoing synthetic developments [14] in shape-persistent macrocycles together with the recognized efficiency of the copper-catalyzed [15] 1, 3-dipolar cycloaddition of terminal azides and acetylenes to generate the five-membered 1, 2, 3-triazole ring system. In recent studies,[16] these triazoles were distinguished from other ring systems by the relief of steric strain provided by the sp2 nitrogen atoms in the ring system. This observation stimulated the prediction, elaborated herein, that 1, 4-disubstitution of triazoles with phenyl rings will produce inter-ring coplanarity that would establish a favorable building block for the preparation of planar macrocycles. To that end, we developed the efficient synthesis (27% yield, seven steps), using click chemistry, of a shape persistent macrocycle incorporating phenylene subunits. It was on the basis of this work that the discovery was made that the