Cucurbit arene

Besides y-cyclodextrin and sulfocalix[8]arene, Geckeler has found that C50 forms a complex with cucurbit[7]uril in mechanochemical conditions (Scheme 8.7) [16]. Retsch MM200 mill was employed, in stainless steel capsule (inner diameter 18 mm) and ball (12 mm) at 20 Hz. Irrespective of the molarity of two components, a supramolecular 1 1 complex 27 was formed through noncovalent binding after 4 h in 77% yield, which was more effective than solution preparation (96h, 55%). 

Nau and coworkers designed a competition assay to monitor cationic species generated in amino acid decarboxylase catalyzed reactions. Two macrocyles, cucurbit[7]uril (CB7, 59) and / -sulfonatocalix[4]arene (CX4, 51), were... 

In this chapter, we present the investigations of the major structural and physical properties of macrocyclic compounds in historical order. First, we compare the chemical and X-ray ciystal structures and the physical properties of the four key classes of compounds, cyclodextrins, crown ethers, calbc[n]arenes and cucurbit[n]urils, which have been dominant in the field of supramolecular chemistry. Other well-known and useful host molecules, and recently discovered compounds with great potential in the field of macrocyclic chemistry, are also described. Second, we discuss the desired properties of macrocyclic compounds, and the advantages of the novel macrocyclic compounds pillar[ ]arenes compared with the four key classes of compounds. 

FeaturesX Pillar[n]arene Crown Ether Cyclodextrin Calix[n]arene Cucurbit[n]urll... 

Hence, the solvent is an important factor for the selective synthesis of pillar[5]arene. However, the effect of the reaction temperature on the cycli-zation reaction has not been investigated. Reaction temperature is a veiy important factor for the synthesis of cucurbit[n]uril and calix[n]arene homologs. This should therefore be the subject of further investigations. 

Scheme 8.4 Synthesis of the hetero[4]- and hetero[5]rotaxanes consisting of pillar[5]arene and cucurbit[6]uril wheels by copper-free AAC reaction.

Macrocyclic compounds act as main players in the field of supramolecular chemistry because they form organized supramolecular assemblies by cavity-size dependent host-guest interactions. Therefore, development of the field of supramolecular chemistry has been pushed by the discovery of four key macrocycles, the cyclodextrins, crown ethers, calix[n]arenes and cucurbit[n]urils. In 2008, we introduced a new class of macrocycles Pillar[n]arenes . On account of their novel cross section of properties and great potential, pillar[n]arenes are becoming dominant in the field of macrocyclic chemistry and are opening up a new supramolecular chemistry, which cannot be achieved by the other four key players. The field called pillar[ ]arene chemistry was started in 2008, and there was a small handful of players in the beginning. Fortunately, many chemists have joined the field of pillar[n]arene chemistry since 2012 and, now, pillar[n]arene chemistry attracts the attention of numerous researchers. 

Fig. 38.24 Packing of molecules and ions in para-sulphonatocalix[6]arene hexaammomum/cucurbit[6] uril co-crystal. View along c crystallographic axis (calix[6]arene hexaions -yellow, cucurbit[6]urils -green, (ammonium cations - blue, water molecules -red) [51]...

Besides the inclusion complexes, calix[6]arenes may fomi co-crystals with other molecules. An interesting example is a co-crystal formed by para-sulphonatocalrx [6]arene hexaammonium with cucurbit[6]uril. As the Authors mention in the paper this structure not only exhibit an intriguing topology but also show clearly the role of hydrophobic—hydrophobic and hydrophilic hydrophilic interactions in directing the supramolecular assembly [51]. It is interesting to notice a significant amount of free space in the crystal lattice (Fig. 38.24). 

---