Calix 6 arene derivatives

Scheme 6. In spite of being good host molecules, there is only one well-documented [61] catalytic system based upon the calixarenes. The acid-catalyzed addition of water to yV-benzyl-l,4-dihydronicotinamide 22 to give 24 via 23 is accelerated by the calix[6]arene derivative 25...

The calix[6]arene-derived cholesteryl hexaester 8 was prepared only to inhibit the rotation of the oxygen functions through the annulus.27 Thus, the coalescence observed by NMR for the Ar-CH2-Ar protons at higher temperature (a broad singlet is observed at 130 °C, while a pair of doublets and a singlet at 30 °C are in agreement with a 1,2,3-altemate conformation), indicates the possibility that the p-substituents rotate through the annulus. 

However, non-bridged calix[6]arene derivatives may also be chiral. It was possible to prepare two diastereomeric 1,2-dibenzyl ethers from /-butyl-calix[6]arenes with a syn and anti orientation of the ether residues. The free energy barrier for their mutual interconversion was found to be about 27 kcal mol". 160 This should be high enough to separate the enantiomers of the a/ift -isomer, which has effective C2 symmetry. The same should be true for another example of this type, a 1,2-p-nitrobenzoate with an anti-configuration161 and for 1,2,4-tri-O-alkyl or acyl derivatives.162... 

Four examples are known of calix[6]arene derivatives which have been used as receptor molecules in potentiometric measuring devices. Calix[6]arene 36 functionalized with six ethylester moieties showed a moderate selectivity for hexylammo-nium ions in the presence of smaller primary alkylammonium ions (logA = —1.0 to — 1.4) in ion-selective electrodes [140]. The same derivative 36 also proved to be sensitive towards Cs ions [141]. CHEMFETs with calix[6]arenes, functionalized with three diethylamido moieties (37) or with three phosphate moieties (38), are selective for guanidinium ions [142]. The fourth example is calix[6]arene 39 functionalized with two thiophosphoryl groups which is selective for Pb " ions... 

Hexasulfonated calix[6]arene derivatives a new class of catalysts, surfactants and host molecules, S. Shinkai, S. Mori, H. Koreishi, T. Tsubaki and O. Manabe, J. Am. Chem. Soc., 1986, 108, 2409. 

The stoichiometries of binding organic ammonium cations, such as trimethylaniiinium and adamantrimethyl-ammonium, to the para-sulfonato-calix[ ]arenas is controlled by the macrocycle size formed. Thus, for the calix[4]arene and calix[6]arene derivatives, complexes of stoichiometry 1 1 are observed, while for the larger calix[8]arene derivatives a 1 2 stoichiometry occurs. 

In contrast to the diaryl-1,10-phenanthrolines 2. the calix[6]arene derivatives 3 contain an oxygen atom and a methylene group between the aryl bridgehead and the... 

Tian H-Y, Chen Y-J, Wang D, Zeng C-C, Li C-J. Calix[6]arene derivatives bearing sulfonate and alkyl groups as surfactants in Sc(OTf)3-catalyzed Mtrkaiyama aldol reactions in water. Tetrahedron Lett 2000 41(15) 2529-32. 

SOLID STATE STUDIES ON p.t-BDTYL-CALIx[6]ARENE DERIVATIVES... 

E. Ghidini, A. Pochini and R. Ungaro - Solid state studies on p-t-butyl-calix[6]arene derivatives... 

Recently, Kobayashi noticed that the presence of a small amount of a surfactant such as sodium dodecyl sulfate (SDS) showed a remarkable enhancement of the reactivity in the Mukaiyama-catalyzed aldol reaction in pure water using Yb(OTf)3 or better Sc(OTf )3 as the catalyst without addition of the surfactant, the reaction was very sluggish (Scheme 8.4). Other surfactants such as calix[6]arene derivatives bearing sulfonate and alkyl groups or aromatic and aliphatic anionic surfactants have also been found to be highly effective in the aqueous Mukaiyama aldol reactions in pure water, affording the aldol products in high yields. This was probably due to the formation of micelles which stabilized the labile silyl enol ethers and thus promoted the aldol reaction. 

The model has been verified experimentally for the transport of alkali metal cations (27) mediated by valinomycin (1), dibenzo-18-crown-6 (2) and calix[4]crown-5 derivative 3 and calix[4]arene tetraester derivative 4 (Chart 1). D , and for the transport of guanidinium ion (22, 23) mediated by calix[6]arene derivatives have been obtained as well. 

By means of fluorescence method, we tested the complexation of the triptycene-derived calix[6]arenes with fullerenes [1 lb]. It was found that lb and 2b could form 1 1 stable complexes with both Cgo and C70, which was different from classical calix[6]arene derivatives [14]. The association constants (Ka) for the complexes formed by lb-2b and Cgo were determined to be more than 5 x 10" by the fluorescence titration experiments, which were significantly higher than the complexes formed by Cgo and the classical calix[5]arene and calix[6]arene derivatives (only 9-1,300 [15]. These results suggested that the introduction of the... 

Inspired by the strong ability of calix[6]arene 1 in complexation of alkali metal ions [4, 8-10], Nomura et al. (1991, 1993) reported that calix[6]arene derivative 1 was an effective catalyst for the esterification reaction of alkyl halide and alkali metal carboxylates (see Fig. 27.3, and Table 27.2) [11, 12]. In order to assess the role of calix[6]arene in the reaction, it needs to take a look the skeleton of calix[6] arene 1. Calix[6]arene 1 contains a hydrophobic aromatic groups and a hydrophilic trioxadecyl functionality. These groups commit calix[6]arene 1 into an octopus-type shape, and indeed this shape provides conformational and structural mobility that brings out a highly efficient catalyst. Similar phase-transfer catalysts... 

In the last two decades calix[6]arene derivatives have proved to be very convenient platforms to further expand the scopes of calixarene chemistry also towards nanoscience and nanotechnology. Because of the relatively large size of their cavity they are capable to accommodate guests with an axle-type shape giving rise to pseudorotaxane and rotaxane systems. Furthermore, upon the functionalization of... 

Zanoni reported on the assembly of AuNPs on calixarene-based SAMs [85]. A silicon surface (Si) was functionalized with a calix[6]arene derivative bearing three undecenyl chains on the lower rim and three phenylurea moieties on the upper rim (Ce). The so-produced SAMs form stable complexes with a redox-active molecule that consists of a 4,4 -bypiridinium unit linked by a dodecyl chain to another pyridinium ring (A). This surface showed binding towards AuNPs functionalized with a calix[4]arene derivative (C4) (Fig. 37.15). The presence of the di-topic guests allows for the reversible and hierarchical assembly of the AuNPs on the Si surface. Moreover, the nanoparticles were demonstrated to be electrochemically removed from the Si/Ce/A surface. 

Among about 200 structures deposited in CSD a large variation of calix[6]arenes derivatives is reported. The derivatization concerns the para-substitution on the upper rim, substitution of hydrogen atom of hydroxyl grout on the lower rim, or both. Other derivatives are also reported. 

The calix[6]arene derivatives are capable to form pseudorotaxanes (Fig. 38.21) [45, 46]. In both complex the calixarene molecules are richly decorated with four types of substituents of different chemical properties enabling formation of C-H - 0, C-H N and C-H - Jt interactions between host and guest. 

Firstly, we examined the esterification with metal acetate, benzyl bromide, and catalyst 9c, 15, or 16. The reaction proceeded in the presence of these catalysts, but not in the absence of them. Therefore, their catalytic activity is apparent. The rate constants remained in the same range for all runs. Moreover, the reaction was slow (k=10 — 10 s ) because of the low nucleophilicity of acetate ion. Since the substitution by acetate did not give much information on their catalytic activity, we chose the Williamson ether synthesis with phenol, benzyl bromide, metal hydroxide, and catalyst (see Equation 1), because phenolate has high nucleophilicity and hydrophobicity [24]. In fact, the difference of their catalytic activities clearly appeared in this case as shown in Table III. Catalysts made the reaction markedly faster than that without them. In carbon tetrachloride as a nonpolar solvent, the catalytic activity of 9c increased remarkably when larger ions were used and the maximum rate constant was recorded in the RbOH system. This behavior of 9c resembles that of calix[6]arene derivative 16 because both 9c and 16 have the same affinity for large ions. The other experiments were performed in... 

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