Aromatic templating

By appending sLe epitopes to an aromatic template and functionalizing the amino group of sLe with a large, hydrophobic residue 21 (O Fig. 15), a compound more effective (8-fold) than the aforementioned dimers was generated. The small increases in functional affinities obtained with these bivalent compounds suggest that they may make favorable contacts outside of the... 

Loops can occur from any point in a graph, as seen in the naphthalenophanes of Bickelhaupt et al. (35) [48] and the anthracenophanes of Tobe et al. (36) [49]. Such motifs also play well in the design of molecular receptors, such as multiple crown ethers organized around a central aromatic template. 

Aromatic templates, in conjunction with coordinative bonds, have been employed by Sanders et al. [42] to self-assemble a [2]catenane incorporating a chiral metallomacro-cycle. The 1,5-dioxynaphthalene-based macrocyclic polyether 60 threads onto the r-elec-tron-deficient compound 61 in MeCN. Thus, when both compounds and Zn(OS02CF3)2 are mixed in this solvent, threading of 60 onto 61 is followed by the [2 + 2] assembly of a helical metallomacrocycle as a result of the tetrahedral coordination of two Zn centers by the bipyridine ligands appended to the r-electron-deficient recognition sites. The resulting [2]catenane 62 was characterized by a combination of H-NMR spectroscopy and electrospray mass spectrometry. 

Upon calcination the template is removed and the zeolite s well-defined pores are available for adsorption and catalysis. Particularly challenging is the field of electrophilic aromatic substitution. Here often non-regenerable metal chlorides serve as the catalyst in present industrial practice. Zeolites are about to take over the job and in fact are doing so for aromatic alkylation. 

One 7i-bond of an aromatic ring can be converted to a cyclohexadiene 1,2-diol by reaction with enzymes associated with P. putida A variety of substituted aromatic compounds can be oxidized, including bromobenzene, chlorobenzene, " and toluene. In these latter cases, introduction of the hydroxyl groups generates a chiral molecule that can be used as a template for asymmetric syntheses. " ... 

Other supramolecular structures such as catenanes and rotaxanes can be formed using zinc as a template ion for example, a benzylic imine catenate formed by Leigh et a/.288 The reversible five-component assembly of a [2]catenane from a chiral metallomacrocycle and a dinaphtho-crown ether has been achieved. Zinc is used as the metal component and drives assembly via the coordination to a bipyridyl unit 7r interactions between the aromatic components are also... 

A variation of this method led to the generation of bis-benzimidazoles [81, 82], The versatile immobilized ortho-phenylenediamine template was prepared as described above in several microwave-mediated steps. Additional N-acylation exclusively at the primary aromatic amine moiety was achieved utilizing the initially used 4-fluoro-3-nitrobenzoic acid at room temperature (Scheme 7.72). Various amines were used to introduce diversity through nucleophilic aromatic substitution. Cyclization to the polymer-bound benzimidazole was achieved by refluxing for several hours in a mixture of trifluoroacetic acid and chloroform. Individual steps at ambient temperature for selective reduction, cyclization with several aldehydes, and final detachment from the polymer support were necessary in order to obtain the desired bis-benzimidazoles. A set of 13 examples was prepared in high yields and good purities [81]. 

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

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