Dendrimers, cyclophanes

Similar dendritic building blocks have been used to prepare dendrophanes [193b (dendrimer + cyclophane), which possess cyclophane cores. Internal Complexation of naphthalene derivatives was subsequently examined by NMR and fluorescence titration. 

Despite some uncertainty in the expected olefin geometry, the utility of the RBR is anply demonstrated by its application to the synthesis of many diverse targets. These include dendrimers, cyclophanes, modified carbohydrates such as C-glycosides and exoglycals, alkaloids, terpene derivatives, enediynes, amino acids, stilbenes, and macrocycles.The remainder of this chapter presents examples of the RBR that are pertinent to the strategic considerations oudined previously and illustrate its scope as a versatile and powerful synthetic method. 

Template effects have been used in rotaxane synthesis to direct threading of the axle through the wheel. Since macrocycHc compounds such as cyclodextrins, crown ethers, cyclophanes, and cucurbiturils form stable complexes with specific guest molecules, they have been widely used in the templated synthesis of rotax-anes as ring (wheel) components. Here, we briefly discuss macrocycles used in the synthesis of rotaxane dendrimers and their important features. 

The fact that the dendritic shell can produce localized microenvironments has been used by Diederich et al. who developed water-soluble dendritic cyclophanes (dendrophanes) as models for globular proteins (Figure 16.13) [5, 170, 171], These dendrimers contain well-defined cyclophane recognition sites as initiator cores for the complexation of small aromatic guests [172-174] and steroids [174-176], Enlargement of the cyclophane core could be used as a tool to complex larger steroid molecules. 

Hartwig first reported the arylation of diarylamines using both (o-to jP/Pd-and DPPF/Pd-catalysts, Eq. (33) [29,64]. The Yale group utilized the (o-tol jP/Pd-and DPPF/Pd-based protocols for the preparation of triarylamine-containing dendrimers and cyclophanes, respectively. 

Convergent dendrimers, with their versatile three-dimensional scaffold, may be tailored to mimic, perhaps crudely, some elements of enzymatic structures. Numerous catalytic moieties, including manganese porphyrins,253,254 bis(oxazoline) copper complexes,304 305 tertiary amines,306 binaphthol titanium complexes,285 307 titanium taddolates,292,308 thiazolio-cyclophanes,309 and fullerene-bound bisoxazoline copper complexes,310 have been incorporated at the core of dendritic molecules to determine the effect of dendritic encapsulation on their catalytic activity. 

Several artificial receptors such as crown ethers, cyclodextrins, cyclophanes, and calixarenes find applications in molecular recognitions processes. Further, there have been several research publications that focus on computational design and analysis of recognition properties of artificial receptors such as cyclodextrins,15 dendrimers,610 crown ethers,1112 and calixarenes.13 5 Typically computational... 

Another possibility that may lead us to chiral dendrimers lies in the axial chirality of substituted [2.2]p-cyclophanes. The salicylaldehyde-containing cyclophane (80) of this type was presented by Belokon et al.28 In contrast to the experiments mentioned above, we tried to bring elements of chirality into the periphery of the molecule by connecting it through an imine bridge (Section IV.A.). The synthesis of 4-hydroxy [2.2]p-cyclophane (79), via the bromide29 and the final formyla-... 

Figure 8. A polyamine dendrimer bearing planar-chiral cyclophane units (Vogtle et al.)...

Cyclophanes Endoacidic, Endobasic, and Endolipophilic Cavities, p. 424 Dendrimers. p. 432 The Diphenylmethane Moiety, p. 452 Enzyme Mimics, p. 546... 

Fig. 36. Structure of the ditopic steroidal guest molecule (structure of the dendrimer is similar to the one shown in Fig. 29, but with a larger cyclophane core).

The artificial P450 analogs evolved in the last years (Figure 20). The first model compounds were simple steri-cally hindered porphyrin compounds. However, in order to achieve higher activity and selectivity, later on capped porphyrins " and porphyrin systems, which were attached to cavities, such as CDs " or cyclophanes were developed (Figure 20). Another approach is the attachment of porphyrins to dendrimers in order to create a hydrophobic environment. The catalytic cycle and mode of action... 

Figure 6 Structures of the cyclophane dendrimer synthesized by Diederich and coworkers plus the fluorescent probe 6-(p-toluidino)naphthalene-2-sulfonate.

Often symmetry operations cannot be used in a simple way to classify chiral forms because, e.g., the molecule consists of a number of conformations. Therefore, independent of the symmetry considerations, a chemical approach to describe chiral molecules has been introduced by the use of structural elements such as chiral centers, chiral axis, and chiral planes. Examples for a chiral center are the asymmetric carbon atom, i.e., a carbon atom with four different substituents or the asymmetric nitrogen atom where a free electron pair can be one of the four different substituents. A chiral axis exists with a biphenyl (Figure 3.2) and chiral planes are found with cyclo-phane structures [17]. Chiral elements were introduced originally to classify the absolute configuration of molecules within the R, S nomenclature [16]. In cases where the molecules are chiral as a whole, so-called inherent dissymmetric molecules, special names have often been introduced atropiso-mers, i.e., molecules with hindered rotation about a helical molecules [18], calixarenes, cyclophanes [17], dendrimers [19], and others [20]. 

Formation of organic and organometallic cyclophane capsules by triple RCM + triple CM and its inhibition to yield functional dendrimers by CM in the presence of CH2=CHC02R (R = H or CH3)... 

Mesitylene, and p-Diisopropylbenzene to Organoiron and Polycyclic Aromatic Cyclophanes, Capsules and Polymers, Angew. Chem. Int. Ed. 42,4366,2003 b) C. Ornelas, D. Mery, J.-C. Blais, E. Cloutet, J. Ruiz Aranzaes - Efficient Mono- and Bifunctionalization of Polyolefin Dendrimers by Metathesis,... 

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