Conjugates, cyclophanes

Inspired by the separation ability of cyclic selectors such as cyclodextrins and crown ethers, Malouk s group studied the synthesis of chiral cyclophanes and their intercalation by cation exchange into a lamellar solid acid, a-zirconium phosphate aiming at the preparation of separation media based on solid inorganic-organic conjugates for simple single-plate batch enantioseparations [77-80]. 

J.-P. Bourgeois, P. Seiler, M. Fibbioli, E. Pretsch, F. Diederich, L. Echegoyen, Cyclophane-Type Fullerene-dibenzo [18] crown-6 Conjugates with trans-1, trans-2, and trans-3 Addition Patterns Regioselective Templated Synthesis, X-ray Crystal Structure, Ionophoric Properties, and Cation-Complexation-Dependent Redox Behavior , Helv. Chim Acta 1999, 82,1572-1595. 

A new type of spiro-conjugated aminopyrans, pyrans, containing a cyclophane moiety 254, were obtained from a carbonyl[2.2]paracyclo-phane derivative 255 in a two-step procedure with isolation of UN 256 (03T1739) (Scheme 98). 

Figure 12 Cyclophane type fullerene-dibenzo[18]crown-6 conjugates with trans-1, trans-2 and trans-3 addition patterns.

In ( )-49 it-electron conjugation between the two free poles is maintained through two tran.v-stilbcnc-likc bridges. As a result of this extended conjugation, the compound is red in solution, with an end absorption extending to 600 nm. This contrasts with the light-yellow color (end adsorption around 450 nm) of the hexakis adducts with a pseudo-octahedral addition pattern, in which the residual tt-electron chromophore is reduced to a benzenoid cubic cyclophane -type substructure [15,54],... 

However, the chemical reduction reaction does not work efficiently for the removal of two Bingel addends, whereas the electrochemical reduction process works very efficiently. One of the most interesting examples that illustrates the difference between the chemical and electrochemical methodologies involves the cyclophane type trans-1 ( -37) conjugate [76], The chemical reductive protocol fails completely with this compound, presumably due to ion complexation by the crown ether group and consequent stabilization. When the electroreductive method was used, a clean retrocyclopropanation reaction was observed (Figure 25). 

Synthesis, structure and conformational behavior of cyclophanes are of interest. Synthesis of a novel chiral cyclophane consisting of indole as one of the core units was achieved [198]. The first bridge of the cyclophane 273 is formed by a conjugate addition of indole (2) to the unsaturated ketone 269. An intramolecular N-alkylation reaction of 271 resulted in the formation of... 

A large number of [2 + 2] photocycloadditions ofvinylarene compounds have been reported in the literature [37], and these are particular suitable for the synthesis of cyclophanes. Based on the fact that conjugation between the olefinic and aromatic 11-systems is rather low, these reactions can be compared to corresponding reactions with nonconjugated alkenes. 

Cyclophanes are the class of synthetic receptors that have a hydrophobic cavity. Water-soluble cyclophane can make organic compounds soluble in water via the formation of inclusion complex. Anderson et al. synthesized rod-like organic compounds in water in the presence of water-soluble cyclophanes, and obtained corresponding rotaxanes. When oxidative coupling of an acetylenic derivative in the presence of a cyclophane, an oligorotaxane having an axle with a conjugated structure was dominantly obtained rather than non-complexed diacetylene.[187,188] (Scheme 31). This rotaxane is a prototype of insulated molecular wire that is expected as an electric wire in a molecular device. 

Larger cyclophanes have been used for metal coordination, too [92]. A recent example is the preparation of the disilver(I) complex of a conjugated polyene with [2.2.2]paracyclophane end groups (144) [93]. The NMR spectroscopic studies and X-ray structure analysis showed that the sites of complexation are exclusively the cyclophane groups and the olefinic spacers do not overly perturb the complexation properties of the cyclophanes. 

Porphyrin-fullerene conjugates attract wide attention for their intramolecular energy and electron transfer properties [87, 88]. By attachment of the porphyrin to two points on the Cgo surface, the interchromophoric spatial relationship in the cyclophane-type molecular dyads trans-2 ( )-52 [67] and trans-1 54 [68] (Scheme 7-8), which controls both energy and electron transfer, is rigorously defined. In the two systems, as well as in the fullerene-porphyrin conjugate 58 [75] (Scheme 7-9), the close proximity between fullerene and porphyrin chromophore leads to a nearly complete quenching of the porphyrin luminescence, presumably as a result of efficient energy transfer between the porphyrin donor and the fullerene acceptor. 

Chemical sensors based on amplifying fluorescent conjugated polymers functionalized, particularly, by crowns, thymine, or cyclophanes 07CRV1339. 

The pioneering dye rotaxane synthesis, reported by Anderson and coworkers in 1996, utilized Glaser coupling under aqueous conditions in the presence of a water soluble cyclophane macrocycle to produce a mixture of [2] and [3]rotaxanes with a conjugated phenylacetylene fiuorophore as the axle component (Figure 11.8). The purpose of the encapsulation was to insulate the conjugated tr-system from quenching processes and both rotaxanes were found to be six fold more fluorescent. 

The chemical vapor deposition (CVD) techniques with respect to the synthesis of r-conjugated polymers have been reviewed in the literature. The CVD method can be very useful for the preparation of a wide variety of insoluble PPV in desired dimensions and shapes. The advent of the technique used in this particular field arose in 1994. At the moment, poly(p-xylyl-ene)s are the only polymers that are eommercially fabricated by CVD. PPV ean be also obtained by CVD teehniques using l,4-bis-(diehloromethyl)-benzene, a, a-dibromo-p-xylene, or ehlorinated cyclophanes. 

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