Cyclophane systems

SJ paracyclophane etc.] refers to the benzene rings in the structure, i.e. [8]-paracyclophane, [2,2,2]-para-cyclophane. Systems based upon heterocyclic molecules are also known. 

In addition to chemical reactions which result in direct valency coupling, other reactions, for example, those that lead to the formation of charge-transfer complexes are rather generally characteristic of the [2.2]para-cyclophane system. 

Further papers relevant to the stereochemistry of the [2.2]Para-cyclophane system are mentioned ... 

Methyl-2-furylmethyl)trimethylammonium hydroxide undergoes 1,6-Hofmann elimination on heating with the production of 2,5-dimethylenedihydrofuran (30), which undergoes dimerization to afford the cyclophane (29). By cross breeding of this intermediate with similar dimethylene compounds, ready access is given to mixed cyclophane systems, an area which has been extensively investigated. 

In the same way, the displacement of the unpaired electron over the whole molecules was observed for (d) and (e) cation radicals from Scheme 1-13, in which 1,4-dimethoxy-naphthalene units are syn- or anti-annelated to [2.2]paracyclophane. Taken together, the experimental results considered provide direct evidence for the through-bond mechanism of electron transfer in these paracyclophane systems. In a recent study, the electron transfer between 1,4-dimethoxybenzene and 7,7-dicyanobenzoquinone methide moieties in syn-or anh -cyclophane systems reached the same conclusion The through-bond mechanism... 

A racemic mixture of three-layered [3.3]paracyclophane (45) was resolved into two enantiomers by chiral HPLC (on a Daicel OD column), and their absolute configuration was determined by a comparison of the experimental CD spectrum with the theoretical one at the TD-DFT-B3-LYP/TZVP level [55]. A simple model, composed of two p-xylenes and durene (the side chains were modeled again by methyl groups), was used to explain the origin of the chiroptical properties of the three-layered cyclophane system. Due to the flexibility of the [3.3]paracyclophanes, the solvent effects on the conformer distribution and thus on the chiroptical properties were significant (Fig. 10). 

A group of researchers from Heidelberg and Munich have studied an extensive series of cyclophane systems related to 22 [77, 86, 92, 94, 95, 123, 129-133]. Dyads with relatively low driving force for electron transfer in polar solvents (comparable to 19) show relatively slow photoinduced electron transfer in nonpolar solvents, and significantly faster transfer in polar solvents. For a few molecules with large negative AG° values, photoinduced electron transfer occurs in about 1 ps in all solvents... 

Over the last 10 years more complex cyclophane systems have become available by modern synthetic methods. Such extended systems make use of the special electronic and steric effects of cyclophanes in physical organic and coordi-... 

To the date, the studies reviewed here about hexaaza-cyclophane systems have been focused in mechanistic aspects. These studies demonstrate that the nature of the interaction between the CO2 molecule and the complexes depends on the metal and on the ligand contrarily to that observed for cyclam systems (see the next section). However, all this information is still not enough to fully understand the relevant steps in the formation or in the kinds of intermediates in order to design a more catalytic and selective complex based on these systems. Also, it is necessary to improve the synthetic approach of these systems with different substituents in order to gain systematic knowledge about the new structures and the understanding of its chemical nature and kind of products obtained in each case. In this way, a feedback between the experimental and theoretical data will be possible and therefore a more efficient system for the target molecule. 

One of the advantages of this procedure over conventional synthetic methods of azacyclophanes (cyclic amide formation) resides in its brevity and simplicity. In addition, the results obtained reveal this procedure to be an efficient diaza[3.3]cyclophane synthetic method, and an acceptable approach for the synthesis of triazaC3.3.3]cyclophanes and tetraaza[3.3.3.3]cyclophanes as host molecules of inclusion compounds. This synthetic method has been successfully applied to other cyclophane systems, such as 2,ll-diaza[3.3](2,6)-, 2,11,20-triaza[3.3.3](2,6)- and 2,11,20,29-tetraaza[3.3.3.3](2,6)pyridinophane, syn- and anti-2,13-diazaC3.3](1,4)naphthalenophane, 2,13,24-triaza[3.3.3](1,4)- and 2,13,24,35-tetraaza[3.3.3.3](l,4)naphthalenophane. 

The perfluoroarene effect has also been probed using cyclophane systems. In particular the interaction of a cation with an arene and a fluorinated arene has been probed in several systems. An interesting comparison between the it effects found for standard arenes and perfluoroarenes can be made simply by examining the electrostatic surface maps shown in Appendix 2 for benzene and hexafluorobenzene. The charges derived from the quadrupole moments for benzene and hexafluorobenzene are opposite on the faces of the arenes, negative for benzene (red in Appendix 2) and positive for hexafluorobenzene (blue in Appendix 2). As expected, fluorination turns an attractive cation-ir interaction into a repulsive cation-fluoroarene interaction, and the difference can be on the order of several kcal / mol. 

Non-conjugated enones have also been coupled by low-valent titanium reagents, as illustrated by the synthesis of 14 [30]. The X-ray crystal structure of the racemic distellene 15 showed that the central C-C double bond is twisted by 10 and 14.5° for the two molecules in the unit cell [31]. Compound 16 should also be considered here since it permitted study of the electronic interaction between two [2.2]meta-cyclophane systems connected with a C=C bond [32],... 

Simple quinolizidine alkaloids of the Lythraceae, "which include the well-known natural products (2S,4S,9aR)-(—)-lasubine I (1341) and (2S,4S,9aS)-(—)-lasubine II (1342) and substituted cinnamate esters thereof such as subcosines I and II, (1343) and (1344), are less common than those in which the quinolizidine forms part of a macroHde or cyclophane system containing a biaryl component (Figure 32). Since the macrocychc alkaloids are not pertinent to this review, they will not—with one exception—be discussed further vide infra). 

The Wulff-Ddtz reaction is another approach to the synthesis of the cyclophane system by formal [2 + 2 + 2] cycloaddition. The intramolecular benzannulation of the Fischer carbene complex, which has an alkyne tethered to the a-position of the alkenyl substituent, gave a para-cyclophane in moderate yield under highly diluted conditions (Scheme 8.6) [6]. 

The above approach could also be used for the enantioselective synthesis of tripodal pyridinophanes. The hetero-[2 + 2 + 2] cycloaddition of diyne nitriles proceeded efficiently to give cycloadducts with [8] to [16]cyclophane systems in good yield with excellent ee (Scheme 8.19) [13b]. 

Cationic rhodium/chiral diphosphine complexes realized a new and facile access to the construction of planar-chiral cyclophane systems by the intra- or intermolecular [2 -I- 2 -I- 2] cycloaddition. 

In (25) there is a true fluorescer moiety in the cyclophane system, and it represents a donor-acceptor complex system, whereas (24) and (23) very probably are forming exciplexes on oxidation [41]. The higher efficiency of this paracyclophane energy transfer in comparison with the methylene-linked energizer and fluorescer as in (22) is seen from the fact that in (22) the DPA-residue, having a fluorescence quantum yield of nearly unity exhibits a chemiluminescence efficiency of 26% of that of luminol whereas in (25) with the 1,4-dimethyl anthracene fluorescer (0jn ca. 0.30) a light yield of 100% luminol [41] is obtained. 

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