Cyclophane moieties

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). 

Upon the first reduction, the voltammetric wave shifts by 20-30 mV, presumably due to donor-acceptor interactions resulting from the naphthalene and cyclophane moieties.39 The second reduction remains relatively unaffected, indicating that the complex disassembles prior to the second reduction of the cyclophane. Alternatively, the complex can disassemble through competitive binding interactions with a tetrathiafulvalene derivative. Thus, Cooke and coworkers demonstrate that self-assembly at exo-active surfaces can be reversibly controlled via an external electrochemical stimulus or competitive binding interactions. 

Intramolecular Cycloadditions. - Intramolecular (2 + 2)-photocycloaddi-tion has been reported within diene 1,1-dicarbonitriles. Both direct and sensitized irradiation is effective. Unlike the singlet process, where an exciplex is involved, the sensitized process proceeds via 1,4-biradicals. The singlet and triplet reactivity has been investigated for a series of 1-alkene-1,1-dicarbonitriles with additional unsaturation at the 5, 6 or 7 positions. The cyclophane moiety shown in the derivative (23) has been suggested as a useful reaction control system. The irradiation of this cinnamate derivative affords the (3-truxinic acid derivative (24), which can be uncoupled from the paracyclophane. ... 

The name of Crownophane was coined for compounds having both crown ether and cyclophane moieties. It is well known that the term Crown Ether was introduced by Pedersen, when he serendipitously discovered the first examples of this compound class. They are defined as species possessing cyclic polyether structures. Cyclophanes, sometimes simply called Phanes - the name was coined by Cram - are defined as compounds having layered aromatic nuclei or having bridges across the surface of an aromatic nucleus. 

Misumi and co-workers made paracyclophane-based crownophanes (1-4) (Structure 1) and concluded that the cyclophane moieties serve as a 7t-donor for the complexation of alkali metal cations [22]. 

Cyclophano-crown ether host (Scheme 8), possessing cyclic polyether and cyclophane moieties in a single molecule and ability to simultaneously bind a potassium cation and 6-methoxy-2-naphthonitrile in a water-methanol mixture, is of particular interest, since the contrasting solvent effects can be examined in the same host. Indeed, neutral 6-methoxy-2-naphthonitrile guest forms a 160-fold more stable complex with the cyclophane moiety in more hydrophilic 60 40 water-methanol solvent than in pnre methanol. In contrast, the affinity toward potassium ion is enhanced by a factor of 120 in pure methanol rather than in 60 40 water-methanol. Scheme 8... 

Generally speaking, when the crown ethers are modified by adding the cyclophane moieties, they become naturally more hydrophobic, open narrower orifice by pinching with cyclophane part, and become more functional than the original crown ether because the cyclophane part provides a variety of platforms or sites for functional groups assisting their supramolecular properties such as lariats, etc. 

The second chapter, Syntheses and Properties of Crownophanes by S. Ino-kuma, M. Ito, and J. Nishimura reviews a variety of crownophanes possessing both crown ether and cyclophane moieties, the latter ranging from benzene to condensed aromatic and heteroaromatic rings whose selective complexation in the solution states principally toward the metal cations are reviewed. The related rotaxanes and catenanes are also described in this chapter. 

Macrocycles containing isoxazoline or isoxazole ring systems, potential receptors in host—guest chemistry, have been prepared by multiple (double, triple or quadruple) 1,3-dipolar cycloadditions of nitrile oxides, (prepared in situ from hydroxamoyl chlorides) to bifunctional calixarenes, ethylene glycols, or silanes containing unsaturated ester or alkene moieties (453). This one-pot synthetic method has been readily extended to the preparation of different types of macrocycles such as cyclophanes, bis-calix[4]arenes and sila-macrocycles. The ring size of macrocycles can be controlled by appropriate choices of the nitrile oxide precursors and the bifunctional dipolarophiles. Multiple cycloadditive macrocy-clization is a potentially useful method for the synthesis of macrocycles. 

The aryl groups of the styryl systems need not be unsubstituted, as has been illustrated before for the cyclizations encountered in the synthesis of naphthalenophanes from 120. Indeed cyclization to afford a cyclobutane derivative where methoxy groups are on the adjacent ring position to the vinyl moieties has also been studied. The irradiation of 138 affords the m-cyclophanes 139 and 14065. Further study has sought to evaluate the steric effect of o-methoxy groups in such molecules66. 

A) almost equals the van der Waals distance. As in [2.2]para-cyclophane, the hydrogen atoms of the aromatic moieties are directed towards the interior of the molecule because of the increased -electron density on the outside of the molecule caused by the intraannular interaction of the 7r-electron clouds. 

The following compounds which have a benzene moiety of [2.2]para-cyclophane replaced by a heteroring (e.g. furan) may be counted among the analogs of [2.2]paracyclophane, as their stereochemistry has many features in common with that of the carbophanes 64> 34—36. 

As seen, cyclophane structures shown in Schemes 1.4b through 1.4e have the following unique feature The through-bond distance within the paracyclophane fragment is held constant, whereas the spatial distance between the ion-radicalized and neutral moieties is changed. Therefore, the relative importance of through-bond and through-space mechanisms for intramolecular electron transfer can be learned directly from experimental data on these molecules. 

For [2.2]paracyclophane-4-carboxylic acid (25) as (—)(R) This result has been mentioned in a footnote in Ref. 1011 but seems never to have been published (see also Ref. 61). The chirality of this acid was correlated via its ( )-aldehyde with a levo-rotatory hexahelicene derivative which, according to the paracyclophane moiety at the terminal, had to adopt (A/)-helicity. Its chiroptical properties are comparable to those of hexahelicene itself101. For the (—)-bromoderivative of the latter the (A/)-helicity was established by the Bijvoet-method 102). In a later study, (—)para-cyclophane-hexahelicene prepared from (—)-l,4-dimethylhexahelicene with known chirality (which in turn was obtained with approximately 12% enantiomeric purity by asymmetric chromatography) confirmed these results. It should be mentioned that [2.2]paracyclophane-4-carboxylic acid (25) was the first planar chiral cyclophane whose chirality was determined 1041 (see also Ref.54 ). The results justmentioned confirmed the assignment (+)( ). 

In the synthesis of concave 1,10-phenanthroline cyclophanes 21 (Scheme 4), the aryl bridgeheads could be easily introduced by the addition of two aryl lithium moieties 16 to 1,10-phenanthroline (15). Although aryl lithium compounds may also be added to pyridine [23], this approach could not be realized for the construction of concave pyridine cyclophanes 29 yet [24]. Therefore another route for the synthesis of the concave pyridines 29 was used (Scheme 5) the cyclization of 1,5-diaryl substituted Cj-units 23 or 27 with ammonia. The resulting 2,6-bis(2,6-dimethoxyphenyl)pyridine 24 [25], the pyridine analogue to the tetramethoxy-1,10-phenanthroline derivative 17, was then treated in the same way. After liberation of the phenol functions, the four OH groups of 28 were reacted with two equivalents of diiodides 19 [25]. As in the synthesis of the concave 1,10-phenanthroline cyclophanes 21, two macrocycles were formed in one reaction step. 

---