Cyclophane chemistry

Meijere, B. Konig, Synl tt 1997, 1221 c) R. Gleiter, H. Hopf, Modern Cyclophane Chemistry, Wiley-VCH, Weinheim, 2004. 

A range of cyclophanes (compounds containing a bridged aromatic ring - for a full discussion of cyclophane chemistry see Section 6.5) with protonated nitrogen functionalities have been used with great success as anion binding hosts. In particular, the diphenylmethane moiety is commonly used... 

Voegtle, F. and Pawlitzki, G. (2002) Cyclophanes from planar chirality and helicity to cyclochirality, in Takemura, H. (ed.), Cyclophane Chemistry for the 21st Century, Research Signpost, Trivandrum, India, pp. 55-90. 

Cram, D. J. Cram, J. M. Cyclophane Chemistry Bent and Battered Benzene Rings. 

Cram, D.J. and Cram, J.M. (1971) Cyclophane chemistry bent and battered benzene rings. Accounts of Chemical Research, 4, 204-213. 

Rozenberg V, Sergeeva E, Hopf H (2004) Cyclophanes as templates in stereoselective synthesis. In Gleiter R, Hopf H (eds) Modem cyclophane chemistry. Wiley-VCH, Weinheim, pp 435 162... 

In recent years further novel classes of compounds were added to cyclophane chemistry. The multilayeredphanesiS derived from [2.2]paracyclophane contain coaxially stacked benzene rings connected by ethano bridges para to one another. The first members of this series were described in 196416. Quadruple layered phane hydrocarbons 3 and 4 reveal in their UV-spectra long range electronic effects penetrating several arene units. 

From its rudimentary beginnings over four decades ago, cyclophane chemistry has developed into an ever-evolving, multifaceted discipline which overlaps with many other areas of chemistry. A rough cross-section (by no means exhaustive) of some of the recent developments in the mainstream of this field, as highlighted here, certainly attests to that. 

The pyrolytic elimination of sulfur dioxide from cyclic sulfones to give (strained) macrocycles (sulfone pyrolysis) counts among the most important reactions in cyclophane chemistry. There is hardly any research group dealing with cyclophanes which did not make use of the sulfone pyrolysis for the synthesis of such molecules. Since its first application in cyclophane synthesis over twenty years ago [1], the sulfone pyrolysis enabled researchers to synthesize a wealth of strained cyclophanes and developed into a reaction of general importance. 

In 1979, Rossa and Vogtle published a review on sulfone pyrolysis which did not only cover examples from cyclophane chemistry but also discussed the pyrolysis of acyclic sulfones, of small-membered cyclic sulfones as well as questions of mechanisms and practical aspects of the reaction [2]. 

Direct pyrolysis of the cyclic sulfides without prior chemical modification [11] special method without general importance in cyclophane chemistry. 

F. V. Vogtle, Cyclophane Chemistry, John Wiley and Sons, Chichester, 1993. 

This work on organic reaction mechanisms and our development of cyclophane chemistry were of great use to us in our later work. We did not shy away from tackling either multistep syntheses (up to 30 reactions) or highly asymmetric, designed systems needed in our studies of enzyme-mimicking systems. We needed both equilibria and kinetic techniques and an understanding of the importance of solvent effects in our more recent studies. 

In their pioneering work in multilayered cyclophane chemistry, Longone and Chow (97) prepared a mixture of four-layered [2.2]paracyclophanes 82 and 85 by making use of the elegant procedure of Cram, which involves coupling of the p-xylylene intermediate 80 derived by a 1,6-Hofmann elimination of the corresponding quaternary ammonium base. There are available two alternatives for coupling the racemic 80 of C2 symmetry either between enantiomers of opposite chirality or between enantiomers of same chirality. The former should provide meso-82 of C2h symmetry, whereas the latter should yield 85 of D2 symmetry. 

More than 90 years after the first reported synthesis of [2.2]metacyclophane [1] and nearly 50 years after the synthesis of [2.2]paracyclophane, [2] cyclophane chemistry is still a field of ongoing research. In the beginning, work had been focused on the development of new synthetic methods yielding cyclophanes and ansa-compounds and the investigation of their physical properties. Later, the scope was extended to the incorporation of heterocycles into phanes and the more sophisticated techniques allowed the synthesis of multibridged and multilayered phanes. All this has been extensively reviewed [3]. 

Non-benzoid phanes have always played an important role in cyclophane chemistry and many structures have been prepared with other Hiickel aromatic rings such as azulene or tropone [49]. A cyclophane with two bridged annulene units was recently synthesized by Mitchell [50,51 ]. Dimethyldihydropyrene (76), an excellent NMR probe first introduced by Boekelheide [52], was converted into the dialcohol 77 in three steps. Reaction with adipoyl chloride afforded the large [10.10]cyclophane 78. Unfortunately the conversion of the dialcohol into the corresponding dibromide 79, an obvious precursor to the interesting phane 80, has failed so far. 

Introduction of the tricarbonylchromium group into cyclophane chemistry has great potential for the preparation of planar- (or helical-)chiral compounds. Besides structure/chiroptics relationships, carrying out stereoselective reactions is of major importance. Recently, inclusion of ferrocenes and benzene-Cr(CO)3 into the cavity of a cyclodextrine was achieved and this makes the connection to supramolecular chemistry [183]. 

Perhaps the most efficient stimulus in cyclophane chemistry goes back to the discovery of crown ethers by C. J. Pedersen in 1967 [(1967) J Am Chem Soc 89 7017] being the starting signal for a very promising field of research called Host-Guest or Supramolecular Chemistry. Actually the first crown ether that was synthesized, dibenzo-18-crown-6, was a cyclophane. 

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