12.2.2.2 -Cyclophanes

2 Host-guest Complexes with Organic Cations 12.2.1 Cyclophanes 

Calixarenes without ionisable substituents at the wider rim are not water soluble. Their complexation behaviour towards organic cations, has, therefore, been studied mainly in lipophilic solvents such as CDCI3 and (CDCl2)2- The cation- r interaction is the main contribution to the stability of complexes and the association constants are rather low, ranging from 10 to lOOOM (see Table 12.1). 

On the basis of this definition (Fig. 1) the following classes of chiral compounds will be treated in this article cyclophanes, bridged anulenes and [8]anulenes, and ( )-cyclooctene and related structures. As mentioned above, metallocenes will be excluded. 

Even for very closely related compounds such procedures frequently lead to utterly different names and - most detrimentally - in many cases to the total disappearance of distinctive cyclic (mostly [het]arenic) subentities. Many efforts have therefore been made to develop a homogeneous nomenclature system for cyclophanes of most divergent appearances. However, none of them, is fully convincing. On the basis of these earlier endeavors the lUPAC Commission on the Nomenclature of Organic Chemistry (CNOC) has finally succeeded in presenting a very simple and easily communicable method for naming cyclophanes of all types. Its salient features will be outlined here. 

The new system consists essentially in an ingenious adaption of replacement nomenclature, in that the cyclic subunits of a cyclophane are each understood as individual superatoms and as such considered equivalent to and sequentially numbered like all other ring atoms. In the final total name, these superatoms are accounted for by arena, cycloalkana, etc. 

In the following examples the polycyclic name reflecting conventional naming procedures is generally given first and then the new lUPAC cyclophane name derived from the associated supergraph. For a better understanding, the basic skeletons are drawn in bold print where appropriate. Current trivial or traditional names of some prototypical compounds are also shown. 

16-(Ethano [ 1,4]benzenoethano)-7,10-etheno-21,17-metheno-17H-dibenzo [Uyh ] cycloheptadecene 

That this new nomenclature concept can also be advantageously utilized with saturated, bridged, hetera-replaced etc. cycla segments is demonstrated by a supplemental example. 

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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. 

Two efficient syntheses of strained cyclophanes indicate the synthetic potential of allyl or benzyl sulfide intermediates, in which the combined nucleophilicity and redox activity of the sulfur atom can be used. The dibenzylic sulfides from xylylene dihalides and -dithiols can be methylated with dimethoxycarbenium tetrafiuoroborate (H. Meerwein, 1960 R.F. Borch, 1968, 1969 from trimethyl orthoformate and BFj, 3 4). The sulfonium salts are deprotonated and rearrange to methyl sulfides (Stevens rearrangement). Repeated methylation and Hofmann elimination yields double bonds (R.H. Mitchell, 1974). 

Treatment of dibenzylic sulfides with triethylphosphite and UV-light also led to cyclophanes in high yield (H.A. Staab, 1979). 

While the previous receptors are typically used in organic solvents, except for the cyclodextrins, there are special cases of cyclophane receptors supphed with peripheral charges (ammonium units) (107—12) or ionizable groups (carboxylate functions) (113,114) (Fig. 17) to allow substrate recognition, as in nature, in an aqueous medium, profiting from the solvophobic effects of water (115). 

F. Diederich, Cyclophanes, Monographs in Supramolecular Chemisty, Vol. 2, The Royal Society of Chemistry, Cambridge, 1991. 

Fig. 5. Cyclophane-type inclusion compounds of different varieties. The guest component is shaded.

F. Viigde, Cyclophane Chemisty, ]ohn Wiley Sons, Inc., Chichester, 1993. 

A dehcate stereochemical balance is clear in the high yield photocyclization of one cyclophane configuration (47) to a cage compound (48), whereas its spatial relative (49) leads only to higher molecular weight product (38). 

Cyclopent-2-en-l-one, 2-hydroxy-3-methyl-synthesis, 3, 693 Cyclopentenone, 4-methoxy-formation, 1, 423 Cyclopenthiazide as diuretic, 1, 174 Cyclopent[2,3-d]isoxazol-4-one structure, 6, 975 Cyclophane conformation, 2, 115 photoelectron spectroscopy, 2, 140 [2,2]Cyclophane conformation, 2, 115 Cyclophanes nomenclature, 1, 27 Cyclophosphamide as pharmaceutical, 1, 157 reviews, 1, 496 Cyclopiloselloidin synthesis, 3, 743 Cyclopolymerization heterocycle-forming, 1, 292-293 6H-Cyclopropa[5a,6a]pyrazolo[l,5-a]pyrimidine pyrazoles from, 5, 285 Cydopropabenzopyran synthesis, 3, 700 Cyclopropachromenes synthesis, 3, 671 Cyclopropa[c]dnnolines synthesis, 7, 597 Cyclopropanation by carbenes... 

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

STEPHENS CASTRO Acetylene cycloptiane synthesis Polyacetylene cyclophane synthesis from an iodophenyl copper acetylide... 

In using the tables, it would be best to survey the list of tables included in each chapter to determine how many categories might possibly contain the compound of interest. It should be noted that a large number of cyclophanes which contain fewer than three heteroatoms are not included in this book since they are not generally useful as cation binders. 

The NMR spectrum of the cyclophane shows three signals at 6 4.27, 6.97, and 7.24 (1 2 1 ratio) due to the benzene ring hydrogens. Examine cyclophane and identify which hydrogens are responsible for each signal. 

As an illustrating example for the application of the Friedel-Crafts acylation in the synthesis of complex molecules, its use in the synthesis of [2.2.2]cyclophane 13 by Cram and Truesdale shall be outlined. The reaction of [2.2]paracyclo-phane 10 with acetyl chloride gives the acetyl-[2.2]paracyclophane 11, which is converted into the pseudo-geminal disubstituted phane 12 by a Blanc reaction, and further to the triple bridge hydrocarbon 13 ... 

Schneider and Busch have showed that tetraazafS 1 8 l paracyclophane catalyzes the nitration of alkyl bromides with sodiiun nitrite In dioxane-water d l at 30 C, the reaction of 2-bromomethylnaphthalene with sodiiun nitrite is accelerated by a factor of 20 in the presence of the catalyst Concomitantly, the product ratio of [R-ONO [RNO-, changes from 0 50 1 to 016 1 Thus, an acciuruiladon of nitrite ions at the positively charged cyclophanes or IRA-900-nitrite form provides a new method for selective nitration of alkyl halides... 

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]. 

An example of the modular preparation of the cyclophane 3 from the substituted bipyridine 2 and a general tripeptide 1 is shown in Scheme 3-3. The host molecule 3 contains a pre-organized binding pocket. The overall basicity of such molecules also facilitates their intercalation within the lamellas of acidic zirconium phosphate, thus making this chemistry well suited for the desired application. 

Fig. 3-4. (A) Changes in chemical shift of protons of cyclophane -CH - groups between bipyridinium and phenyl in H NMR spectra of 3 as a function of (R)-DOPA concentration (a) 0, (b) 0.111, and (c) 0.272 mol (B) Change in chemical shift plotted against the analytical concentration of (R)- and (5)-DOPA. The solid line is calculated for 1 1 host - guest complexation. (Reprinted with permission from ref. [79]. Copyright 1998, American Chemical Society.)...

Harrowfield et al. [37-39] have described the structures of several dimethyl sulfoxide adducts of homo bimetallic complexes of rare earth metal cations with p-/e rt-butyl calix[8]arene and i /i-ferrocene derivatives of bridged calix[4]arenes. Ludwing et al. [40] described the solvent extraction behavior of three calixarene-type cyclophanes toward trivalent lanthanides La (Ln = La, Nd, Eu, Er, and Yb). By using p-tert-huty ca-lix[6Jarene hexacarboxylic acid, the lanthanides were extracted from the aqueous phase at pH 2-3.5. The ex-tractability is Nb, Eu > La > Er > Yb. 

Murakami et al. reported that a cyclophane 27 having two imidazole groups is activated by Cu2+ ions in the hydrolysis of p-nitrophenyl dodecanoate 25,26), although the activation seemed to be small. 

Bohrer, I. M. Evaluation Systems in Quantitative Thin-Layer Chromatography, 126,95-118 (1984). Boekelheide, V. Syntheses and Properties of the [20] Cyclophanes, 113, 87-143 (1983). 

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