16-membered cyclophanes

Cyclizations by formation of carbon-sulfur-bonds belong to the best studied reactions which use the dilution principle. Usually bromides react with thiols [7 b, 17, 18], thiuronium salts [19], or with sodium sulfide [20] and thioacetamide, respectively. The formation of C—S bonds represents one of the most valuable methods to synthesire medium-membered cyclophanes such as 4-8 [7 b, 18 b, 20d, 21]. 

The C3 symmetry of the cup-lilie trimers indicates that they are chiral typically being formed as a racemate. In some cases, the cups are resolvable via suitable dia-stereomers. as the enantiomers are somewhat stable to racemization via conformational inversion of the nine-membered cyclophane ring (AG 298 = 110-1 i5 kJ/mol). Chirality in the cup-shaped units implies that two types of cryptophanes exist Joining two cups of opposite... 

Dynamic transacetalization experiments targeting cyclophane formation have also been described by Mandolini and coworkers [34]. Production of a cyclic polyether DCL by direct reaction of triethylene glycol and 4-nitrobenzaldehyde has been reported by Berkovich-Berger and Lemcoff amplification of small macrocyclic members of the library by ammonium ion was observed [35]. With these few examples demonstrating feasibility, we can anticipate increased use of transacetalization in future DCC efforts. 

The photorearrangement of 7V-aryl lactams 34 to the ortho-position offers an interesting possibility for the preparation of cyclic benzo-aza-ketones of type 35, whereas the rearrangement to the para-position should lead to para-cyclophane 144 formation. 7-, 8-, and 13-Membered ring jV-aryl lactams (34, n = 5, 6, and 11) were successfully rearranged in ethanol to 35 in chemical yields of 60, 83, and 80%,13 and in quantum yields of 0.071, 0.11, and 0.082, respectively.14... 

The cyclobutane rings of 1,2-ethano[2.n]cyclophanes can be opened in a Birch reduction at — 60°C in tetrahydrofuran and liquid ammonia to give [4.n]cyclophanes.212-214 In this manner, macrocyclic rings with twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen and twenty-seven members have been synthesized. 

Intramolecular photocyclodimerizations of styrene systems of type 66 have been applied50 for the synthesis of cyclophanes (Scheme 14). The irradiation of compound 66a afforded straight photoproducts 67, subsequently transformed, upon reductive cleavage of the produced four-membered ring, to cyclophane 68. The approach seems successful for longer chains between the styrene units and allows introduction of heteroatoms such as oxygen51, 52 (69) and silicon53 (66b). 

Cyclodextrins and calixarenes are members of a general class of macrocycles commonly referred to as cyclophanes, although the naturally occurring CDs are usually considered separately from the synthetic members of the cyclophane family of compounds. The properties and guest-host complexes of cyclophanes... 

One of the main reasons why nodal nomenclature [42] was created was that the IUPAC organic nomenclature did not allow for assigning unique canonical names to members of the class of molecules referred to as "cyclophanes" a problem that would not have arisen had beta bonds been available. This is not to devalue the many virtues of nodal nomenclature, rather merely to show how the proposed system nomenclates these compounds without difficulty. 

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. 

The 10-membered ring cyclophanes 183-185 are novel compounds bearing unique molecular structures (Figure 44) <2006JOC6110>. 

In general, yields decrease in cesium assisted cyclizations changing to smaller ring sizes (7a) or by introduction of hetero atoms into the ring skeleton. The cesium method is also well suited for the preparation of cyclophane compounds like the 23-membered macrocycle 9 or the tetraoxa cycle 10, which were obtained in 60 and 46% yields respectively, starting with the ditosylates [19]. 

Vogtle and Meurer explained the favoured formation of strain ring compounds in the synthesis of cyclophanes by cyclizations with cesium thiolates by a preorientation (preorganization) of the reactants at the cesium cation [82], For the cesium ion in contrast to the smaller alkali metal cations the capabiUty of forming an 11-membered intermediate is ascribed, which would favour an intramolecular course of the reaction (Fig. 4). 

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]. 

The consequences of increasing the size of the polyether macrocycle to 68 members (that is, by a factor of two over the small ring system) was investigated. Accordingly, the synthesis of tetrakis-/ -phenylene-68-crown-20 was achieved in dimethylformamide at room temperature in excellent yield and this, in turn, was initially used to produce the [2]-catenane 22 (Figure 5.13). From the temperature dependence of the H NMR spectrum, 22 appears to behave like a molecular train - with the tetracationic cyclophane travelling from station to station around the... 

Nearly all work on cyclophanes has been carried out in the [2.2] series because the members are relatively accessible. This situation may change now that a good method has been discovered for making members of the [4.2] series. The method is a simple extension of the standard procedure in which two suitable quinonoid dienes are cogenerated, but employs a vinyl-ogous system as one component (Scheme 65). Two products result, but since... 

Timmermans et al. report that diastereoselectivity can be induced in the intramoleuclar meta photocycloaddition of ethenes to the benzene ring as a result of minimisation of steric interactions between substituents on the linking tether of the bichromophore and a methoxy group at the 2-position of the arene unity this type of photoprocess has also been used as a key step in a formal synthesis of crinipellin B (Wender and Dore). New polycyclic cage compounds 43 have been obtained by irradiation of the [3.3,3] (1,3,5) cyclophane 44 (Sakamoto et al.) and Kubo et al. have described the intramolecular [3 + 2] photocycloaddition of bichromophores such as 45 which gives rise to nine- to eleven-membered ring systems 46. 

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