Paracyclophane, preparation

The substituted [2.2]paracyclophanes prepared by the present procedure have proven to be useful starting materials for the synthesis of cyclophanes with extended aromatic ring systems,16 additional ethano bridges,17-18 and chromium tricarbonyl complexes.19... 

Paracyclophanes Prepared by Diels-Alder Reaction of Disubstituted Acetylenes with 1,2,4,5-Hexatetraene13- 14... 

The unsubstituted C-16 hydrocarbon, [2.2]paracyclophane (3), is DPXN. Both DPXC and DPXD are prepared from DPXN by aromatic chlorination and differ only in the extent of chlorination DPXC has an average of one chlorine atom per aromatic ring and DPXD has an average of two. 

Macrocyclic polyethers containing the 2.2-paracyclophane unit are interesting structures and several such compounds have been prepared . Despite the diverse structural possibilities, the syntheses of these molecules have generally been accomplished by straightforward Williamson ether syntheses. The only unusual aspect of the syntheses appears to be a novel approach to certain paracyclophanes developed by Helgeson (see footnote 7a in Ref. 91). The first step of Eq. (3.28) illustrates the formation of the required tetrol, which is then treated with base (KOH or KO-t-Bu) and the appropriate diol dito-sylate to afford the macrocycle. 

Optical Activity Caused by Restricted Rotation of Other Types. Substituted paracyclophanes may be optically active and 25, for example, has been resolved. In this case, chirality results because the benzene ring cannot rotate in such a way that the carboxyl group goes through the alicyclic ring. Many chiral layered cyclophanes (e.g., 26) have been prepared. ... 

Gade and Bellemin-Laponnaz have reported the synthesis, in good yields, of chiral oxazoline-imidazoliums salts 10a (Scheme 8) obtained by reaction of 2-bromo-4(S)-t-butyl oxazoline with several mono-N-substituted imidazoles [16]. Similaly an imidazolium salt 10b bearing a paracyclophane substituent was prepared by Bolm [17]. 

Vogtle et al. have prepared chiral poly(imine) dendrimers of various generations by condensation of non-racemic 5-formyl-4-hydroxy[2.2]paracyclophane moieties with poly(amine) dendrimers [71]. They have found that the optical activity of these dendrimers was nearly constant with increasing generation number. 

The substance 4,12-dibromo[2.2]paracyclophane is the key intermediate en route to several functional C2-symmetric planar-chiral 4,12-disubstituted[2.2]paracydo-phanes. Braddock and coworkers have shown that this important intermediate can be obtained by microwave-assisted isomerization of 4,16-dibromo[2.2]paracydo-phane, itself readily prepared by bromination of [2.2]paracyclophane (Scheme 6.88) [182], By performing the isomerization in N,N-dimethylformamide as solvent (microwave heating at 180 °C for 6 min), in which the pseudo-para isomer is insolu-... 

Polymeric pseudocrown ether networks have been generated in situ by the photopolymerization of poly(ethylene glycol) diacrylate transition metal complexes <00CM633>, and the effect of metal ion templation was evaluated. The 1,6,13,18-tetraoxa[6.6]paracyclophane-3,15-diyne (termed pyxophanes) was prepared from hydroquinone and l,4-dichlorobut-2-yne it forms size-selective 7i-complexes with alkali metal cations <00CC2377>. Dibenzo[ ]crown-m have been used in numerous elegant studies in which they were the needles that were threaded by diverse reagents the resultant... 

For comparison, it seemed extremely interesting to prepare octa-methyltetrastanna[2.2]paracyclophane (19). However, the attempted reductive coupling of l,4-bis(chlorodimethylstannyl)benzene did not... 

The smallest [n]paracycloph ane so far isolated is the [6]paracyclo-phane, first prepared by Jones et al. in 1974. Bickelhaupt prepared and succeeded in spectroscopic characterization of [5]paracyclophane, which is stable at low temperature in solution, but not isolable. As the first example of [n paracyclophanes bridged by heteroatom chains, Ando et al. reported preparation and the crystal structure of heptasila[7]paracyclophane (47) (42) (Scheme 12). 

Poly(l,4-naphthylenevinylenes) have been prepared by metathesis polymerization of benzobarrelenes [181,182] and the photoluminescence properties of homopolymers and block-copolymers have been studied in some detail [183]. PPV also has been prepared via ROMP of [2.2]paracyclophane-l,9-diene [184] and ROMP of a paracyclophene that contains a solubilizing leaving group [185]. The resulting polymer is converted to PPV upon acid catalysis at room temperature. ADMET of 2,5-dialkyl-l,4-divinylbenzenes using Mo or W catalysts has... 

A single crystal ENDOR study on V(bz)2 diluted into 2,2-paracyclophane is in preparation, which will allow to get deeper insight into the dynamic behavior of the benzene rings in these types of compounds281. ... 

During the synthesis of [2.2]paracyclophanediene, Dewhirst and Cram 83> prepared the bis-geminal dibromides 4a and 4b, which were subsequently converted into the diketones 5 a and 5 b. The UV spectra of the bromides 4a and 4 b show maxima at 236 nm. A comparison with the Amax values of other [2.2]paracyclophanes brominated at the bridges suggests that the absorption at 236 nm is the 235 nm band of [2.2]para-cyclophane, shifted bathochromically by the inductive effect of the... 

Less than two years after Chan and I disclosed the synthesis of 72 and 73, a more practical synthesis of 72 based on palladium-mediated reactions was reported by Armin de Meijere. I was deeply impressed by the highly efficient way Armin and his co-worker, Oliver Reiser, were preparing 72 as well as its derivatives. Immediately, I realized that it was impractical to compete with them. I therefore quit the dibenzo[2.2]paracyclophane field, with the strong conviction that many other unknown theoretically interesting molecules were still waiting for our pursuit. 

Fourfold Heck coupling (twofold on each dibromobenzene moiety) and Jeffery conditions has been applied on the two easily accessible tetrabromo[2.2]paracyclophane isomers 21 and 23, respectively, to prepare new double-layered 1,2- and 1,4-distyrylbenzene chromophoric systems 22-R and 24-R respectively, to enable studies of intramolecular charge-transfer phenomena in such systems (Scheme... 

Obviously carboxy derivatives such as 11-19 are simple chiral structures suitable for optical resolutions through diastereomeric salts. For this purpose carboxylic groups have been introduced into [10]- and [8]paracyclophane either by chloro-methylation and oxidation of the carboxaldehydes obtained thereof 39,44) or by lithiation and subsequent carboxylation40). Electrophilic substitution of strained paracyclophanes is not advisable since it may initiate rearrangement to the more stable metacyclophanes. Carboxy[7]paracyclophane (72) was first prepared in 1972 by ring contraction of a diazoketone derived from 4-carboxy[8]paracyclophane (75) 45). 

Optically active chochins were prepared by the Hofmann route 641 starting from (i )(—)-4-methyl[2.2]paracyclophane (38) with known chirality 54,67) (see 2.9.). Introduction of the trimethyl-ammoniomethyl group (via acetylation and subsequent transformations) afforded (—)-39 which was then cross-coupled with the ammonium base 36 to give a mixture of [2.2]paracyclophane and the levorotatory[3] and [4]chochins (40,43) with ( )-chirality in these cases the descriptors (/ ) and (5) specify the planar chirality of the inner rings(s) as shown in Fig. 2, in accordance with the rules presented in Section 1.2. 

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 (+)( ). 

Both of the tetraaza[3.3.3.3]paracyclophane (1) and tetraaza[n.l.n.l]paracyclo-phane (n = 6, 7, 8 cf. 2) rings have frequently been used as fundamental molecular skeletons for preparation of functionalized macrocyclic hosts [24-36]. Formation of three-dimensionally extended hydrophobic cavities was approached by introducing multiple hydrocarbon branches into the macrocyclic skeletons. Multiple hydrophobic chains thus placed in a macrocycle must be extended in the same direction and undergo mutual association to attain their optimal hydrophobic interactions in aqueous media due to thermodynamic reasons, while in nonaqueous media they presumably assume a free and separated configuration to minimize their mutual steric interactions. Consequently, such hydrophobic branches may provide a large hydrophobic cavity in aqueous media. 

In order to construct a hydrophobic three-dimensional cavity that is in-tramolecularly limited in space, we have prepared cage-type cyclophanes by linking macrocyclic rings. First we prepared a macropolycyclic host, which is constructed with two rigid macrocyclic skeletons of different size, tetraaza[3.3.3.3]paracyclophane as the larger one and tetraazacyclotetradecane as the smaller one, and four flexible hydrocarbon chains that connect the two macrocycles [40]. The flexibility of four hydrocarbon chains connecting the two macrocycles allows the induced-fit host-guest interaction in aqueous media. 

A similar 1,6-elimination of 3, prepared as shown, induced by fluoride ion results inp-quinodimelhane (a), which dimerizes to [2.2] paracyclophane (4).2... 

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