A preparative microwave method for the isomerisation of 4,16-dibromo[2.2]paracyclophane into 4,12-dibromo[2.2]paracyclophane

4,16-Dibromo[2.2]paracyclophane (4) is isomerised to 4,12-dibromo[2.2]paracyclophane (1) by the application of microwaves in DMF solution.     

The first three aromatic tribromides of the [2.2]paracyclophane series

From the reaction mixtures in the uncatalyzed polybromination of [2.2]paracyclophane by the action of excess Br₂ in CCl₄, there have been found along with the known products — 4,15- and 4,16-dibromo[2.2]paracyclophanes — two new aromatic tribromides of this series, which have been isolated in pure form: 4,12,15- and 4,15,16-tribromo[2.2]paracyclophanes. Special experiments demonstrated that the mixtures of these tribromides are formed as a result of competitive monobromination of 4,15-dibromo[2.2]paracyclophane; the 4,15,16-tribromo[2.2]paracyclophane, together with still another newly isolated isomer of this series — 4,8,12-tribromo[2.2]paracyclophane — is formed as a result of competitive monobromination of 4,16-dibromo[2.2]paracyclophane. As an explanation of the features of the orienting effect of substituents in these competing reactions, a rule was proposed: On the conventional orientation (from the electronic point of view) of entry of the bromine atom into the substituted ring (para > ortho > meta), a steric limitation is imposed on its attack in the pseudo-gem-position, owing to the bulky bromine atom that is transannularly positioned above it in the neighboring aromatic ring. The structures of all of the tribromides were established on the basis of elemental analyses, mass spectrometry, and¹H NMR spectrometry (including PMR using the homonuclear Overhauser effect). The data obtained in this work indicate that the 4,12,15-tribromo[2.2]paracyclophane and 4,15,16-tribromo[2.2]paracyclophane are predecessors of the two tetrabromides previously obtained by Cram — 4,7,12,15- and 4,5,15,16-tetrabromo[2.2]paracyclophanes; and the 4,8,12-tribromo[2.2]paracyclophane is a possible predecessor of 4,8,12,16-tetrabromo[2.2]paracyclophane, which is unknown up to the present time.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1837–1843, August, 1992.     

Suzuki aryl cross-coupling chemistry using derivatives of 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

An exploration into the scope of Suzuki aryl cross-coupling chemistry using derivatives of 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane is reported. The coupling of 4-iodo-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane with various aryl boronic acids and boronic acid pinacol esters was successful, with the exception of very sterically demanding systems, such as mesityl. The synthesis of the previously unreported 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophanyl-4-boronic acid is described, together with various Suzuki aryl cross-coupling reactions of this new system. Using standard Suzuki methodology, it was possible to prepare dicyclophanes bearing two octafluoro[2.2]paracyclophane units separated by both one and two benzene rings.     

Ethynyl[2.2]paracyclophanes and 4-isocyano[2.2]paracyclophane as ligands in organometallic chemistry

An alternative synthesis of (±)-4-ethynyl[2.2]paracyclophane (PCPCCH) (5) and 4,16-diethynyl[2.2]paracyclophane (6) via the Corey-Fuchs reaction has been developed. The olefinic intermediate 4-dibromovinyl[2.2]paracyclophane (3) has been isolated and structurally characterized. The racemic terminal alkyne 5 was employed as starting material for assembling of a luminescent extended π-conjugated system containing a thiophene unit and for a catalytic bis-silylation reaction yielding the olefinic dithioether Z-PhSCH₂Me₂SiC(H)C(PCP)SiMe₂CH₂SPh (9). The dimetallatetrahedran [Co₂(CO)₆(μ-η²-PCP-CCH)] (10) has been prepared and its crystal structure determined by an X-ray diffraction analysis. Alkyne 5 has also been used for the preparation of the Pt(0) complex [Pt(PPh₃)₂(PCPCCH)] (11) and the heterodinuclear dimetallacyclopentenone [(OC)₂Fe{μC(O)C(PCP)C(H)}(μ-dppm)Pt(PPh₃)] (12). The synthesis and reactivity of 4-isocyano[2.2]paracyclophane (15) towards heterobimetallic iron-platinum and palladium-platinum complexes is also presented. Opening of the dative iron → platinum bond of [(OC)₄Fe(μ-dppm)PtCl₂] (16) occurred upon addition of 15 to a CH₂Cl₂ solution of 16 leading to [(OC)₄Fe{μ-dppm}PtCl₂(CNPCP)] (17). Treatment of [ClPd(μ-dppm)₂PtCl] (18) with isocyanide 15 in a 1:1 ratio affords the A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)PtCl] (19), resulting from formal insertion of 15 into the Pd-Pt bond. Addition of 2 equiv. of 15-18 leads to the ionic A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)Pt(CNPCP)]Cl (20).     

Stereoselective synthesis of homoallylic alcohols of the [2.2]paracyclophane series and their use as auxiliaries in asymmetric allylboration of aldehydes

Stereoselectivity of allylboration of 4-formyl[2.2]paracyclophane, 4-acetyl[2.2]paracyclophane, and 4-hydroxy-5-formyl[2.2]paracyclophane was studied and the relative configurations of the homoallylic alcohols obtained were established. Optically pure (Sp,Sc)-(+)-4-(4-hydroxy-1-methylbut-3-enyl)[2.2]paracyclophane and (Rc,Sc)-(+)-4-hydroxy-5-(4-hydroxybut-3-enyl)[2.2]paracyclophane were synthesized. The possibility of using (Sp,Sc)-(+)-4-(4-hydroxy-4-methylbut-3-enyl)[2.2]paracyclophane as a recoverable chiral auxiliary in asymmetric allylboration of aldehydes was demonstrated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 914–921, May, 2000.     

Synthesis of novel planar-chiral [2.2]paracyclophane derivatives as potential ligands for asymmetric catalysis

The synthesis of a variety of new 4,5-disubstituted [2.2]paracyclophane derivatives has been achieved employing different cross-coupling reactions. By this methodology, a heteroatom-variation of successful catalyst ligands was achieved, giving rise to a modular ligand system. The X-ray structure of 4-hydroxy-5-(1′-hydroxy-1′-phenylethyl)-[2.2]paracyclophane was determined to elucidate the configuration. Additionally, a diastereoselective synthesis of planar- and central-chiral 4-([2.2]paracyclophanyl)ethylamine was achieved, thus resulting in a planar- and central-chiral phenyl ethylamine analogue.     

Full multinuclear resonance analysis of 4-amino-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

The complete assignment of 19F, 1H and 13C NMR spectra for a monosubstituted octafluoro[2.2]paracyclophane derivative is described for the first time. The unambiguous assignments were achieved through the combination of 19F--1H HOESY, 1H COSY and 19F COSY techniques and then further confirmed employing a complementary approach using a Karplus-dependent 3JCF interaction. Interesting aspects of the coupling patterns for various JHH, JHF, JCF and JFF interactions are also discussed.     

Conformational rigidity and flexibility of the paracyclophane skeleton in substituted [2.2]paracyclophanes

The character of distortions of the paracyclophane skeleton in various substituted [2.2]paracyclophanes was analyzed based on X ray diffraction data. The rigidity of the skeleton is provided by ethylene bridges and flexibility of the benzene rings, which adopt a boat conformation. The flexibility of the skeleton is manifested in the displacement of the benzene rings with respect to each other and conformational changes of ethylene bridges. The changes in these characteristics are very sensitive to intra- and intermolecular steric factors and are indicative of the absence of strong specific stacking interactions between the be nzene rings. Precision X-ray diffraction study and quantum-chemical calculations for unsubstituted [2.2]paracyclophane and 4,7-benzoquinono[2.2]paracyclophane demonstrated that there are no attractive interactions between the benzene rings, and the electron density is localized predominantly on the outer surface of the rings. This fact can be considered as the cage molecular effect of the [2.2]paracyclophane skeleton.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1707–1732, September, 2004.     

Synthesis of 1,1,9,9-tetrafluoro[2.2]paracyclophane and its polymerization by vapor deposition method

1,1,9,9-Tetrafluoro[2.2]paracyclophane ( 1 ) was prepared successfully as white crystals in 72% yield via two-step reactions from 1,9-diketo[2.2]-paracyclophane. The polymerization of 1 by the vapor deposition method was carried out at pyrolysis temperature range of 400 to 800°C and deposition temperature range of ?20 to 20°C, and a tough, transparent poly(α,α-difluoro-p-xylylene) film was obtained in 72% yield at the pyrolysis temperature of 750°C and the deposition temperature of ?20°C. It was found that the pyrolysis of 1 gave a reactive α,α-difluoro-p-xylylene, which polymerized on the head-to-tail addition to give poly(α,α-difluoro-p-xylylene). Some properties such as solubility, thermal stability, glass transition temperature, and density for poly(α,α-difluoro-p-xylylene) were studied. © 1995 John Wiley & Sons, Inc.     

Synthesis of through‐space conjugated polymers containing [2.2]paracyclophane and thieno[3,4‐b]pyrazine in the main chain

We synthesized through‐space conjugated polymers with [2.2]paracyclophane and thieno[3,4‐b]pyrazine units in the main chain by the Sonogashira–Hagihara coupling reaction. The obtained polymers were soluble in common organic solvents, and homogeneous thin films were readily obtained from the polymer solutions by spin‐coating techniques. The polymers exhibited the extension of the conjugation length via the through‐space interaction. The polymers showed orangish‐red emission with peak maxima of around 610 nm in diluted solutions and their thin films, which were derived from the thieno[3,4‐b]pyrazine moieties. The optical and electrochemical behaviors of the polymers containing pseudo‐para‐ and pseudo‐ortho‐linked [2.2]paracyclophane were identical. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

An exploration of Suzuki aryl cross coupling chemistry involving [2.2]paracyclophane derivatives

Suzuki aryl cross coupling reactions using derivatives of [2.2]paracyclophane were examined. A variety of aryl boronic acids and pinacolate esters were successfully cross coupled with 4-bromo[2.2]paracyclophane under standard Suzuki conditions. Whilst an excellent tolerance for electron donating and withdrawing groups was observed, cross coupling reactions with highly sterically demanding borates (e.g. mesityl) were unsuccessful. The preparation and stability of the previously unreported [2.2]paracyclophanyl-4-boronic acid, -pinacolate ester and -dimethyl ester are described, along with the utility of these systems in Suzuki aryl cross coupling reactions. Application of this methodology led to a dicyclophane containing two [2.2]paracyclophane units separated by a 4-4' connected biphenyl spacer group.     

Cyclophane,XIV : darstellung polymethylierter [2.2]paracyclophane

Starting from 4, 5, 12, 13-tetrakis(methoxycarbonyl)[2.2]paracyclophane ($\text{1}$), the penta-($\text{4}$), hexa-($\text{6a}$–$\text{c}$), hepta-($\text{7}$), and octamethyl-($\text{8}$) derivatives have been prepared by a repetitive formylation-reduction sequence.     

Theoretical investigation of [2.2]paracyclophane as a donor toward a Cr(CO)3 group

A comparative molecular orbital study of [2.2]paracyclophane and simple arenes as ligands toward a Cr(CO)₃ group was performed with the aim of accounting for the observed coordination patterns. While the inter-ring repulsion is an important factor in [2.2]paracyclophane activation, it is not the only one. The molecular orbitals of two arene rings stacked parallel to each other were analyzed in some detail. The inward hybridization (toward the other ring) of the (arene)₂ HOMO was shown to reduce the strength of consequent bonding with the Cr(CO)₃ is fragment. The overall stabilization of [2.2]paracyclophane complex with Cr(CO)₃ is enhanced by a reduction of the inter-ring repulsion and strengthening of the Ar−Cr bond, and reduced by weakening of the intra-ring carbon-carbon bonds. The inter-ring repulsion increases with approach of the arenes to each other, as appears to happen in the structure of [2.2]paracyclophane complex with Cr(CO)₃. This explains the high donor ability of the free ring of the (arene)₂Cr(CO)₃ complex toward another Cr(CO)₃ fragment. It was proposed that the stabilization of the [2.2]paracyclophane complex with Cr(CO)₃ results ultimately from the relaxation of the strained framework of [2.2]paracyclophane. The kinetic factor in Cr(CO)₃ complexation was also studied by analyzing the charges on competing arene rings in monoaryl-substituted derivatives of [2.2]paracyclophanes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 151–157, January, 1998.     

Vapor deposition polymerization of heteroatom-bridged [2.2]paracyclophanes: 1,9-dithia[2.2]paracyclophane and 1,9-dithia[2.2]paracyclophane-1,1,9,9-tetroxide

1,9-Dithia[2.2]paracyclophane-1,1,9,9-tetroxide ( 3 ) was synthesized as white needles in a high yield from 1,9-dithia[2.2]paracyclophane ( 2 ) by oxidation with m-chloroperbenzoic acid, and its molecular structure was determined with single-crystal X-ray diffraction analysis. Vapor deposition polymerizations of 2 and 3 gave amorphous and brittle polymer films along with considerable amounts of nonpolymeric byproducts. A polymer film from 2 was a copolymer of p-(phenylene-methylenesulfide) with p-(phenylene-methylene) units, and a polymer film from 3 was a homopolymer of p-(phenylene-methylene) units with head-to-tail, head-to-head, and tail-to-tail placements. The elimination of sulfur atoms in 2 and sulfone units in 3 took place during their pyrolysis reactions. Plausible mechanisms for vapor deposition polymerizations of both cyclophanes are proposed. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1892–1900, 2001     

Spatial ring current model of the [2.2]paracyclophane molecule

A representation of the current density induced in the [2.2]paracyclophane molecule by a homogeneous magnetic field parallel to the line joining the centers of the phenylene rings is given in compact form by a stagnation graph that conveys essential information. Analogous graphs were obtained for two perpendicular directions. Plots of streamlines are also reported to complete a ring current model that has been proved useful to understand the magnetropicity of the system. Stagnation graphs, maps of streamlines and moduli of the current density, and plots of Biot-Savart magnetic shielding density provide a basic tool kit for rationalizing magnetic response of complex systems.     

Phane properties of [2.2]paracyclophane/dehydrobenzoannulene hybrids

A series of [2.2]paracyclophane/dehydrobenzo[14]annulene (PC/DBA) hybrids (hydrocarbons 5, 6, 9, 10 b, and 10 c), [2.2]paracyclophane/dehydro[14]annulene (PC/DA) hybrids (7 and 8) and suitable model systems (11, 12, and 33) has been synthesized. Comparison of the electronic absorption spectra in each series of compounds provides further insight into the global communication between the decks in the [2.2]paracyclophane unit.