New chiral β-diketones based on [2.2]paracyclophane

Two chiral β-diketones, 1,3-bis[(S)-(4-[2.2]paracyclophanyl)]propane-1,3-dione (BPPD) and [1-(S)-(4-[2.2]paracyclophanyl)-3-phenyl]propane-1,3-dione (PPPD), were synthesized by acylation of (S)-4-acetyl[2.2]paracyclophane with methyl esters from the corresponding carboxylic acids. 4-Acetyl[2.2]paracyclophane was synthesized in a quantitative yield by the reaction of [2.2]paracyclophane-4-carboxylic acid with methyllithium.     

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.     

C—H...π interactions in five ethynyl‐substituted [2.2]paracyclophanes: further examples of the `7,11' packing pattern

The monosubstituted derivative 4‐ethynyl[2.2]paracyclophane, C₁₈H₁₆, (I), and the four disubstituted isomers, 4,12‐, (II), 4,13‐, (III), 4,15‐, (IV), and 4,16‐diethynyl[2.2]paracyclophane, (V), all C₂₀H₁₆, show the usual distortions of the [2.2]paracyclophane framework. The crystal packing is analyzed in terms of C—H...π interactions, some with H...π as short as 2.47 Å, in which the cyclophane rings and/or the triple‐bond systems may act as acceptors. For compounds (I) and (IV), the known `7,11'‐type cyclophane packing is observed, with a herring‐bone pattern of molecules in a layer structure.     

New Types of Planar Chiral [2.2]Paracyclophanes and Construction of One‐Handed Double Helices

New types of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes were synthesized from racemic 4,12‐dihydroxy[2.2]paracyclophane as the starting compound. Regioselective dibromination and transformation afforded a series of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes, which can be used as chiral building blocks. In this study, left‐ and right‐handed double helical structures were constructed via chemoselective Sonogashira–Hagihara coupling. The double helical compounds were excellent circularly polarized luminescence (CPL) emitters with large molar extinction coefficients, good photoluminescence quantum efficiencies, and large CPL dissymmetry factors.     

Elaboration of a novel type of planar-chiral methylene bridged biphenols based on [2.2]paracyclophanes

A new class of chiral methylene bridged biphenols with planar chirality has been designed and elaborated. The synthetic approach is based on the use of 4-hydroxy-5-hydroxymethyl[2.2]paracyclophane 9 derived from either racemic or enantiomerically pure (S)-4-formyl-5-hydroxy[2.2.]paracyclophane (FHPC) by reduction with LiAlH₄. The condensation of 9 with chiral racemic 4-hydroxy[2.2]paracyclophane 4 and achiral phenols, such as 2,5-dimethylphenol 10 and 2-isopropyl-5-methylphenol 11, afforded the target bridged biphenols 6, 12 and 13, respectively. The preliminary results on the asymmetric addition of Et₂Zn to benzaldehyde promoted by (S,S)-6 are reported.     

Novel planar chiral P,N-[2.2]paracyclophane ligands: synthesis and application in palladium-catalyzed allylic alkylation

A series of planar chiral P,N-[2.2]paracyclophane ligands were synthesized and applied in enantioselective palladium-catalyzed allylic alkylation, in which the central chirality of [2.2]paracyclophane is the dominant stereocontrol element. The effect of the substituents attached to the phosphorus atom of these ligands on the yield and stereoselectivity of the reaction was also investigated.     

Zur frage transanularer II-II-wechselwirkungen im [2.2]metacyclophan, [2.2]Paracyclophan und 2,2′-spirobiindan

Concerning the question of transanular II-II-interactions in [2.2]metacyclophane, [2.2]paracyclophane and 2,2′-spirobiindane.From the quotient of the two dissociation constants (K₁/K₂) of [2.2]metacyclophane-bis-chromtricarbonyl (9·0 ± 1·9) it was concluded that there are no transanular II-II-interactions between the two benzene rings. The corresponding values for the bis-chromtricarbonyl-complexes of 2,2′-spirobiindane and [2.2]paracyclophane are 8·0 ± 1·5 and 10⁴, resp. These results are supported by IR-spectroscopical data of the CO-frequencies of the Cr(CO)₃-complexes of [2.2]metacyclophane and some derivatives, of 2,2′-spirobiindane and [2.2]paracyclophane.Moreover, UV-spectroscopic studies of tetracyanoethylene complexes of arenes are shown to be insignificant with regard to transanular II-II-interactions.     

A novel class of bidentate ligands with a conformationally flexible biphenyl unit built into a planar chiral [2.2]paracyclophane backbone

We report the synthesis of a novel class of planar chiral bidentate aryl[2.2]paracyclophane ligands. For the first time in the [2.2]paracyclophanyl series the Pd-catalyzed Suzuki cross-coupling was employed for the formation of the arylparacyclophanyl skeleton. From the two possible approaches: (a) cross-coupling of [2.2]paracyalophanylboronic acids with aryl halides; (b) cross-coupling of [2.2]paracyclophanyl halides with arylboronic acids, the latter was found to be more efficient. This approach was successfully used for the synthesis of a wide range of aryl[2.2]paracyclophanes with different types of substitution patterns (ortho-, pseudo-ortho- or pseudo-gem-arrangement of the functionally-substituted aryl fragment with respect to the substituent in the paracyclophane ring).     

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.     

Subcomponent Self-Assembly of a Cyclic Tetranuclear FeII Helicate in a Highly Diastereoselective Self-Sorting Manner

An enantiomerically pure diamine based on the 4,15-difunctionalized [2.2]paracyclophane scaffold and 2-formylpyridine self-assemble into an optically pure cyclic metallosupramolecular Fe₄L₆ helicate upon mixing with iron(II) ions in a diastereoselective subcomponent self-assembly process. The cyclic assembly results from steric strain that prevents the formation of a smaller linear dinuclear triple-stranded helicate, and hence, leads to the larger strain-free assembly that fulfils the maximum occupancy rule. Interestingly, use of the racemic diamine also leads to a racemic mixture of the homochiral cyclic helicates as the major product in a highly diastereoselective narcissistic chiral self-sorting manner given the fact that the assembly contains ten stereogenic elements, which can in principle give rise to 149 different diastereomers. The metallosupramolecular aggregates could be characterized by NMR, UV/Vis and CD spectroscopy, mass spectrometry, and X-ray crystallography.     

Synthesis of iridium complexes with new planar chiral chelating phosphinyl-imidazolylidene ligands and their application in asymmetric hydrogenation

The synthesis of planar chiral phosphinoimidazolium salts such as (R_p)-3-(4-diphenyl-phosphino[2.2]paracyclophan-12-ylmethyl)-1-(2,6-diisopropylphenyl)imidazolium bromide (R_p)-11c starting from enantiopure 4,12-dibromo[2.2]paracyclophane (R_p)-6 is reported. After deprotonation of these salts and a subsequent reaction with [Ir(COD)Cl]₂, chelating iridium imidazolylidene complexes (R_p)-5a–c are obtained. These complexes catalyze the asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee.     

An Approach to Paracyclophane-Based Tetrathiafulvalenes: Synthesis and Characterization of a Pseudo-Geminal [2.2]Paracyclophane 1,3-Dithia-2-Thione

The synthesis of paracyclophane-based tetrathiafulvalene precursors is described in the context of the importance of these compounds in the field of material chemistry. Pseudo-geminal bis(1,3-dithia-2-thione) was synthesized via the corresponding 1,3-dithiol-2-ylium salt. The latter was obtained by a synthetic procedure that involves 4,15-bis(acetyl)[2.2]paracyclophane, a new compound of interest for many researchers.     

Photochemical synthesis of [2.2](3,8)-pyridazinophane and quinolinophane-2(1H)-one as well as synthesis of [2](5,8)-quinolinophanes and fused spiro-pyranoindanoparacyclophanes

Syntheses of various classes of unreported heterophanes derived from [2.2]paracyclophane are herein reported. The key to their successful synthesis depends on the photochemical synthesis of pyridazinophane and quinolinophane-2(1H)-one from freshly prepared 4-([2.2]paracyclophanyl)-azo-4′-[2.2]paracyclophane and 4-([2.2]paracyclophanyl)cinnnamanilide, respectively. Reactions of 4-amino-[2.2]paracyclophane with either acetyl- or benzoylacetone afforded condensed products. Then ring closure using polyphosphoric acid (PPA) at 120°C gave, in near quantitative yields, quinolinophanes. Reactions of [2](4,7)-indano-[2]paracyclophane-1-ylidene-propanedinitrile with active methylene compounds afforded fused spiro-pyranoindanoparacyclophane derivatives.     

Diastereoselective Hartwig-Buchwald reaction of chiral amines with rac-[2.2]paracyclophane derivatives

A Hartwig-Buchwald addition of a variety of chiral amines to rac-4-bromo-[2.2]paracyclophane and rac-trifluoromethanesulfonic acid (4-[2.2]paracyclophane) ester was performed with high diastereoselectivities. Kinetic racemic resolution of the starting materials was achieved, providing a rapid access to enantiomerically enriched 4-bromo-[2.2]paracyclophane and the corresponding enantiomerically pure [2.2]paracyclophane amines. Additionally, the first reaction of a secondary amine with a [2.2]paracyclophane halide was achieved.     

Multilayered transition metal complexes of cyclophanes

The reaction of arene-ruthenium complexes ([RuCl₂(ν⁶-arene)]₂) with [2.2]paracyclophane in the presence of AgBF₄ provides double- and triple-layered arene-ruthenium complexes of [2.2]paracyclophane in excellent yield.     

Synthesis of new planar chiral [2.2]paracyclophane Schiff base ligands and their application in the asymmetric Henry reaction

A series of new planar and central chiral ligands based on [2.2]paracyclophane backbones were designed and prepared from enantiomerically pure 4-amino-13-bromo[2.2]paracyclophane and commercially available chiral amino alcohols. Their application in a copper-catalyzed asymmetric Henry reaction resulted in secondary alcohols with high yield and excellent selectivity for active aldehydes (up to 94% ee). This is a successful example of employing planar chiral [2.2]paracyclophane ligands in copper-catalyzed reaction.     

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.     

An improved synthesis of (S)-(+)- and (R)-(−)-4-ethenyl[2.2]paracyclophane

The resolution of the 4-acetyl[2.2]paracyclophane by the SAMP-hydrazone method is described. A new, short, high yield synthesis of both enantiomers (S)-(+)- and (R)-(−)-4-ethenyl[2.2]paracyclophane is reported.     

4,5-dehydro- and 4,5,15,16-bis(dehydro)octafluoro[2.2]paracyclophanes: facile generation and extraordinary Diels-Alder reactivity

Dehydroiodination of 4-iodo- and 4,15-diiodo-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane by treatment with KO(t)Bu in the presence of benzene, naphthalene, anthracene, and [2.2]paracyclophane affords each of the corresponding Diels-Alder mono- and bis-cycloadducts derived from the presumed aryne intermediates in high yield. Monoadducts of t-butylbenzene and furan are also obtained in excellent yield. All of the products were characterized by their NMR spectra, with four of them also being confirmed by X-ray crystallography. The extraordinary selectivity/reactivity of the aryne intermediate is discussed.