The [2.2]paracyclophane moiety is used as a spacer to connect the ends of a hex-3-ene-1,5-diyne unit, a π-system that on thermolysis usually cycloaromatizes to a benzene ring (Bergman cyclization). For the preparation of the pseudo-geminally-bridged system 9, the diacetylene 3 was chain-extended to the diol 16, which after conversion to the pseudo-geminal dibromide 17 was ring-closed by treatment with LiHMDS/HMPA to the [2.2]paracyclophane enediyne 9. Whereas the McMurry coupling of the pseudo-ortho bisaldehyde 24 resulted in the formation of the hexadienyne-bridged cyclophane 27, the pseudo-ortho-bridged hydrocarbon 11 was obtained by preparing first the diol 28 from 24, converting the latter into the dioxolane 29, which in the last step furnished the olefin 11 by treatment with Tf2O/EtN(iPr)2. The authentic Bergman product 10 of the pseudo-gem-bridged hexenediyne 9 was synthesized by a conventional sequence starting from the ethynyl formyl substrate 18. Since the pseudo-ortho-enediyne-bridged hydrocarbon 11 is thermally labile, its benzannelated derivate 34 was prepared. No classical Bergman cyclization reactions could be observed for any of the [2.2]paracyclophane-bridged hexenediynes prepared here. In the pseudo-gem-series the fulvenes 14 and 15 were the only products that could be identified under thermal conditions (McMurry coupling); the benzannelated substrate 34 gave the benzofulvene-bridged cyclophane 36 on photolysis. Bergman cyclizations yielding fulvene derivatives are extremely rare. The mechanism of the cyclization of 9 and 34 is discussed, using compliance constants. The structure assignments of the hydrocarbons synthesized in this study are based on spectroscopic studies as well as X-ray structural analyses for 9, 10, 11, 27, and 34.
Propargylallenes offer the varied reactivity patterns of two different multiple bond linkages either separately or in concert. Their syntheses, structures, rearrangement mechanisms and synthetic utility are reviewed, together with their behaviour when treated with transition-metal reagents such as gold(I), silver(I), platinum metals or metal carbonyls.
A novel palladium-catalyzed route for the synthesis of substituted 3(2H)-furanones from activated alkenes and 4-chloroacetoacetate was developed. The first step of the tandem reaction is the Michael addition of an acetoacetate to the alkene followed by palladium-catalyzed ring closure of the adduct to form the furanone. The reaction was extended to a number of substituted alkenes, and the corresponding substituted 3(2H)-furanones were obtained in good to excellent yields.
A combined X-ray diffraction and theoretical study of the solid-state molecular and crystal structures of tribenzotriquinacene (TBTQ, 2) and its centro-methyl derivative (3) is presented. The molecular structure of the parent hydrocarbon displays C3v symmetry and the three indane wings adopt mutually orthogonal orientations, similar to the case in its previously reported methyl derivative (3). Also similarly to the latter structure, the bowl-shaped molecules of compound 2 form infinite molecular stacks with perfectly axial, face-to-back (convex–concave) packing and with parallel and unidirectional orientation of the stacks. The experimentally determined intra-stack molecular distance is 4.75 Å for compound 2 and 5.95 Å for compound 3. Whereas the molecules of compound 2 show a slight alternating rotation (±6°) about the common axis of each stack, those of compound 3 show perfect translational symmetry within the stacks. We used dispersion-corrected density functional theory to compute the crystal structures of tribenzotriquinacenes 2 and 3. The London dispersion correction was crucial for obtaining an accurate description of the crystallization of both analyzed systems and the calculated results agreed excellently with the experimental measurements. We also obtained reasonable sublimation energies for both compounds. In addition, the geometries and dimerization energies of oligomeric stacks of compound 2 were computed and showed smooth convergence to the properties of the infinite polymeric stack.
Glaser coupling of 4-ethynyl[2.2]paracyclophane (1) led to a mixture of dimers that could not be separated by either chromatographic or chemical methods. That two diasteromers of the dimer 2 were produced in a 7:3 ratio was demonstrated by the resolving power of modern NMR spectroscopy.
The structures of the three benzocyclobutenophanes 1 a, 1 b (2 stereoisomers), and 11 have been determined by NMR spectroscopy and X-ray structural analysis. The preparation of 11 from 4,5-diethynyl[2.2]paracyclophane (9) is described.
Vor 27 Jahren veröffentlichte H. Hopf den bisher einzigen umfassenden Übersichtsartikel zu verzweigten Oligoenen mit dem Titel “Dendralene – eine vernachlässigte Gruppe hochungesättigter Kohlenwasserstoffe”. Die Dendralene werden heutzutage nicht mehr vernachlässigt. Die Forschung zu Synthese, Eigenschaften und Anwendungen der Dendralene hat in jüngster Zeit viele neue Impulse erhalten, und der vorliegende Aufsatz fasst die bedeutenden Ergebnisse der letzten Jahre zusammen. Von grundlegend wichtigen Eigenschaften (der ersten Demonstration von alternierendem Verhalten seit den Annulenen) bis zu unvergleichbaren, molekulare Komplexität erzeugenden, chemischen Transformationen: Die als Dendralene bekannte Klasse der Oligoene ist erwachsen geworden! Die verschiedenen Synthesewege zu acyclischen und cyclischen Dendralenen werden analysiert und klassifiziert. Die leistungsfähigste Umwandlung der Dendralene – die Dien-transmissive Diels-Alder-Reaktion (DTDA-Reaktion) – wird in einer detaillierten Übersicht vorgestellt.
Twenty-seven years ago, H. Hopf published the only previous comprehensive review on branched oligoenes that had the title “Dendralenes: A Neglected Family of Hydrocarbons”. The dendralenes are no longer neglected. Research into the synthesis, properties, and applications of dendralenes is rapidly gaining momentum and this Review summarizes important recent findings. From significant fundamental properties (the first demonstration of alternating behavior since the annulenes) through to unparalleled complexity-generating synthetic transformations, this fundamental oligoene family is coming of age. Effective synthetic approaches to cyclic and acyclic dendralene systems are analyzed and classified. The most powerful synthetic transformations of the dendralenes, diene-transmissive Diels–Alder reactions, are surveyed in detail.
The cross-conjugated allenes (“allenic dendralenes”) 2-allenylbuta-1,3-diene (2), 1,1-divinylallene (3, prepared here as the methyl derivative 49), and 1,1-diallenylethene (4) are prepared either by SN2′-substitution processes from appropriate allenic or acetylenic precursors or by base-catalyzed isomerizations of propargylic substrates. Thermal elimination/isomerization routes to these highly unsaturated hydrocarbons require reaction conditions under which these allenes undergo secondary transformations. The new oligoolefins, the structures of which have been calculated by MP2 methods, are interesting substrates for addition and isomerization reactions.
[3]Dendralene (2) has been converted into the benz[a]anthracene tetraester 13 in a protocol involving diene-transmissive Diels–Alder addition of dimethyl acetylenedicarboxylate to 2 followed by a sequence of reduction–addition–aromatization reactions. Likewise, the next higher vinylog [4]dendralene (19) provided the phenanthrene hexaester 21. An attempt to prepare the double o-xylylene intermediate 17 failed.
The conjugated tetraenes 3 and 4 a–c have been prepared and shown to possess an orthogonal structure. This was not only demonstrated by their spectroscopic properties and X-ray structural analysis of solid representatives (e.g., 4 a–c) but also by the resolution of these chiral compounds by GC and HPLC chromatography using various chiral selector systems. The chemical behavior of the typical tetraene 4 a has been studied using bromination, hydrogenation, epoxidation, and photo equilibration reactions.
A series of novel styrene functionalized monomers with phenylbenzo[d]imidazole units and the corresponding homopolymers are prepared. These side-chain polymers show high glass-transition temperatures that even exceed the corresponding value for the common electron-transporting material 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI). Similar electronic behavior between the polymers and TPBI is shown. The polymers are used as matrices for phosphorescent dopants. The fabricated devices exhibit current efficiencies up to 38.5 cd A−1 at 100 cd m−2 and maximum luminances of 7400 cd m−2 at 10 V with a minimum turn-on voltage as low as 2.70 V in single-layer devices with an ITO/PEDOT:PSS anode (ITO = indium tin oxide, PEDOT:PSS = poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)) and a CsF/Ca/Ag cathode.
The title compound 3,4-benzocycloocten-1,5-diyne (1) is a highly reactive hydrocarbon that has been shown to undergo addition reactions with tetraphenyl-cyclopentadienone(tetracyclone) to the 2:1 adduct 6, with octacarbonyldicobalt to the bis metal complex 7, with lithium aluminium hydride to the bis diene 9, and with various electrophilic reagents. In these latter cases cationic intermediates are generated from 1 and a transannular cyclization takes place leading to novel derivatives of 1,2-dihydropentalene (31, 32, 35, 36, 43, 44).
The terminal enynes 10–12 were prepared from the corresponding aldehydes 6–8 by applying conventional methods of acetylene chemistry. After exploratory study of the reactivity of these hydrocarbons (preparation of 13, 18, and 19 from 10) these building blocks were subsequently oxidatively dimerized (Glaser coupling) to the sterically protected oligoenynes 22–25; McMurry coupling of 13 yielded 26 as a mixture of diastereomers. Whereas 22 is inert towards sodium sulfide the higher vinylogs/ethynylogs 23–25 furnished the novel thiophene derivatives 28–31. The structures of several (22–25, 28, 29) of the new highly unsaturated compounds were determined by single-crystal X-ray structural analysis.
By cyclopropanation of tetramethyl[2.2]paracyclophane 9 the tetramethylene adduct 10 has been prepared. This hydrocarbon is the first stable cis-bis-σ-homobenzene for which a structure has been determined by X-ray diffraction.
In support of a deeper understanding of the chemistry of cyanoacetylene—a known constituent of planetary atmospheres and interstellar space—theoretical and experimental studies address the chemical mechanism of dimerization and trimerization, and provide high-resolution rotational spectra of two of the trimeric products, 1,2,3- and 1,2,4-tricyanobenzene. Analysis of the rotational spectra is particularly challenging because of quadrupolar coupling from three 14N nuclei. The laboratory rotational spectra provide the basis for future searches for these polar aromatic compounds in interstellar space by radio astronomy.
Starting from the readily available α,β-unsaturated ketone, 3-tert-butyl-4,4-dimethyl-2-pentenal, higher vinylogues, and fully terminally tert-butylated polyolefins with up to 13 consecutive conjugated double bonds have been prepared by either McMurry dimerization or Wittig chain-elongation routes. The highly unsaturated conjugated π systems, which show a remarkable stability, have been characterized by spectroscopic methods and, in many cases, by X-ray structural analysis. The yields are high enough to allow for thorough chemical reactivity studies.
On treatment with potassium tert-butoxide in tert-butyl alcohol the two hydrocarbons 10 and 11 isomerize to the [6.6]paracyclophanes 12 and 13, respectively, with fully conjugated bridges, thus transferring the Sondheimer annulene chemistry to three-dimensional space. The structures of the new hydrocarbons were established by spectroscopic data (12, 13) and X-ray structural analysis (13) as well as by computational methods. According to ACID calculations these three-dimensional aromatics are not Möbius systems.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Diketone 4 was prepared by hydrolysis of hexendiyne 5, the latter being available through McMurry coupling of acetylenic ketone 26. Upon treatment with dimethyltitanium dichloride, 4 cyclizes into fully alkylated furan derivative 30; the still unknown tetra-tert-butylethene (1, TTBE, 3,4-di-tert-butyl-2,2,5,5-tetramethylhex-3-ene) was not produced. The structural properties of 4 and the mechanism of its cyclization into 30 are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
In contrast to its bis(oxa) analog 1 (DDOA), the hydrocarbon 11 was not found to form organogels with linear alcohols, alkanes, toluene, acetonitrile and other solvents. Whereas the photoreactivity of 1 did not follow the usual behaviour of anthracene derivatives, compound 11, irradiated in cyclohexane, produced the two expected [4+4]cycloadducts 12 and 13 (anti and syn photodimers, respectively). These facts point to the role of the connecting link between the rigid core and the flexible chain for some self-assembled systems.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Preparatively satisfactory routes to [3.2]paracyclophane (10), [4.2]paracyclophane (14), [4.3]paracyclophane (19) as well as several derivatives of these compounds – among others the bromides 25, the ester 31, the diesters 40–43 – are described using well-established methods of cyclophane chemistry (ring-closure reactions leading to thiacyclophanes, ring contraction by sulfone pyrolysis). The parent systems and their derivatives are now available in gram quantities allowing a study of their chemical properties.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
[m.n]Paracyclophanes with bridges of equal and unequal length (m,n ≤ 4) undergo electrophilic aromatic substitution (Friedel–Crafts acylation, bromination) under very mild conditions as long as the bridge contains less than four atoms. Whenever there is a choice, the aromatic ring is attacked at the position closest to the shorter alkano bridge, which indicates that the transannular benzene moiety acts as a neighboring group. By brominating the acetyl derivatives obtained, and the acids and esters derived therefrom, a second substituent is introduced into the pseudo-geminal position, that is, directly opposite the directing group. However, this effect is observed only for those [m.n]phanes in which the length of the neighboring bridge does not exceed three atoms. For the butano-bridged derivatives, the regioselectivity is lost completely. Very similar results were observed for [m.n]paracyclophanes carrying two ester substituents on one benzene ring, the limiting case being the [4.3]paracyclophane derivative. We propose that the stereocontrolling effect of a substituent can only occur when the intra-annular distance is below 4 Å. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Tropylidenes 16 and 17 were prepared from [2.2]paracyclophane (10). On treatment with the corresponding trityl salts they were converted into tropyliophanes 26a (tetrafluoroborate) and 26b (perchlorate). With acetone, 26a furnished trapping product 27, which underwent a homo-Diels–Alder addition with tetracyanoethylene to afford adduct 29. All new compounds were characterized by their spectroscopic and analytical data and for most – including 17 and 26b – the structures were also determined by X-ray diffraction.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
The pseudo-geminally substituted paracyclophane 4,5-bis(phenylethynyl)[2.2]paracyclophane (13) was prepared and its photochemical behaviour in solution was studied. Irradiation with a medium-pressure mercury lamp converts 13 into two dimers: cyclooctatetraene 14 and bicyclo[4.2.0]octatriene derivative 15. The structures of both the substrate and the photolysis products were determined by the usual spectroscopic methods and also by X-ray structural analysis; an unusually long C–C bond of 1.659 Å opposite the double bond in the cyclobutene ring of 15 was found. It is suggested that product formation involves cyclobutadiene 16 as an intermediate. Photolysis of 13 in the presence of pentacarbonyliron furnishes cyclopentadienone complex 19 in quantitative yield. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
After a long period as model compounds in basic research [2.2]paracyclophanes are quickly gaining in practical importance. They can be incorporated into numerous polymeric systems in which they either lose (the so-called Parylenes) or retain their layered structure, and they can be used for the construction of unsaturated molecular scaffolds characterized not only by conventional (lateral) π-electron overlap but also by cofacial π-electron interactions. Surfaces generated from and with [2.2]paracyclophanes possess interesting biological, photophysical, and optoelectronic properties.
Nach einer langen Zeit als Modellverbindungen in der Grundlagenforschung werden [2.2]Paracyclophane immer wichtiger in der Anwendung. Sie lassen sich auf vielfältige Weise in polymere Systeme einbauen, wobei ihre Lagenstruktur entweder verloren geht (so genannte Parylene) oder beibehalten wird, und sie können zum Aufbau ungesättigter Molekülgerüste eingesetzt werden, die sich nicht nur durch konventionelle laterale π-Elektronenwechselwirkungen auszeichnen, sondern auch durch cofaciale Überlappung zwischen den Ringen. Aus [2.2]Paracyclophanen hergestellte Oberflächen haben interessante biologische, photophysikalische und optoelektronische Eigenschaften.
MP2 and DFT calculations have been carried out for [n]circulenes for n=3 to 20 in order to predict the strain energy and topology of these cyclically condensed aromatic systems. To synthesise [4]circulene (2), 1,5,7,8-tetrakis(bromomethyl)biphenylene (14) was prepared from the corresponding tetramethyl derivative (8) and subjected to various dehalogenation reactions; all attempts to obtain [2.2]biphenylenophane (7) as a precursor for 2 by this route failed. Treatment of 14 with sodium sulfide furnished the thiaphanes 16 and 17, thermal and photochemical desulfurization of which also failed to provide 7. In a second approach [2.2]paracyclophane was converted to the pseudo-geminal dithiol 23, which was subsequently bridged to the thiaphanes 22 and 24. On flash vacuum pyrolysis at 800 °C these were converted exclusively into phenanthrene (30). An approach to dehydrochlorinate the commercial product PARYLENE C® to the tetrahydro[4]circulene 7 led only to polymerisation. The X-ray structures of the intermediates 8, 14, 17, 23, 24, 26, and 35 are reported.
Two routes for preparing functionalized [2.2](1,4)phenanthrenoparacyclophanes are described: either the parent system 2 is subjected to electrophilic substitution (bromination, Friedel–Crafts acylation, Rieche formylation: preparation of 5, 6, 7, 11 and 12) or the desired substituents are incorporated in the early stages of the synthesis by the preparation of the corresponding functionalized styryl paracyclophanes and their photocyclization to the respective phenanthrenocyclophanes. By these specific routes various bromides (22a,b), ethers (28a–c) and phenols (29a,b) were synthesized. The latter derivatives, on oxidation, furnish para- (31) and ortho-quinonophanes (30, 32, 33), useful substrates for the preparation of cyclophanes containing phenazine subunits (36). The stilbene phenanthrene photocyclization can also be employed for the preparation of benzothiophenophanes, e.g. 43 and 44, from the respective precursors. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
A selection of pseudo-geminally substituted [2.2]paracyclophanes, the alkynes 6, 7, 10, 11 a, and 11 b and the alkenes 8 and 9 were prepared for the study of intraannular reactions between functional groups in direct juxtaposition. Whereas 9 and 10 provide the corresponding cyclobutane and cyclobutene derivatives on irradiation (12 and 13, respectively), the bis-alkynes 7 and 11 b do not lead to a cyclobutadiene intermediate. In the latter case the “half-closed” butadiene derivative 17 was isolated. A Paterno–Büchi reaction took place on irradiation of 8 and 6, although the oxetene intermediate 21 produced in the second example did not survive the reaction conditions (ring-opening to 22). Bromine addition to 9, 10, and 7 occurred with high stereoselectivity (formation of the dibromides 27, 30, and 33, respectively), and is rationalized by postulating the formation of the cationic intermediates 26, 29, and 32, respectively. To study the interaction of a carbocation with a facing triple bond, the alcohol 34 was prepared from 6. On acid treatment ring closure to the triply-bridged phane 38 took place, accompanied by the hydration of the triple bond to the ketoalcohol 37. In an interesting intraannular [2+3]cycloaddition reaction the bis-acetylene 11 a, on treatment with n-butyl lithium, provided the cyclopentadiene derivative 42. That the two triple bonds of a pseudo-geminal diacetylene can engage in a cyclization reaction leading to the cyclopentadienone complex 44 was also shown by treating 11 b with iron pentacarbonyl.
α,ω-Dibromo derivatives in which the two terminal carbon atom are separated by an unsaturated spacer unit (“π spacer”) undergo 1,x-elimination reactions (with x = 6, 8, 10, and 14), using Mori's reagent (nBu3SnSiMe3/CsF). The resulting cumulenic intermediates cyclodimerize in a subsequent step yielding novel macrocyclic acetylenic and bridged aromatic compounds (cyclophanes). Thus 1,6-eliminations were carried out with dibromide 17 to yield 1,3,7,9-cyclododecatetrayne (20) and with benzylbromide 24 to provide cyclophanes 26 and 27. By 1,8-eliminations the 16-membered macrocycle 33 could be prepared from enediyne 31, the benzannelated 1,5-cyclooctadiyne 41 from dibromide 38, and a mixture of cyclophanes 45 and 46 from the precursor 43. 1,10-Eliminations were carried out successfully with dibromides 47, 50, and 53 yielding the corresponding unsaturated cyclophanes (“cyclophynes”) 49, 52, and 55. The influence of the solvent on the cyclodimerization 4749 was investigated, with acetonitrile providing the highest yields. The heterophanes 59 a and b were obtained by 1,10-elimination of the precursor dibromides 57 a and b, and in an elimination experiment involving a 1:1 mixture of the dibromides 50 and 57 b the “mixed dimer” 60 was isolated, besides the homodimers 52 and 59 b. The method reached its limits with the 1,14-elimination of 68, 70, and 74 providing the cyclophanes 69, 71, and 75 in varying amounts. Two final debrominations with 76 and 77, which in principle could undergo 1,16- and 1,20-eliminations reactions, respectively, failed. The structures of the new cyclophanes 49, 50, 59 a, and 59 b were established by X-ray structural analysis; all other structure assignments rest on the usual spectroscopic and analytical data.
When N,α-dimethyl-α-(4-[2.2]paracyclophanyl)nitrone (1) is treated with dimethyl acetylenedicarboxylate (5), phenyl isocyanate (9), benzyne (13), or ethyl propiolate (16), the [2.2]paracyclophane-based pyrrole 6, imidazole 10, and isoxazole derivatives 14, 15, and 17 are formed in good yields. The stereoisomeric benzisoxazoles 14 and 15 obtained from the reaction between 1 and benzyne (13) could be separated and the structure of one of these stereoisomers, 15, was assigned by X-ray structural analysis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
A novel approach for the synthesis of cis/trans-fused perhydroazulenes 13–19 is reported. The stereochemistry of the derivatives of carbene addition products 9a–c/20–22, of the 2,6-disubstituted perhydroazulenes 12a–c/23–25, and that of compounds 26–27 has been studied by single-crystal X-ray crystallography. The hydrogenation of the tropylidene to the perhydroazulene skeleton under various conditions is described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
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.
4-Acetyl[2.2]paracyclophane (1) is converted into the nitrone 2 by treatment with N-methylhydroxylamine·hydrochloride. When 2 is reacted with (E)-1,2-dibenzoylethene (4) the pyridinyl[2.2]paracyclophane 13 is formed in a novel condensation reaction. The structures of 2 and 13, and the mechanism of formation of the latter are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
A novel approach for the synthesis of carbene adducts 9a/9b and 10/11 is reported. Identification of the geometric and positional isomers of carbene addition was carried out by reversed-phase HPLC, and the establishment of the structure and configuration of 9a/9b was performed by means of 2D-NMR.
The TiCl4/Zn-mediated intermolecular pinacol coupling of the planar chiral carbonyl compounds [2.2]paracyclophane-4-carbaldehyde, 4-acetyl[2.2]paracyclophane (ketone) and the four regioisomeric 5-, 7-, 12- and 13-methoxy[2.2]paracyclophane-4-carbaldehydes as well as the pTosOH–Zn/Cu-promoted coupling of their N-substituted imines is described. Coupling of the enantiomerically pure substrates (most of carbonyl compounds and all imines) occurs stereoselectively giving rise to diastereomerically pure 1,2-diols and 1,2-diamines. Racemic aldehydes and ketone react with different degrees of stereoselectivity (depending on the substituents in certain positions) and produce one to three diastereomers. 7-Methoxy[2.2]paracyclophane-4-carbaldehyde undergoes a tandem pinacol coupling–pinacol rearrangement to yield bis-(7-methoxy[2.2]paracyclophane-4-yl)acetaldehyde. Coupling of the racemic imines produces a mixture of single racemic D,L-diamine and single meso-diamine in each case. The stereoselective formation of the asymmetric centres is governed by the planar chiral [2.2]paracyclophanyl moiety. The techniques elaborated are extended to the intramolecular coupling of [2.2]paracyclophane-4,13-dicarbaldehyde and its bis-N-phenylimine, resulting in stereoselective formation of the chiral triply-bridged diol and exclusive formation of the meso-diamine. X-Ray investigations of several diols and diamines have been carried out and the structural features of these derivatives are discussed.
The absorption, fluorescence and fluorescence excitation spectra for 3,20-di(tert-butyl)-2,2,21,21-tetramethyl-all-trans-3,5,7,9,11,13,15,17,19-docosanonaen (ttbP9) in dilute solutions of 2-methylbutane were recorded at temperatures over the range 120–280 K. The high photostability of this nonaene allows us to assert that it exhibits a single fluorescence and that this can be unequivocally assigned to emission from its 11Bu excited state, it being the first excited electronic state. Available photophysical data for this polyene and the wealth of information reported for shorter all-trans polyenes allow us to conclude that if the first excited electronic state for the chromophore possessed 21Ag symmetry, then the energy of such a state might have been so close to that of the 11Bu state that: 1) the radiationless internal conversion mechanism would preclude the observation of the emission from the 11Bu state reported in this work and 2) the 21Ag state reached through internal conversion would be vibrationally coupled to 11Bu and would facilitate the detection of the emission from 21Ag, which was not observed in any of the solvents used in this work. The spectroscopic and photochemical implications of these findings for other polyenes are discussed.
Whereas the thermal isomerization of perphenylbutenyne (11) at 290 °C in toluene leads to the benzannelated semibullvalene derivative 13, pyrolysis at 360 °C furnishes the triphenylnaphthalene 12. The mechanisms of both cycloisomerizations, which presumably proceed via the isobenzene intermediate 14, are discussed. The structure of the rearrangement product 13 was proven by single-crystal X-ray analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
By using 3,20-di-tert-butyl-2,2,21,21-tetramethyl-3,5,7,9,11, 13,15,17,19-docosanonaene (ttbP9) as a probe, the inductive and dispersive interactions of solvents were empirically evaluated for the first time. This probe exhibits a very strong first electronic transition with a marked vibronic structure that is very well resolved from the second electronic transition. One hundred solvents were used to construct a solvent polarizability (SP) scale ranging from zero for the gas phase (i.e. the absence of solvent) to unity for carbon disulfide. The probe was found to exhibit an ideal spectroscopic behaviour towards a variety of polar, acidic and basic solvents. The polarizability scale provides an accurate description of the solvatochromism of such interesting apolar chromophores as anthracene, molecular oxygen, and C60 among a wider variety of solvents spanning very broad ranges of polarity, acidity and basicity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
[6]Radialene (2d) and its hexa- (2a) and dodecamethyl (2c) derivatives were subjected to several novel chemical reactions. Pyrolysis of 2a under flash vacuum conditions provided a mixture of 1,5-hydrogen shift products 9 and 10, and the benzocyclobutenes 5 and 6, produced by electrocyclization of an intermediate o-xylylene derivative 7. At the higher end of the investigated temperature range (200−400 °C) the formation of cyclization products 11 was also observed. The hydrocarbon 2c isomerized to the benzocyclobutene 12 under these conditions. Photolysis at 254 nm converted 2c into a novel isomer that, according to X-ray structural analysis, has the unusual twist configuration 14. Compound 2c was photoisomerized through photoinduced hydrogen shift reactions to 15, and the stable p-xylylenes 16 and 17. Dichloro- and dibromocarbene add to 2d with formation of the rotaradialene anti adducts 19a and 19b, respectively, the structures of which were also established by X-ray structural analysis. With dichlorocarbene, 2a provided the three dichlorocarbene adducts 20, 22, and 23, whereas methylenation with diiodomethane/trimethylaluminium afforded a complex product mixture from which the monoadduct 21 could be isolated. The analogous product 24 and the bisadduct 25 were obtained from 2c under the same conditions. Epoxidation of 2a with m-chloroperbenzoic acid gave the monoadduct 26, together with higher epoxidation products, which, however, could not be separated. Depending on the reaction conditions, 2c could be oxidized with m-chloroperbenzoic acid to give the epoxides 27, 28, and 29. Hydrochlorination of 2a gave a complex mixture of addition products, which was converted into the olefins 9 and 10 by base treatment, showing that the addition step takes place less regioselectively than previously assumed. With Fe2(CO)9, 2a was converted into the iron tricarbonyl complex 33 in poor yield. Repetition of the literature procedure for the preparation of 2a allowed the isolation of novel diastereomers of this oldest hexaradialene; according to NMR experiments the methyl substituents of this hydrocarbon are arranged as shown in the structure cccaca-2a. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The planar chiral 15-hydroxy[2.2]paracyclophane-4-carbaldehyde (2, iso-FHPC) was synthesized and resolved via its Schiff bases 8 by using the enantiomers of α-phenylethylamine. The absolute configurations of the enantiomers of 2 were determined by a combined X-ray diffraction and chemical correlation study. Derivatives 9, the first representatives of cyclophane-derived aminophenols with a pseudo-gem arrangement of the functional groups were synthesized. All new chiral compounds can be regarded as prospective ligands for asymmetric synthesis and catalysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Efficient syntheses of different enantiomerically and diastereomerically pure N,O-ligands with alkylamino and phenol groups attached to the [2.2]paracyclophane framework are described. Several transformations of the ortho-lithiated [2.2]paracyclophan-4-yl diethylcarbamate 7 and the reduction of the [2.2]paracyclophane imino derivatives 3, 4, 17, 18, and 21 allow the preparation of a wide range of compounds in which the chiral environment can be controlled by the planar chiral fragment and modified by the presence of one or two additional chiral centers in the alkylamino group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Diazotization of the title compound 3, followed by treatment of the formed bis(diazonium ion) with cuprous chloride, yields the pseudo-geminal dichloride 1. Similarly, 3 is converted into the bis(azide) 5 when sodium azide is used as the trapping nucleophile. Hypochlorite oxidation of 3 furnishes the azo compound 4, the first multi-bridged cyclophane with a bridge consisting only of heteroatoms. Reduction of 4 with zinc/acetic acid affords the substrate 3 again. Treatment of 4 with bromine/iron powder or iodine monochloride causes deazotization accompanied by halogen introduction in pseudo-geminal position (i.e., formation of 2 and 6, respectively). Flash vacuum pyrolysis (450 °C, 0.01 Torr) of 4 produces the phenanthrene derivatives 13 and 14, while with tetracyanoethylene (TCNE) the azophane undergoes rapid cycloaddition at room temperature to give the [2+4] cycloadduct 16. The structures of 1, 2, 4−6, and 16 have been determined by X-ray structural analysis. Molecular packing patterns are determined by weak hydrogen bonds; a common packing pattern for cyclophane derivatives is ascribed to C−H···π interactions. Full bandshape analyses of the bridge proton signals in the 1H NMR spectra of 1, 2, 6, and of the difluoro analogue 17 yielded the vicinal 1H,1H coupling constants. These reflect the 1:1 equilibrium between the two skew conformations of the bridges. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
(Z)-1,4-Diethynyl-1,4-dimethoxycyclohexa-2,5-diene has been used as a building block for the synthesis of two novel macrocycles containing buta-1,3-diyne units as bridges. The tetrayne derivative 5c has been structurally characterized by single crystal X-ray crystallographic data. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A girl's best friend and diamondoid hydrocarbons have something in common: transparent glass crystals of [121312]hexamantane (1) appear like diamonds with a pronounced luster. Regarding 1 as a jewel, it may be thought of as a nanometer-sized diamond of 10−20 carat (1 carat=0.2 g). This and other advances in adamantane chemistry are presented herein.
Ladderane wurden kürzlich als Membranlipide in zwei Ammonium-oxidierenden Bakterien („Anammox-Bakterien“) identifiziert (siehe Strukturformeln) – eine angesichts des ungewöhnlichen Strukturmotivs und der nichttrivialen Synthese dieser Verbindungsklasse überraschende Beobachtung.
Die Könige der Edelsteine und diamantanoide Kohlenwasserstoffe haben etwas gemeinsam: Die glasklaren Kristalle des [121312]Hexamantan (1) zeichnen sich wie Diamanten durch einen ausgeprägten Glanz aus. Fasst man 1 als Edelstein auf, so kann man ihn als einen nanodimensionierten Diamanten betrachten, der es auf 10−20 Karat bringt (1 Karat=0.2 g).
Ladderanes were identified recently as membrane lipids (see structural formulas) in two ammonium-oxidizing bacteria, which is an astonishing observation considering the unusual structural motif and the nontrivial synthesis of this class of compounds.
An efficient synthesis of [2.2]paracyclophane-4,15-dicarboxylic acid (11) from [2.2]paracyclophane (8) has been developed. The diacid was converted via the diazide 14 into the 4,15-diisocyanato[2.2]paracyclophane (15), a versatile intermediate that could be transformed into many new pseudo-geminally substituted derivatives of 8. For example, treatment of 15 with alcohols provided the carbamates 16 and 17. On treatment of 15 with diisopropylamine, the urea 18 was obtained, whereas reduction with lithium aluminium hydride afforded the cyclic urea 20. Hydrolysis of 15 furnished the diamine 19, which was used as a reusable spacer in a [2+2]photoaddition experiment. Thus, treatment of 19 with trans-cinnamoyl chloride (25) provided the bis(amide) 26, which on irradiation in acetone ring-closed to give the cyclobutane 28. Saponification of this yielded 3,4-diphenyl-1,2-cyclobutanedicarboxylic acid (27, β-truxinic acid) and returned the spacer system 19, both in quantitative yield. The X-ray structures of 15 and 20 are reported. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
The cross-conjugated 1,1-diethynylethylene derivatives 8b−10b were prepared from the corresponding bromides 16, 19, and 17 by Sonogashira coupling with trimethylsilylethyne and hydrolysis of the TMS-protected intermediates thus formed. Coupling of the tetrabromide 18 with (trimethylsilylethynyl)magnesium bromide in the presence of 1,3-[bis(diphenylphosphanyl)propane]nickel(II) chloride yielded the protected tetraalkyne 32, from which the 7,7,8,8-tetraethynyl-tetrahydro-p-quinodimethane 33 was liberated by fluoride treatment. Although 33 is a highly unstable cross-conjugated hydrocarbon, it could be converted into its tetraphenyl derivative by Sonogashira coupling with phenyl iodide. Both 32 and the corresponding tetraphenyl derivative were oxidized to the 7,7,8,8-tetraethynyl-dihydro-p-quinodimethane derivatives 35 and 36, respectively, on treatment with DDQ in dioxane. Further dehydrogenation of 35 to 34 failed, however. Alkylation of 9b with trimethylaluminium in the presence of zirconocene dichloride as catalyst yielded the semicyclic dendralene 37, which on irradiation isomerized to the tricyclic diene 42, presumably via the bicyclobutane 39 and a vinylcyclopropane rearrangement. Hydration of 9b furnished 43 and 44, the primary hydration product 38 either undergoing ketene elimination (formation of 43) or a 1,5-hydrogen shift reaction (to 44) from its tautomer 41. Analogously, the still more highly unsaturated derivative 31 was alkylated to give the [5]dendralene derivative 45 and hydrated to give a mixture of the β-diketones 46 and 49, the latter being produced from 46 by 1,2-methyl migration. The thermal cyclization of 10b to the homoacepentalene derivative 51 failed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
The resolution of racemic 4-hydroxy[2.2]paracyclophane (1) by fractional crystallization of the diastereomeric esters 3 with (1S)-(−)-camphanic acid and the determination of the absolute configurations of (R)- and (S)-4-hydroxy[2.2]paracyclophanes by X-ray diffraction have been carried out. The Friedel−Crafts oxaloylation of 1 with AlCl3 was found to occur with formation of both ortho- and para-hydroxy[2.2]paracyclophanylglyoxylic acids, whereas in the presence of TiCl4, quantitative formation of 2,3-dioxo-2,3-dihydrofurano[4,5-d][2.2]paracyclophane (8) as a product of an unusual cooperative C- and O-acylation was observed. Replacement of the OH group in the substrate for OCH3 (compound 18) changes the regioselectivity of the oxaloylation, which now occurs with formation of a para-substituted α-diketone 19. A novel technique for the synthesis of 4-formyl-5-hydroxy[2.2]paracyclophane (FHPC, 15) involving stereoselective reduction of 8 followed by oxidative cleavage of the intermediate diol 14 is also presented.
The 4-fulvenyl[2.2]paracyclophane (1) was transformed, by treatment with lithium aluminium hydride and methyllithium in tetrahydrofuran, to the corresponding cyclopentadienyl anions 6 and 8, respectively. The iron complex 7 was prepared from 6, while 8 was converted into the metal complexes 9 (Fe complex), 10 (Ti), 11 (Zr), 12 (Ti), and 13 (Zr). All new metallocene complexes were characterized by their spectroscopic data. In addition, a single crystal X-ray crystallographic analysis was performed for complex 11. The metallacyclic zirconocene complex 15 was synthesized by the reaction of the dichloride derivative 13 with two equivalents of n-butyllithium. After activation of complexes 10−13 and 15 with methylalumoxane (MAO) they were used for the catalytic polymerization of ethene and propene.
4-(2-Ethynylphenyl)pyridine (10), 3-(2-ethynylphenyl)pyridine (11), 2-(2-trimethylsilylethynylphenyl)pyridine (26), and 3-ethynyl-2-phenylpyridine (13) were prepared from readily available pyridine precursors by standard coupling reactions. Pyrolysis of 10 at 810 °C/0.5 Torr provided benzo[f]isoquinoline (45) and the benzopentalene dimer 47. Pyrolysis of 11 (820 °C/0.5 Torr) afforded benzo[f]quinoline (50), benzo[h]isoquinoline (52), and a mixture of isomers of 47. Pyrolysis of 13 (820 °C/0.3 Torr) provided benzo[h]quinoline (56) and the novel azulene derivative azuleno[1,2-b]pyridine (58). When 26 was desilylated by treatment with TBAF in THF/water, the unusual “dimerization” product 37 was produced; its structure was confirmed by X-ray structural analysis. The mechanisms of these transformations are discussed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
New thermotropic mesomorphic compounds containing a [2.2]paracyclophane (PC) unit were synthesized and investigated (Scheme). Carboxylic acids were selected as the starting PC building blocks. The influence of structural features on the stability of the mesomorphic phases was studied (Figs. 1 and 2): for this purpose, the structures of the PC-carboxylate unit and the organic fragment of the aryl-ester moiety were varied systematically. Esters derived from PC-monocarboxylic acid did not exhibit liquid-crystalline (LC) properties, while diaryl PC-dicarboxylates favored mesomorphism. Dicarboxylate substituents arranged in the para-position provided LC phases in a broad temperature range and considerably increased the mesomorphic interval in comparison with that of the structurally related pseudo-para PC derivatives.
The way in which chirality is introduced in a mesogenic molecule is important for determining the properties of the resultant liquid-crystalline material. The thermotropic liquid-crystalline compounds (see figure) based on planar, chiral [2.2]paracyclophane (PC) exhibit stable mesophases over a wide temperature range, while the mesophase type could be tuned by altering the nature of the substituents in the PC unit. The planar chiral PC derivatives also reveal a sufficiently high twisting ability in a nematic host.
Die Eigenschaften von flüssigkristallinem Material werden durch die Weise, in der Chiralität in das mesogene Molekül eingeführt wird, entscheidend beeinflusst. Den beschriebenen thermotropen flüssigkristallinen Verbindungen (siehe Abbildung), die über einen breiten Temperaturbereich stabile Mesophasen ausbilden, liegt ein planar-chirales [2,2]Paracyclophan (PC) zugrunde. Durch Veränderung des PC-Substituenten lässt sich der Mesophasentyp gezielt einstellen. In einer nematischen Gastphase verdrehen sich die planar-chiralen PC-Derivate zu Helices.
The chemical behavior of the tetrahydro- and dihydro[2.2]paracyclophanes, 3 and 4, respectively, was investigated. In particular, 3 was subjected to carbene addition (methylenation with triethylaluminum/diiodomethane, dichloro- and dibromocarbene addition) and epoxidation with m-chloroperbenzoic acid. The resulting mono adducts 5a, 5b, and 5d were characterized by spectroscopic methods and by chemical transformations to 6, 7, and 10. Reaction of 3 with dehydrobenzene (8) furnished the ene-product 9. Similarly, the bis adducts 14a−c were formed, each in good to excellent yield, from the bis-olefin 4. When 14c was ring-opened by treatment with trifluoroacetic acid, the chiral diol 16 was produced, which was then oxidized to the diketone 18 and brominated to give the dibromide 19. When the latter was treated with potassium tert-butoxide in tetrahydrofuran, it produced the bridged benzobarrelene 21, the smallest and most highly strained representative of this class of hydrocarbons. On pyrolysis, 21 underwent a retro-Diels−Alder reaction to pyracene (20) and ethylene. The derivatives 14b and 16, which show polymorphism and crystallized in two macroscopically distinguishable crystal forms 16-I and 16-II, together with compounds 19 and 21 were amenable to X-ray crystal structure analysis. The structural properties of these compounds are discussed in detail.
Gas phase thermal isomerizations of twelve acetylenic systems, all of which can in principle undergo two successive pericyclic steps, are described. The substrates, the syntheses and spectroscopic properties of which are presented, are formal derivatives of but-2-yne, with different functional groups in the 1- and the 4-positions. The Cope, Claisen, Claisen ester, retro-ene, 1,5-hydrogen shift, and 1,5-homo hydrogen-shift processes were employed as the pericyclic steps from which the tandem processes were composed. The compositions of the pyrolysates obtained were determined over broad temperature ranges, and the mechanisms of the individual steps producing the pyrolysis products are discussed.
The highly strained conjugated aldehyde 3-tert-butyl-4,4-dimethyl-2-pentenal (3,3-di-tert-butylpropenal; abbreviated D33; 4) has been prepared, and its molecular structure and conformation have been studied experimentally by the gas electron diffraction method and by theoretical ab initio (HF/6-31G*) calculations. The propenal skeleton assumes an anti conformation, and the steric strain is primarily manifested in the following structural details: The C=C−C angle is substantially larger than normal [GED: 132.6(7)°; HF/6-31G*: 132.5°]; the (Z)-oriented tert-butyl group is twisted to a nearly staggered position relative to the C=C double bond, forming a cogwheel system with the other tert-butyl group, which has the normal eclipsed conformation relative to C=C; the C3−CtBu (formally sp2−sp3) bonds are elongated compared to those in unstrained compounds, and are longer than the (formally sp3−sp3) C−CH3 bonds.
Two efficient routes have been developed for the lateral functionalization of monosubstituted [2.2]paracyclophanes. After protection of the ortho site of an O-([2.2]paracyclophanyl) diisopropylcarbamate, an anionic Fries rearrangement resulted in a substitution of the benzylic position to give syn-4-hydroxy-N,N-diisopropyl-5-triethylsilyl-2-[2.2]paracyclophanecarboxamide (4b) with a syn/anti diastereoselectivity of more than 99:1. An alternate route consisted of the direct functionalization of the lateral position of N-tert-butyl-4-[2.2]paracyclophanecarboxamide (9) by directed metalation. The reaction was found to be highly stereoselective, with only the syn isomer 11 being formed.
Cycloadditions between the indenone derivatives prepared in situ from the bromides 12a and 12b and 4-vinyl[2.2]paracyclophane (11) yielded the Diels−Alder adducts 13a and 13b in acceptable yields. When these were heated in the presence of DDQ in toluene, the fluorenophanes 14a and 14b were produced in good yields. The diol 17 obtained from the tetralonophane 15 on treatment with POCl3/pyridine was dehydrated to the diene 18, which could be trapped by p-benzoquinone (19) to provide the cycloadducts 20 and 21; the former was oxidized to the latter by DDQ treatment. Although the even more highly annelated helical phane system 22 could be prepared from 17 and 12a, its aromatization to the ketone 24 or the hydrocarbon 25 failed. All new compounds were characterized by their spectroscopic data, in particular by extensive NMR investigations. A single-crystal X-ray structure analysis for the parent hydrocarbon phenanthreno[2.2]paracyclophane (5) is reported.
Auf erhöhte globale Delokalisierung innerhalb der „stufigen“ π-Elektronensysteme der [2.2]Paracyclophan/Dehydrobenzoannulen(PC/DBA)-Hybridmoleküle 1 und 2 deuten Vergleiche der elektronischen Absorptionsspektren mit Spektren von Modellverbindungen mit vollständiger oder unterbrochener klassischer Arendelokalisierung hin. Man beobachtet gegenüber den Modellverbindungen eine ausgeprägte bathochrome Verschiebung (für 1) und eine größere Absorptionsintensität bei höheren Wellenlängen (für 1 und 2).
Cyclo-1,3-dien-5-ynes with ring sizes from 10 to 14 (6 a–e) have been prepared for the first time by using a five-step synthesis starting from the alkynols 7 a–e. The final ring-closure was achieved by McMurry coupling of the α,ω-dialdehydes 12 a–e with the complex TiCl3(DME)1.5. Thermal isomerization of the cyclodienynes leads to the corresponding benzocycloalkenes, and it has been shown that the ring size has a considerable influence on the temperature necessary for thermocylization.
Enhanced global delocalization throughout the “stepped” π-electron systems of the [2.2]paracyclophane/dehydrobenzoannulene (PC/DBA) hybrids 1 and 2 is strongly suggested by a comparison of their electronic absorption spectra with those of model compounds with complete and interrupted classical aromatic delocalization. A distinct bathochromic shift (for 1) and greater absorption intensity at higher wavelengths (for 1 and 2) is observed versus the corresponding model hydrocarbons.
The thermal cycloisomerization of both parent and benzannelated hexa-1,3-dien-5-yne, as well as of carbocyclic 1,3-dien-5-ynes (ring size 7–14), was investigated by using pure density functional theory (DFT) of Becke, Lee, Yang, and Parr (BLYP) in connection with the 6–31G* basis set and the Brueckner doubles coupled-cluster approach [BCCD(T)] with the cc-pVDZ basis set for the parent system. The initial cyclization product is the allenic cyclohexa-1,2,4-triene (isobenzene), while the respective biradical is the transition structure for the enantiomerization of the two allenes. Two consecutive [1,2]-H shifts further transform isobenzene to benzene. For the benzannelated system, the energetics are quite similar and the reaction path is the same with one exception: the intermediate biradical is not a transition state but a minimum which is energetically below isonaphthalene. The cyclization of the carbocyclic 1,3-dien-5-ynes, which follows the same reaction path as the parent system, clearly depends on the ring size. Like the cyclic enediynes, the dienynes were found to cyclize to products with reduced ring strain. This is not possible for the 7- and 8-membered dienynes, as their cyclization products are also highly strained. For 9- to 11-membered carbocycles, all intermediates, transition states, and products lie energetically below the parent system; this indicates a reduced cyclization temperature. All other rings (12- to 14-membered) have higher barriers. Exploratory kinetic experiments on the recently prepared 10- to 14-membered 1,3-dien-5-ynes rings show this tendency, and 10- and 11-membered rings indeed cyclize at lower temperatures.
Thiele condensation of the [2.2]paracyclophane derivatives 8, 12, 22, and 23 with cyclopentadiene (9) led to the monofulvenes 10, 11, and 13 and the bis(fulvenes) 24 and 25. Likewise, condensations of 8 with 1,2,3,4-tetrachlorocyclopentadiene (14) and 1,2,3,4-tetraphenylcyclopentadiene (16) provided the 4-fulvenyl[2.2]paracyclophanes 15 and 17. For comparison purposes, 8 was also condensed with lithium fluorenide (18) and lithium indenide (20) to give the benzo-annelated derivatives 19 and 21, respectively. Reactions of the dialdehydes 22 and 23 led to the bis(indenes) 26 and 27. 4-(6-Fulvenyl)[2.2]paracyclophane exists as two conformational isomers, 10 (major product) and 11 (minor product). By temperature-dependent NMR spectroscopy, the rotational barrier associated with 11 ⇄ 10 interconversion has been determined as ca. 26 kcal mol−1 at 70 °C. The structures of 19 and 27 have been established by single-crystal X-ray crystallography.
Reactions of 4-ethenyl[2.2]paracyclophane (3) and its derivatives or of 4-ethynyl[2.2]paracyclophane (27) with benzyne (4) afforded [2.2](1,4)phenanthrenoparacyclophanes 2, 7, and 9. The diethenyl[2.2]paracyclophanes 16, 19 and 22 reacted with 4 to give the stereoisomeric phenanthrenophanes 18, 21 and 23, respectively. The NMR spectra, in particular the 1H chemical shifts, of the diethenylparacyclophanes, the [2.2]phenanthrenoparacyclophanes and the [2.2]phenanthrenophanes are discussed.
4,5,12,13-Tetraformyl[2.2]paracyclophane (1f) has been prepared for the first time by the cycloaddition of 4,4-diethoxy-2-butynal (3) to 1,2,4,5-hexatetraene (2) under various conditions and hydrolysis of the initially produced bis-acetals 5a and 5b. An X-ray crystal structural analysis of 5a is reported.
The pyrolyses of two isomeric pairs of alkylcyclopropenes, namely 1,3-dimethyl- (15) and 1-ethyl-cyclopropene (16), and 1,3,3-trimethyl- (5) and 1-isopropyl-cyclopropene (17), have been studied in the gas phase. Complete product analyses at various conversions up to 95 % were obtained for the decomposition of each compound at five temperatures over a 40 °C range. The time-evolution data showed that the isomerisation reactions 15⇌16 and 5⇌17 were occurring. Kinetic modelling of each system allowed the determination of rate constants for these and all other decomposition processes. Tests confirmed that all reactions were unimolecular and homogeneous. Arrhenius parameters are reported for overall reactions and individual product pathways. Further kinetic analysis allowed us to extract the propensities (at 500 K) for 1,3-C−H insertion of the dialkylvinylidene intermediates involved in the rearrangements as follows: kprim:ksec:ktert=1:16.5:46.4. Additional experiments with 13C-labelled cyclopropenes yielded alkyl group migration aptitudes for the dialkylvinylidenes (from the pattern of 13C in the alkyne products) as follows: Me:Et:iPr=1:3.1:1.5. Explanations for these trends are given. Another important finding is that of the dramatic rate enhancements for 1,3-diene product formation from the 1-alkylcyclopropenes; this can be explained by either hyperconjugative stabilisation of the vinylcarbene intermediates involved in this pathway, or their differing propensities to 1,2 H-shift. The observed large variations in product distribution amongst these four cyclopropenes is interpreted in terms of these specific effects on individual pathways.
DasGeheimnis des Mechanismus von Vinyliden-Umlagerungen wurde durch die Verwendung von spezifisch markierten Cyclopropenen unter milden, thermischen Bedingungen gelüftet (siehe Gleichungen). 13C-Markierung liefert die überraschende 1,2-Alkyl-Wanderungstendenz Et>iPr>Me. Durch D-Markierung gelang die erste Bestimmung des primären Isotopeneffektes der Ringöffnung eines Cyclopropens zu einem Vinyliden.
The secret of the mechanism of vinylidene rearrangements has been unlocked by the use of specifically labeled cyclopropenes under mild thermal conditions (see the Equations). 13C labeling gives the surprising 1,2-alkyl migratory aptitude sequence Et>iPr>Me. Deuterium labeling yields the first measurement of the primary kinetic isotope effect in the ring opening of a cyclopropene to form a vinylidene.
The synthesis of optically pure (S)-5-formyl-4-hydroxy-[2.2]paracyclophane (S)-3 (ee > 99 %) was achieved by a three-step chemoenzymatic procedure consisting of (i) kinetic enzymatic resolution of (R, S)-4-acetoxy[2.2]para-cyclophane (R, S)-1 to produce optically pure starting material, which after (ii) hydrolysis was subjected to (iii) stereoselective ortho-formylation with an overall yield of 51 %. All attempts to use a biocatalyst directly for the preparation of optically pure disubstituted [2.2]para-cyclophanes failed because of either total lack of activity (bioreduction) or low enantioselectivities of the enzymes screened (hydrolases). Using the chemoenzymatic approach from (R, S)- 1, optically pure (S)-1 and after subjecting (S)-1 to hydrolysis and finally to formylation (S)-3 was obtained. As confirmed by chiral GC, hydrolysis and formylation took place without racemization. During the optimization of the enzymatical part of the synthesis a strong influence of both the nature of the cosolvent and the pH of the buffer-phase on the enantioselectivity value E were observed. Using a two-phase system consisting of diethyl ether and phosphate buffer an E value higher than 100 was achieved at a pH of 7.0 and at room temperature.
The thermal cycloisomerization of the 1,3-hexadiene-5-ynes 1a–e has been studied at temperatures above 500°C and reaction times of about 0.3 s (1a–d) and at a pressure of 1.5 · 10−2 Torr (FVP, 1e), respectively, at low partial pressures in quartz flow systems. While 1a and 1b cycloisomerize exclusively to the corresponding benzenes and pentafulvenes, substrates 1c–e cyclize primarily to 4-substituted 1,2-dihydronaphthalenes and biphenyls. The experimental results suggest a predominance of unimolecular reactions such as electrocyclic ring closures and 1,6-C,H-insertion processes of alkenylidene carbenes initially formed by an acetylenevinylidene rearrangement.
Treatment of perhydro[2.2]paracyclophane (1) with trifluoromethanesulfonic acid for 15 h at room temperature in dichloromethane results in a quantitative yield of stereoisomer 2, in which one of the bridgehead hydrogen atoms points towards the inside of the molecule (mono-endo isomer). The constitution of 2 is derived from 2D-NMR C,C-INADE-QUATE experiments and its stereochemistry from dynamic NMR experiments and molecular mechanics computations (MM3). A mechanism is suggested for the 1–2 interconversion.
The pseudo-gem cinnamophane dicarboxylic acid 1 was shown to undergo a stereospecific [2 + 2] photocycloaddition in the solid state, generating the truxinic acid derivative 2 in 100% chemical yield; the reaction can proceed to completion because it is not an “independent site” solid state reaction. The X-ray structure of 1 reveals that its molecules are associated in dimers formed from four almost linear hydrogen bonds. A salient feature is the intramolecular centre-to-centre distance between the reacting double bonds of ≈3.37 Å, the smallest known to date. In contrast to trans-cinnamic acid, the topochemical [2 + 2] photocycloaddition occurs also in solution, with a quantitative chemical yield and a quantum yield of ≈0.55 (in methanol).
The catalytic hydrogenation of [2.2]paracyclophane 1 has been reinvestigated with the following results: a) Best yields (95%) of the perhydrocyclophane 3 are obtained when 1 is hydrogenated over ruthenium on charcoal in ethanol at 200°C and 300 atm in the presence of lithium hydroxide; b) hydrogenation of 1 in ethyl acetate/acetic acid over platinum at room temperature and normal pressure leads to the monoene 7 and one diene, to which we assign structure 11 since dichlorocyclopropanation converts it to the bis-adduct 12, whose structure was determined by X-ray structural analysis; c) when the tetraene 13 (prepared from 1 by Birch reduction) is hydrogenated over palladium on charcoal in petroleum ether, the triene 14 is obtained in addition to the dienes 4 and 11. Again, dichlorocyclopropanation followed by X-ray structural analysis of the resulting tris-adduct 17 was employed for the structure determination of the hydrocarbon precursor. The strain energies of the anti-Bredt hydrocarbons 11 and 17 have been calculated by molecular mechanics calculations.
The title compound 2, an electron-rich macrocyclic paracyclophane of the coronand type, known to form a charge-transfer complex with paraquat, was found to encapsulate strontium cations and to bind to magnesium cations. X-ray analysis revealed that 2 forms a 2:1 (metal/substrate) complex with Sr(ClO4)2, in which the two benzene rings weakly overlap, whereas in the single crystals grown from Mg(ClO4)2, the metal cation prefers to lie outside the coronand (1:1 stoichiometry). In acetonitrile solution, cations were observed to trigger an hypsochromic shift of the UV absorption spectra, proportional to their size and charge density. The stoichiometries and binding constants were also determined by UV absorption titration in acetonitrile using the LETAGROP-SPEFO program for several monovalent and divalent cations. For Na+, Ca2+, and Sr2+, 1:1 and 2:1 complexes were shown to be formed. In the free ligand, a weak interaction between the benzene rings was detected by fluorescence decay kinetic analysis, indicating the presence of two conformer populations within the nanosecond time scale. In solution, metal cations neither induce detectable excimer formation nor seem to have a strong influence on the fluorescence emission spectra, except a heavy atom quenching with Sr2+ and Ba2+, in contrast to the effect observed in absorption. However, Sr2+ and Mg2+induce a clear hypsochromic shift in the single crystal fluorescence spectra. Compound 2 was prepared by a new and efficient route which is compared to the previous procedures.
The behavior of 2-ethynyl-1,3-butadiene (1) as the diene component in Diels-Alder additions has been studied using a selection of representative double and triple bond dienophiles. The latter include maleic anhydride (5a), diethyl fumarate (6), benzoquinone (7), methyl acrylate (11), juglone (20), 1-methylcyclopropene (23), dimethyl acetylenedicarboxylate (26), propiolic aldehyde (32), 4-phenyl-1,2,4-triazolin-3,5-dione (35) and diethyl azodicarboxylate (37). [2 + 4] Cycloadducts were formed in all cases in varying yields. The addition is accompained by thermal dimerization of 1 which leads to 1,4-diethynyl-4-vinyl-1-cyclohexene (43) and 1,6-diethynyl-1,5-cyclooctadiene (39). The mechanism of this dimerization is discussed. In a competition experiment towards maleic anhydride (5a), diene 1 was shown to be ca. five times less reactive than isoprene.
The two 2,3-diethynyl-1,3-butadiene derivatives 1b and 1c were prepared from 2,3-dichloro-1,3-butadiene (26) and the Grignard reagents 19b and 19c by Kumada coupling. Desilylation of 1b provided the parent molecule 1a. The title compounds were used for the preparation of numerous new enediyne systems by [2 + 4] cycloaddition. The dienophiles employed include maleic anhydride (27a), diethyl fumarate (29), tetracyanoethylene (31), diethyl azodicarboxylate (33), and dimethyl acetylenedicarboxylate (35). With p-quinones such as p-benzoquinone (44) as dienophiles the expected mono-and bisadducts are formed which were dehydrogenated to the bis- and tetrakis(trimethylsilylethynyl)naphtho- and -anthraquinones 47 and 48, respectively, by treatment with DDQ. Heating of 1b in THF at 65°C caused dimerization to the 1,5-cyclooctadiene derivative 56, which was desilylated to 1,2,5,6-tetraethynyl-1,5-cyclooctadiene (59) by treatment with potassium fluoride in DMF. 1b is approximately 15 times less reactive than 2,3-dimethyl-1,3-butadiene (54) towards maleic anhydride (27a).
The thermal isomerization of [1,4-D2]- (3a) and [1,2-13C2]benzene (1a) has been studied in excess hydrogen at 750–850°C with contact time less than 1.2 s and very low partial pressure in a quartz flow system. In both cases, the main isomerization products are the corresponding meta isomers. The data suggest a radical intramolecular interchange of the benzene carbon atoms by 1,2-C shifts. The multistep reaction cascade is initiated by H addition to the benzene ring followed by transannular homoallyl rearrangements involving the intermediate formation of bicyclo[3.1.0]hexenyl and cyclopentadienylmethyl radicals. This pathway constitutes a side reaction competing with the direct stabilization of the cyclohexadienyl radicals formed preferentially at high temperature.
Model substances for oligomeric systems based on the incorporation of [2.2.2]paracyclophane into the repeating unit are linear polyenes bearing a paracyclophanyl residue in the terminal positions. The preparation of the polyenes 2a–c is described. In addition to the characterisation as diarylpolyenes, consideration of model compounds revealed that the [2.2.2]paracyclophanyl residues interact with pendent substituents according to a magnetic anisotropic mechanism.
![Phosphonic acid, (benzo[b]thien-2-ylmethyl)-, diethyl ester](http://img.cochemist.com/ccimg/84300/84258-56-0.png)
![Phosphonic acid, (benzo[b]thien-2-ylmethyl)-, diethyl ester](http://img.cochemist.com/ccimg/84300/84258-56-0_b.png)
![3-[(1R,2R)-2-(3-hydroxyprop-1-ynyl)cyclobutyl]prop-2-yn-1-ol](http://img.cochemist.com/ccimg/80400/80344-44-1.png)
![3-[(1R,2R)-2-(3-hydroxyprop-1-ynyl)cyclobutyl]prop-2-yn-1-ol](http://img.cochemist.com/ccimg/80400/80344-44-1_b.png)
![Phosphonic acid, (benzo[b]thien-3-ylmethyl)-, diethyl ester](http://img.cochemist.com/ccimg/80100/80090-41-1.png)
![Phosphonic acid, (benzo[b]thien-3-ylmethyl)-, diethyl ester](http://img.cochemist.com/ccimg/80100/80090-41-1_b.png)
![2,5-Bis[(trimethylsilyl)ethynyl]thiophene](http://img.cochemist.com/ccimg/79200/79109-69-6.png)
![2,5-Bis[(trimethylsilyl)ethynyl]thiophene](http://img.cochemist.com/ccimg/79200/79109-69-6_b.png)
![DINAPHTHO[2,1,8,7-GHIJ:2',1',8',7'-NOPQ]PLEIADENE](http://img.cochemist.com/ccimg/76300/76276-09-0.png)
![DINAPHTHO[2,1,8,7-GHIJ:2',1',8',7'-NOPQ]PLEIADENE](http://img.cochemist.com/ccimg/76300/76276-09-0_b.png)
![1,10-ETHANODIBENZO[A,E]CYCLOOCTENE, 5,6,11,12-TETRAHYDRO-](http://img.cochemist.com/ccimg/73200/73121-25-2.png)
![1,10-ETHANODIBENZO[A,E]CYCLOOCTENE, 5,6,11,12-TETRAHYDRO-](http://img.cochemist.com/ccimg/73200/73121-25-2_b.png)
![Dibenzo[b,e][1,4]dioxin, trichloro-](http://img.cochemist.com/ccimg/69800/69760-96-9.png)
![Dibenzo[b,e][1,4]dioxin, trichloro-](http://img.cochemist.com/ccimg/69800/69760-96-9_b.png)
![1,10:2,9-Diethanodibenzo[a,e]cyclooctene,5,6,11,12-tetrahydro- (9CI)](http://img.cochemist.com/ccimg/69700/69631-55-6.png)
![1,10:2,9-Diethanodibenzo[a,e]cyclooctene,5,6,11,12-tetrahydro- (9CI)](http://img.cochemist.com/ccimg/69700/69631-55-6_b.png)
![Acetamide, N-[2,4-bis(1,3-diphenyl-2-imidazolidinyl)-5-hydroxyphenyl]-](http://img.cochemist.com/ccimg/67200/67149-22-8.png)
![Acetamide, N-[2,4-bis(1,3-diphenyl-2-imidazolidinyl)-5-hydroxyphenyl]-](http://img.cochemist.com/ccimg/67200/67149-22-8_b.png)
![2,9-Ethanodibenzo[a,e]cyclooctene,5,6,11,12-tetrahydro-](http://img.cochemist.com/ccimg/58100/58002-98-5.png)
![2,9-Ethanodibenzo[a,e]cyclooctene,5,6,11,12-tetrahydro-](http://img.cochemist.com/ccimg/58100/58002-98-5_b.png)
![1-METHOXY-4-[(4-METHOXYPHENOXY)METHOXY]BENZENE](http://img.cochemist.com/ccimg/56300/56207-34-2.png)
![1-METHOXY-4-[(4-METHOXYPHENOXY)METHOXY]BENZENE](http://img.cochemist.com/ccimg/56300/56207-34-2_b.png)
![PHOSPHONIC ACID, [2-(2-FURANYL)-2-OXOETHYL]-, DIETHYL ESTER](http://img.cochemist.com/ccimg/56000/55984-13-9.png)
![PHOSPHONIC ACID, [2-(2-FURANYL)-2-OXOETHYL]-, DIETHYL ESTER](http://img.cochemist.com/ccimg/56000/55984-13-9_b.png)
![Phosphonic acid, [2-(cyclohexylimino)ethyl]-, diethyl ester](http://img.cochemist.com/ccimg/54400/54364-57-7.png)
![Phosphonic acid, [2-(cyclohexylimino)ethyl]-, diethyl ester](http://img.cochemist.com/ccimg/54400/54364-57-7_b.png)
![PHOSPHONIC ACID, [2-(4-NITROPHENYL)-2-OXOETHYL]-, DIETHYL ESTER](http://img.cochemist.com/ccimg/54200/54109-18-1.png)
![PHOSPHONIC ACID, [2-(4-NITROPHENYL)-2-OXOETHYL]-, DIETHYL ESTER](http://img.cochemist.com/ccimg/54200/54109-18-1_b.png)
![3,11:4,10-Dimethenobenzo[1,2:4,5]dicyclooctene,1,2,5,6,8,9,12,13-octahydro-](http://img.cochemist.com/ccimg/54200/54100-59-3.png)
![3,11:4,10-Dimethenobenzo[1,2:4,5]dicyclooctene,1,2,5,6,8,9,12,13-octahydro-](http://img.cochemist.com/ccimg/54200/54100-59-3_b.png)
![AZULENO[1,2-B]PYRIDINE](http://img.cochemist.com/ccimg/53900/53835-37-3.png)
![AZULENO[1,2-B]PYRIDINE](http://img.cochemist.com/ccimg/53900/53835-37-3_b.png)
![1H,3H-FURO[3,4-C]FURAN, 4,6-DIHYDRO-](http://img.cochemist.com/ccimg/53800/53720-71-1.png)
![1H,3H-FURO[3,4-C]FURAN, 4,6-DIHYDRO-](http://img.cochemist.com/ccimg/53800/53720-71-1_b.png)
![TRICYCLO[9.3.1.14,8]HEXADECA-1(15),4,6,8(16),11,13-HEXAENE-5-CARBOXALDEHYDE](http://img.cochemist.com/ccimg/50500/50471-62-0.png)
![TRICYCLO[9.3.1.14,8]HEXADECA-1(15),4,6,8(16),11,13-HEXAENE-5-CARBOXALDEHYDE](http://img.cochemist.com/ccimg/50500/50471-62-0_b.png)
![2H-Pyran, 2-[(1-ethynylcyclohexyl)oxy]tetrahydro-](http://img.cochemist.com/ccimg/43000/42969-66-4.png)
![2H-Pyran, 2-[(1-ethynylcyclohexyl)oxy]tetrahydro-](http://img.cochemist.com/ccimg/43000/42969-66-4_b.png)
![Dibenzo[b,e][1,4]dioxin,tetrachloro-](http://img.cochemist.com/ccimg/42000/41903-57-5.png)
![Dibenzo[b,e][1,4]dioxin,tetrachloro-](http://img.cochemist.com/ccimg/42000/41903-57-5_b.png)
![Tetracyclo[3.3.1.03,9.07,9]nonane](http://img.cochemist.com/ccimg/40300/40220-30-2.png)
![Tetracyclo[3.3.1.03,9.07,9]nonane](http://img.cochemist.com/ccimg/40300/40220-30-2_b.png)
![2-METHYLADAMANTAN-2-YLBICYCLO[2.2.1]HEPT-5-ENE-2-CARBOXYLATE](http://img.cochemist.com/ccimg/39000/38998-75-3.png)
![2-METHYLADAMANTAN-2-YLBICYCLO[2.2.1]HEPT-5-ENE-2-CARBOXYLATE](http://img.cochemist.com/ccimg/39000/38998-75-3_b.png)
![Dibenzo[b,e][1,4]dioxin,pentachloro-](http://img.cochemist.com/ccimg/36100/36088-22-9.png)
![Dibenzo[b,e][1,4]dioxin,pentachloro-](http://img.cochemist.com/ccimg/36100/36088-22-9_b.png)
![Dibenzo[b,e][1,4]dioxin,1,2,3,4,6,7,8-heptachloro-](http://img.cochemist.com/ccimg/35900/35822-46-9.png)
![Dibenzo[b,e][1,4]dioxin,1,2,3,4,6,7,8-heptachloro-](http://img.cochemist.com/ccimg/35900/35822-46-9_b.png)
![Benzene, 1,1'-[1,2-ethenediylbis(sulfonyl)]bis-](http://img.cochemist.com/ccimg/35400/35387-59-8.png)
![Benzene, 1,1'-[1,2-ethenediylbis(sulfonyl)]bis-](http://img.cochemist.com/ccimg/35400/35387-59-8_b.png)
![Dibenzo[b,e][1,4]dioxin,hexachloro-](http://img.cochemist.com/ccimg/34500/34465-46-8.png)
![Dibenzo[b,e][1,4]dioxin,hexachloro-](http://img.cochemist.com/ccimg/34500/34465-46-8_b.png)
![Spiro[2.3]hexane, 1,1-dibromo-](http://img.cochemist.com/ccimg/33700/33669-81-7.png)
![Spiro[2.3]hexane, 1,1-dibromo-](http://img.cochemist.com/ccimg/33700/33669-81-7_b.png)
![2-[(4-METHOXYPHENYL)METHYLIDENE]-1,3-DIPHENYLPROPANE-1,3-DIONE](http://img.cochemist.com/ccimg/29000/28918-07-2.png)
![2-[(4-METHOXYPHENYL)METHYLIDENE]-1,3-DIPHENYLPROPANE-1,3-DIONE](http://img.cochemist.com/ccimg/29000/28918-07-2_b.png)
Cyclophane](http://img.cochemist.com/ccimg/27200/27165-88-4.png)
Cyclophane](http://img.cochemist.com/ccimg/27200/27165-88-4_b.png)
![Tricyclo[8.2.2.24,7]hexadeca-4,6,10(14),12-tetraene](http://img.cochemist.com/ccimg/26100/26050-79-3.png)
![Tricyclo[8.2.2.24,7]hexadeca-4,6,10(14),12-tetraene](http://img.cochemist.com/ccimg/26100/26050-79-3_b.png)
![Tetraspiro[2.0.2.0.2.0.2.0]dodecane](http://img.cochemist.com/ccimg/24400/24375-17-5.png)
![Tetraspiro[2.0.2.0.2.0.2.0]dodecane](http://img.cochemist.com/ccimg/24400/24375-17-5_b.png)
![Trispiro[2.0.2.1.2.0]decane, methylene-](/data/chemimg/1161600/24375-16-4.png)
![Trispiro[2.0.2.1.2.0]decane, methylene-](/data/chemimg/1161600/24375-16-4_b.png)
![Silane, trimethyl[(6-methyl-1-cyclohexen-1-yl)oxy]-](http://img.cochemist.com/ccimg/20000/19980-33-7.png)
![Silane, trimethyl[(6-methyl-1-cyclohexen-1-yl)oxy]-](http://img.cochemist.com/ccimg/20000/19980-33-7_b.png)
![Phosphonic acid, [2-(4-methoxyphenyl)-2-oxoethyl]-, diethyl ester](http://img.cochemist.com/ccimg/18300/18276-85-2.png)
![Phosphonic acid, [2-(4-methoxyphenyl)-2-oxoethyl]-, diethyl ester](http://img.cochemist.com/ccimg/18300/18276-85-2_b.png)
![Phosphonic acid, P-[2-(4-methylphenyl)-2-oxoethyl]-, diethyl ester](/data/chemimg/1767000/18276-81-8.png)
![Phosphonic acid, P-[2-(4-methylphenyl)-2-oxoethyl]-, diethyl ester](/data/chemimg/1767000/18276-81-8_b.png)
![2H-Pyran, 2-[(3-bromo-2-propynyl)oxy]tetrahydro-](http://img.cochemist.com/ccimg/14500/14420-47-4.png)
![2H-Pyran, 2-[(3-bromo-2-propynyl)oxy]tetrahydro-](http://img.cochemist.com/ccimg/14500/14420-47-4_b.png)
![3-Pentyn-2-ol, 2-methyl-5-[(tetrahydro-2H-pyran-2-yl)oxy]-](http://img.cochemist.com/ccimg/14100/14092-32-1.png)
![3-Pentyn-2-ol, 2-methyl-5-[(tetrahydro-2H-pyran-2-yl)oxy]-](http://img.cochemist.com/ccimg/14100/14092-32-1_b.png)
![Poly[(chloro-1,4-phenylene)-1,2-ethanediyl]](http://img.cochemist.com/ccimg/9100/9052-19-1.png)
![Poly[(chloro-1,4-phenylene)-1,2-ethanediyl]](http://img.cochemist.com/ccimg/9100/9052-19-1_b.png)
![5,7,12,14-TETRAHYDRODIBENZO[C,H][1,6]DITHIECINE (EN)DIBENZO[C,H][1,6]DITHIECIN, 5,7,12,14-TETRAHYDRO- (EN)](http://img.cochemist.com/ccimg/7300/7215-69-2.png)
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![DIBENZO[A,G]CYCLODODECENE, 5,6,7,8,13,14,15,16-OCTADEHYDRO-](http://img.cochemist.com/ccimg/7300/7203-21-6.png)
![DIBENZO[A,G]CYCLODODECENE, 5,6,7,8,13,14,15,16-OCTADEHYDRO-](http://img.cochemist.com/ccimg/7300/7203-21-6_b.png)
![2-[(5-bromothiophen-2-yl)sulfonyl]-1-pyridin-4-yl-1,2,3,4-tetrahydroisoquinoline](http://img.cochemist.com/ccimg/7100/7062-94-4.png)
![2-[(5-bromothiophen-2-yl)sulfonyl]-1-pyridin-4-yl-1,2,3,4-tetrahydroisoquinoline](http://img.cochemist.com/ccimg/7100/7062-94-4_b.png)
![dibenzo[ghi,mno]fluoranthene](http://img.cochemist.com/ccimg/5900/5821-51-2.png)
![dibenzo[ghi,mno]fluoranthene](http://img.cochemist.com/ccimg/5900/5821-51-2_b.png)
![bicyclo[8.2.2]tetradeca-1(12),10,13-triene](http://img.cochemist.com/ccimg/4700/4685-74-9.png)
![bicyclo[8.2.2]tetradeca-1(12),10,13-triene](http://img.cochemist.com/ccimg/4700/4685-74-9_b.png)
![3-METHYL-N-[4-(TRIFLUOROMETHYL)PHENYL]-1,2-OXAZOLE-4-CARBOXAMIDE](http://img.cochemist.com/ccimg/4000/3917-41-7.png)
![3-METHYL-N-[4-(TRIFLUOROMETHYL)PHENYL]-1,2-OXAZOLE-4-CARBOXAMIDE](http://img.cochemist.com/ccimg/4000/3917-41-7_b.png)
![3H-PYRAZOL-3-ONE,4-[[4-(DIMETHYLAMINO)PHENYL]METHYLENE]-2,4-DIHYDRO-5-METHYL-2-PHENYL-](http://img.cochemist.com/ccimg/3200/3100-04-7.png)
![3H-PYRAZOL-3-ONE,4-[[4-(DIMETHYLAMINO)PHENYL]METHYLENE]-2,4-DIHYDRO-5-METHYL-2-PHENYL-](http://img.cochemist.com/ccimg/3200/3100-04-7_b.png)
![Tricyclo[10.2.2.25,8]octadeca-5,7,12,14,15,17-hexaene](http://img.cochemist.com/ccimg/3000/2913-24-8.png)
![Tricyclo[10.2.2.25,8]octadeca-5,7,12,14,15,17-hexaene](http://img.cochemist.com/ccimg/3000/2913-24-8_b.png)
![Tricyclo[9.3.1.14,8]hexadeca-1(15),4,6,8(16),11,13-hexaene](http://img.cochemist.com/ccimg/2400/2319-97-3.png)
![Tricyclo[9.3.1.14,8]hexadeca-1(15),4,6,8(16),11,13-hexaene](http://img.cochemist.com/ccimg/2400/2319-97-3_b.png)
![1-Propanol, 3-[(tetrahydro-2H-pyran-2-yl)oxy]-](http://img.cochemist.com/ccimg/2200/2162-33-6.png)
![1-Propanol, 3-[(tetrahydro-2H-pyran-2-yl)oxy]-](http://img.cochemist.com/ccimg/2200/2162-33-6_b.png)
![Dibenzo[a,e]cyclooctene,5,6,11,12-tetrahydro-](http://img.cochemist.com/ccimg/1500/1460-59-9.png)
![Dibenzo[a,e]cyclooctene,5,6,11,12-tetrahydro-](http://img.cochemist.com/ccimg/1500/1460-59-9_b.png)
![Tetracyclo[2.2.0.02,6.03,5]hexane](http://img.cochemist.com/ccimg/700/650-42-0.png)
![Tetracyclo[2.2.0.02,6.03,5]hexane](http://img.cochemist.com/ccimg/700/650-42-0_b.png)
![8H-Cyclopent[a]acenaphthylen-8-one,7,9-diphenyl-](http://img.cochemist.com/ccimg/700/641-57-6.png)
![8H-Cyclopent[a]acenaphthylen-8-one,7,9-diphenyl-](http://img.cochemist.com/ccimg/700/641-57-6_b.png)
![BICYCLO[1.1.1]PENTANE](http://img.cochemist.com/ccimg/400/311-75-1.png)
![BICYCLO[1.1.1]PENTANE](http://img.cochemist.com/ccimg/400/311-75-1_b.png)
![Tetracyclo[14.2.2.24,7.210,13]tetracosa-4,6,10,12,16,18,19,21,23-nonaene](/data/chemimg/452700/283-80-7.png)
![Tetracyclo[14.2.2.24,7.210,13]tetracosa-4,6,10,12,16,18,19,21,23-nonaene](/data/chemimg/452700/283-80-7_b.png)
![Tricyclo[8.2.2.24,7]hexadecane](http://img.cochemist.com/ccimg/300/283-68-1.png)
![Tricyclo[8.2.2.24,7]hexadecane](http://img.cochemist.com/ccimg/300/283-68-1_b.png)
![Pentacyclo[4.2.0.02,5.03,8.04,7]octane](http://img.cochemist.com/ccimg/300/277-10-1.png)
![Pentacyclo[4.2.0.02,5.03,8.04,7]octane](http://img.cochemist.com/ccimg/300/277-10-1_b.png)
![tricyclo[4.2.0.02,5]octane](http://img.cochemist.com/ccimg/300/277-08-7.png)
![tricyclo[4.2.0.02,5]octane](http://img.cochemist.com/ccimg/300/277-08-7_b.png)
![benzo[h]isoquinoline](http://img.cochemist.com/ccimg/300/229-71-0.png)
![benzo[h]isoquinoline](http://img.cochemist.com/ccimg/300/229-71-0_b.png)
![Benz[f]isoquinoline](http://img.cochemist.com/ccimg/300/229-67-4.png)
![Benz[f]isoquinoline](http://img.cochemist.com/ccimg/300/229-67-4_b.png)
![Benzo[f]quinoline](http://img.cochemist.com/ccimg/100/85-02-9.png)
![Benzo[f]quinoline](http://img.cochemist.com/ccimg/100/85-02-9_b.png)
![SILANE, [1,2-BIS(2-METHYL-1-PROPENYLIDENE)-1,2-ETHANEDIYL]BIS[TRIMETHYL-](http://img.cochemist.com/ccimg/503700/503605-53-6.png)
![SILANE, [1,2-BIS(2-METHYL-1-PROPENYLIDENE)-1,2-ETHANEDIYL]BIS[TRIMETHYL-](http://img.cochemist.com/ccimg/503700/503605-53-6_b.png)
![TRICYCLO[8.2.2.24,7]HEXADECA-4,6,10,15-TETRAENE](http://img.cochemist.com/ccimg/198500/198481-78-6.png)
![TRICYCLO[8.2.2.24,7]HEXADECA-4,6,10,15-TETRAENE](http://img.cochemist.com/ccimg/198500/198481-78-6_b.png)
![17-Oxatricyclo[10.2.2.14,9]heptadeca-1(14),4,6,8,12,15-hexaene-5,6-di
carbonitrile](http://img.cochemist.com/ccimg/147300/147287-47-6.png)
![17-Oxatricyclo[10.2.2.14,9]heptadeca-1(14),4,6,8,12,15-hexaene-5,6-di
carbonitrile](http://img.cochemist.com/ccimg/147300/147287-47-6_b.png)
![Silane, [(2-iodophenyl)ethynyl]trimethyl-](http://img.cochemist.com/ccimg/137700/137648-47-6.png)
![Silane, [(2-iodophenyl)ethynyl]trimethyl-](http://img.cochemist.com/ccimg/137700/137648-47-6_b.png)
![Phenol, 4,4'-[methylenebis(oxy)]bis-](http://img.cochemist.com/ccimg/86100/86072-79-9.png)
![Phenol, 4,4'-[methylenebis(oxy)]bis-](http://img.cochemist.com/ccimg/86100/86072-79-9_b.png)
![Bicyclo[4.2.0]oct-1(6)-ene, 2,3-bis(methylene)-](http://img.cochemist.com/ccimg/85000/84980-66-5.png)
![Bicyclo[4.2.0]oct-1(6)-ene, 2,3-bis(methylene)-](http://img.cochemist.com/ccimg/85000/84980-66-5_b.png)
![Propanedinitrile, [3-phenyl-1-(phenylethynyl)-2-propynylidene]-](http://img.cochemist.com/ccimg/18700/18627-98-0.png)
![Propanedinitrile, [3-phenyl-1-(phenylethynyl)-2-propynylidene]-](http://img.cochemist.com/ccimg/18700/18627-98-0_b.png)
![15-oxatricyclo[8.2.2.1~4,7~]pentadeca-1(12),4,6,10,13-pentaene](http://img.cochemist.com/ccimg/5100/5040-51-7.png)
![15-oxatricyclo[8.2.2.1~4,7~]pentadeca-1(12),4,6,10,13-pentaene](http://img.cochemist.com/ccimg/5100/5040-51-7_b.png)
![Tricyclo[8.2.2.24,7]hexadeca-4,6,10,12,13,15-hexaene,5-bromo-](http://img.cochemist.com/ccimg/2000/1908-61-8.png)
![Tricyclo[8.2.2.24,7]hexadeca-4,6,10,12,13,15-hexaene,5-bromo-](http://img.cochemist.com/ccimg/2000/1908-61-8_b.png)
![2,3,7,8-Tetrachlorodibenzo[b,e][1,4]dioxine](http://img.cochemist.com/ccimg/1800/1746-01-6.png)
![2,3,7,8-Tetrachlorodibenzo[b,e][1,4]dioxine](http://img.cochemist.com/ccimg/1800/1746-01-6_b.png)
![7,16:10,13-Diethenocyclododeca[a]naphthalene, 8,9,14,15-tetrahydro-](/data/chemimg/2080100/98395-18-7.png)
![7,16:10,13-Diethenocyclododeca[a]naphthalene, 8,9,14,15-tetrahydro-](/data/chemimg/2080100/98395-18-7_b.png)
![2,3,5',6'-tetramethyl-[2.2]paracyclophane](http://img.cochemist.com/ccimg/71800/71779-89-0.png)
![2,3,5',6'-tetramethyl-[2.2]paracyclophane](http://img.cochemist.com/ccimg/71800/71779-89-0_b.png)
