Synthesis and Properties of Conjugated Nanohoops Incorporating

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Cite This: J. Org. Chem. XXXX, XXX, XXX−XXX

Synthesis and Properties of Conjugated Nanohoops Incorporating Dibenzo[a,e]pentalenes: [2]DBP[12]CPPs Daniel Wassy,† Manuel Pfeifer,† and Birgit Esser*,†,‡,§ †

Institute for Organic Chemistry, University of Freiburg, Albertstraße 21, 79104 Freiburg, Germany Freiburg Materials Research Center, University of Freiburg, Stefan-Meier-Straße 21, 79104 Freiburg, Germany § Cluster of Excellence livMatS @ FIT - Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg, Germany Downloaded via KEAN UNIV on July 20, 2019 at 05:40:54 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: Conjugated nanohoops allow studying the effect of cyclic conjugation and bending on the incorporated πsystems. To date, no such system containing antiaromatic units has been reported. We herein present [12]cycloparaphenylenes incorporating two dibenzo[a,e]pentalene units: [2]DBP[12]CPP nanohoops. Dibenzo[a,e]pentalene is a nonalternant hydrocarbon with antiaromatic character. The syntheses and optoelectronic properties of two different [2]DBP[12]CPP nanohoops with electronically modifying substituents are reported, accompanied by TDDFT calculations.

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INTRODUCTION Conjugated nanohoops have received significant attention in recent years.1−7 This is due in particular to the extensive synthesis and investigation of cycloparaphenylenes (CPPs) and derivatives since 2008.8−10 CPPs are of interest due to their size-dependent optoelectronic properties,11,12 host−guest chemistry, and as segments of carbon nanotubes.13−15 Many derivatives have been synthesized with aromatic units other than benzene incorporated into the ring such as fluorene,16,17 carbazole,18 naphthalene,19−21 anthracene,22,23 pyrene,24 chrysene,25 anthanthrene,26 and hexabenzocoronene.27−30 However, to the best of our knowledge, only one example has been reported to date, containing a nonalternant hydrocarbon, namely rubicene,31 and no example exists incorporating an antiaromatic unit. Dibenzo[a,e]pentalene (DBP, 1, Figure 1) is a nonalternant hydrocarbon with antiaromatic character.32 Compared to the parent compound pentalene, the antiaromaticity in DBP is significantly reduced due to the presence of the fused benzene rings.32 DBP possesses a small bandgap caused by an increased HOMO and decreased LUMO energy in comparison to an alternant hydrocarbon of similar size.1 This makes it attractive as an ambipolar material for, e.g., fieldeffect transistors.33−35 We herein present the synthesis of DBPcontaining conjugated nanohoops 2 and 3 as well as their electrochemical and optical properties supported by TDDFT calculations (Figure 1). These nanohoops contain two DBP © XXXX American Chemical Society

units incorporated into a [12]CPP framework, and we named them [2]DBP[12]CPPs. This is the first synthetic report of conjugated rings incorporating DBP36 and the second report of bent DBP derivatives.37 Such compounds allow investigation of the degree of (cyclic) conjugation between the CPP part and the DBP and the altered properties of the DBP units due to the bending.

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RESULTS AND DISCUSSION Synthesis. One of the main challenges in the synthesis of conjugated nanohoops is the buildup of strain energy.38 To incorporate DBP units into a bent conjugated shape, we employed a strategy developed for CPP synthesis using Lshaped diphenylcyclohexane units 8 as precursors to terphenyl units (Scheme 1).39 For substituents on the DBP units we chose mesityl (2), 3,5-bis(trifluoromethyl)phenyl groups (3), and n-hexyl. The syntheses commenced from dibromosubstituted diketone 9.37,40 Reaction with the respective Grignard reagent in a cerium trichloride-mediated addition followed by acid-catalyzed double water elimination furnished dibromo-substituted DBP derivatives 10−12 in good yields. Special Issue: Functional Organic Materials Received: May 3, 2019 Published: June 12, 2019 A

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

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These were then converted into the respective boronic esters 13−15 by palladium-catalyzed Miyaura reaction. Suzuki− Miyaura coupling with a fourfold excess of L-shaped unit 839 afforded U-shaped compounds 16−18. These U-shaped precursors were then subjected to nickel-mediated coupling under high dilution conditions to afford macrocycles 19−21 in yields of 28−46%. Semipreparative gel-permeation chromatography allowed separation of these compounds from larger macrocycles or linear oligomers formed in the reaction. The last step was the oxidative aromatization of the masked terphenyl units. Reaction with sodium hydrogen sulfate under oxidative conditions (air) afforded [2]DBP[12]CPPs 2 and 3 in 18 and 12% yield, respectively. For hexyl-substituted precursor 21, the oxidative aromatization led to mixtures of different products, and the desired conjugated macrocycle could not be isolated. This was likely caused by an acidcatalyzed isomerization of the double bonds in the DBP units, as shown for bromo-substituted 12 in Scheme 2. Due to the bent structure of isomerization product 22 (see solid-state structure in Scheme 2), such an isomerization in the corresponding macrocycle would relieve strain. We observed the formation of 22 as a side product and its isomerization to 12 in the first step of the synthetic route shown in Scheme 1. Here, the formation of 12 was favored due

Figure 1. Dibenzo[a,e]pentalene (DBP, 1), [2]DBP[12]CPP nanohoops 2 and 3, synthesized in this study, methyl-substituted nanohoop 4, used for calculations, and model compounds 5−7.

Scheme 1. Synthesis of [2]DBP[12]CPP Nanohoops 2 and 3 and Hexyl-Substituted Precursor 21

B

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

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torsional angle between the phenyl rings assumed an average value of ΘDihedral = 36°, which was close to that in linear paraphenylenes.11 Cyclic voltammetry provided information on the oxidation and reduction potentials (Figure 3 and Table 1). Mesitylsubstituted [2]DBP[12]CPP 2 showed a reversible reduction wave and two reversible oxidations (Figure 3a). Compared to planar model compound 5 (Figure 3c, structure in Figure 1), the reduction was shifted to higher potential by 0.14 V due to the bending of the DBP units, and it most likely originated from the latter because CPPs do not show reductions in that potential range.11 The two oxidation waves of nanohoop 2 might have either corresponded to one-electron oxidations of each of the two DBP units or to oxidations of the DBPs and the sexiphenyl units. The oxidation potential of [12]CPP lies at a similar half-wave potential of 0.83 V vs Fc/Fc+.12 Relative to planar model compound 5, the first oxidation in [2]DBP[12]CPP 2 was shifted to lower potential by 0.10 V, and the second one lay 0.17 V higher. We have demonstrated before that the HOMO/LUMO energy in DBP derivatives can be tuned by substitution, in particular at the 5,10-positions (numbering in Figure 1).34,40,42 Bis(trifluoromethylphenyl)substituted [2]DBP[12]CPP 3 displayed two reversible reduction waves, the first of which was shifted to lower potential by 0.46 V relative to mesityl-substituted ring 2 (Figure 3b). Compared to planar model compound 6 (structure shown in Figure 1), both reduction processes took place at 0.09 V higher potentials due to the bending of the DBP units (Figure 3d). Nanohoop 3 furthermore showed two overlapping oxidation waves, the first of which was shifted to higher potential (by 0.17 V) compared to ring 2 and to lower potential (by 0.26 V) relative to planar model compound 6. These processes might again have originated from the two DBP units alone or from the sexiphenyl parts and DBP units. Calculations showed that HOMO and HOMO−1 as well as the LUMO and LUMO+1 of nanohoop 4 were localized on the DBP units and were almost degenerate in energy (Figure 4). HOMO−2 and LUMO+2 were localized on the psexiphenyl parts of the ring. Hence, the frontier molecular orbitals were separated between the DBP units and the psexiphenyl moieties. This separation of orbitals was also reflected in the absorption spectra of [2]DBP[12]CPPs 2 and 3 (Figure 5). Comparison with planar model compounds 5 and 6 as well as with [12]CPP showed that the absorption spectra of the nanohoops reflected the presence of both molecular units: the DBPs and the p-sexiphenyl structures. The largest absorption bands with maxima at 346 nm (log10 ε = 5.4) for 2 and 342 nm (log10 ε = 5.2) for 3 stemmed from the p-sexiphenyl parts (absorbance maximum of [12]CPP at 339 nm, log10 ε = 5.1,11,12 absorbance maximum of p-sexiphenyl at 320 nm, log10 ε = 4.744). The absorption bands above 400 nm with maxima at 411 and 438 nm (log10 ε = 4.5 and 4.4, respectively) for 2 and maxima at 435 and 461 nm (log10 ε = 4.3 each) for 3 were ascribed to the DBP units. These appeared red-shifted by 26− 34 nm compared to planar model compounds 5 and 6. Characteristic was the weak absorption band from the HOMO to LUMO transition at 503 nm for 2 and the shoulder around 550 nm in 6. This transition is forbidden in planar and centrosymmetric DBP derivatives according to Laporte’s rule when both orbitals are of au symmetry.45 Due to the bending and symmetry breaking of the DBP units in nanohoop 2, however, this transition had a significantly higher intensity

Scheme 2. Double Bond Isomers12 and 22 and Molecular Structures of Both Compounds in the Solid Statea

a

Displacement ellipsoids are shown at 50% probability; hydrogen atoms are omitted for clarity.

to its lower relative energy compared to 22 (energy difference 8.4 kcal mol−1 (PW6B95-D3/def2-QZVP//TPSS-D3/def2TZVP)). The structures of 12 and 22 were confirmed by single crystal X-ray diffraction (Scheme 2, see Supporting Information for details). Planar model compounds 5 and 6 were synthesized from DBP derivatives 13 and 11, respectively, using Suzuki− Miyaura reactions (Scheme 3). Scheme 3. Synthesis of Planar Model Compounds 5 and 6

Optoelectronic and Structural Properties. DFT calculations (TPSS-D3/def2-TZVP) showed that the methylsubstituted ring 4 possessed a diameter of 2.1 nm, similar to that of [15] and [16]CPP (Figure 2).12 The strain energy, calculated using a homodesmotic equation (see Supporting Information, TPSS-D3/def2-TZVP//PBE/def2-SV(P)), amounted to 36.5 kcal mol−1. This was similar to the strain energy of [16]CPP of 35.6 kcal mol−1 (B3LYP/6-31G*), which has a similar diameter.41 The bending of the DBP units was characterized using the bend angle ΘDBP (Figure 2), describing the bending of the entire DBP framework. In 4, ΘDBP amounted to 36.7°, which indicated a small distortion of the DBP moieties from planarity compared to DBP-phanes reported previously with bend angles up to 91.9°.37 The C

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

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Figure 2. Calculated structure of [2]DBP[12]CPP nanohoop 4 (TPSS-D3/def2-TZVP) and geometrical parameters.

Figure 3. Cyclic voltammograms of nanohoops 2 (a) and 3 (b) and planar model compounds 5 (c) and 6 (d) (0.1 mM (2, 3) or 1 mM (5, 6) in CH2Cl2, 0.1 M n-Bu4NPF6, scan rate 0.05−0.2 V s−1, glassy carbon electrode).

(log10 ε = 3.3) than in planar 5, where it was solely visible as a shoulder. This band was also responsible for the red or brownish color of nanohoops 2 and 3. In [2]DBP[12]CPP nanohoop 3 as well as in model compound 6 with electronwithdrawing substituents, all absorption bands of the DBP units appeared bathochromically shifted compared to the mesityl-substituted compounds. We had observed the same effect in DBP-phanes reported previously.37 Mesityl-substituted nanohoop 2 showed fluorescence with an emission maximum at 471 nm and a shoulder at 505 nm (Figure 6). This most likely originated from the p-sexiphenyl units. In comparison, [12]CPP emits with a maximum at 450 nm.11 The emission was very weak, however, with a quantum yield below 1%.

Figure 4. Selected orbital energies and plots for methyl-substituted [2]DBP[12]CPP nanohoop 4 (B3LYP-D3/def2-TZVP//TPSS-D3/ def2-TZVP).

Nucleus independent chemical shift (NICS) values46 provided information on the (anti)aromatic character of the DBP units. In methyl-substituted [2]DBP[12]CPP nanohoop 4, NICS(0)iso in the five- and six-membered rings amounted to 8.6 and −4.7, respectively (calculated with the GIAO method on the B3LYP/6-31G* level of theory). In planar model compound 7, these values lay at 10.4 and −3.8, respectively. This indicated a slightly reduced antiaromaticity in the pentalene units of nanohoop 4 and a small increase in

Table 1. Electrochemicala and Optical Data for [2]DBP[12]CPP Nanohoops 2 and 3 and Planar Model Compounds 5 and 6 2 3 5 6

E1/2,Ox (V)b

E1/2,Red (V)b

EHOMO (eV)c

ELUMO (eV)d

0.72/0.99 0.89 0.82 1.08

−1.87 −1.41/−1.77 −2.01 −1.50/−1.86

−5.23 −5.63 −5.61 −5.83

−3.40 −3.81 −3.47 −3.92

λmax (nm) (log10 ε) 346 342 298 263

(5.36) (5.24) (4.89) (4.40)

Eg,opt (eV)e 1.83 1.82 2.14 1.91

1 mM in CH2Cl2, 0.1 M n-Bu4NPF6, scan rate 0.1 V s−1, glassy carbon electrode. bVersus Fc/Fc+. cFrom the onsets of the first oxidation peak, assuming an ionization energy of 4.8 eV for ferrocene.43 dELUMO = EHOMO + Eg,opt. eIn CH2Cl2, from the onsets of the longest wavelength absorption band. a

D

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

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investigations of conjugated nanohoops containing antiaromatics.

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EXPERIMENTAL PROCEDURES

Materials and Methods. Commercially available chemicals were purchased and used directly without further purification unless otherwise noted. Moisture- or oxygen-sensitive reactions were carried out in dried glassware, heated under vacuum (10−3 mbar), using standard Schlenk techniques in a dry argon atmosphere (Argon 5.0 from Sauerstoffwerk Friedrichshafen). Anhydrous solvents (THF, toluene, CH2Cl2) were obtained from an MBRAUN solvent purification system (MB-SPS-800) and stored over 3 Å molecular sieves for a minimum duration of 48 h before use. Other anhydrous solvents were obtained by drying over activated molecular sieves (3 Å) for several days. Cyclohexane for flash chromatography was purchased in technical grade and purified by distillation using a rotary evaporator. Other solvents were purchased and used in analytical or HPLC grade. Analytical thin layer chromatography was carried out using silica gel-coated aluminum plates with a fluorescence indicator (Merck 60 F254). Detection was carried out by using short wave UV light (λmax = 254 nm). Flash column chromatography was carried out using silica gel 60, grain size 40−63 μm (230−400 mesh) from Machery-Nagel. NMR spectra were recorded at 300 K unless otherwise noted, on the following spectrometers: Bruker Avance III HD [300.1 MHz (1H), 282.4 MHz (19F)], Bruker Avance II [400.1 MHz (1H), 100.6 MHz (13C), 376.5 MHz (19F)], and Bruker Avance III HD [500.3 MHz (1H), 125.8 MHz (13C), 470.8 MHz (19F)]. Chemical shifts are reported in parts per million (ppm, δ scale) relative to the signal of tetramethylsilane (δ 0.00 ppm). 1H NMR spectra are referenced to tetramethylsilane as an internal standard or the residual solvent signal of the respective solvent: CDCl3: δ 7.26 ppm; CD2Cl2: δ 5.32 ppm. 13C NMR spectra are referenced to the following signals: CDCl3: δ 77.16 ppm; CD2Cl2: δ 53.84 ppm. 19F NMR spectra are referenced to tetramethylsilane following IUPAC recommendations.47 Analysis followed first order, and the following abbreviations for multiplets were used: singlet (s), broad singlet (br. s), doublet (d), triplet (t), quartet (q), septet (sept), multiplet (m), and combinations thereof, i.e. doublet of doublets (dd). Coupling constants (J) are given in Hertz (Hz). High resolution mass spectra were measured on a Thermo Fisher Scientific Inc. Exactive via electron spray ionization (ESI) or atmospheric pressure chemical ionization (APCI) with an orbitrap analyzer. UV/vis absorption spectra were measured on a PerkinElmer Lambda 950 and were performed in a 10 mm quartz cuvette. Fluorescence spectra were measured on a PerkinElmer LS55 and were performed in a 10 mm quartz cuvette. Oligomer mixtures were measured by using an analytical GPC unit composed of an IsoPump G1310A, a ALS G1329A auto sampler, a VWD G1314B UV-detector, and an RID G1362A RI detector from Agilent Technologies. A set of three columns was used (PSS Polymer Standard Service GmbH, polystyrene, 8 × 300 mm with a porosity of 102, 103, and 105 Å with integrated precolumn). As eluent stabilized THF with 2.5 ppm BHT (p. a., Acros) was used with a flow rate of 1 mL/min. For calibration, a polystyrene standard by PSS Polymer Standard Service GmbH was used. For semipreparative gel permeation chromatography a Shimadzu Prominence GPC system composed of a SPD-20A UV-detector, a CTO-20AC column oven, a SIL-20AHT Autosampler, a RID-10A RI-detector, and a set of three columns (PSS SDV preparative linear S) with one precolumn was used. Distilled THF was used as eluent with a flow rate of 6 mL/min at 35 °C. Cyclic voltammetry measurements were performed with a PGSTAT128N potentiostat from Metrohm Autolab inside an argon-filled glovebox at room temperature in CH2Cl2 solution (0.1 or 1 mM substance concentration) with a glassy carbon working electrode (d = 2 mm), a platinum rod counter electrode, a Ag/AgNO3 reference electrode (containing a silver wire immersed in an inner chamber filled with 1 M AgNO3 and 1 M n-Bu4NPF6 in anh. MeCN), and 0.1 M nBu4NPF6 as the supporting electrolyte. All cyclic voltammograms were measured vs a Fc/Fc+ standard.

Figure 5. Absorption spectra of [2]DBP[12]CPP nanohoops 2 and 3 as well as model compounds 5 and 6 in CH2Cl2.

Figure 6. Absorption and emission spectrum of mesityl-substituted [2]DBP[12]CPP nanohoop 2 CH2Cl2.

aromatic character in the six-membered rings of the DBP units compared to the planar DBP derivative 7. We previously observed a similar trend upon bending of the DBP units in DBP-phanes.37

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CONCLUSION In summary, we herein presented the first synthetic report on conjugated nanohoops incorporating antiaromatic units. The dibenzo[a,e]pentalene-containing [12]CPPs 2 and 3 were synthesized in six steps, including a nickel-mediated macrocyclization reaction. Optoelectronic measurements and (TD)DFT calculations showed the presence of both π-systems in [2]DBP[12]CPP nanohoops 2 and 3, the DBP units and the sexiphenyl linkers. The nanohoops displayed ambipolar electrochemical behavior due to the presence of the dibenzopentalene units, and 2 was fluorescent because of the sexiphenyl linkers. Incorporating the dibenzo[a,e]pentalene units in the [12]CPP framework reduced their antiaromatic character, as seen from nucleus-independent chemical shift calculations. When electron-withdrawing substituents were attached to the DBP units, the orbital energies of nanohoop 3 were lowered. This report can stimulate further syntheses and E

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry Synthetic Manipulations. 2,7-Dibromo-5,10-dimesitylindeno[2,1-a]indene (10). The synthesis of 10 proceeded via diol 23, whose structure is shown in the Supporting Information. 2,7-Dibromo-5,10-dimesityl-4b,5,9b,10-tetrahydroindeno[2,1-a]indene-5,10-diol (23). Anhydrous CeCl3 (1.89 g, 7.65 mmol, 3.00 equiv) was dried at 130 °C in vacuo (10−3 mbar) for 3 h. After cooling to rt, argon was introduced, and anhydrous THF (25 mL) was added. The mixture was stirred at rt for 18 h. A solution of mesityl magnesium bromide (0.94 M, 8.14 mL, 7.65 mmol, 3.00 equiv), precooled to −10 °C, was added to the CeCl3 suspension at −10 °C. The resulting mixture was stirred at −10 °C for 3 h. Diketone 937 (1.00 g, 2.55 mmol, 1.00 equiv) was added, and the mixture was stirred at −10 °C for 3 h. The solution was allowed to warm to rt and was stirred for another 3 h. Aq. AcOH (10%, 10 mL) was added, and the mixture was extracted with CH2Cl2, washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/EtOAc: 9/1). Title compound 23 (1.20 g, 5.66 mmol, 74%) was obtained as an off-white solid. Rf 0.76 (cyclohexane/EtOAc: 9/1); 1H NMR (400 MHz, CDCl3) δ 7.40 (dd, J = 8.0, 1.9 Hz, 2H), 7.14 (d, J = 1.8 Hz, 2H), 7.08 (d, J = 8.1 Hz, 2H), 6.93−6.92 (m, 2H), 6.85−6.82 (m, 2H), 4.52 (s, 2H), 3.01 (s, 2H), 2.55 (s, 6H), 2.30 (s, 6H), 1.73 (s, 6H); 13C NMR (101 MHz, CDCl3) δ 154.9, 138.3, 137.8, 136.7, 136.3, 135.6, 132.8, 131.9, 131.5, 127.9, 126.8, 122.6, 87.7, 61.7, 25.5, 23.8, 20.6; HRMS (pos. APCI): m/z calcd for C34H31Br2O1+ 613.0736 [M−OH]+, found 613.0729. 2,7-Dibromo-5,10-dimesitylindeno[2,1-a]indene (10). Diol 23 (500 mg, 790 μmol, 1.00 equiv) and p-toluenesulfonic acid monohydrate (14 mg, 79.0 μmol, 0.1 equiv) were dissolved in toluene (80 mL). The solution was refluxed for 5 h, cooled to rt, and stirred at that temperature overnight. The solvent was removed under reduced pressure, and the residue was diluted with cyclohexane and CH2Cl2, washed with water and brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the title compound 10 (427 mg, 719 μmol, 91%) was obtained as a dark-red solid. Mp > 220 °C; 1H NMR (500 MHz, CDCl3) δ 7.00−6.98 (m, 4H), 6.90 (dd, J = 7.8, 1.8 Hz, 2H), 6.62 (d, J = 1.7 Hz, 2H), 6.40 (d, J = 7.8 Hz, 2H), 2.36 (s, 6H), 2.25 (s, 12H); 13C NMR (126 MHz, CDCl3) δ 152.4, 144.6, 139.7, 138.1, 136.2, 133.4, 130.0, 128.8, 128.6, 125.4, 123.3, 122.3, 21.3, 20.3; HRMS (pos. APCI): m/z calcd for C34H29Br2O1+ 611.0580 [M+OH]+, found 611.0583. 2,2′-(5,10-Dimesitylindeno[2,1-a]indene-2,7-diyl)bis(4,4, 5,5-tetramethyl-1,3,2-dioxaborolane) (13). Dibenzopentalene 10 (400 mg, 671 μmol, 1.00 equiv), bis(pinacolato)diboron (375 mg, 1.48 mmol, 2.20 equiv), Pd(dppf)Cl2 (34.0 mg, 47.0 μmol, 7 mol %), and KOAc (395 mg, 4.02 mmol, 6.00 equiv) were suspended in anhydrous 1,4dioxane (13.4 mL) and stirred at 85 °C for 19 h under argon atmosphere. Water was added, and the mixture was extracted with CH2Cl2, washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/CH2Cl2: 2/1 to 1/1). The title compound 13 (329 mg, 240 μmol, 71%) was obtained as a red solid. Rf 0.38 (cyclohexane/CH2Cl2: 1/1); mp > 220 °C; 1H NMR (500 MHz, CH2Cl2) δ 7.21 (dd, J = 7.3, 1.0 Hz, 2H), 7.04− 7.02 (m, 4H), 6.80−6.79 (m, 2H), 6.55 (dd, J = 7.3, 0.9 Hz, 2H), 2.38 (s, 6H), 2.24 (s, 12H), 1.25 (s, 24H); 13C NMR* (126 MHz, CDCl3) δ 149.6, 144.2, 141.2, 138.1, 137.4, 136.4, 135.0, 130.0, 128.4, 128.0, 121.5, 83.7, 24.8, 21.3, 20.3; HRMS (pos. ESI): m/z calcd for C46H53B2O4+ 691.4124 [M + H]+, found 691.4121.*The signal for the quaternary carbon atom connected to boron could not be detected in the 13C NMR spectrum because of coupling to 10B and 11B. 2,7-Bis(4-((1s,4s)-4-(4-bromophenyl)-1,4-bis(methoxy methoxy)cyclohexyl)phenyl)-5,10-dimesitylindeno[2,1-a]indene (16). Lshaped corner unit 839 (114 mg, 224 μmol, 5.00 equiv), dibenzopentalene 13 (31.0 mg, 45.0 μmol, 1.00 equiv), and Pd(dppf)Cl2 (3.0 mg, 4.5 μmol, 10 mol %) were added to a mixture of toluene (20 mL) and aq. K2CO3 (2.0 M, 2.2 mL, 4.50 mmol, 100 equiv). The mixture was purged with argon for 30 min and then refluxed for 24 h under argon atmosphere. Water was added, and the mixture was extracted with CH2Cl2. The organic layer was washed

with brine and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, CH2Cl2/EtOAc: 19/1 to 1/1). The title compound 16 (41.0 mg, 31.5 μmol, 70%) was obtained as a red solid. Rf 0.44 (CH2Cl2/EtOAc: 9/1); mp > 220 °C; 1H NMR (400 MHz, 333 K, CDCl3) δ 7.45−7.41 (m, 4H), 7.40−7.36 (m, 8H), 7.32−7.28 (m, 4H), 7.01−7.00 (m, 4H), 6.97 (dd, J = 7.6, 1.6 Hz, 2H), 6.71 (dd, J = 1.7, 0.6 Hz, 2H), 6.63 (dd, J = 7.6, 0.5 Hz, 2H), 4.43 (s, 4H), 4.42 (s, 4H), 3.40 (s, 6H), 3.39 (s, 6H), 2.38 (s, 6H), 2.32 (s, 12H), 2.36− 2.26 (m, 8H), 2.17−1.95 (m, 8H); 13C NMR (101 MHz, CDCl3) δ 151.5, 144.8, 140.5, 140.3, 139.7, 137.6, 136.4, 134.1, 131.5, 129.7, 128.7, 128.5, 127.1, 126.7, 125.9, 122.4, 121.7, 121.1, 92.3, 92.2, 78.1, 77.9, 56.1, 33.0*, 21.3, 20.4; HRMS (pos, ESI): m/z calcd, for C78H81Br2O8+ 1303.4293 [M + H]+, found 1303.4306.*Broad signal assigned to (missing) cyclohexane carbons. Cyclic Precursor 19. U-shaped unit 16 (50 mg, 38 μmol, 1.00 equiv), bis(1,5-cyclooctadiene)nickel(0) (26 mg, 96 μmol, 2.50 equiv), and 2,2′-bipyridine (18 mg, 115 μmol, 3.00 equiv) were dissolved in anhydrous THF (38 mL). The mixture was stirred at rt for 40 min and then at 65 °C for 2 d under argon atmosphere. The mixture was cooled to rt, and passed through a pad of Celite (CH2Cl2/EtOAc). The solvent was removed under reduced pressure, and the crude product was purified by semipreparative gel permeation chromatography (THF) to yield the product 19 (20 mg, 17 μmol, 46%) as a dark-red solid. Mp > 220 °C; MP = 1995 Da (vs polystyrene standard); 1H NMR (500 MHz, CDCl3) δ 7.53−7.44 (m, 16H), 7.42−7.32 (m, 16H), 6.95* (s, 8H), 6.95* (dd, J = 7.6, 1.6 Hz, 4H), 6.68 (d, J = 1.6 Hz, 4H), 6.61 (d, J = 7.6 Hz, 4H), 4.44 (s, 8H), 4.43 (s, 8H), 3.41 (s, 12H), 3.40 (s, 12H), 2.31 (s, 12H), 2.28 (s, 24H), 2.38−2.24* (m, 16H), 2.21−1.93 (m, 16H); 13C NMR (126 MHz, CDCl3) δ 151.5, 144.8, 140.6, 140.3, 139.7, 139.6, 137.6, 136.4, 134.1, 129.7, 128.4, 127.4**, 127.2**, 126.9, 126.7, 125.9, 122.3, 121.1, 92.3, 92.3, 78.2, 78.1, 56.1, 33.1***, 21.3, 20.4; HRMS (pos. ESI): m/ z calcd for C 156 H 160 O 16 Na 2312.1599 [M + Na] + , found 2312.1602.*Signal overlap. **Broad signal. ***Broad signal assigned to (missing) cyclohexane carbons. Mesityl-Substituted Nanohoop [2]DBP[12]CPP 2. Cyclic precursor 19 (5.0 mg, 2.0 μmol, 1.00 equiv) and NaHSO4·H2O (10 mg, 65 μmol, 30.0 equiv) were dissolved in mesitylene (1 mL) and DMSO (0.5 mL) and stirred at 155 °C in air for 2 d. The mixture was passed through a pad of Celite (CH2Cl2/EtOAc). The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/CH2Cl2: 1/0 to 1/1) followed by semipreparative gel permeation chromatography (THF) to yield cycle 2 (1.5 mg, 0.8 μmol, 38%) as a dark-red solid. Mp > 220 °C; MP = 1507 Da (vs polystyrene standard); 1H NMR (400 MHz, CDCl3) δ 7.72−7.65 (m, 24H), 7.65−7.61 (m, 8H), 7.59−7.55 (m, 8H), 7.54−7.50 (m, 8H), 7.09 (dd, J = 7.9, 1.7 Hz, 4H), 7.00−6.98 (m, 8H), 6.78 (dd, J = 1.8, 0.5 Hz, 4H), 6.61 (dd, J = 7.9, 0.5 Hz, 4H), 2.39 (s, 12H), 2.22 (s, 24H); 13C NMR (101 MHz, CDCl3) δ 151.5, 144.5, 139.9, 139.8, 139.2, 139.2, 139.2, 139.0, 138.9, 138.8, 137.5, 136.5, 134.0, 129.8, 128.4, 127.5, 127.4, 127.4, 127.3**, 126.9, 125.7, 122.7, 120.4, 21.3, 20.3; HRMS (pos. ESI): m/z calcd for C140H104* 1784.8133 [M]+, found 1784.8130. *The radical cation M+ (although unusual for ESI mass spectrometry) was detected as the molecule ion peak. This phenomena can also be seen for other molecules in this work and was described in the literature as a competing ionization process in electrospray mass spectrometry for molecules with low ionization potentials and in aprotic solvents.48 **Overlapping signal assigned to two carbon atoms. 5,10-Bis(3,5-bis(trifluoromethyl)phenyl)-2,7-dibromoindeno[2,1a]indene (11). The synthesis of 11 proceeded via diol 24, whose structure is shown in the Supporting Information. 5,10-Bis(3,5-bis(trifluoromethyl)phenyl)-2,7-dibromo-4b,5,9b,10tetrahydroindeno[2,1-a]indene-5,10-diol (24). Anhydrous CeCl3 (959 mg, 3.89 mg, 3.10 equiv) was dried at 130 °C in vacuo (2 × 10−3 mbar) for 2 h. After cooling to rt, argon was introduced, and anhydrous THF (15 mL) was added. The mixture was stirred at rt for 18 h. Magnesium turnings (94 mg, 3.82 mmol, 3.00 equiv) were heated in vacuo (2 × 10−3 mbar). After cooling to rt, argon was F

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry

polystyrene standard); Rf 0.40 (CH2Cl2/EtOAc: 9/1); 1H NMR (500 MHz, 333 K, CDCl3) δ 8.14 (s, 4H), 8.00 (s, 2H), 7.55−7.40 (m, 12H), 7.31−7.28 (m, 4H), 7.13 (dd, J = 7.8, 1.6 Hz, 2H), 7.08 (d, J = 1.5 Hz 2H), 7.06 (d, J = 7.8 Hz 2H), 4.44 (s, 4H), 4.42 (s, 4H), 3.41 (s, 6H), 3.40 (s, 6H), 2.35−2.28 (m, 8H), 2.10−2.04 (m, 8H); 13C NMR (126 MHz, CDCl3) δ 149.7, 145.2, 141.8, 139.4, 138.1, 135.7, 132.7, 132.6 (q, J = 33.5 Hz), 131.6, 128.8*, 128.6*, 127.5*, 127.2, 126.5, 124.3, 122.7*, 122.5, 122.1, 121.8, 121.1, 92.3, 92.2, 78.1, 77.9, 56.1, 33.0**; 19F NMR (471 MHz, CDCl3) δ − 62.8; HRMS***. *Broad signal. **Broad signal assigned to (missing) cyclohexane carbons. ***Molecule ion could not be detected via APCI or ESI mass spectrometry. Cyclic Precursor 20. U-shaped unit 17 (19 mg, 13 μmol, 1.00 equiv), bis (1,5-cyclooctadiene)nickel(0) (11 mg, 36 μmol, 3.00 equiv), and 2,2′-bipyridine (8 mg, 51 μmol, 4.00 equiv) were dissolved in anhydrous THF (13 mL) and stirred at rt for 50 min and then at 65 °C for 48 h under argon atmosphere. The mixture was passed through a pad of Celite (CH2Cl2/EtOAc). The solvent was removed under reduced pressure, and the crude product was purified by preparative gel permeation chromatography (THF). The title compound 20 (6 mg, 2 μmol, 35%) was obtained as a red solid. MP = 2520 Da (vs polystyrene standard); 1H NMR (500 MHz, 323 K, CDCl3) δ 8.10 (s, 8H), 7.94 (s, 4H), 7.54−7.50 (m, 8H), 7.49−7.44 (m, 16H), 7.44−7.39 (m, 8H), 7.11 (dd, J = 7.8, 1.6 Hz, 4H), 7.06 (d, J = 1.6 Hz, 4H), 7.03 (d, J = 7.8 Hz, 4H), 4.45 (s, 8H), 4.44 (s, 8H), 3.40 (s, 12H), 3.39 (s, 12H), 2.42−2.30 (m, 16H), 2.18−2.03 (m, 16H); 13C NMR*; HRMS (pos. ESI): m/z calcd for C152H128O16F24 2664.8814 [M]+•, found 2664.8831. *No 13C NMR spectrum could be obtained due to the low solubility of the compound. 3,5-Bis(trifluoromethyl)phenyl-Substituted Nanohoop [2]DBP[12]CPP 3. Cyclic precursor 20 (12 mg, 5 μmol, 1 equiv) and NaHSO4·H2O (19 mg, 135 μmol, 30.0 equiv) were dissolved in mesitylene (2 mL) and DMSO (2 mL) and stirred at 155 °C in air for 21 h. The mixture was passed through a pad of Celite (CH2Cl2/ EtOAc). The solvent was removed under reduced pressure, and the crude product was purified by semipreparative gel permeation chromatography (THF). The title compound 3 (2.7 mg, 1.4 μmol, 28%) was obtained as a red solid. MP = 2190 Da (vs polystyrene standard); 1H NMR (300 MHz, CDCl3) δ 8.11 (s, 8H), 7.99 (s, 4H), 7.76−7.59 (m, 40H), 7.59−7.50 (m, 8H), 7.23 (dd, J = 8.6, 1.6 Hz, 4H), 7.14 (d, J = 1.7 Hz, 4H), 7.08 (d, J = 8.0 Hz, 4H); 13C NMR (126 MHz, CDCl3) δ 149.9, 144.9, 141.5, 139.9, 139.2, 139.1, 139.0, 138.9, 138.4, 137.9, 135.8, 132.6 (q, J = 34.3 Hz), 128.7, 127.7, 127.6, 127.6, 127.4, 127.0, 124.4, 122.9, 122.7, 122.2, 120.9 ppm; 19F NMR (471 MHz, CDCl3) δ −63.0; HRMS (pos. ESI): m/z calcd for C136H72F24* 2160.5245 [M]+•, found 2160.5266. *The radical cation M+ (although unusual for ESI mass spectrometry) was detected as the molecule ion peak. This phenomena can also be seen for other molecules in this work and was described in the literature as a competing ionization process in electrospray mass spectrometry for molecules with low ionization potentials and in aprotic solvents.50 2,7-Dibromo-5,10-dihexylindeno[2,1-a]indene (12). The synthesis of 12 proceeded via diol 25, whose structure is shown in the Supporting Information. 2,7-Dibromo-5,10-dihexyl-4b,5,9b,10-tetrahydroindeno [2,1-a]indene-5,10-diol (25). Anhydrous CeCl3 (0.38 g, 1.55 mmol, 3.03 equiv) was dried at 130 °C in vacuo (10−3 mbar) for 3 h. After cooling to rt, argon was introduced, and anhydrous THF (25 mL) was added. The mixture was stirred at rt for 18 h. A solution of n-hexylmagnesium bromide (0.56 M, 2.73 mL, 1.53 mmol, 3.00 equiv) was cooled to 0 °C and added to the CeCl3 suspension at 0 °C. The resulting mixture was stirred at 0 °C for 3 h. Diketone 9 (0.20 g, 0.51 mmol, 1.00 equiv) was added, and the mixture was stirred at 0 °C for 3 h. The solution was allowed to warm to rt and was stirred for another 1 h. Aq. AcOH (10%, 10 mL) was added, and the mixture was extracted with CH2Cl2, washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/EtOAc, 4/1). The title compound 25 (0.21 g, 1.15 mmol, 74%) was obtained as an off white solid. Rf 0.76 (cyclohexane/EtOAc: 9/1); 1H NMR

introduced, and 3,5-bis(trifluoromethyl)phenyl bromide (0.66 mL, 1.12 g, 3.82 mmol, 3.00 equiv) and anhydrous THF (2 mL) were added. The mixture was heated occasionally over a period of 2 h. The two mixtures were cooled to −10 °C, and the Grignard solution was added to the CeCl3 suspension. The resulting mixture was stirred at −10 °C for 2 h. Diketone 937 (500 mg, 1.28 mmol, 1.00 equiv) was added, and the resulting mixture was stirred at −10 °C for 3 h. The solution was allowed to warm to rt and was stirred for 18 h. Aq. AcOH (10%, 10 mL) was added, and the mixture was extracted with CH2Cl2, washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/EtOAc: 15/1). Diol 24 (810 mg, 0.98 mmol, 77%) was obtained as a beige solid. Rf 0.40 (cyclohexane/EtOAc: 15/1); 1H NMR (500 MHz, CDCl3) δ 7.95 (s, 6H), 7.56 (dd, J = 8.1, 1.9 Hz, 2H), 7.12 (d, J = 1.8 Hz, 2H), 6.93 (d, J = 8.1 Hz, 2H), 4.33 (s, 2H), 3.25−3.22 (m, 2H); 13C NMR (126 MHz, CDCl3) δ 150.6, 147.0, 138.0, 133.6, 132.3 (q, J = 33.5 Hz), 128.4, 127.2, 126.4, 123.7, 123.3 (q, J = 273 Hz), 122.2−122.1 (m), 83.4, 63.7; 19F NMR (282 MHz, CDCl3) δ − 62.7; HRMS (neg. ESI): m/z calculated for C32H15Br2F12O2 816.9253 [M−H]−, found 816.9257. 5,10-Bis(3,5-bis(trifluoromethyl)phenyl)-2,7-dibromo indeno[2,1-a]indene (11). Diol 24 (810 mg, 980 μmol, 1.00 equiv) and ptoluenesulfonic acid monohydrate (94 mg, 490 μmol, 0.50 equiv) were dissolved in toluene (100 mL). The solution was refluxed for 5 h. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/CH2Cl2: 10/1). The title compound 11 (579 mg, 740 μmol, 75%) was obtained as a brown solid. Rf 0.60 (cyclohexane/ CH2Cl2: 10/1); 1H NMR (500 MHz, CDCl3) δ 8.04−8.02 (m, 4H), 8.02−8.00 (m, 2H), 7.09 (dd, J = 7.9, 1.7 Hz, 2H), 7.00 (d, J = 1.7 Hz, 2H), 6.84 (d, J = 7.9 Hz, 2H); 13C NMR (126 MHz, CDCl3) δ 150.5, 144.9, 138.0, 134.9, 132.9 (q, J = 33.2 Hz), 132.2, 131.4, 128.4, 125.8, 123.6, 123.2, 132.2−123.1 (m); 19F NMR (282 MHz, CDCl3) δ − 62.9; HRMS (pos. ESI): m/z calcd C32H12Br2F12 781.9109 [M]+•, found 781.9121. 2,2′-(5,10-Bis(3,5-bis(trifluoromethyl)phenyl)indeno[2,1-a]indene-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (14). Dibenzopentalene 11 (200 mg, 250 μmol, 1.00 equiv), bis(pinacolato)diboron (143 mg, 530 μmol, 2.20 equiv), Pd(dppf)Cl2 (11 mg, 15 μmol, 6 mol %), and KOAc (150 mg, 1.53 mmol, 6.00 equiv) were suspended in anhydrous 1,4-dioxane (5 mL). The resulting mixture was stirred at 85 °C for 18 h under argon atmosphere. Water was added, and the mixture was extracted with CH2Cl2 (3 × 100 mL), washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (borylated silica gel,49 cyclohexane/CH2Cl2: 10/1). The title compound 14 (208 mg, 240 μmol, 93%) was obtained as a red solid. Rf 0.50 (cyclohexane/ CH2Cl2: 10/1); mp > 220 °C; 1H NMR (500 MHz, CDCl3) δ 8.11 (br. s, 4H), 8.00−7.99 (m, 2H), 7.41 (dd, J = 7.4, 0.9 Hz, 2H), 7.33− 7.28 (m, 2H), 7.02 (dd, J = 7.3, 0.7 Hz, 2H), 1.30 (s, 24H); 13C NMR (126 MHz, CDCl3) δ 150.5, 144.9, 138.0, 134.9, 132.9 (q, J = 33.2 Hz), 132.2, 131.4, 128.4, 125.8, 123.6, 123.2, 132.2−123.1 (m); 84.1, 24.9; 19F NMR (282 MHz, CDCl3) δ −62.9; HRMS (pos. ESI): m/z calcd for C44H36O4B2F12 878.2603 [M]+•, found 878.2596. 5,10-Bis(3,5-bis(trifluoromethyl)phenyl)-2,7-bis(4-((1s,4s)-4-(4bromophenyl)-1,4-bis(methoxymethoxy) cyclohexyl)phenyl)indeno[2,1-a]indene (17). L-shaped corner unit 839 (234 mg, 457 μmol, 4.00 equiv) and dibenzopentalene 14 (100 mg, 114 μmol, 1.00 equiv) were dissolved in a mixture of toluene (40 mL) and aq. K2CO3 (2 M, 5.7 mL, 11.6 mmol, 100 equiv). The mixture was purged with argon for 2 h. Pd(dppf)Cl2 (8 mg, 11 μmol, 10 mol %) was added, and the mixture was refluxed for 24 h at 85 °C under argon atmosphere. The mixture was extracted with CH2Cl2. The combined organic layers were washed with brine and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, CH2Cl2/EtOAc: 19/1 to 1/1). The title compound 17 (74 mg, 49 μmol, 43%) was obtained as a brown solid. Mp > 220 °C; MP = 1507 Da (vs G

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

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The Journal of Organic Chemistry (400 MHz, CDCl3) δ 7.45 (dd, J = 8.2, 1.8 Hz, 2H), 7.43 (m*, 2H), 7.27 (dd, J = 8.2, 1.8 Hz, 2H), 3.89 (s, 2H), 2.16 (s, 2H), 2.05−1.88 (m, 4H), 1.54−1.45 (m, 4H), 1.40−1.28 (m, 12H), 0.92−0.89 (m, 6H); 13C NMR (101 MHz, CDCl3) δ 150.4, 138.6, 131.8, 127.9, 127.2, 122.0, 82.5, 55.9, 40.4, 31.7, 29.8, 24.6, 22.6, 14.0; HRMS (neg. APCI): m/z calcd for C28H35Br2O2+ 561.1009 [M−H]−, found 561.1010. *Part of the expected d lies under the preceding dd signal. **Part of the expected dd lies under the solvent signal. 2,7-Dibromo-5,10-dihexylindeno[2,1-a]indene (12). Diol 25 (66 mg, 0.16 mmol, 1.00 equiv) and p-toluenesulfonic acid monohydrate (28 mg, 0.16 mmol, 1.00 equiv) were dissolved in toluene (20 mL). The solution was refluxed for 24 h and cooled to rt. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/EtOAc, 2/1). The title compound 12 (61 mg, 156 μmol, 98%) was obtained as a deep red solid. 1H NMR (400 MHz, CDCl3) δ 7.05 (dd, J = 7.8, 1.8 Hz, 2H), 7.01 (d, J = 1.7 Hz, 2H), 6.93 (d, J = 7.8 Hz, 2H), 2.52 (t, J = 7.6 Hz, 4H), 1.66−1.56 (m, 4H), 1.46−1.37 (m, 4H), 1.34−1.24 (m, 12H), 0.91−0.84 (m, 6H); 13C NMR (101 MHz, CDCl3) δ 152.4, 143.1, 141.4, 134.1, 129.6, 124.4, 123.0, 121.4, 31.8, 29.6, 28.6, 26.7, 22.7, 14.1; HRMS (pos APCI): m/z calcd for C28H33Br2+ 527.0944 [M + H]+, found 527.0944. 2,2′-(5,10-Dihexylindeno[2,1-a]indene-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (15). Dibenzopentalene 12 (70 mg, 132 μmol, 1.00 equiv), bis(pinacolato)diboron (74 mg, 291 μmol, 2.20 equiv), Pd(dppf)Cl2 (7.0 mg, 9.0 μmol, 7 mol %), and KOAc (78 mg, 0.79 mmol, 6.00 equiv) were suspended in anhydrous 1,4-dioxane (6 mL) and stirred at 85 °C for 18 h under argon atmosphere. Water was added, and the mixture was extracted with CH2Cl2, washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/CH2Cl2, 1/1). The title compound 15 (60 mg, 96 μmol, 73%) was obtained as a red solid. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J = 7.3, 1.0 Hz, 2H), 7.33 (dd, J = 0.9, 0.7 Hz, 2H), 7.13 (dd, J = 0.9, 0.7 Hz, 2H), 2.65 (t, J = 7.6 Hz, 4H), 1.71−1.62 (m, 4H), 1.47−1.40 (m, 4H), 1.34 (s, 24H), 1.33− 1.25 (m, 12H); 13C NMR* (101 MHz, CDCl3) δ 149.5, 143.0, 142.7, 138.7, 134.5, 126.6, 121.2, 83.7, 31.7, 29.4, 28.8, 26.7, 24.9, 22.6, 14.1; HRMS (pos ESI): m/z calcd for C40H57B2O4+ 623.4437 [M + H]+, found 623.4432. *The signal for the quaternary carbon atom connected to boron could not be detected in the 13C NMR spectrum because of coupling to 10B and 11B. 2,7-Bis(4-((1s,4s)-4-(4-bromophenyl)-1,4-bis(methoxymethoxy)cyclohexyl)phenyl)-5,10-dihexylindeno[2,1-a]indene (18). L-shaped corner unit 8 (201 mg, 0.39 mmol, 3.30 equiv), dibenzopentalene 15 (73.0 mg, 0.12 mmol, 1.00 equiv), and Pd(dppf)Cl2 (14.0 mg, 20.0 μmol, 16 mol %) were added to toluene (22 mL) and aq. K2CO3 (2.0 M, 2.4 mL, 4.78 mmol, 40.0 equiv). The mixture was purged with argon for 60 min and then refluxed for 24 h under argon atmosphere. Water was added, and the mixture was extracted with CH2Cl2. The combined organic layers were washed with brine and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, CH2Cl2/EtOAc, 19/1 to 1/1). The title compound 18 (121 mg, 99 μmol, 83%) was obtained as a red solid. Mp > 220 °C; Rf 0.26 (CH2Cl2/EtOAc: 19/1); 1H NMR (500 MHz, 333 K, CDCl3) δ 7.56−7.47 (m, 8H), 7.47−7.42 (m, 4H), 7.36−7.29 (m, 4H), 7.18 (d, J = 8.1 Hz, 2H), 7.14−7.09 (m, 4H), 4.47 (s, 4H), 4.43 (s, 4H), 3.43 (s, 6H), 3.41 (s, 6H), 2.65 (t, J = 7.5 Hz, 4H), 2.42−2.25 (m, 8H), 2.21−1.98 (m, 8H), 1.76−1.62 (m, 4H), 1.53−1.40 (m, 4H), 1.38− 1.23 (m, 12H), 0.92−0.84 (m, 6H).; 13C NMR (126 MHz, 333 K, CDCl3) δ 151.5, 143.5, 141.5, 140.7, 139.8, 135.0, 131.6, 128.8, 127.3, 126.7, 125.8, 122.2, 121.8, 119.9, 92.5, 92.3, 78.2, 78.0, 56.0, 33.2*, 31.9, 29.7, 29.0, 26.9, 22.7, 14.1.; HRMS (pos ESI): m/z calcd for C72H84Br2O8+ 1234.4527 [M + H]+, found 1234.4535. *Broad signal assigned to (missing) cyclohexane carbons. Hexyl-Substituted Precursor 21. U-shaped unit 18 (50 mg, 40 μmol, 1.00 equiv), bis(1,5-cyclooctadiene)nickel(0) (28 mg, 101 μmol, 2.50 equiv), and 2,2′-bipyridine (19 mg, 121 μmol, 3.00 equiv) were dissolved in anhydrous THF (40 mL) and stirred at rt for 60

min and then at 65 °C for 60 h under argon atmosphere. The mixture was cooled to room temperature and passed through a pad of Celite (CH2Cl2). The solvent was removed under reduced pressure, and the crude product was purified by preparative gel permeation chromatography (THF) to yield the title compound 21 (12 mg, 11 μmol, 28%) as a deep red solid. MP = 2069 Da (vs polystyrene standard); 1H NMR (500 MHz, CDCl3) δ 7.57−7.55 (m, 8H), 7.54−7.51 (m, 8H), 7.51−7.48 (m, 12H), 7.15−7.13 (m, 4H), 7.11−7.08* (m, 8H), 4.50 (s, 8H), 4.48 (s, 8H), 3.43 (s, 12H), 3.42 (s, 12H), 2.63 (t, J = 7.6 Hz, 8H), 2.44−2.35 (m, 16H), 2.23−2.10 (m, 16H), 1.72−1.65 (m, 8H), 1.48−1.41 (m, 8H), 1.35−1.26 (m, 24H), 0.87−0.84 (m, 12H). 13C NMR (126 MHz, CDCl3) δ 151.5, 143.5, 141.5, 140.7, 139.9, 139.8, 135.0, 127.5, 127.4, 126.9, 126.7, 125.7, 122.1, 119.9, 92.5, 92.4, 78.3, 78.3, 78.2, 56.1, 56.0, 33.3**, 33.2**, 31.8, 29.7, 28.9, 27.1, 26.9, 22.7, 14.1.; HRMS (pos. ESI): m/z calcd for C144H168O16+ 2153.2327 [M]+, found 2153.2349. *Signal overlap. **Broad signal assigned to (missing) cyclohexane carbons. 2,5,7,10-Tetramesitylindeno[2,1-a]indene (5). DBP derivative 13 (50.0 mg, 70.0 μmol, 1.00 equiv) and 2-bromomesitylene (0.02 mL, 29.0 mg, 15.0 μmol, 2.00 equiv) were dissolved in a mixture of toluene (7 mL) and aq. K2CO3 (2.0 M, 0.7 mL, 1.4 mmol, 20.0 equiv). The mixture was purged with argon for 45 min. Pd(dppf)Cl2 (4.0 mg, 5.0 μmol, 7 mol %) was added, and the mixture was refluxed for 20 h under argon atmosphere. Water was added, and the mixture was extracted with CH2Cl2, washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane/EtOAc: 1/0 to 20/1). The title compound 5 (54 mg, 70.0 μmol, quant.) was obtained as a dark red solid. Rf 0.81 (cyclohexane/EtOAc: 20/1); mp > 220 °C; 1H NMR (500 MHz, CDCl3) δ 6.94−6.91 (m, 4H), 6.85−6.83 (m, 4H), 6.62 (dd, J = 7.4, 0.6 Hz, 2H), 6.52 (dd, J = 7.4, 1.5 Hz, 2H), 6.25 (dd, J = 1.5, 0.6 Hz, 2H), 2.32 (s, 12H), 2.31 (s, 6H), 2.26 (s, 6H), 2.03 (s, 12H); 13C NMR (126 MHz, CDCl3) δ 151.0, 144.8, 140.8, 139.3, 139.0, 137.3, 136.5, 136.3, 136.0, 133.3, 129.9, 128.3, 128.0, 127.8, 123.4, 122.0, 21.2, 21.0, 20.8, 20.4; HRMS (pos. APCI): m/z calcd for C52H51 675.3985 [M + H]+, found 675.3979. 5,10-Bis(3,5-bis(trifluoromethyl)phenyl)-2,7-dimesityl indeno[2,1-a]indene (6). DBP derivative 11 (200 mg, 255 μmol, 1.00 equiv) and 2-mesityl-4,4,5,5-tetramethyl-1,3,2-dioxa-borolane (151 mg, 613 μmol, 2.40 equiv) were dissolved in toluene (20 mL) and aq. K2CO3(2 M, 3.82 mL, 30.0 equiv). The mixture was purged with argon for 2 h. Pd(dppf)Cl2 (19 mg, 26 μmol, 10 mol %) was added, and the mixture was refluxed for 20 h at 85 °C under argon atmosphere. The mixture was extracted with CH2Cl2, washed with brine, and dried over Na2SO4. The solvent was removed under reduced pressure, and the crude product was purified by column chromatography (silica gel, cyclohexane). The title compound 6 (38 mg, 44 μmol, 10%) was obtained as a brown solid. Rf 0.40 (cyclohexane); mp > 220 °C; 1H NMR (500 MHz, CDCl3) δ 8.09 (s, 4H), 7.94 (s, 2H), 7.07 (dd, J = 7.5, 0.6 Hz, 2H), 6.92 (s, 4H), 6.69 (dd, J = 7.5, 1.5 Hz, 2H), 6.67 (dd, J = 1.5, 0.6 Hz, 2H), 2.30 (s, 6H), 2.08 (s, 12H); 13C NMR (126 MHz, CDCl3) δ 149.1, 145.2, 142.4, 138.1, 137.9, 137.0, 135.7, 135.7, 132.5 (q, J = 33.0 Hz), 129.5, 128.4, 128.3, 124.2, 123.5, 122.1, 122.0, 21.0, 20.6; 19F NMR (471 MHz, CDCl3) δ − 62.9; HRMS (pos. ESI): m/z calcd for C50H34F12 862.2463 [M]+•, found 862.2466. CCDC Numbers. CCDC 1562988 (12) and 1562989 (22) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.9b01195. NMR and mass spectra, additional cyclic voltammograms, details on the isomerization between 12 and 22, computational details, including energies and Cartesian H

DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX

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The Journal of Organic Chemistry

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(17) Liu, Y.-Y.; Lin, J.-Y.; Bo, Y.-F.; Xie, L.-H.; Yi, M.-D.; Zhang, X.W.; Zhang, H.-M.; Loh, T.-P.; Huang, W. Synthesis and Crystal Structure of Highly Strained [4]Cyclofluorene: Green-Emitting Fluorophore. Org. Lett. 2016, 18, 172−175. (18) Kuroda, Y.; Sakamoto, Y.; Suzuki, T.; Kayahara, E.; Yamago, S. Tetracyclo(2,7-Carbazole)s: Diatropicity and Paratropicity of Inner Regions of Nanohoops. J. Org. Chem. 2016, 81, 3356−3363. (19) Sun, Z.; Suenaga, T.; Sarkar, P.; Sato, S.; Kotani, M.; Isobe, H. Stereoisomerism, Crystal Structures, and Dynamics of Belt-Shaped Cyclonaphthylenes. Proc. Natl. Acad. Sci. U. S. A. 2016, 113, 8109− 8114. (20) Okada, K.; Yagi, A.; Segawa, Y.; Itami, K. Synthesis and Properties of [8]-, [10]-, [12]-, and [16]Cyclo-1,4-Naphthylenes. Chem. Sci. 2017, 8, 661−667. (21) Jia, H.; Gao, Y.; Huang, Q.; Cui, S.; Du, P. Facile Three-Step Synthesis and Photophysical Properties of [8]-, [9]-, and [12]Cyclo1,4-Naphthalene Nanorings via Platinum-Mediated Reductive Elimination. Chem. Commun. 2018, 54, 988−991. (22) Li, P.; Wong, B. M.; Zakharov, L. N.; Jasti, R. Investigating the Reactivity of 1,4-Anthracene-Incorporated Cycloparaphenylene. Org. Lett. 2016, 18, 1574−1577. (23) Huang, Z.-A.; Chen, C.; Yang, X.-D.; Fan, X.-B.; Zhou, W.; Tung, C.-H.; Wu, L.-Z.; Cong, H. Synthesis of OligoparaphenyleneDerived Nanohoops Employing an Anthracene Photodimerization− Cycloreversion Strategy. J. Am. Chem. Soc. 2016, 138, 11144−11147. (24) Iwamoto, T.; Kayahara, E.; Yasuda, N.; Suzuki, T.; Yamago, S. Synthesis, Characterization, and Properties of [4]Cyclo-2,7-Pyrenylene: Effects of Cyclic Structure on the Electronic Properties of Pyrene Oligomers. Angew. Chem., Int. Ed. 2014, 53, 6430−6434. (25) Hitosugi, S.; Nakanishi, W.; Yamasaki, T.; Isobe, H. Bottom-up Synthesis of Finite Models of Helical (n,m)-Single-Wall Carbon Nanotubes. Nat. Commun. 2011, 2, 492. (26) Matsuno, T.; Kamata, S.; Hitosugi, S.; Isobe, H. Bottom-up Synthesis and Structures of π-Lengthened Tubular Macrocycles. Chem. Sci. 2013, 4, 3179−3183. (27) Quernheim, M.; Golling, F. E.; Zhang, W.; Wagner, M.; Räder, H.-J.; Nishiuchi, T.; Müllen, K. The Precise Synthesis of PhenyleneExtended Cyclic Hexa-Peri-Hexabenzocoronenes from Polyarylated [n]Cycloparaphenylenes by the Scholl Reaction. Angew. Chem., Int. Ed. 2015, 54, 10341−10346. (28) Lu, D.; Wu, H.; Dai, Y.; Shi, H.; Shao, X.; Yang, S.; Yang, J.; Du, P. A Cycloparaphenylene Nanoring with Graphenic Hexabenzocoronene Sidewalls. Chem. Commun. 2016, 52, 7164−7167. (29) Lu, D.; Zhuang, G.; Wu, H.; Wang, S.; Yang, S.; Du, P. A Large π-Extended Carbon Nanoring Based on Nanographene Units: Bottom-Up Synthesis, Photophysical Properties, and Selective Complexation with Fullerene C 70. Angew. Chem., Int. Ed. 2017, 56, 158−162. (30) Huang, Q.; Zhuang, G.; Jia, H.; Qian, M.; Cui, S.; Yang, S.; Du, P. Photoconductive Curved-Nanographene/Fullerene Supramolecular Heterojunctions. Angew. Chem., Int. Ed. 2019, 58, 6244−6249. (31) Hitosugi, S.; Sato, S.; Matsuno, T.; Koretsune, T.; Arita, R.; Isobe, H. Pentagon-Embedded Cycloarylenes with Cylindrical Shapes. Angew. Chem., Int. Ed. 2017, 56, 9106−9110. (32) Hopf, H. Pentalenes-From Highly Reactive Antiaromatics to Substrates for Material Science. Angew. Chem., Int. Ed. 2013, 52, 12224−12226. (33) Kawase, T.; Fujiwara, T.; Kitamura, C.; Konishi, A.; Hirao, Y.; Matsumoto, K.; Kurata, H.; Kubo, T.; Shinamura, S.; Mori, H.; et al. Dinaphthopentalenes: Pentalene Derivatives for Organic Thin-Film Transistors. Angew. Chem., Int. Ed. 2010, 49, 7728−7732. (34) Hermann, M.; Wu, R.; Grenz, D. C.; Kratzert, D.; Li, H.; Esser, B. Thioether- and Sulfone-Functionalized Dibenzopentalenes as nChannel Semiconductors for Organic Field-Effect Transistors. J. Mater. Chem. C 2018, 6, 5420−5426. (35) Sekine, K.; Schulmeister, J.; Paulus, F.; Goetz, K. P.; Rominger, F.; Rudolph, M.; Zaumseil, J.; Hashmi, A. S. K. Gold-Catalyzed Facile Synthesis and Crystal Structures of Benzene-/Naphthalene-Based

coordinates of calculated structures, and X-ray crystallographic data (PDF) Crystallographic information for 12 (CIF) Crystallographic information for 22 (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Daniel Wassy: 0000-0002-8196-9926 Birgit Esser: 0000-0002-2430-1380 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. O. Gidron and H. Yakir for measuring the quantum efficiency of emission for 2. Generous support by the German Research Foundation (Emmy Noether Grant ES 361/ 2-1 and INST 40/467-1 FUGG) and the state of BadenWürttemberg through bwHPC is gratefully acknowledged.

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DOI: 10.1021/acs.joc.9b01195 J. Org. Chem. XXXX, XXX, XXX−XXX