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Oct 23, 2017 - Molecular Spur Gears Based on a Switchable Quinquepyridine Foldamer Acting as a Stator ... the intermeshed and demeshed states of molec...
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Molecular Spur Gears Based on a Switchable Quinquepyridine Foldamer Acting as a Stator Fu Huang,†,‡,§ Guangxia Wang,†,§ Lishuang Ma,‡ Ying Wang,‡ Xuebo Chen,‡ Yanke Che,*,† and Hua Jiang*,†,‡ †

CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P.R.China College of Chemistry, Beijing Normal University, Beijing 100875, P.R.China § University of Chinese Academy of Sciences, Beijing 100149, P.R.China ‡

S Supporting Information *

ABSTRACT: Two triptycene rotators have been covalently linked to the backbone of a quinquepyridine (QPY) foldamer at the second and fourth pyridine rings, respectively, to form molecular spur gears. The studies revealed that a QPY foldamer as a stator can reversibly control the intermeshed and demeshed states of molecular spur gears due to the linear-to-helical conformational switching triggered by complexation/decomplexation.

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binding, light, and protonation,11 but such dynamic structural change has seldom been utilized to the manipulate motions of molecular machines.12 In spite of that, oligoamide foldamers were successfully engineered as molecular machines on the basis of the host−guest interaction by us and others.13 Inspired by the observed geometric change in helicates,14 we envisaged that helicate could be used to reversibly control gearing systems as molecular machines by the interconversion between complexation and decomplexation. To this end, pyridine-type ligands were chosen because they are able to assemble monoand binuclear helical complexes upon reaction with many transition-metal ions,15 such as CuI, CuII, AgI, NiII, PdII, and ReIII. In these helicates, the dynamic structure of the ligand changes significantly in comparison with that before complexation. Although there are many polydentate ligands based on oligopyridines, the 2,2′/6′,2′′/6′′,2′′′/6′′′,2′′′′-quinquepyridine foldamer was chosen to fulfill our purpose based on the following facts: (1) It is well-known that the QPY foldamer adopts a linear conformation due to the steric and electronic demands between adjacent pyridines in the absence of metal ions. However, the QPY foldamer is capable of forming mononuclear complexes with a helical conformation upon reaction with AgI, ReIII, and ZnII,16 demonstrating a dynamic structural change with a large amplitude; (2) the QPY foldamer is long enough to allow the inductions of two triptycene groups at the 4-position of the second and fourth pyridine rings in the sequence (Scheme 1). We expected that these unique features would warrant that the QPY foldamer can not only act as a stator but also switch the conformation of the QPY foldamer in response to the interconversion between complexation and

INTRODUCTION Artificial molecular machines have attracted chemists with considerable attention in constructing functional molecular devices,1 which have showed many potential applications in the field of catalysis2 and nanotechnology.3 One of the key issues is how to control the motion of the molecular machine at the molecular level at will so that molecular machines are able to perform the desired function. For this purpose, many approaches,1 such as light, acid−base, metal coordination, redox, etc., have been developed and successfully applied to manipulate the motions of the molecular machines including molecular shuttles,4 molecular turnstiles,5 and molecular rotors.6 Molecular gears, containing two or more rotators in one molecule, display the correlated motions to mimic macroscopic mechanical devices. The paradigms of the molecular gearing systems have been focused on triptycene (TP) or derivatives7 because triptycene, composed of three benzenes with a D3h symmetric structure, resembles a macroscopic gearwheel. Previous efforts mainly focused on the dynamic gearing of the molecular bevel gear of the type TP2X (X = CH2, O, S, CO, SiH2).8 Recently, molecular spur gears comprising triptycene rotators have been synthesized and studied.9 However, investigations into the operation of gearing systems utilized as a molecular machines have rarely been reported. One early elegant example in bevel gear systems is to introduce clutch function into a molecular bevel gear system by silane−silicate interconversion using the reversible addition of a fluoride ion.10 The lack of extensive investigations in manipulating gearing motion highlights a great challenge of using gearing systems as a motion controllable molecular machine. Foldamers display a dynamic structural change of a large amplitude upon triggering by various stimuli such as ion © 2017 American Chemical Society

Received: July 26, 2017 Published: October 23, 2017 12106

DOI: 10.1021/acs.joc.7b01864 J. Org. Chem. 2017, 82, 12106−12111

Article

The Journal of Organic Chemistry Scheme 1. Molecular Spur Gears Based on a QPY Foldamer Performing a Switch Function in Response to Complexation and Decomplexation

decomplexation. In this report, we present our effort on controlling the intermeshed and demeshed states of molecular spur gears by a switchable QPY foldamer.

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Figure 1. Crystal structure of 1: the side view and bottom view in the stick model (top); the side view and bottom view with TP moieties in the CPK model (bottom).

RESULTS AND DISCUSSION The synthetic routes for compounds 1 and 2 are outlined in Scheme 2. First, a toluene solution of anthracene-9-

lowest energy ground state minimum as demonstrated by the theoretic calculation.9 Since the structure of 1 is highly symmetric, it is not surprising to find that the 1H NMR spectrum of 1 is very simple and that all protons of the backbone of QPY and the two triptycene rotators consist of 13 well-resolved resonances as shown in Figure 3a, indicative of a highly symmetric conformation. Decreasing the temperature as low as 183 K did not cause any complex spectral patterns (Figure S1). In the case of molecular spur 2, whose structure carries two dimethyl groups on one of the blades in the triptycene rotators, one could expect that the 1H NMR spectrum of 2 should be complex because of the existence of phase isomers.17 Surprisingly, such a scenario was not observed even while the solution was cooled to 183 K (Figure S2). However, upon cooling of the solution, the well-resolved peaks of the triptycene moieties started to broaden but did not display the anticipated tendency of decoalescence. The similar phenomena were also observed in the Siegel’s molecular spurs in which the stator is rigid.9 An effort to carry out variable temperature (VT) 1 H NMR experiments in a low-freezing solvent was deterred due to no commercially available resource. The absence of clear decoalescence could be mainly attributed to the flexibility of the stator, i.e., QPY foldamer, whose backbone is too flexible to hold the gear slippage to take place even in low temperatures. Other factors like technical limits proposed by Siegel may also potentially disturb the observation of splitting of signals.9 To shed light on the conformation of molecular spur 1 in solution, the molecular geometry of 1 was studied in both gas phase and methylene chloride solution by using the density functional theory (DFT). Molecular geometry optimizations together with the frequency calculation at the B3LYP/6-31G* level confirm that the linear conformation of QPY in 1 is the global energy minimum in both gas phase and solution. As shown in Figures 2a and S27, the backbone of QPY in 1 adopts a linear conformation with two triptycene groups intermeshed each other in both gas phase and solution, and the molecule displays a C2 symmetry as observed in the crystal structure. The geometry of 1 in the gas phase is essentially the same as that in solution (Figure S27). Moreover, as shown in Figure 2b, the optimized structure of 1 is almost superimposable with the structure in the crystals. The theoretic calculations thus strongly imply that 1 adopts a molecular gearing conformation in solution as demonstrated in the solid phase.

Scheme 2. Synthesis of Molecular Spur Gears

carboxaldehyde and ethylene glycol were refluxed in the presence of p-toluenesulfonic acid to provide 4. To a solution of 4 was added benzenediazonium-2-carboxylate 5 in portions to yield 7, followed by deprotection with hydrochloric acid to generate 9, which was subjected to an aldol reaction with 2acetylpyridine using t-BuONa in THF to afford 11. Finally, compound 1 was obtained by the reaction of 2,6-diacetylpyridine and 11 in the presence of excess NH4OAc and t-BuONa. Compound 2 was synthesized similarly according to the procedures described for 1. Compound 3 was designed as a control compound. All compounds have been fully characterized by 1H and 13C NMR and mass spectrometry. The crystal structure of 1 was obtained by the liquid phase diffusion of hexane to a solution of 1 in chloroform at room temperature (Figure 1). The crystal structure reveals that five pyridine rings almost adopt a linear conformation due to the electronic repulsion between two adjacent pyridyl moieties. The distance between the axles of two triptycene rotators is 7.00 Å, which is obviously shorter than that in the Siegel’s spur gears in which the interaxle distance is about 8.42 Å.9 As shown in Figure 1, two triptycene rotators intermesh with each other and adopt a C2 conformation in which one of the phenyl groups in each TP rotators displays face-to-face and edge-to-face π−π interactions. Such interactions are able to stabilize the C2 conformation and ensure that the C2 conformation is the 12107

DOI: 10.1021/acs.joc.7b01864 J. Org. Chem. 2017, 82, 12106−12111

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The Journal of Organic Chemistry

Figure 2. (a) Molecular model of 1 (bottom view and side view) calculated at the B3LYP/6-31G* level of the DFT as the global energy minimum. (b) Superimposition of the structures of 1 in the crystal (labeled in purple) and obtained from the DFT calculation (bottom view and side view).

Figure 3. Partial reversible changes of 1H NMR spectra (600 MHz, rt) of 1 and 2 in response to the titrations of AgPF6 and Et4NCl in CD2Cl2/CD3CN = 20/1. (a) 1 (2 mM); (b) part a and 1 equiv of AgPF6 added; (c) part b and 1 equiv of Et4NCl added; (d) 2 (2 mM); (e) part d and 1 equiv of AgPF6 added; (f) part e and 1 equiv of Et4NCl added.

The flexibility of the QPY foldamer leads to the absence of decoalescence in the VT-NMR experiments and consequently prevents the determination of the activation parameters of the gear slippage. However, it provides us a chance to demonstrate its conformational diversity in response to interconversion between complexation and decomplexation triggered by the alternate addition of Ag+ and Cl−. The 1H NMR titration experiments of 1 were first carried out in CD2Cl2 with 5% acetonitrile-d3. The NMR spectra show that the well-resolved resonances of all protons started to get broadened on the NMR time scale while aliquots of a solution of AgPF6 were titrated into a solution of 1. However, the wellresolved spectral feature appeared again to be one set of completely different resonances while the amount of AgPF6 reached 1 equiv and beyond (Figure S3). No evidence was observed for supporting the formation of other species including double helicates, consistent with the previous observations.16 Evidence for the formation of 1/1 silver complexes from a mixture of 1 or 2 and AgPF6 (1/1) in CH2Cl2/CH3CN was obtained by HRMS-ESI mass spectrometry. The HRMS-ESI mass spectrum of a mixture of 1 or 2 and AgPF6 (1/1) displayed a main peak at m/z 998.2420 or m/z 1054.3042 (Figures S15 and S17), assignable for cationic [Ag1]+ and [Ag2]+, respectively. These data further support that [Ag1]·[PF6] and [Ag2]·[PF6] complexes were formed in solution. As shown in Figure 3a,b, all of the protons of the stator QPY except of H2 and H3 underwent significant upshifts upon the addition of 1 equiv of AgPF6. For example, the maximum upshift was observed for H7 with Δδ = −0.63 ppm. These changes are attributed to the complexation between the QPY and silver ion, consequently giving rise of a linear-to-helical conformational switch (Figure S3). However, all of the protons of the two TP rotators demonstrated significant downshifts under the same conditions. For example, protons H10 and H11 dramatically shifted downfield with the chemical shift change Δδ = 0.74 and 0.44 ppm, respectively (Table S1). Such a strong deshielding implies that two triptycene rotators adopt a demeshed state rather than an intermeshed one. Under such a scenario, the original face-to-face and edge-to-face π−π interactions between two triptycene groups in the intermeshed state as observed in the solid phase (Figure 1) and in the optimized structure (Figures 2 and S27) have been completely destroyed. However, in the control NMR titrating experiments, all of the protons of triptycene group in model 3 show very

little change upon the titration of AgPF6 under the same conditions (Figure S5). This finding clearly displays that the complexation between polypyridines and silver ions pose no direct effect on the chemical shifts of the triptycene groups. Thus, one can conclude that the strong deshielding of the rotators in molecular spur 1 results from the linear-to-helical conformational switching of the backbone of molecular spurs. The conformation of the two rotators in 1 changes from the intermeshed state to the demeshed one, clearly demonstrating that the QPY foldamer acts as a switch in response to metal complexation. The similar result was also found for molecular spur gear 2 (Figures 3d and S4). In order to examine the reversibility of the switch function of the stator QPY, we first decided to decomplex the silver complexes of 1 by adding chloride anions to precipitate silver ions. As shown in Figures 3c and S6, the NMR spectral patterns of the QPY stator and triptycene rotators in the resulting 1 appear identical to those of the free 1 while 1 equiv of the chloride anion was introduced. Such interconversions between complexation and decomplexation could be operated at least three cycles without losing fidelity (Figure S6). The similar phenomenon was also observed for the molecular spur 2 (Figures 3f and S7). These findings demonstrate that the QPY foldamers in the present systems can reversibly control the intermeshed and demeshed states of the triptycene rotators in the molecular spur gears. In order to shed light on the linear-to-helical conformational switching of the QPY in 1 and 2, NOESY experiments have been carried out and reveal that no NOE correlations between adjacent pyridines have been observed for the free 1 and 2 (Figure 4a,c). On the contrary, strong NOE correlations between H4 and H5 and H6 and H7 in the adjacent pyridines (Figure 4b,d) have been detected when 1 equiv of silver ions was added to a solution of 1 and 2, respectively. The NOE observations confirm that the QPY foldamer underwent a linear-to-helical conformational change while complexing with the silver ion. The linear-to-helical conformational switching in 1 and 2 should cause change in their volumes, which can be assessed by 1 H DOSY experiments. Diffusion coefficients were calculated from 1H DOSY measurements recorded at 298 K using 2 mM 12108

DOI: 10.1021/acs.joc.7b01864 J. Org. Chem. 2017, 82, 12106−12111

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Figure 4. Partial changes of the NOE spectra (600 MHz) of 1 and 2 in response to the titrations of AgPF6 and Et4NCl in CD2Cl2 with 5% acetonitrile-d3. (a) 1 (2 mM); (b) [Ag1]·[PF6] (2 mM); (c) 2 (2 mM); (d) [Ag2]·[PF6] (2 mM); (e) illustration of the conformational change of the molecular spur in response to the interconversions between complexation and decomplexation.

samples. The diffusion coefficients of free 1 and 2 are 6.61 × 10−10 and 6.37 × 10−10 m2 s−1, respectively (Figures S22 and S24). The diffusion coefficients of the silver complexes of [Ag1]·[PF6] and [Ag2]·[PF6] are 6.14 × 10−10 and 5.98 × 10−10 m2 s−1, respectively (Figures S23 and S25). The diffusion coefficients of silver complexes are slightly smaller than those of free ligands, implying that the volumes of the silver complexes are larger than those of their corresponding free ligands. Although the approximation of the molecular shape to spheres prevents a refined analysis of these data, the DFT calculations reveal that the volumes of molecular spur 1 and its silver complex are 7138.593 and 7298.950 bohr,3 respectively, clearly showing that the calculated volume of the silver complex of foldamer 1 is slightly larger than that of the free folamer, which are consistent with the diffusion coefficient data. Therefore, the difference of the diffusion coefficients of the free ligands and its silver complexes could be attributed to the linear-to-helical conformational switching induced by complexation.

MHz) or a JEOL Delta spectrometer (1H−1H NOESY and DOSY, JEOL 400 MHz and JEOL 600 MHz) using chloroform (CDCl3), dichloromethane-d2 (CD2Cl2), acetonitrile-d3, or the mixture of them as a solvent. The chemical shift references were as follows: (1H) dichloromethane-d2, 5.31 ppm; (13C) dichloromethane-d2, 53.8 ppm; (1H) chloroform-d, 7.26 ppm; (13C) chloroform-d, 77.2 ppm; (1H) acetonitrile-d3, 1.94 ppm; (13C) acetonitrile-d3, 118.26 ppm; (1H) tetramethylsilane (TMS), 0.00 ppm (the mixture of dichloromethaned2 and acetonitrile-d3). X-ray reflections were collected on an Oxford CCD X-ray diffractometer (Saturn724+, Rigaku) equipped with a Mo Kα radiation (λ = 0.710 69 Å) source. Mass spectra (ESI, MALDI) were acquired on GCT and FT-ICR (Bruker Daltonics Inc. APEX, BIFLEX III) and MALDI-TOF (AutoflexIII) spectrometers, respectively. 2-(2,3-Dimethyl-9,10-[1,2]benzenoanthracen-9(10H)-yl)-1,3dioxolane (8). A mixture of 4 (5.0 g, 20.0 mmol, 1 equiv) with benzynes 6S3 (4.25 g, 20.0 mmol, 1 equiv) and 1,2-epoxypropane in dichloroethane was refluxed overnight, during which time three additional portions of benzynes were added. The reaction mixture was concentrated under reduced pressure. Then the residue was washed with methanol and then filtrated. The final product was a colorless solid (3.68 g, yield 50%): Rf = 0.4 (CH2Cl2/hexane, 1/1); mp 262− 264 °C; 1H NMR (400 MHz, CDCl3) δ 7.63 (d, J = 6.8 Hz, 1H), 7.53−7.55 (m, 1H), 7.43 (s, 1H), 7.33−7.35 (m, 2H), 7.16 (s, 1H), 6.94−6.99 (m, 4H), 6.32 (s, 1H), 5.27 (s, 1H), 4.51−4.53 (m, 2H), 4.37−4.38 (m, 2H), 2.17 (s, 3H), 2.14 (s, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ 146.8, 144.5, 144.2, 141.9, 141.8, 133.1, 132.6, 126.0, 125.1, 124.8, 124.7, 124.6, 124.5, 123.3, 123.2, 104.3, 65.0, 55.9, 54.2, 19.9, 19.5 ppm; HRMS-ESI (m/z) [M + H]+ calcd for C25H23O2 355.1698, found 355.1693 (−1.3 ppm). 2,3-Dimethyl-9,10-[1,2]benzenoanthracene-9(10H)-carbaldehyde (10). To a stirring mixture of 8 (0.71 g, 2 mmol) in glacial acetic acid (30 mL) was added concentrated HCl (4 mL). The mixture was stirred at reflux for 18 h, then allowed to cool to rt, and poured into water. The resulting precipitate was filtered, washed with water, and dried in vacuo to afford 10 as a white solid (0.57 g, 92%): Rf = 0.4 (PE/EA, 4/1); mp 218−220 °C; 1H NMR (400 MHz, CDCl3) δ 11.21 (s, 1H), 7.60−7.63 (m, 2H), 7.39−7.42 (m, 3H), 7.24 (s, 1H), 7.02−7.06 (m, 4H), 5.34 (s, 1H), 2.18 (s, 6H) ppm; 13C NMR (100 MHz, CDCl3) δ 210.3, 146.2, 143.5, 143.0, 140.3, 133.9, 133.2, 125.8, 125.6, 125.2, 124.0, 123.9, 122.4, 60.7, 53.8, 19.7, 19.6 ppm; HRMSESI (m/z) [M + H]+ calcd for C23H19O 311.1436, found 311.1433 (−0.8 ppm). (E)-3-(9,10-[1,2]Benzenoanthracen-9(10H)-yl)-1-(pyridin-2yl)prop-2-en-1-one (11). A mixture of 9 (0.56 g, 2.0 mmol, 1 equiv),

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CONCLUSIONS In conclusion, the QPY foldamer has been successfully engineered as a stator in molecular spur gears. All of these results indicate that the QPY foldamer in the molecular spurs exhibits a dynamic structure change with a large amplitude upon complexation and decomplexation, which renders the QPY foldamer able to control the intermeshed/demeshed states of the molecular spur gears. The data in hand indicate that the QPY foldamer is likely to have a range of useful properties in molecular switching and supramolecular polymers.

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EXPERIMENTAL SECTION

All starting chemicals were obtained from commercial sources and used without further purification, unless indicated otherwise. Anhydrous tetrahydrofuran (THF) and toluene were dried from sodium/benzophenone and then distilled under an inert atmosphere, while anhydrous 1,2-dichloroethane (DCE) was distilled over calcium hydride (CaH2). Compounds 4, 7, and 9 were prepared using procedures reported in the literature.9 Crude compounds were purified by flash column chromatography, using flash grade silica gel and 0−20 psig pressure, performed at ambient pressure. NMR spectra were obtained with a Bruker spectrometer (1H, 13C, Bruker AVANCE 400 12109

DOI: 10.1021/acs.joc.7b01864 J. Org. Chem. 2017, 82, 12106−12111

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The Journal of Organic Chemistry

CDCl3) δ 9.48 (s, 2H), 9.25 (s, 2H), 9.04 (d, J = 7.8 Hz, 2H), 8.86 (d, J = 8.0 Hz, 2H), 8.67 (d, J = 4.2 Hz, 2H), 8.23 (t, J = 7.8 Hz, 1H), 7.92−7.96 (m, 2H), 7.31−7.36 (m, 6H), 7.20 (d, J = 8.0 Hz, 4H), 7.11 (d, J = 2.4 Hz, 4H), 6.71 (t, J = 7.2 Hz, 6H), 6.36 (t, J = 7.6 Hz, 6H), 5.29 (s, 2H), 1.95 (s, 6H), 1.59 (s, 6H) ppm; 13C NMR (100 MHz, CDCl3) δ 156.6, 155.9, 155.8, 149.5, 147.9, 146.6, 145.9, 144.3, 142.8, 138.1, 136.9, 132.9, 132.3, 125.6, 125.3, 124.6, 123.9, 123.8, 123.3, 123.1, 121.7, 121.3, 59.9, 54.8, 29.9, 19.3 ppm; HRMS-ESI (m/z) [M + H]+ calcd for C69H50N5 948.4066, found 948.4051 (−1.6 ppm). 4′-(9,10-[1,2]Benzenoanthracen-9(10H)-yl)-2,2′/6′,2″-terpyridine (3). The procedure was slightly modified from the one previously reported in the literature (S4). A mixture of 11 (0.56 g, 2.0 mmol, 1 equiv), 2-acetylpyridine (0.22 mL, 2.0 mmol, 1 equiv), dry NH4OAc (1.5 g, 20 mmol, 10 equiv), and CH3COOH (20 mL) was refluxed for 24 h. The cooled mixture was filtered, and the precipitate washed with cold MeOH to give 3 as a light-yellow solid (0.58 g, yield 60%): Rf = 0.5 (CH2Cl2/methanol, 20/1); mp 272−274 °C; 1H NMR (400 MHz, CDCl3) δ 9.30 (s, 2H), 8.80 (d, J = 8 Hz, 2H), 8.67 (d, J = 4 Hz, 2H), 7.92 (t, J = 8 Hz, 2H), 7.46 (d, J = 8 Hz, 3H), 7.42 (d, J = 8 Hz, 3H), 7.35 (dd, J = 6.4, 4 Hz, 2H), 6.98−7.05 (m, 6H), 5.46 (s, 1H) ppm; 13C NMR (100 MHz, CDCl3) δ 156.5, 156.2, 149.5, 147.6, 146.8, 145.8, 136.9, 125.4, 125.1, 124.5, 123.9, 123.8, 121.3, 60.5, 55.3 ppm; HRMS-ESI (m/z) [M + H]+ calcd for C35H24N3 486.1970, found 486.1971 (0.2 ppm).

2-acetylpyridine (0.22 mL, 2.0 mmol, 1 equiv), and potassium tertbutoxide (64 mg, 1.0 mmol, 0.5 equiv) in dry THF (20 mL) was stirred at rt for 16 h under nitrogen. The reaction mixture was quenched with diluted HCl and was extracted with dichloromethane. The combined organic extract was washed with water and brine, dried over MgSO4, and concentrated. The crude product was purified by silica gel column chromatography (petroleum ether/ethyl acetate, 4/1, v/v) to give 11 as a light-yellow solid (0.47 g, yield 61%): Rf = 0.4 (PE/EA, 3/1); mp 280−282 °C; 1H NMR (400 MHz, CDCl3) δ 8.58 (d, J = 4.2 Hz, 2H), 8.02 (d, J = 7.8 Hz, 3H), 7.79−7.83 (m, 2H), 7.74−7.76 (m, 2H), 7.51−7.53 (m, 1H), 7.39−7.43 (m, 2H), 7.30− 7.33 (m, 2H), 7.21−7.25 (m, 1H), 7.14−7.17 (m, 1H), 6.88−6.95 (m, 4H), 5.33 (s, 1H), 4.86−4.91 (m, 1H), 4.47−4.54 (m, 2H), 4.14−4.19 (m, 2H) ppm; 13C NMR (100 MHz, CDCl3) δ 201.7, 153.7, 148.9, 148.2, 146.6, 146.5, 136.9, 127.1, 125.8, 125.7, 125.0, 124.6, 124.1, 123.5, 123.4, 122.1, 59.7, 55.4 ppm; HRMS-ESI (m/z) [M + H]+ calcd for C28H20NO 386.1545, found 386.1540 (−1.1 ppm). (E)-3-(2,3-Dimethyl-9,10-[1,2]benzenoanthracen-9(10H)-yl)1-(pyridin-2-yl)prop-2-en-1-one (12). A mixture of 10 (0.31 g, 1.0 mmol, 1 equiv), 2-acetylpyridine (0.11 mL, 1 mmol, 1 equiv), and potassium tert-butoxide (32 mg, 0.5 mmol, 0.5 equiv) in dry THF (20 mL) was stirred at rt for 16 h under nitrogen. The reaction mixture was quenched with diluted HCl and was extracted with dichloromethane. The combined organic extract was washed with water and brine, dried over MgSO4, and concentrated. The crude product was purified by silica gel column chromatography (petroleum ether/ethyl acetate, 4/1, v/v) to give 12 as a light-yellow solid (0.21 g, yield 51%): Rf = 0.5 (PE/EA, 3/1); mp 272−274 °C; 1H NMR (400 MHz, CDCl3) δ 8.71−8.73 (m, 1H), 8.39−8.51 (m, 2H), 8.34−8.36 (m, 1H), 7.93−7.97 (m, 1H), 7.51−7.54 (m, 3H), 7.39−7.42 (m, 2H), 7.34 (s, 1H), 7.23 (s, 1H), 7.00−7.03 (m, 4H), 5.38 (s, 1H), 2.17 (s, 3H), 2.16 (s, 3H) ppm; 13C NMR (100 MHz, CDCl3) δ 189.9, 154.3, 149.3, 146.2, 145.7, 143.6, 143.0, 140.2, 137.2, 133.5, 132.8, 132.6, 127.3, 125.5, 125.4, 125.0, 124.1, 123.8, 123.2, 122.5, 56.2, 54.1, 19.5, 19.9 ppm; HRMS-ESI (m/z) [M + H]+ calcd for C30H24NO 414.1858, found 414.1852 (−1.4 ppm). 4′,4‴-Di(9,10-[1,2]benzenoanthracen-9(10H)-yl)-2,2′/6′,2″/ 6″,2‴/6‴,2′′′′-quinquepyridine (1). 2,6-Diacetylpyridine (33 mg, 0.2 mmol, 0.5 equiv) was added to a stirred solution of potassium tertbutoxide (6.4 mg, 0.1 mmol, 0.25 equiv) in anhydrous THF (15 mL). After stirring the mixture at room temperature for 2 h, 11 (170 mg, 0.44 mmol, 1 equiv) was added to the reaction mixture. The solution was stirred at room temperature overnight, and then NH4OAc (3 g) and ethanol (15 mL) were added sequentially; the mixture was refluxed for 4 h. After evaporation, the residue was washed with water and purified by silica gel column chromatography (CH2Cl2/CH3OH = 20/1, v/v), and then washed with CH3OH to give a pure yellow solid (82 mg, yield 22%): Rf = 0.4 (CH2Cl2/methanol, 20/1); mp > 300 °C; 1 H NMR (400 MHz, CDCl3) δ 9.41 (d, J = 1.6 Hz, 2H), 9.21 (s, J = 1.6 Hz, 2H), 8.94 (d, J = 7.6 Hz, 2H), 8.83 (d, J = 8.0 Hz, 2H), 8.66 (dd, J = 4.0, 3.2 Hz, 2H), 8.20 (t, J = 7.8 Hz, 1H), 7.93 (td, J = 8.0, 2.0 Hz, 2H), 7.30−7.36 (m, 8H), 7.22 (d, J = 8.0 Hz, 6H), 6.69 (td, J = 7.2, 0.4 Hz, 6H), 6.40 (td, J = 7.6, 1.2 Hz, 6H), 5.33 (s, 2H) ppm; 13C NMR (100 MHz, CDCl3) δ 156.1, 155.9, 155.8, 149.3, 147.3, 146.4, 145.3, 138.2, 137.0, 125.3, 124.4, 123.9, 123.8, 123.7, 123.6, 123.3, 121.4, 121.1, 60.0, 54.9 ppm; HRMS-ESI (m/z) [M + H]+ calcd for C65H42N5 892.3440, found 892.3416 (−2.7 ppm). 4′,4‴-Bis(2,3-dimethyl-9,10-[1,2]benzenoanthracen-9(10H)yl)-2,2′/6′,2″/6″,2‴/6‴,2′′′′-quinquepyridine (2). 2,6-Diacetylpyridine (33 mg, 0.2 mmol, 0.5 equiv) was added to a stirred solution of potassium tert-butoxide (6.4 mg, 0.1 mmol, 0.25 equiv) in anhydrous THF (15 mL). After stirring the mixture at room temperature for 2 h, 12 (182 mg, 0.44 mmol, 1 equiv) was added to the reaction mixture. The solution was stirred at room temperature overnight, and then NH4OAc (3 g) and ethanol (15 mL) were added sequentially; the mixture was refluxed for 4 h. After evaporation, the residue was washed with water, purified by silica gel column chromatography (CH2Cl2/CH3OH, 20/1, v/v), and then washed with CH3OH to give a pure yellow solid (75 mg, yield 18%): Rf = 0.4 (CH2Cl2/methanol, 20/1); mp > 300 °C; 1H NMR (400 MHz,

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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.7b01864. 1 cocrystallized with chloroform and hexane (CIF) X-ray crystallographic data of 1, computational details, DFT calculations, and DOSY, VT, 1H, 13C, and 2D NMR spectra (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Ying Wang: 0000-0002-7015-7228 Xuebo Chen: 0000-0002-9814-9908 Yanke Che: 0000-0002-9671-3704 Hua Jiang: 0000-0002-9917-2683 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China (21472015 and 21332008). REFERENCES

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Article

The Journal of Organic Chemistry

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