Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
A Trefoil Macrocycle Synthesized by 3‑Fold Benzannulation Xuejin Yang, Luyan Yuan, Ziyi Chen, Zhifeng Liu, and Qian Miao* Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
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S Supporting Information *
ABSTRACT: A new trefoil-shaped molecular architecture consisting of three conjugated macrocycles was synthesized through an unprecedented 3-fold copper catalyzed [4 + 2] benzannulation. DFT calculations indicate that the most stable conformation of this trefoil macrocycle is D3-symmetric. In agreement with the calculated results, the trefoil macrocycle in single crystals exists as a pair of enantiomers with D3-symmetry and exhibits interesting honeycomb-like supramolecular structures.
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[4 + 2] benzannulation reaction of o-alkynylbenzaldehyde (2) with alkynes11 (Scheme 1a) proved to be an efficient method for the synthesis of naphthalene derivatives,12 resulting in a variety of molecular architectures containing multiple naphthalene moieties.13,14 When the substrate contained two aldehyde groups, the 2-fold benzannulation reaction of 3 gave the corresponding anthracene derivative as shown in Scheme 1b.15 On the basis of these reactions, we envisioned that hexasubstituted triphenylene derivatives could be prepared by a 3-fold benzannulation reaction (Scheme 1c) of 2,4,6tris(phenylethynyl)benzene-1,3,5-tricarbaldehyde (4), which was synthesized following the reported procedures with minor modification.16 To verify this hypothesis, a model reaction of 4 with diphenylacetylene as catalyzed by Cu(OTf)2 in the presence of CF3CO2H gave hexaphenyltriphenylene 5 in a yield of 25%, which corresponds to a yield of 63% for each benzannulation. This 3-fold benzannulation reaction appears to be a new approach to hexasubstituted triphenylene derivatives.17 Scheme 2 shows the synthesis of trefoil macrocycles 1a/b starting from 3,6-dibromo-9,10-dialkyloxyphenathrene (6a/ b),13,18 which reacted with acetylenedicarboxylic acid in a decarboxylative Sonogashira coupling19 giving 7a/b in fairly good yields. A large excess (10 equiv) of 6a or 6b was used in this reaction so that only one C−Br bond in each substrate molecule reacted. The 3-fold benzannulation reaction of 4 with 7a/b as catalyzed by Cu(OTf)2 under acidic conditions resulted in hexaphenanthrenylated triphenylene 8a or 8b, in yields of ca. 33%, which corresponds to a yield of 69% for each aldehyde group. In comparison to trialdehyde 4, monoaldehyde 2 reacted with 7b under the same conditions giving the corresponding naphthalene derivative 9b (Scheme S2a in
yclic assemblies of aromatic units through covalent bonds result in shape-persistent macrocycles,1 which have become an important class of π-conjugated molecules having their optical and electronic properties readily modified by changing the type, number, and connection mode of aromatic building blocks. These conjugated macrocycles are regarded as monomeric and well-defined precursors to graphene nanomeshes.2 For example, surface-assisted polymerization of iodinated cyclohexa-m-phenylene resulted in regular porous graphenes.3 Other known applications of the conjugated macrocycles include supramolecular hosts, fluorescent materials for sensing,4 and organic semiconductors in electronic devices.5 Benzene is the most commonly employed aromatic building block for the construction of conjugated macrocycles, such as cyclo-m-phenylenes6 and cyclo-p-phenylenes,7 while polycyclic aromatic building blocks offer structural versatility and optical/electronic properties that are not available to macrocycles consisting exclusively of benzene units.8 Connecting conjugated macrocycles into larger molecular architectures, such as polyphenylene spoked wheels9 and geodesic frameworks of phenine,10 is a promising bottom-up approach to porous carbon-rich nanomaterials, which, however, remain largely unexplored. Herein, we report a new molecular architecture that consists of three conjugated macrocycles fused together and thus is shaped like a trefoil. As shown in Figure 1, this trefoil macrocycle (1a/b) contains six phenanthrene subunits surrounding a triphenylene moiety and can be mapped onto a porous graphene. The π-backbone of 1a/b is not flat, but helical at the three o-diphenylbenzene moieties that are highlighted in yellow in Figure 1a because of atom crowding in these regions. Detailed below are the synthesis, stereochemistry, and assembly of 1a/b. To synthesize 1a/b, an unprecedented 3-fold coppercatalyzed benzannulation reaction was utilized as a key step to construct the central triphenylene moiety. Copper-catalyzed © XXXX American Chemical Society
Received: September 27, 2018
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DOI: 10.1021/acs.orglett.8b03099 Org. Lett. XXXX, XXX, XXX−XXX
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Organic Letters Scheme 2. Synthesis of 1a and 1b
Figure 1. (a) Structure of trefoil macrocycle 1a/b; (b) the πbackbone of 1a/b as mapped onto a porous graphene.
20% and 23%, respectively. Attempted treatment of 1b with FeCl3, MoCl5, Sc(OTf)3, or DDQ/MeSO3H for cyclodehydrogenation did not yield 12b with formation of three more C−C bonds, but led to decomposition of the starting material. The unsuccessful Scholl reaction of 1b could be explained with the Mulliken spin density of 1b•+, which is essentially not located at the desired reaction sites20 as shown in Figure S1 in the SI. Moreover, 1b appeared almost innert toward photocyclization although o-terphenyl was reported to photocyclize into triphenylene under the same conditions.21 The 1H NMR spectra of 1a and 1b exhibited three singlets and four doublets in the aromatic region, in agreement with a structure of 3-fold symmetry. The almost colorless solutions of 1a and 1b exhibited nearly identical UV−vis absorption spectra with the longest absorption maximum at 370 nm (Figure S4 in the SI), which bathochromically shifts relative to 9,10-dihexyloxyphenathrene13 and triphenylene,22 as a result of conjugation along the cyclic π-backbone. When excited with UV light of 370 nm, the solutions of 1a and 1b were resplendently blue-emissive with an emission peak at about 441 nm. By comparison with 9,10-diphenylanthracene, the photoluminescence quantum yields of 1a and 1b were determined to be 58% and 57%, respectively. The trefoil macrocycle in 1a/b can, in principle, exist as two pairs of enantiomers depending on the helicity of the three odiphenylbenzene regions (highlighted in yellow in Figure 1a). The homochiral pair, (P,P,P) and (M,M,M), have a D3symmetry and are shaped like a three-blade propeller, while the heterochiral pair, (M,P,P) and (P,M,M), have a C2-symmetry. The stereochemistry of this trefoil macrocycle was studied with density functional theory (DFT) calculations and X-ray crystallography. To reduce computational cost, 1c, a simplified model molecule with methoxy groups replacing the longer
Scheme 1. Copper-Catalyzed Benzannulation Reactions of Mono-, Di-, and Trialdehydes for Synthesizing Derivatives of Naphthalene (a), Anthracene (b), and Triphenylene (c), Respectively
the Supporting Information (SI)) in a yield of 94%, and dialdehyde 10 (Scheme S2b) reacted with 7b under the same conditions giving the corresponding anthracene derivative 11b (Scheme S2b) in a yield of 51%, which corresponds to a yield of 71% for each aldehyde group. The relatively low yield for the 3-fold benzannulation of 4 may be attributed to a possible side reaction that is not applicable to the mono- and dialdehyde as shown in Scheme S5 in the SI, although the hypothetic byproducts (18a−b) were not isolated. The subsequent 3-fold intramolecular Yamamoto coupling reactions of 8a and 8b afforded macrocycles 1a and 1b in yields of B
DOI: 10.1021/acs.orglett.8b03099 Org. Lett. XXXX, XXX, XXX−XXX
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Organic Letters
of 7.26 × 10−3 s−1 at 25 °C, as estimated using the Eyring equation k = κ(kBT/h) exp(−ΔG‡/RT) and assuming a value of unity for the transmission coefficient (κ). 23 The interconversion of the (M,P,P) and (P,M,M) isomers occurs through meso-TS with a smaller energy barrier of 17.30 kcal/ mol. Single crystals of 1b were obtained by slow diffusion of ethyl acetate and acetonitrile into a solution of 1b in chloroform. Xray crystallography revealed the racemic crystal containing a pair of enantiomers of 1b with D3-symmetry. As shown in Figure 4a, the π-backbone of (P,P,P)-1b is shaped like a three-
alkoxy groups in 1a/b, was calculated at the B3LYP/6-31G* level of DFT. Structural optimization of 1c revealed the D3symmetric isomers, (P,P,P) and (M,M,M)-1c, as the global energy minimum and the C2-symmetric heterochiral isomers as the local energy minimum as shown in Figure 2. The D3-
Figure 2. Molecular models of (P,P,P)-1c (a) and (M,P,P)-1c (b) as calculated at the B3LYP/6-31G* level of DFT with the symmetric axes. (Hydrogen atoms are removed for clarity, and the helical odiphenylbenzene regions are highlighted.)
isomers are more stable than the C2-isomers by 4.82 kcal/mol in Gibbs free energy, which corresponds to an equilibrium constant of 3.41 × 103 at 25 °C or 5.62 × 102 at 110 °C. This indicates that the D3-isomers are dominant from 25 to 110 °C, in agreement with the fact that the 1H NMR spectra of 1b as recorded in this temperature range (Figure S5 in the SI) were essentially the same exhibiting a 3-fold symmetry. Figure 3
Figure 4. (a) (P,P,P)-1b in the crystal; (b) the honeycomb-like assembly of 1b in the crystal as viewed along the c axis of the unit cell with (P,P,P)- and (M,M,M)-1b shown in red and blue, respectively. (All the hexyl groups and hydrogen atoms are removed for clarity, and carbon and oxygen atoms in (a) are shown as ellipsoids at 50% probability level.)
blade propeller. The three helical o-diphenylbenzene regions exhibit the same dihedral angle of 60.68° between the corresponding orange and yellow benzene rings. The central triphenylene subunit in 1b is not flat, but contorted with three identical torsion angles (C4−C4a−C4b−C5, C8−C8a−C8b− C9, and C12−C12a−C12b−C1) of 11.30°. An interesting finding from the crystal structure of 1b is an unusual honeycomb-like supramolecular structure, which is formed by stacking one layer of (P,P,P)-1b (colored in red) over one layer of (M,M,M)-1b (colored in blue) with π−π interactions as shown in Figure 4b. The phenanthrene subunits of two enantiomers of 1b overlap with a π-to-π distance of 3.47 Å as shown in Figure S2 (SI). The purple regions surrounded by
Figure 3. Calculated pathway for enantiomerization of (P,P,P)-1c. (The structures of intermediates and transition states were calculated at the B3LYP/6-31G* level of DFT, and hydrogen atoms in the models are removed for clarity.)
shows the calculated pathway for enantiomerization of (P,P,P)1c, where (M,P,P) and (P,M,M)-1c are the intermediates. This pathway has three transition states, P-TS and M-TS as a pair of enantiomers and meso-TS as a meso isomer. (P,P,P)-1c converts to (M,P,P)-1c through P-TS and the (M,M,M)-1c converts to (P,M,M)-1c through M-TS with the same energy barrier of 20.37 kcal/mol, which corresponds to a rate constant C
DOI: 10.1021/acs.orglett.8b03099 Org. Lett. XXXX, XXX, XXX−XXX
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N.; Bai, C.; Cao, Y.; Wang, J.; Pei, J.; Zhao, D. Chem. Commun. 2010, 46, 5725−5727. (c) Zhao, T.; Wei, Z.; Song, Y.; Xu, W.; Hu, W.; Zhu, D. J. Mater. Chem. 2007, 17, 4377−4381. (d) Ball, M.; Zhong, Y.; Fowler, B.; Zhang, B.; Li, P.; Etkin, G.; Paley, D. W.; Decatur, J.; Dalsania, A. K.; Li, H.; Xiao, S.; Ng, F.; Steigerwald, M. L.; Nuckolls, C. J. Am. Chem. Soc. 2016, 138, 12861−12867. (e) Zhang, B.; Sánchez, R. H.; Zhong, Y.; Ball, M.; Terban, M. W.; Paley, D.; Billinge, S. J. L.; Ng, F.; Steigerwald, M. L.; Nuckolls, C. Nat. Commun. 2018, 9, 1957. (6) (a) Staab, H. A.; Binnig, F. Tetrahedron Lett. 1964, 5, 319−321. (b) Staab, H. A.; Binnig, F. Chem. Ber. 1967, 100, 293−305. (7) (a) Hirst, E. S.; Jasti, R. J. Org. Chem. 2012, 77, 10473−10478. (b) Omachi, H.; Segawa, Y.; Itami, K. Acc. Chem. Res. 2012, 45, 1378−1389. (c) Yamago, S.; Kayahara, E.; Hashimoto, S. Polycyclic Arenes and Heteroarenes: Synthesis, Properties, and Applications; Miao, Q., Ed.; Wiley-VCH: Weinheim, Germany, 2016; Chapter 6, pp 143− 162. (8) For examples of conjugated macrocycles with polycyclic aromatic building blocks, see: (a) Chan, J. M. W.; Tischler, J. R.; Kooi, S. E.; Bulovic, V.; Swager, T. M. J. Am. Chem. Soc. 2009, 131, 5659−5666. (b) Höger, S.; Cheng, X. H.; Ramminger, A.-D.; Enkelmann, V.; Rapp, A.; Mondeshki, M.; Schnell, I. Angew. Chem., Int. Ed. 2005, 44, 2801−2805. (c) Nakamura, K.; Okubo, H.; Yamaguchi, M. Org. Lett. 2001, 3, 1097−1099. (d) Nakanishi, W.; Yoshioka, T.; Taka, H.; Xue, J. Y.; Kita, H.; Isobe, H. Angew. Chem., Int. Ed. 2011, 50, 5323−5326. (e) Yamamoto, Y.; Tsurumaki, E.; Wakamatsu, K.; Toyota, S. Angew. Chem., Int. Ed. 2018, 57, 8199− 8202. (f) Lorbach, D.; Keerthi, A.; Figueira-Duarte, T. M.; Baumgarten, M.; Wagner, M.; Müllen, K. Angew. Chem., Int. Ed. 2016, 55, 418−421. (9) (a) Liu, Y.; Narita, A.; Teyssandier, J.; Wagner, M.; De Feyter, S.; Feng, X.; Müllen, K. J. Am. Chem. Soc. 2016, 138, 15539−15542. (b) Idelson, A.; Sterzenbach, C.; Jester, S.-S.; Tschierske, C.; Baumeister, U.; Höger, S. J. Am. Chem. Soc. 2017, 139, 4429−4434. (10) (a) Ikemoto, K.; Kobayashi, R.; Sato, S.; Isobe, H. Angew. Chem., Int. Ed. 2017, 56, 6511−6514. (b) Ikemoto, K.; Lin, J.; Kobayashi, R.; Sato, S.; Isobe, H. Angew. Chem., Int. Ed. 2018, 57, 8555−8559. (11) Asao, N.; Nogami, T.; Lee, S.; Yamamoto, Y. J. Am. Chem. Soc. 2003, 125, 10921−10925. (12) (a) Lehnherr, D.; Alzola, J. M.; Lobkovsky, E. B.; Dichtel, W. R. Chem. - Eur. J. 2015, 21, 18122−18127. (b) Hein, S. J.; Lehnherr, D.; Dichtel, W. R. Chem. Sci. 2017, 8, 5675−5681. (13) He, Z.; Xu, X.; Zheng, X.; Ming, T.; Miao, Q. Chem. Sci. 2013, 4, 4525−4531. (14) (a) Arslan, H.; Uribe-Romo, F. J.; Smith, B. J.; Dichtel, W. R. Chem. Sci. 2013, 4, 3973−3978. (b) Hein, S. J.; Arslan, H.; Keresztes, I.; Dichtel, W. R. Org. Lett. 2014, 16, 4416−4419. (c) Arslan, H.; Saathoff, J. D.; Bunck, D. N.; Clancy, P.; Dichtel, W. R. Angew. Chem., Int. Ed. 2012, 51, 12051−12054. (d) Lehnherr, D.; Chen, C.; Pedramrazi, Z.; DeBlase, C. R.; Alzola, J. M.; Keresztes, I.; Lobkovsky, E. B.; Crommie, M. F.; Dichtel, W. R. Chem. Sci. 2016, 7, 6357−6364. (15) Lin, S.-H.; Wu, F.-Iy; Liu, R.-S. Chem. Commun. 2009, 6961− 6963. (16) Anthony, J. E.; Khan, S. I.; Rubin, Y. Tetrahedron Lett. 1997, 38, 3499−3502. (17) For examples of synthesizing hexasubstituted triphenylene derivatives using other methods, see: (a) Barnett, L.; Ho, D. M.; Baldridge, K. K.; Pascal, R. A., Jr. J. Am. Chem. Soc. 1999, 121, 727− 733. (b) Hosokawa, T.; Takahashi, Y.; Matsushima, T.; Watanabe, S.; Kikkawa, S.; Azumaya, I.; Tsurusaki, A.; Kamikawa, K. J. Am. Chem. Soc. 2017, 139, 18512−18521. (c) Berezhnaia, V.; Roy, M.; Vanthuyne, N.; Villa, M.; Naubron, J.-V.; Rodriguez, J.; Coquerel, Y.; Gingras, M. J. Am. Chem. Soc. 2017, 139, 18508−18511. (d) Yin, J.; Qu, H.; Zhang, K.; Luo, J.; Zhang, X.; Chi, C.; Wu, J. Org. Lett. 2009, 11, 3028−3031. (e) Rüdiger, E. C.; Rominger, F.; Steuer, L.; Bunz, U. H. F. J. Org. Chem. 2016, 81, 193−196. (f) Wu, Y.; Zhang, W.; Peng, Q.; Ran, C.-K.; Wang, B.-Q.; Hu, P.; Zhao, K.-Q.; Feng, C.; Xiang, S.-K. Org. Lett. 2018, 20, 2278−2281.
these trefoil macrocycles are occupied by the hexyl groups, while the green regions surrounded by the hexyl groups are occupied by disordered solvent molecules, which were removed by using the PLATON/SQUEEZE program.24 In summary, the above study has put forth a new trefoilshaped molecular architecture consisting of three conjugated macrocycles. Trefoil macrocycles 1a and 1b were synthesized from 3,6-dibromo-9,10-dialkyloxyphenathrene via an unprecedented 3-fold copper catalyzed [4 + 2] benzannulation reaction, which is a new approach to hexsubsituted triphenylene derivatives. DFT calculations indicate that the D3-symmetric conformers of this trefoil macrocycle are more stable than the C2-symmetric conformers by 4.82 kcal/mol in Gibbs free energy. In agreement with this, 1b in single crystals exists as a pair of enantiomers with D3-symmetry and exhibits interesting honeycomb-like supramolecular 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.orglett.8b03099. Details of synthesis and characterization, DFT calculations, optical properties, NMR spectra, and crystallographic information for 1b (PDF) Accession Codes
CCDC 1859405 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Qian Miao: 0000-0001-9933-6548 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank Ms. Hoi Shan Chan (the Chinese University of Hong Kong) for the single-crystal crystallography. This work was supported by the Research Grants Council of Hong Kong (CRF C4030-14G).
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REFERENCES
(1) Iyoda, M.; Yamakawa, J.; Rahman, M. Angew. Chem., Int. Ed. 2011, 50, 10522−10553. (2) (a) Bai, J.; Zhong, X.; Jiang, S.; Huang, Y.; Duan, X. Nat. Nanotechnol. 2010, 5, 190−194. (b) Jiang, L.; Fan, Z. Nanoscale 2014, 6, 1922−1945. (3) Bieri, M.; Treier, M.; Cai, J.; Aït-Mansour, K.; Ruffieux, P.; Gröning, O.; Gröning, P.; Kastler, M.; Rieger, R.; Feng, X.; Müllen, K.; Fasel, R. Chem. Commun. 2009, 6919−6921. (4) Naddo, T.; Che, Y.; Zhang, W.; Balakrishnan, K.; Yang, X.; Yen, M.; Zhao, J.; Moore, J. S.; Zang, L. J. Am. Chem. Soc. 2007, 129, 6978−6979. (5) (a) Zhao, W.; Tang, Q.; Chan, H. S.; Xu, J.; Lo, K. Y.; Miao, Q. Chem. Commun. 2008, 4324−4326. (b) Luo, J.; Yan, Q.; Li, T.; Zhu, D
DOI: 10.1021/acs.orglett.8b03099 Org. Lett. XXXX, XXX, XXX−XXX
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Organic Letters (18) Boden, B. N.; Hui, J. K.-H.; Maclachlan, M. J. J. Org. Chem. 2008, 73, 8069−8072. (19) Park, K.; Bae, G.; Moon, J.; Choe, J.; Song, K. H.; Lee, S. J. Org. Chem. 2010, 75, 6244−6251. (20) Chaolumen; Murata, M.; Wakamiya, A.; Murata, Y. Angew. Chem., Int. Ed. 2017, 56, 5082−5086. (21) (a) Kharasch, N.; Alston, T. G.; Lewis, H. B.; Wolf, W. Chem. Commun. 1965, 0, 242−243. (b) Cammidge, A. N.; Gopee, H. J. Mater. Chem. 2001, 11, 2773−2783. (22) (22) Kokkin, D. L.; Reilly, N. J.; Troy, T. P.; Nauta, K.; Schmidt, T. W. J. Chem. Phys. 2007, 126, 084304. (23) Anslyn, E. V.; Dougherty, D. A. Modern Physical Organic Chemistry; University Science Books: Sausalito, CA, 2004; Chapter 7. (24) The crystals contained solvent molecules that could not be properly located due to severe disorder. Therefore, the scattering contribution of disordered area was removed by using the PLATON/ SQUEEZE program. For reference, see: (a) Spek, A. J. J. Appl. Crystallogr. 2003, 36, 7−13. (b) Liu, X.; Zhang, D.; Li, L.; Sun, X.; Zhang, L.; Yuan, H. Dalton Trans 2017, 46, 9103−9109.
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DOI: 10.1021/acs.orglett.8b03099 Org. Lett. XXXX, XXX, XXX−XXX
