G. Zyryanov, Manuel A. Palacios, P. Anzenbacher
2020
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Abstract
1,4-Diarylpentiptycenes (1a-e) were synthesized from 1,4-dichloroor 1,4-difluoro-2,5-diarylbenzene derivatives by double base-promoted dehydrohalogenation to give corresponding arynes, which in the presence of anthracene undergo cycloaddition providing 1,4-diarylpentiptycenes in moderate overall yields. The resulting 1,4-diarylpentiptycenes show fluorescence modulated by the 1,4-aryl residues. The fluorescence is quenched in the presence of vapors of nitroaromatic compounds suggesting potential application in sensing of explosives. Host materials that form inclusion complexes with small molecules are the subject of considerable interest owing to potential applications in the preparation of sensors and materials for selective sequestration of substrates of interest. Growing attention is currently devoted to studying supramolecular complexes of a wide variety of lipophilic hosts for electroneutral species that include calixarenes and related macrocycles, cyclodextrins, cycloveratrylenes, cryptophanes, cucurbiturils, and their derivatives. The interest in pentiptycene receptors was sparked by the discovery that iptycenes bind nitroaromate explosives used in landmines and improvised explosive devices. The materials successfully used for detection of nitroaromates are fluorescent polymers with the ability to form complexes with nitroaromates while changing their emission. Examples are polyphenyleneethynylenes with integrated pentiptycene receptors, polyphenylenebutadiynylenes, polyacetylenes, and polymetalloles such as polysiloles. As a part of our work on polythiophene conductivity-based sensors we decided to investigate electropolymerizable pentiptycene receptors carrying thiophene moieties to be deposited as electrochemical sensors for TNT. Pentiptycene derivatives are most frequently synthesized by the Clar synthesis, which involves double Diels-Alder (1) Calixarenes 2001; Asfari, Z., Bohmer, V., Harrowfield, J., Vicens, J, Eds.; Kluwer Academic Publishers: Dordrecht, 2001. (2) ComprehensiVe Supramolecular Chemistry; Atwood, J. L., Davies, J. E., MacNicol, D. D., Vögtle, F., Reinhoudt, D. N., Lehn, J.-M., Eds.; Volume 3: Cyclodextrins; Szejtl, J., Osa, T., Volume Eds.; PergamonElsevier Science: Oxford, 1996. (3) ComprehensiVe Supramolecular Chemistry; Volume 6: Solid-state supramolecular chemistry; MacNicol, D. D., Toda, F., Bishop, R., Volume Eds.; Pergamon-Elsevier Science, Oxford, 1996; pp 281-303. (4) Collet, A. Tetrahedron 1987, 43, 5725. (5) Lagona, J.; Mukhopadhyay, P.; Chakrabarti, S.; Isaacs, L. Angew. Chem., Int. Ed. 2005, 44, 4844. (6) (a) Thomas, S. W., III.; Joly, G. D.; Swager, T. M. Chem. ReV. 2007, 107, 1339. (b) Yang, J.-S.; Swager, T. M. J. Am. Chem. Soc. 1998, 120, 5321. (c) Yang, J.-S.; Swager, T. M. J. Am. Chem. Soc. 1998, 120, 11864. (7) (a) Forensic InVestigation of Explosions, 1st ed.; Beveridge, A., Ed.; Forensic Science Series; Taylor & Francis: London, 1998. (b) Containing the Threat from Illegal Bombings: An Integrated National Strategy for Marking, Tagging, Rendering Inert, and Licensing ExplosiVes and Their Precursors; National Academy Press: Washington DC, 1998. (8) (a) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. ReV. 2000, 100, 2537. (b) Zhao, D.; Swager, T. M. Macromolecules 2005, 38, 9377. (c) Liu, Y.; Mills, R. C.; Boncella, J. M.; Schanze, K. S. Langmuir 2001, 17, 7452. (d) Sohn, H.; Sailor, M. J.; Magde, D.; Trogler, W. C. J. Am. Chem. Soc. 2003, 125, 3821. (e) Sohn, H.; Calhoun, R. M.; Sailor, M. J.; Trogler, W. C. Angew. Chem., Int. Ed. 2001, 40, 2104. (9) Aldakov, D.; Anzenbacher, P., Jr. J. Am. Chem. Soc. 2004, 126, 4752. ORGANIC LETTERS 2008 Vol. 10, No. 17 3681-3684 10.1021/ol801030u CCC: $40.75 2008 American Chemical Society Published on Web 07/26/2008 cycloaddition of an acene to benzoquinone. The resulting pentiptycene quinone 2 may then be reacted with organometallic reagents such as lithium acetylides to yield 1,4substituted derivatives 3 according to Scheme 1, which was utilized by Swager to generate poly-(phenyleneethynylene)s comprising pentiptycene moieties. Unfortunately, there is no literature describing a similar approach using aryllithiums or arylmagnesium halides. This pattern of limited reactivity of both iptycenebenzoquinone carbonyls was also observed by Yang et al., who synthesized pentiptycenes with middle ring substituents (described here as 1,4-positions based on the p-benzoquinone). Yang et al. successfully attached a variety of substituents to 1,4-positions, however, carbon substituents proved difficult to introduce to both 1,4-positions. Notable exceptions are the acetylene derivatives introduced following the outline in Scheme 1. Originally, we believed the lack of a direct coupling method to be due to the limited availability of the 1,4-dihalo derivatives. However, Yang et al. were able to successfully perform a Suzuki-Miyaura coupling on 1-alkoxy-4-iodopentiptycene in 72% yield. In an effort to circumvent the problem of limited availability of 1,4-dihalo derivatives, we synthesized the corresponding 1,4-triflate 4, which we hoped would react in Pd0-catalyzed reactions such as the Stille, Suzuki-Miyaura, and Negishi couplings (Scheme 2). The reduction of quinone 2 to the corresponding hydroquinone form followed by reaction with triflic anhydride in pyridine at 0 °C gave the corresponding bistriflate 4 in a quantitative yield (>99%). Triflate 4 is a stable crystalline compound that can be prepared at a multigram scale. The coupling procedures, however, failed to yield 1,4diarylpentiptycenes 1 in yields exceeding 9%. The starting material 4 was recovered regardless of the coupling method or reaction conditions. Simultaneously with the above approach, we attempted to construct the 1,4-diarylpentiptycene using the aryneanthracene [4 + 2] cycloaddition approach. Toward this end we considered several strategies to generate a 1,4-diaryl bisaryne precursor 5 to be reacted with anthracene. Numerous methods of generating benzyne are known from the literature, starting, for example, from haloaromates using sodium amide or other strong bases, 1,2-dihaloarenes, from arenediazonium ions derived from anthranilic acid, 2-(trimethylsilyl)phenyl triflates, aminotriazoles, and aryl[2-(trimethylsilyl)phenyl]iodonium triflates, etc. Compared to the double dehydrohalogenation, these methods of generating aryne are often carried out using mild conditions and furnish moderate to high yields of corresponding arynes. However, the preparation of the hexasubstituted benzene precursors requires multiple-steps syntheses that with exception of tetrahalo-1,2-diarylbenzenes in our hands did not (10) (a) Clar, E. Chem. Ber. 1931, 64, 1676. (b) Cadogan, J. I. G.; Hall, J. K. A.; Sharp, J. T. J. Chem. Soc. C. 1967, 1860. (c) Cadogan, J. I. G.; Harger, M. J. P.; Sharp, J. T. J. Chem. Soc. B. 1971, 602. (11) Zhu, X.-Z.; Chen, C.-F. J. Org. Chem. 2005, 70, 917. (12) Yang, J. S.; Ko, C.-W. J. Org. Chem. 2006, 71, 844. (13) Yang, J. S.; Yan, J. L. Chem. Commun. 2008, 1501. (14) Hart, H.; Shamouilian, S.; Takehira, Y. J. Org. Chem. 1981, 46, 4427. (15) Williams, V. E.; Swager, T. M. Macromolecules 2000, 33, 4069. (16) Rare Sonogashira coupling of 1,4-diiodopentiptycene was reported by: Williams, V. E.; Yang, J. S.; Lugmair, C. G.; Miao, Y. J.; Swager, T. M. Proc. SPIE 1999, 3710 (Pt. 1), 402. (17) (a) Miyaura, N. In Metal-Catalyzed Cross-Coupling Reactions; De Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, 2004; p 41. (b) Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122, 4020. (18) Mitchell, T. N. In Metal-Catalyzed Cross-Coupling Reactions; De Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, 2004; p 125. (19) Negishi, E.-I.; Dumond, Y. In Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi, E.-I., Ed.; Wiley: New York, 2002; Vol. 1, p 229. (20) Yang, J.-S.; Lee, C.-C.; Yau, S.-L.; Chang, C.-C.; Lee, C.-C.; Leu, J.-M. J. Org. Chem. 2000, 65, 871. (21) (a) Hoffman, R. W. Dehydrobenzene and Cycloalkynes; Academic Press: New York, 1967. (b) Gilchrist, T. L. In The Chemistry of Functional Groups; Supplement C, Chapter 11; Patai, S.; Rappoport, Z.; Eds.; Wiley, Chichester, 1983. (c) Hart, H. In The Chemistry of Triple-Bonded Functional Groups; Supplement C2, Chapter 18; Patai, S. ; Ed.; Wiley, Chichester, 1994. (22) Pellisier, H.; Santenelli, M. Tetrahedron 2003, 59, 701. (23) Shahlai, K.; Acquaah, S. O.; Hart, H. Organic Syntheses 2004, 10, 678; Organic Syntheses 1998, 75, 678. (24) Buxton, P. C.; Heaney, H. J. Chem. Soc., Chem. Commun. 1973, 545. (25) Campbell, C. D.; Rees, C. W. J. Chem. Soc. (C) 1969, 742. (26) Hart, H.; Ok, D. J. Org. Chem. 1986, 51, 979. (27) (a) Kitamura, T.; Yamane, M.; Inoue, K.; Todaka, M.; Fukatsu, N.; Meng, Z.; Fujiwara, Y. J. Am. Chem. Soc. 1999, 121, 11674. (b) Kitamura, T.; Yamane, M. J. Chem. Soc. Chem. Commun. 1995, 9, 983. Scheme 1. Synthesis of 1,4-Substituted Pentiptycenes Scheme 2. Alternative Synthesis of 1,4-Diaryl Pentiptycenes X-ray ORTEP representation of 4 (displacement ellipsoids are scaled to the 50% probability level). 3682 Org. Lett., Vol. 10, No. 17, 2008 result in overall yields exceeding 40% of the precursor for the preparation of diaryl bisaryne 5. Because we are targeting low-cost precursors for the sensor polymers, we decided to focus on a more straightforward method that would utilize few synthetic steps and would be easy to scaleup. For this reason, we decided to investigate the simple dehydrohalogenation/Diels-Alder cycloaddition of an in situ generated aryne to anthracene. There are literature precedents, albeit not for diarylpentiptycenes, suggesting that this reaction would proceed. For example, Hart described a Bu-Li promoted reaction of 3,6-substituted 1,2,4,5-tetrabromobenzene derivatives in the presence of anthracene to yield pentiptycene, 1,4-dimethylpentiptycene, and 1,4-dimethoxypentiptycene in 26, 14, and 21% yield, respectively. An earlier report by Cadogan describes t