Synlett 2017; 28(12): 1422-1426
DOI: 10.1055/s-0036-1588796
letter
© Georg Thieme Verlag Stuttgart · New York

Thieme Chemistry Journal Awardees – Where are They Now?
The Influence of Electron-Withdrawing Groups at the 2- and 2′-Positions of Dibenzothienylethenes on Molecular Switching

Robert Hofsäß, David Rombach, Hans-Achim Wagenknecht*
  • Karlsruhe Institute of Technology (KIT), Institute of Organic Chemistry, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany   Email: Wagenknecht@kit.edu
Further Information

Publication History

Received: 13 February 2017

Accepted after revision: 28 March 2017

Publication Date:
02 May 2017 (eFirst)

Abstract

Three dibenzothienylethenes that carry a methyl, a trifluoromethyl, or a fluoro substituent in the 2- and 2′-position were synthesised in short multistep syntheses, respectively. The trifluoromethyl and fluoromethyl substituents significantly improve the absorption properties of the corresponding open and closed isomers (both in the UV-A and in the visible range). The increasing electron deficiency (i) enlarges the portion of the closed and coloured diarylethene isomer in the corresponding photostationary states and slows down the closing and opening isomerisation, (ii) the switching reactions, both closing and opening, are slowed down, and (iii) the switching quantum yields are lowered.

Supporting Information

 
  • References and Notes

  • 1 Irie M. Chem. Rev. 2000; 100: 1685
  • 2 Irie M. Fukaminato T. Matsuda K. Kobatake S. Chem. Rev. 2014; 114: 12174
  • 3 Szymanski W. Beierle JM. Kistemaker HA. V. Velema WA. Feringa BL. Chem. Rev. 2013; 113: 6114
  • 4 Lubbe AS. Szymanski W. Feringa BL. Chem. Soc. Rev. 2017; 46: 1052
  • 5 Barrois S. Beyer C. Wagenknecht H.-A. Synlett 2012; 23: 711
  • 6 Barrois S. Wagenknecht H.-A. Beilstein J. Org. Chem. 2012; 8: 905
  • 7 Singer M. Jäschke A. J. Am. Chem. Soc. 2010; 132: 8372
  • 8 Cahova H. Jäschke A. Angew. Chem. Int. Ed. 2013; 52: 3186
  • 9 Singer M. Nierth A. Jäschke A. Eur. J. Org. Chem. 2013; 2766
  • 10 Wang H.-X. Xi D.-D. Xie M.-S. Wang H.-X. Qu G.-R. Guo H.-M. ChemBioChem 2016; 17: 1216
  • 11 Hanazawa M. Sumiya R. Horikawa Y. Irie M. J. Chem. Soc., Chem. Commun. 1999; 747
  • 12 Herder M. Schmidt BM. Grubert L. Pätzel M. Schwarz J. Hecht S. J. Am. Chem. Soc. 2015; 137: 2738
  • 13 Herder M. Eisenreich F. Bonasera A. Grafl A. Grubert L. Pätzel M. Schwarz J. Hecht S. Chem. Eur. J. 2017; 23: 3743
  • 14 Morimitsu K. Kobatake S. Nakamura S. Irie M. Chem. Lett. 2003; 32: 858
  • 15 Higashiguchi K. Matsuda K. Asano Y. Murakami A. Nakamura S. Irie M. Eur. J. Org. Chem. 2005; 91
  • 16 Under inert conditions benzo[b]thiophene (7.00 g, 51.1 mmol, 1.00 equiv) was dissolved in dry THF and stirred for 30 min at –78 °C. n-BuLi (26.6 mL, 2.5 M in hexane, 66.5 mmol, 1.30 equiv) was added slowly, and the mixture was stirred for 30 min. MeI (4.90 mL, 11.2 g, 78.9 mmol, 1.54 equiv) was added over 15 min. The reaction was stirred for 20 min at –78 °C, for 3 h at r.t., quenched with water (100 mL), and extracted with EtOAc (4 × 50 mL). The organic layer was dried over Na2SO4, and the solvents were removed in vacuo. After purification by flash chromatography (silica, hexane), 5 could be obtained as a colourless solid in 97% yield (7.26 g, 49.0 mmol). TLC (SiO2, hexane): Rf = 0.54. 1H NMR (400 MHz, DMSO-d 6): δ = 7.85 (dp, J = 7.8, 0.7 Hz, 1 H), 7.74–7.64 (m, 1 H), 7.35–7.21 (m, 2 H), 7.12 (p, J = 1.2 Hz, 1 H), 2.56 (d, J = 1.2 Hz, 3 H) ppm. 13C NMR (101 MHz, DMSO-d 6): δ = 140.57, 140.09, 138.88, 124.19, 123.46, 122.57, 122.05, 121.78, 15.74 ppm. MS (EI): m/z [M]+ calcd for C9H8S: 148.0342; found: 148.0341.
  • 17 A solution of Br2 (2.10 mL, 6.55 g, 41.5 mmol, 1.02 equiv) in CHCl3 (60 mL) was slowly added to a solution of 5 (6.00 g, 40.8 mmol, 1.00 equiv) in CHCl3 (300 mL) over 5 h at r.t. The mixture was stirred for 15 h at r. t., quenched with sat. aq Na2SO3 (50 mL), and extracted with CH2Cl2 (4 × 100 mL). The combined organic layers were washed with sat. aq NaCl (2 × 100 mL), dried over Na2SO4, and the solvents were removed in vacuo. Purification by flash chromatography (silica, hexane) gave 6 as a colourless solid in 96% yield (8.68 g, 38.2 mmol). TLC (SiO2, hexane): Rf = 0.25. 1H NMR (400 MHz, DMSO-d 6): δ = 8.00–7.94 (m, 1 H), 7.68–7.63 (m, 1 H), 7.51–7.38 (m, 2 H), 2.54 (s, 3 H) ppm. 13C NMR (101 MHz, DMSO-d 6): δ = 137.62, 136.57, 135.65, 125.38, 125.14, 122.75, 121.92, 105.78, 15.17 ppm. MS (EI): m/z [M] + calcd for C9H7BrS: 225.9448; found: 225.9446.
  • 18 Under inert conditions, a solution of 6 (1.33 g, 5.86 mmol, 1.00 equiv) in dry THF (8 mL) was stirred at –78 °C for 20 min. n-BuLi (2.80 mL, 2.5 M in hexane, 7.00 mmol, 1.20 equiv) was added. The mixture was stirred for 1 h. Octafluorocyclopentene (1.32 mL, 2.0 M in THF, 2.20 mmol, 0.38 equiv) was added. The reaction was warmed up to r.t. overnight. Water (2 mL) was added, and the reaction was extracted with Et2O (4 × 20 mL). The organic layer was washed with sat. aq NaCl (2 × 30 mL), dried over Na2SO4, and the solvents were removed in vacuo. Flash chromatography (silica, hexane) gave 1 as a colourless solid in 73% yield (1.00 g, 2.15 mmol, isomeric mixture). 1H NMR (400 MHz, DMSO-d 6): δ = 7.92 (d, J = 8.0 Hz, 2 H), 7.88–7.79 (m, 2 H), 7.62 (d, J = 8.7 Hz, 4 H), 7.46 (t, J = 7.6 Hz, 2 H), 7.41–7.35 (m, 2 H), 7.26 (d, J = 9.2 Hz, 4 H), 2.27 (s, 6 H) ppm. 13C NMR (126 MHz, CDCl3-d 1): δ = 141.64, 141.13, 137.29, 137.16, 137.03, 133.18, 133.04, 131.60, 131.45, 128.11, 126.16, 126.07, 123.58, 123.42, 123.33, 123.04, 121.18, 121.13, 121.06, 120.77, 120.62, 118.37, 115.15, 110.45, 97.33, 14.12 ppm. MS–FAB: m/z [M]+ calcd for C23H14F6S2: 468.0438; found: 468.0436.
  • 19 Ye Y. Künzi SA. Sanford MA. Org. Lett. 2012; 14: 4979
  • 20 To a solution of benzo[b]thien-2-yl-boronic acid (1.00 g, 5.62 mmol, 1.00 equiv), CuCl (0.56 g, 5.62 mmol, 1.00 equiv), and NaSO2CF3 (2.63 g, 16.9 mmol, 3.00 equiv) in a mixture of MeOH–CH2Cl2–H2O (11.2 mL/11.2 mL/8.99 mL), tert-butyl hydroperoxide solution (3.82 mL, 70% in H2O, 28.1 mmol, 5.00 equiv) were added at 0 °C and stirred overnight. Et2O (90 mL) was added, and the organic layer was washed with sat. aq NaHCO3 (70 mL), sat. aq Na2SO3 (25 mL), and dried over Na2SO4. The solvents were removed in vacuo. Purification by flash chromatography (silica, hexane) gave 8 as a colourless solid in 77% yield (769 mg, 4.33 mmol). TLC (SiO2, hexane): Rf = 0.64. 1H NMR (400 MHz, DMSO-d 6): δ = 8.19–8.12 (m, 2 H), 8.06–8.01 (m, 1 H), 7.61–7.50 (m, 2 H) ppm. 13C NMR (101 MHz, DMSO-d 6): δ = 139.43, 137.56, 129.01, 127.35, 127.19, 125.66, 123.79, 123.16, 121.28 ppm. MS (EI): m/z [M]+ calcd for C9H5F3S: 202.0059; found: 202.0057.
  • 21 Under inert conditions 8 (250 mg, 1.24 mmol, 1.00 equiv) were dissolved in dry THF (5 mL) and stirred for 20 min at –78 °C. n-BuLi (544 μL 2.0 M in hexane; 1.36 mmol, 1.10 equiv) were added slowly, and the mixture was stirred for 1 h. Octafluorocyclopentene (279 μL, 2.0 M in THF, 0.560 mmol, 0.450 equiv) were added, and the mixture was warmed to r.t. overnight. The reaction was quenched with sat. aq NH4Cl (4 mL) and extracted with Et2O (3 × 30 mL). The organic layer was dried over Na2SO4, and the solvents were removed in vacuo. Purification by flash chromatography (silica, hexane) gave 2 as a colourless solid in 75% yield (267 mg, 0.463 mmol). TLC (SiO2, hexane): Rf = 0.21. 1H NMR (400 MHz, DMSO-d 6): δ = 8.24 (dd, J = 6.4, 2.7 Hz, 1 H), 8.14 (d, J = 7.9 Hz, 2 H), 8.06 (d, J = 8.1 Hz, 2 H), 7.78–7.65 (m, 3 H), 7.59–7.46 (m, 4 H) ppm. 13C NMR (126 MHz, CDCl3-d 1): δ = 141.23, 141.00, 140.80, 140.53, 138.65, 138.44, 137.57, 136.80, 132.08, 131.78, 131.49, 131.16, 127.68, 127.46, 125.83, 125.54, 124.38, 124.36, 122.77, 122.34, 121.72, 120.56, 120.45, 118.40, 117.67, 117.47, 115.58, 115.41, 115.19, 113.50, 113.30, 113.13, 111.33, 111.13, 110.93 ppm. MS–FAB: m/z [M]+ calcd for C23H8F12S2: 575.9870; found: 575.9869.
  • 22 Under inert conditions, benzo[b]thiophene (2.30 g, 17.2 mmol, 1.00 equiv) was dissolved in dry THF (140 mL) and stirred for 20 min at –78 °C. n-BuLi (12.8 mL, 2.5 M in hexane, 32.0 mmol, 1.86 equiv) was added dropwise, and the resulting mixture was stirred for 1 h at –78 °C. N-Fluorobenzenesulfonimide (12.5 g, 39.7 mmol, 3.21 equiv) was added in two portions at an interval of 15 min. The reaction mixture was stirred for 2 h at –78 °C, 16 h at r.t., stopped by addition of water (30 mL), and extracted with EtOAc (4 × 50 mL). The organic layer was dried over Na2SO4, and the solvents were removed in vacuo. After flash chromatography (silica, hexane) 9 could be obtained as a colourless oil in 59 % yield (1.53 g, 10.1 mmol). TLC (SiO2, hexane): Rf = 0.71. 1H NMR (300 MHz, DMSO-d 6): δ = 7.90 (d, J = 7.7 Hz, 1H), 7.73 (d, J = 6.3 Hz, 1 H), 7.44–7.32 (m, 2 H), 7.11 (d, J = 2.7 Hz, 1 H) ppm. 13C NMR (75 MHz, DMSO-d 6): δ = 161.88, 135.63, 131.20, 125.28, 124.51, 124.45, 123.60, 123.51, 122.81, 104.09, 103.94 ppm. MS (EI): m/z [M]+ calcd for C8H5FS: 152.0091; found: 152.0092.
  • 23 Under inert conditions, 9 (1.18 g, 7.72 mmol, 1.00 equiv) was dissolved in dry CHCl3 (8 mL). NaOAc (1.17 g, 14.2 mmol, 1.85 equiv) was added, and the mixture was stirred for 15 min at r.t. A solution of Br2 (394 μL 1.23 g, 7.72 mmol, 1.00 equiv) in dry CHCl3 (2 mL) was added dropwise over 30 min. The solution was stirred for 2 h at r.t., quenched with sat. aq Na2SO3, and extracted with hexane (4 × 25 mL). The organic layer was dried over Na2SO4, and the solvent was removed under reduced pressure. Purification of the crude product was done by flash chromatography (silica, hexane). The product was dried in vacuo overnight to remove last traces of the volatile starting material 9. The pure product 10 was isolated as pale yellow oil in 76% yield (1.35 g, 5.56 mmol). TLC (SiO2, hexane): Rf = 0.76. 1H NMR (300 MHz, DMSO-d 6): δ = 8.02 (d, J = 8.0 Hz, 1 H), 7.68 (d, J = 7.8 Hz, 1 H), 7.55 (dd, J = 7.6 Hz, 1 H), 7.48 (dd, J = 7.7 Hz, 1 H) ppm. 13C NMR (75 MHz, DMSO-d 6): δ = 160.02, 157.15, 133.58, 129.34, 126.35, 126.08, 126.03, 123.69, 122.19, 122.13, 88.45, 88.32 ppm. MS (EI): m/z calcd for C8H4SFBr: 229.2; found: 230.1.
  • 24 Under inert conditions, n-BuLi (1.05 mL, 2.0 M in hexane, 2.10 mmol, 1.01 equiv) was dissolved in dry THF (1 mL) at –78 °C. A solution of 10 (480 mg, 2.08 mmol, 1.00 equiv) in dry THF (700 μL) was added dropwise over 15 min and stirred for 45 min at –78 °C. Octafluorocyclopentene (261 μL, 3.6 M in THF, 0.936 mmol, 0.45 equiv) was added, and the reaction mixture was stirred for 24 h at r.t. The reaction was quenched with water (4 mL) and extracted with Et2O (4 × 20 mL). The organic layer was dried over Na2SO4, and the solvents were removed in vacuo. The product was purified by flash chromatography (silica, hexane) and 3 was isolated as a colourless solid in 46% yield (204 mg, 0.428 mmol, isomeric mixture). TLC (SiO2, hexane): Rf = 0.35. 1H NMR (500 MHz, CDCl3-d 1): δ = 7.61–7.55 (m, 1 H), 7.50 (dd, J = 6.5, 2.5 Hz, 1 H), 7.35–7.27 (m, 2 H) ppm. 13C NMR (126 MHz, CDCl3-d 1): δ = 165.63, 163.24, 141.69, 138.37, 137.49, 137.28, 137.06, 133.59, 130.58, 127.23, 126.00, 125.50, 125.47, 122.72, 122.16, 117.98, 117.97, 117.60, 115.92, 115.73, 115.54, 113.87, 113.68, 113.48, 113.28, 111.52, 111.31, 111.11, 109.35, 109.15, 108.95, 104.00, 103.94, 77.41, 77.16, 76.91 ppm. MS–FAB: m/z calcd for C23H8F8S2: 475.9934; found: 475.9935.
  • 25 Megerle U. Lechner R. König B. Riedle E. Photochem. Photobiol. Sci. 2010; 9: 1400
  • 26 Sumi T. Takagi Y. Yagi A. Morimoto M. Irie M. Chem. Commun. 2014; 50: 3928