3,3′,5,5′-Tetra-tert-butyl-4,4′-diphenoquinone (DPQ)-Air as a New Organic Photocatalytic System: Use in the Oxidative Photocyclization of Stilbenes to Phenacenes

Abstract

We report an organic photocatalytic system, namely 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone (DPQ) and air, capable of coupling efficiently with the photocyclization of stilbenes to afford phenacenes. The potential of this new and mild process is shown with the synthesis of [5]- and [7]phenacene, two semiconductors recently implemented into organic electronic devices, with high yields and remarkable purity.

Key words

photocatalysis - solar light - fused-ring aromatic system - armchair junctions - diphenoquinone - phenacene

• References and Notes

• 1 Wang C, Dong H, Hu W, Liu Y, Zhu D. Chem. Rev. 2012; 112: 2208
• 2a Allard S, Forster M, Souharce B, Thiem H, Scherf U. Angew. Chem. Int. Ed. 2008; 47: 4070
• 2b Kubozono Y, He X, Hamao S, Teranishi K, Goto H, Eguchi R, Kambe T, Gohda S, Nishihara Y. Eur. J. Inorg. Chem. 2014; 3806
• 3 Okamoto H, Kawasaki N, Kaji Y, Kubozono Y, Fujiwara A, Yamaji M. J. Am. Chem. Soc. 2008; 130: 10470
• 4a Sugawara Y, Kaji Y, Ogawa K, Eguchi R, Oikawa S, Gohda S, Fujiwara A, Kubozono Y. App. Phys. Lett. 2011; 98: 013303
• 4b Komura N, Goto H, He X, Mitamura H, Eguchi R, Kaji Y, Okamoto H, Sugawara Y, Gohda S, Sato K, Kubozono Y. Appl. Phys. Lett. 2012; 101: 083301
• 5 Mitsuhashi R, Suzuki Y, Yamanari Y, Mitamura H, Kambe T, Ikeda N, Okamoto H, Fujiwara A, Yamaji M, Kawasaki N, Maniwa Y, Kubozono Y. Nature (London, U.K.) 2010; 464: 76
• 6 Heguri S, Kobayashi M, Tanigaki K. Phys. Rev. B 2015; 92: 014502
• 7 Mallory FB, Mallory CW. Org. React. 1984; 30: 1
• 8a Goedicke C, Stegemeyer H. Ber. Bunsenges. Phys. Chem. 1969; 73: 782
• 8b Sension RJ, Repinec ST, Szarka AZ, Hochstrasser RM. J. Chem. Phys. 1993; 98: 6291
• 9 Fujiya A, Kariya A, Nobuta T, Tada N, Miura T, Itoh A. Synlett 2014; 25: 884
• 10 Liu L, Yang B, Katz TJ, Poindexter MK. J. Org. Chem. 1991; 56: 3769
• 11 Jørgensen KB. Molecules 2010; 15: 4334
• 12a Kahlich D, Wiechern U, Lindner J. Propylene Oxide, In Ullmann's Encyclopedia of Chemical Technology . Wiley-VCH; Weinheim: 2003. 6th ed., Vol. 30 279-303
• 12b International Agency for Research on Cancer (IARC), Propylene Oxide (Group 2B) in IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Overall Evaluations of Carcinogenicity, An Updating of IARC Monographs, Vol. 60, Suppl. 7, 1994, 181–213.
• 13 Artioli GA, Malavasi L. J. Mater. Chem. C 2014; 2: 1577
• 14 Okamoto H, Yamaji M, Gohda S, Kubozono Y, Komura N, Sato K, Sugino H, Satake K. Org. Lett. 2011; 13: 2758
• 15 Chang N.-H, Chen X.-C, Nonobe H, Okuda Y, Mori H, Nakajima K, Nishihara Y. Org. Lett. 2013; 15: 3558
• 16 Okamoto H, Takane T, Gohda S, Kubozono Y, Sato K, Yamaji M, Satake K. Chem. Lett. 2014; 43: 994
• 17 Protti S, Artioli GA, Capitani F, Marini C, Dore P, Postorino P, Malavasi L, Fagnoni M. RSC Adv. 2015; 5: 27470
• 18 Synthesis of [5]Phenacene (2) A solution of 1,2-dinaphthylethene (1, 0.5614 g, 2.0 mmol) and DPQ (0.0409 g, 0.1 mmol) in CHCl₃ (600 mL) was prepared in a 1 L jacketed Pyrex reactor and was mechanically stirred at ca. 160 rpm, open to the air. The recirculation chiller was turned on, and the solution was irradiated with a 400 W high-pressure Hg lamp for 8 h (Figure S1). The advance of the reaction was followed by TLC (1 has a strong blue fluorescence). After the reaction was completed, the solution was concentrated to dryness at a reduced pressure (15 Torr). The CHCl₃ was recycled, and acetone was added to the residue (50 mL). After stirring, this suspension was filtered off, washed with fresh acetone, and dried at 110 °C to afford 0.5193 g (93%) of an off-white powder. A sample of picene was recrystallized for analytical purposes from toluene to give white crystals; mp 364.9 °C (T _onset by DSC). ¹H NMR (300 MHz, CDCl₃): δ = 7.63–7.70 (m, 1 H), 7.71–7.79 (m, 1 H), 7.99–8.07 (m, 2 H), 8.80 (d, J = 9.2 Hz, 1 H), 8.87 (d, J = 8.6 Hz, 1 H), 8.97 (s, 1 H). MS (EI): m/z = 280 (2.7) [M⁺ + 2], 279 (23) [M⁺ + 1], 278 (100) [M⁺], 277 (11), 276 (25), 139 (13), 138 (13). IR (neat): ν_max = 3050, 1597, 1526, 1474, 1446, 1432, 1275, 1264, 1134, 1024, 945, 869, 852, 807, 754, 739, 671 cm^–1. Anal. Calcd for C₂₂H₁₄: C, 94.93; H, 5.07. Found: C, 94.73; H, 5.09. For the reaction using sunlight (Figure S2), a solution of 1,2-dinaphthylethene (1, 0.0569 g, 0.2 mmol) and DPQ (0.0148 g, 0.02 mmol) in CHCl₃ (10 mL) was exposed to sunlight and allowed to stand for 7 d (this includes days and nights). The flask was opened regularly to follow the advance of the reaction by TLC. Working up the reaction as described above produced 0.0391 g (69%) of picene as an off-white crystalline powder.

The molar solubility of O₂ in isooctane (1.6·10⁻² mol O₂/l at 20 °C, 1 atm) is a 76% higher than in CHCl₃, a 41% higher than in cyclohexane, and a 77% higher than in benzene, all of them typical solvents for this reaction:
• 19a Battino R. Rettich T. R. 1983; 12: 163
• 19b Shirono K, Morimatsu T, Takemura F. J. Chem. Eng. Data 2008; 53: 1867
• 20 Wardman P. J. Phys. Chem. Ref. Data 1989; 18: 1637
• 21 Takahashi K, Suzuki T. J. Am. Chem. Soc. 1989; 111: 5483
• 22 Görner H. Quinone Photochemistry . In CRC Handbook of Organic Photochemistry and Photobiology . Vol. 1. Griesbeck A, Oelgemöller M, Ghetti F. CRC Press; Boca Raton: 2012: 683-702
• 23 Görner H. Photochem. Photobiol. 2010; 86: 1202
• 24 This is backed up by the fact that DPQ was recovered unchanged (84% after recrystallization) with no signs of any reaction after 50 d of irradiation with four 300 W tungsten filament lamps, being described to be entirely photostable: Bruce JM, Chaudhry A.-U.-H. J. Chem. Soc., Perkin Trans. 1 1974; 295
• 25 In control experiments, a sample of DPQH₂ in CHCl₃ (4·10^–3 M, standard reaction conditions) open to the air was stirred (160 rpm) in the dark for 7 d. Subsequent GLC analysis showed no detectable amounts of DPQ. However, the same sample under UV irradiation turned quickly into reoxidized DPQ, the conversion being >90% complete in less than 1 h.
• 26 Concerning the yield of 4, we noticed that our experimental set-up works better for larger π-conjugated systems, so we suspect that our current source of UV light is the limiting parameter. A careful analysis of the reaction crude reveals small amounts of chrysene (C₁₈H₁₂), indicating that an oxidative pathway affecting the methyl substituent probably followed by decarboxylation might be taking place. As this byproduct only accounts for a small amount of the missing yield (<3%), and we were not able to identify the bulk of it, it is likely that radical polymerization occurs accounting for the unexpected medium yield reported.
• 27 Synthesis of [7]Phenacene (7) A suspension of 1-[(E)-2-(1-naphtyl)vinyl]chrysene (6, 0.3841 g, 1 mmol) and DPQ (0.1223 g, 0.1 mmol) in CHCl₃ (600 mL) was irradiated following the same procedure explained for picene (2). The advance of the reaction could be followed by TLC (6 has a white-blue fluorescence). After the reaction was completed (8 h) the mixture was concentrated under reduced pressure (15 Torr), the solid was filtered off, washed with acetone, and dried to give 0.3501 g (92%) of 7 as off-white plates. The product was recrystallized for analytic purposes with 1,2-dichlorobenzene; mp (decomp.) = 569.9 °C (T _peak by DSC). ¹H NMR (400.13 MHz, (CDCl₂)₂ at 358 K): δ = 7.71–7.77 (m, 2 H), 7.79–7.85 (m, 2 H), 8.07–8.11 (m, 2 H), 8.14 (d, J = 9.2 Hz, 2 H), 8.90–8.95 (m, 4 H), 9.06 (d, J = 9.3 Hz, 2 H), 9.09 (s, 2 H), 9.15 (d, J = 9.2 Hz, 2 H). MS (EI, DIP): m/z = 380 (5) [M⁺ + 2], 379 (32) [M⁺ + 1], 378 (100) [M⁺], 376 (18), 189 (27), 188 (19), 187 (13). IR (neat): ν_max = 3056, 1469, 1442, 1432, 1282, 1234, 1145, 1128, 1028, 944, 866, 842, 805, 768, 740, 711 cm^–1. Anal. Calcd for C₃₀H₁₈: C, 95.21; H, 4.79. Found: C, 95.21; H, 4.50. For the reaction using sunlight (Figure S2), a solution of 6 (0.0076 g, 0.02 mmol) and DPQ (0.0015 g, 0.002 mmol) in CHCl₃ (30 mL) was exposed to sunlight in a 50 mL flask and was allowed to stand for 7 d (this includes days and nights). Working up the reaction as described above gave 0.0056 g (74%) of [7]phenacene as off-white crystalline plates.