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Synlett 2013; 24(9): 1142-1146
DOI: 10.1055/s-0032-1316909
letter
© Georg Thieme Verlag Stuttgart · New York

Indium-Catalyzed Friedel–Crafts Alkylation of Monosubstituted Benzenes by 1-Bromoadamantane

Paul Mosset*
Université de Rennes 1, Institut des Sciences Chimiques de Rennes, CNRS UMR 6226, Avenue du Général Leclerc, 35042 Rennes Cedex, France   Fax: +33(2)23236978   Email: paul.mosset.1@univ-rennes1.fr
,
René Grée
Université de Rennes 1, Institut des Sciences Chimiques de Rennes, CNRS UMR 6226, Avenue du Général Leclerc, 35042 Rennes Cedex, France   Fax: +33(2)23236978   Email: paul.mosset.1@univ-rennes1.fr
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Publication History

Received: 12 February 2013

Accepted after revision: 19 March 2013

Publication Date:
12 April 2013 (online)

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Abstract

Indium salts such as InCl3 and InBr3 (ca. 1–5 mol%) ­efficiently catalyzed the Friedel–Crafts reaction of 1-bromo­adamantane with benzene and monosubstituted benzenes to give 1-adamantyl benzenes. Indium bromide enabled faster reactions than indium chloride but the latter was more suitable in the case of halobenzenes.

Key words

adamantanes - alkylation - catalysis - indium - Lewis ­acids

Supporting Information

    for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett.
  • Supporting Information
 

  • References and Notes

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  • 20 Using more InBr3 than 0.05 equiv favored the formation of a small amount of the more polar 1,3-diphenyladamantane.
  • 21 Indium mesylate and tosylate were prepared by dissolving metallic indium powder in aqueous methanesulfonic acid (3.2 equiv) or p-toluenesulfonic acid (3.0 equiv) at 70 °C (respectively 0.3 and 0.8 mL H2O/mmol In was used) for respectively 2 and 20 h, followed by removal of water under vacuum at 70 °C. Remarkably, in contrast to indium mesylate and halides, indium tosylate did not exhibit appreciable hygroscopicity, a fact that made it far more convenient to handle.
  • 22 Representative Procedure: InBr3 (7.1 mg, 0.02 mmol) was introduced in an oven- or flame-dried 10 mL round-bottomed flask followed by an olive-shaped magnetic stirring bar. The apparatus was dried by heating for 1–2 min with a heat gun under vacuum. 1-Bromoadamantane (1; 86 mg, 0.4 mmol) and the monosubstituted benzene 2a–h (or benzene itself, 1 mL) were added. The flask was flushed under nitrogen and well stoppered.26 The reaction was left under gentle stirring in a water or oil bath at the specified temperature (see Tables) with protection against light by aluminum foil. After reaction for the specified time (see Tables), abundant evolution of hydrogen bromide (white smoke, caution!) occurred on opening. The reaction mixture was taken up with pentane and washed with water until neutral. After drying (Na2SO4) and concentration, chromatography on silica gel (ca. 3 g), eluting with pentane, afforded monoadamantylated benzene 3a–h followed in some cases by more polar 1-bromo-3-aryladamantane (4) and 1,3-diaryladamantane (5). 1-Phenyladamantane (3a): Mp 82 °C. 1H NMR (400 MHz, CDCl3): δ = 7.37 (dm, J ~ 8 Hz, 2 H), 7.31 (ddm, J = 8.2, 6.8 Hz, 2 H), 7.17 (ddt, J = 7.6, 6.7, 1.4 Hz, 1 H), 2.12–2.07 (m, 3 H), 1.92 (d, J = 2.8 Hz, 6 H), 1.83–1.72 (m, 6 H). 13C NMR (100 MHz, CDCl3): δ = 151.34 (1Cq), 128.10 (2CH), 125.50 (1CH), 124.84 (2CH), 43.23 (3CH2), 36.88 (3CH2), 36.22 (1Cq), 29.04 (3CH). 1-(4-Methylphenyl)adamantane (3b): Mp 97–98 °C. 1H NMR (400 MHz, CDCl3): δ = 7.26 (half of an A2X2 system, 2 H), 7.13 (half of an A2X2 system coupled with CH3, J with Me = 0.7 Hz, 2 H), 2.32 (t, J = 0.7 Hz, 3 H, CH 3), 2.12–2.05 (m, 3 H), 1.90 (broad d, J = 2.8 Hz, 6 H), 1.82–1.71 (m, 6 H). 13C NMR (100 MHz, CDCl3): δ = 148.48 (1Cq), 134.90 (1Cq), 128.81 (2CH), 124.72 (2CH), 43.30 (3CH2), 36.87 (3CH2), 35.85 (1Cq), 29.03 (3CH), 20.87 (1CH3). 1-(4-Ethylphenyl)adamantane (3c): Mp 58 °C. 1H NMR (400 MHz, CDCl3): δ = 7.28 (half of an A2X2 system, 2 H), 7.15 (half of an A2X2 system coupled with CH2, J with CH2 = 0.6 Hz, 2 H), 2.62 (q, J = 7.6 Hz, 2 H, CH 2CH3), 2.12–2.05 (m, 3 H), 1.91 (broad d, J = 2.8 Hz, 6 H), 1.82–1.71 (m, 6 H), 1.23 (t, J = 7.6 Hz, 3 H, CH2CH 3). 13C NMR (100 MHz, CDCl3): δ = 148.68 (1Cq), 141.23 (1Cq), 127.55 (2CH), 124.75 (2CH), 43.29 (3CH2), 36.87 (3CH2), 35.88 (1Cq), 29.03 (3CH), 28.29 (1CH2), 15.45 (1CH3). 1-(4-Isopropylphenyl)adamantane (3d): Mp 87 °C. 1H NMR (400 MHz, CDCl3): δ = 7.28 (half of an A2X2 system, 2 H), 7.18 (half of an A2X2 system coupled with CH, J with CH = 0.6 Hz, 2 H), 2.88 [qq, J = 6.9, 6.9 Hz, 1 H, CH(CH3)2], 2.12–2.05 (m, 3 H), 1.91 (broad d, J = 2.8 Hz, 6 H), 1.82–1.70 (m, 6 H), 1.24 [d, J = 6.9 Hz, 6 H, CH(CH 3)2]. 13C NMR (100 MHz, CDCl3): δ = 148.74 (1Cq), 145.81 (1Cq), 126.09 (2CH), 124.69 (2CH), 43.29 (3CH2), 36.88 (3CH2), 35.87 (1Cq), 33.55 (1CH), 29.03 (3CH), 24.02 (2CH3). 1-(4-Isobutylphenyl)adamantane (3e): Mp 34.5 °C. 1H NMR (400 MHz, CDCl3): δ = 7.25 (half of an A2X2 system, 2 H), 7.08 (half of an A2X2 system coupled with CH2, J with CH2 = 0.6 Hz, 2 H), 2.44 (d, J = 7.2 Hz, 2 H, CH2 of i-Bu), 2.12–2.05 (m, 3 H), 1.91 (broad d, J = 2.8 Hz, 6 H), 1.85 [tqq, J = 7.2, 6.6, 6.6 Hz, 1 H, CH(CH3)2], 1.82–1.70 (m, 6 H), 0.90 (d, J = 6.6 Hz, 6 H, CH(CH 3)2). 13C NMR (CDCl3, 100 MHz): δ = 148.67 (1Cq), 138.70 (1Cq), 128.80 (2CH), 124.49 (2CH), 45.00 (CH2), 43.30 (3CH2), 36.89 (3CH2), 35.88 (1Cq), 30.19 (1CH), 29.04 (3CH), 22.48 (2CH3). Anal. Calcd for C20H28 (268.44): C, 89.49; H, 10.51. Found: C, 89.57; H, 10.46. 1-(4-tert-Butylphenyl)adamantane (3i): Mp 127.5 °C. 1H NMR (CDCl3, 400 MHz): δ = 7.34 (half of an A2X2 system, 2 H), 7.29 (half of an A2X2 system, 2 H), 2.12–2.05 (m, 3 H), 1.91 (d, J = 2.8 Hz, 6 H), 1.83–1.70 (m, 6 H), 1.31 [s, 9 H, C(CH 3)3]. 13C NMR (CDCl3, 100 MHz): δ = 148.30 (1Cq), 148.06 (1Cq), 124.92 (2CH), 124.42 (2CH), 43.22 (3CH2), 36.85 (3CH2), 35.76 (1Cq), 34.25 (1Cq), 31.40 (3CH3), 28.99 (3CH). 1,4-Di-1-adamantylbenzene (3j) 1H NMR (400 MHz, CDCl3): δ = 7.31 (s, 4 H), 2.12–2.05 (m, 6 H), 1.91 (d, J = 2.8 Hz, 12 H), 1.82–1.71 (m, 12 H). 13C NMR (100 MHz, CDCl3): δ = 148.35 (2Cq), 124.45 (4CH), 43.21 (6CH2), 36.86 (6CH2), 35.79 (2Cq), 28.99 (6CH). For data of other compounds, see the Supporting Information.
  • 23 For instance, no reaction was observed with 1 and isobutylbenzene at 40 °C in CCl4. In 1,2-dichloroethane and 1-chlorobutane at 35–40 °C, the reactions of 1 with isobutylbenzene and tert-butylbenzene afforded complex mixtures.
  • 24 Halobenzenes were not studied in CH2Cl2 as solvent because of their reduced reactivity and also due to the fact that InBr3 was not a good catalyst in their case.
  • 25 The same procedure as previously described was used, except that a reduced amount of aromatic substrate was used (see Table 3) and dichloromethane was added (its amount was adjusted by weight after flushing with nitrogen and stoppering).
  • 26 Based on two experiments that were performed with toluene and ethylbenzene with HBr vented through a bubbler, no change was observed in reaction rate or selectivity (same para/meta ratios). Yields of 99% were obtained compared with 90 and 92% (InCl3 as a catalyst).