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Synlett 2002(4): 0598-0600
DOI: 10.1055/s-2002-22711
LETTER
© Georg Thieme Verlag Stuttgart · New York

Selective and Effective Iodination of Alkyl-substituted Benzenes with Elemental Iodine Activated by SelectfluorΤ Μ F-TEDA-BF4

Stojan Stavber*, Petra Kralj, Marko Zupan
Laboratory for Organic and Bioorganic Chemistry, ”Jožef Stefan" Institute and Department of Chemistry, University of Ljubljana, Jamova 39, 1000 Ljubljana, Slovenia
Fax: +386(1)4773811; e-Mail: stojan.stavber@ijs.si;
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Publication History

Received 13 December 2001
Publication Date:
05 February 2007 (online)

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Abstract

Selective direct introduction of an iodine atom into alkyl-substituted benzene derivatives was effectively achieved by reaction of target molecules with elemental iodine in the presence of 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (SelectfluorΤ Μ F-TEDA-BF4). The number of iodine atoms introduced could be modulated by the molar ratio between substrate, iodine and F-TEDA-BF4.

Key words

iodination - iodine - N-F reagents - alkyl benzenes

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The following reaction procedure is typical. To a solution of 5 mmol of alkyl-substituted benzene derivative 2 in MeCN (50 mL) corresponding molar amounts (see Table) of iodine and F-TEDA-BF4(1) were added and the reaction solution stirred at 55-65 °C for 1-24 h (see Table). The solvent was removed under reduced pressure and the crude reaction mixture dissolved in 100 mL of CH2Cl2, insoluble material filtered off, the solution washed with aq sodium thiosulfate pentahydrate (10%, 50 mL) and water (50 mL), and dried over anhyd Na2SO4. The solvent was evaporated, the crude reaction mixtures analysed by 1H NMR, MS and TLC and pure products obtained after flash chromatography over SiO2 or in the case of solid materials by crystallisation from methanol. The physico-chemical and spectroscopic characteristics of already known aryliodides 3 were compared with published data, while new compounds were validated as stated below. [10] [11]

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1,3,5-Triiodo-2,4-trimethylbenzene (3b′): Yellow crystals; mp 124.0-125.0 °C; 1H NMR (300 MHz, CDCl3): δ = 2.8 (s, 6 H), 8.3 (s, 1 H); 13C NMR (75.5 MHz, CDCl3): δ = 36.8 (CH3), 95.5 (CI), 105.4 (CI), 144.1, 147.8 (ArC); IR: ν (cm-1) = 3051, 1407, 1374, 1318, 982, 926, 872. MS (EI): m/z (%) = 484(100) [M+], 357(31), 230(28), 103(38), 77(16), 69(31). HRMS: m/z calcd for C8H7I3 [M+]: 483.7682; found: 483.7697. Anal. Calcd for C8H7I3: C, 19.86; H, 1.46. Found: C, 19.12; H, 1.14.

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1,3,4-Triiodo-2,5-dimethylbenzene (3c′): White crystals; mp 101.0-101.5 °C; 1H NMR (300 MHz, CDCl3): δ = 2.4 (s, 3 H), 3.0 (s, 3 H), 7.8 (s, 1 H); IR: ν (cm-1): 2950, 2911, 1430, 1404, 1375, 1055, 1028, 982, 863. MS (EI): m/z (%) = 484(100) [M+], 357(27), 230(36), 103(47), 77(26), 69(16). HRMS: m/z calcd for C8H7I3 [M+]: 483.7682; found: 483.7669. Anal. Calcd for C8H7I3: C, 19.86; H, 1.46. Found: C, 19.08; H, 1.26.

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Details concerning our investigations of the reactions of F-TEDA-BF4 with alkyl aromatics will be published elsewhere.