Selective and Effective Iodination of Alkyl-substituted Benzenes with Elemental Iodine Activated by Selectfluor^{Τ Μ} F-TEDA-BF₄

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) (Selectfluor^{Τ Μ} F-TEDA-BF₄). The number of iodine atoms introduced could be modulated by the molar ratio between substrate, iodine and F-TEDA-BF₄.

iodination - iodine - N-F reagents - alkyl benzenes

References

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<A NAME="RG34001ST-9">9</A>

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]

<A NAME="RG34001ST-10">10</A>

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.

<A NAME="RG34001ST-11">11</A>

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.

<A NAME="RG34001ST-12">12</A> Lal GS. J. Org. Chem.  1993,  58:  2791 

<A NAME="RG34001ST-13">13</A>

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