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Synlett 2006(2): 227-230  
DOI: 10.1055/s-2005-923604
LETTER
© Georg Thieme Verlag Stuttgart · New York

An Efficient Preparation of 2-Imidazolines and Imidazoles from Aldehydes with Molecular Iodine and (Diacetoxyiodo)benzene

Midori Ishiharaa, Hideo Togo*a,b
a Graduate School of Science and Technology, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
b Faculty of Science, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
e-Mail: togo@faculty.chiba-u.jp;
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Publication History

Received 17 October 2005
Publication Date:
23 December 2005 (online)

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An Efficient Preparation of 2-Imidazolines and Imidazoles from Aldehydes with Molecular Iodine and (Diacetoxyiodo)benzeneSynlett 2006; 2006(06): 964-964
DOI: 10.1055/s-2006-939067

Abstract

2-Imidazolines were easily prepared in quite good yields from the reaction of aldehydes and ethylenediamine with molecular iodine in the presence of potassium carbonate. Moreover, 2-imid­azolines obtained were smoothly oxidized to the corresponding ­imidazoles in good yields using (diacetoxyiodo)benzene at room temperature.

Key words

2-imidazoline - imidazole - iodine - (diacetoxyiodo)benzene - aldehyde - ethylenediamine

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Typical Procedure for Preparation of 2-Imidazolines from Aldehydes: To a solution of p-tolualdehyde (120.2 mg, 1 mmol) in t-BuOH (10 mL) was added ethylenediamine (66.1 mg, 1.1 mmol). The obtained mixture was stirred at r.t. under an argon atmosphere for 30 min, and then K2CO3 (414.6 mg, 3 mmol) and I2 (317.3 mg, 1.25 mmol) were added to the mixture and stirred at 70 °C. After 3 h, the mixture was quenched with sat. aq Na2SO3 until the iodine color almost disappeared, and was extracted with CHCl3. The organic layer was washed with sat. aq NaHCO3 and brine, and dried over Na2SO4. After filtration, the mixture was evaporated in vacuo to provide 160.2 mg of 2-(4-methylphenyl)imidazoline in 100% yield in an almost-pure state. Mp 181-182 °C (lit. [11] mp 181 °C). IR (KBr): 3140, 2925, 1600, 1495, 985, 830 cm-1. 1H NMR (400 MHz, CDCl3): δ = 2.38 (s, 3 H), 3.77 (s, 4 H), 7.21 (d, J = 8.3 Hz, 2 H), 7.67 (d, J = 8.3 Hz, 2 H).

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Typical Procedure for Oxidation of 2-Imidazolines to Imidazoles: To a mixture of 2-(4-methylphenyl)imidazoline (160.2 mg, 1 mmol) and K2CO3 (152.0 mg, 1.1 mmol) in DMSO (10 mL) was added DIB (354.3 mg, 1.1 mmol). Then the mixture was stirred for 24 h at r.t. under an argon atmosphere. After the reaction, the reaction mixture was diluted with sat. aq NaHCO3 and EtOAc, and was stirred for 5 min. The mixture was extracted with EtOAc and the organic layer was dried over Na2SO4. After filtration, the mixture was evaporated in vacuo. The residue was chromatographed on neutral silica gel (EtOAc-MeOH, 30:1) to give 128.1 mg of 2-(4-methylphenyl)imidazole in 81% yield in an almost-pure state. Mp 217-218 °C (lit. [5d] mp 218-220 °C). IR (KBr): 3460, 1515, 1445, 1100, 820, 730 cm-1. 1H NMR (400 MHz, DMSO-d 6): δ = 2.31 (s, 3 H), 6.97 (br s, 1 H), 7.19 (br s, 1 H), 7.21 (d, J = 8.2 Hz, 2 H), 7.81 (d, J = 8.2 Hz, 2 H), 12.38 (s, 1 H).