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Synlett 2005(6): 0959-0962  
DOI: 10.1055/s-2005-865194
LETTER
© Georg Thieme Verlag Stuttgart · New York

An Efficient Synthesis of Bis(indolyl)methanes Catalyzed by Recycled Acidic Ionic Liquid

Da-Gong Gua, Shun-Jun Ji*a, Zhao-Qin Jianga, Min-Feng Zhoua, Teck-Peng Loha,b
a Jiangsu Province Key Laboratory of Fine Petrochemical Technology, College of Chemistry and Chemical Engineering of Suzhou University, Suzhou, 215006, P. R. China
Fax: +86(512)65224873; e-Mail: shunjun@suda.edu.cn;
b Department of Chemistry, 3 Science Drive 3, National University of Singapore, Singapore 11754, Singapore
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Publikationsverlauf

Received 5 January 2005
Publikationsdatum:
23. März 2005 (online)

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Abstract

Green, mild and efficient electrophilic substitution ­reactions of indoles with various aldehydes were carried out using task-specific ionic liquids to afford the corresponding bis(indolyl)methanes in excellent yields.

Key words

acidic ionic liquids - indoles - carbonyl compounds - bis(indolyl)methanes

15

Representative Experimental Procedure.
A mixture of indole (0.117 g, 0.50 mmol), 4-(benzo[d]ox-azol-2-yl)benzaldehyde (0.115 g, 0.25 mmol) and [hmim]HSO4 (0.0264g, 0.50 mmol × 5% mol) in EtOH (4.0 mL) was stirred at r.t. After completion of the reaction as indicated by TLC, the mixture was concentrated in vacuo to remove the solvent. The resulting solution was extracted with Et2O (5 × 10 mL). The organic layer was dried (Na2SO4), concentrated under vacuum and purified by column chromatography to afford the pure product. 3,3′-Bis-indolyl-4-(benzo[d]oxazol-2-yl)phenylmethane (2g): pale powder; mp 234-236 °C. IR (KBr): ν = 3421, 3053 cm-1. 1H NMR (400 MHz, CDCl3): δ = 5.99 (s, 1 H), 6.72 (s, 2 H), 7.03 (dd, J 1 = 7.6 Hz, J 2 = 7.2 Hz, 2 H), 7.19 (t, J = 7.2 Hz, 2 H), 7.35 (s, 2 H), 7.40 (dd, J 1 = 7.6 Hz, J 2 = 8.0 Hz, 4 H), 7.77 (s, 1 H), 8.02 (s, 2 H), 8.18 (d, J = 8.0 Hz, 2 H). HRMS: m/z calcd for C23H20N2S: [M] 439.1685; found: 439.1666 [M+].
3,3′-Bis-(5-methyl) indolyl-3-thienylmethane (3c): pink powder; mp 217-219 °C. IR (KBr): ν = 3410, 2909, 2848 cm-1. 1H NMR (400 MHz, CDCl3): δ = 2.38 (s, 6 H), 5.90 (s, 1 H), 6.69 (s, 2 H), 6.94 (s, 1 H), 7.00-7.06 (m, 4 H), 7.24 (d, J = 5.2 Hz, 4 H), 7.83 (s, 2 H). HRMS: m/z calcd for C23H20N2S: [M] 356.1347; found: 356.1334 [M+].