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DOI: 10.1055/s-2005-865194
An Efficient Synthesis of Bis(indolyl)methanes Catalyzed by Recycled Acidic Ionic Liquid
Publication History
Publication Date:
23 March 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
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References
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+].