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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Representative Experimental Procedure.
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 Et2 O (5 × 10 mL). The organic layer was dried (Na2 SO4 ), 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 . 1 H 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 C23 H20 N2 S: [M] 439.1685; found: 439.1666 [M+ ].3c ): pink powder; mp 217-219 °C. IR (KBr): ν = 3410, 2909, 2848 cm-1 . 1 H 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 C23 H20 N2 S: [M] 356.1347; found: 356.1334 [M+ ].
