Facile Ionic Liquids-Promoted One-Pot Synthesis of Polyhydroquinoline
Derivatives under Solvent Free Conditions

Abstract

An efficient synthesis of polyhydroquinoline derivatives were reported via four-component coupling reactions of aldehydes, dimedone, ethyl acetoacetate and ammonium acetate in the presence of a catalytic amount of ionic liquid under solvent free conditions. In the meantime, the catalytic effect of different ionic liquids on the reaction has also been investigated.

Key words

ionic liquids - catalyze - one-pot synthesis - polyhydroquinoline derivatives

References

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Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 226173 for compounds 2d. Copies of this information may be obtained free of charge from: The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK [E-mail: [e-mail] or deposit@ ccdc.cam.ac.uk; Fax:[phone]]. Structural parameters for 2d: data collection: Rigaku Mercury CCD area detector; radiation: MoK. wavelength = 0.71070 Å; crystal size: 0.24 × 0.15 × 0.70 mm³; crystal system: monoclinic; space group: Cc (#9); unit cell: a = 18.607 (6) Å, b = 9.136 (3) Å, c = 12.157 (4) Å, α = 111.623 (5)°.

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Typical Experimental Procedure: 4-Chlorobenzaldehyde (1 mmol), dimedone (1 mmol), ammonium acetate (1.5 mmol), ethyl acetoacetate (1 mmol) and [hmim]BF₄ (12 mmol%) were successively charged into a 25 mL round-bottomed flask equipped with a magnetic stirrer. Then the reaction proceeded at 90 °C for 8 min and a solid product gradually formed. After the completion of reaction as indicated by TLC, the resulting solid product was crushed, washed with water, filtered and dried in vacuum to afford the crude product. A pure product was obtained by further recrystallization using absolute alcohol. 2a: IR (KBr): 3290, 1698, 1612 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 0.92 (s, 3 H, CH₃), 1.06 (s, 3 H, CH₃), 1.08 (m, 3 H, CH₂CH₃), 2.18 (m, 4 H, 2 × CH₂), 2.41 (s, 3 H, CH₃), 4.08 (q, J ₁ = J ₂ = 6.0 Hz, 2 H, CH₂CH₃), 5.06 (s, 1 H, CH), 5.90 (s, 1 H, NH), 7.03-7.4 (m, 5 H, ArH). Anal. Calcd for C₂₁H₂₅NO₃: C, 74.31; H, 7.42; N, 4.13. Found: C, 74.57; H, 7.51; N, 4.06. 2f: IR (KBr): 3275, 1702, 1647 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 0.92 (s, 3 H, CH₃), 1.08 (s, 3 H, CH₃), 1.24 (t, J ₁ = J ₂ = 7.2 Hz, 3 H, CH₂CH₃), 2.16 (s, 3 H, CH₃), 2.26 (m, 4 H, 2 × CH₂), 2.40 (s, 3 H, CH₃), 4.08 (m, 2 H, CH₂CH₃), 5.00 (s, 1 H, CH), 5.80 (s, 1 H, NH), 7.00 (d, J = 8.0 Hz, 2 H, ArH) 6.80 (d, J = 8.0 Hz, 2 H, ArH). Anal. Calcd for C₂₂H₂₇NO₃: C, 74.76; H, 7.70; N, 3.96. Found: C, 74.92; H, 7.79; N, 3.90. 2i: IR (KBr): 3399, 3293, 1698, 1644 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 0.94 (s, 3 H, CH₃), 1.06 (s, 3 H, CH₃), 1.22 (t, J ₁ = J ₂ = 7.2 Hz, 3 H, CH₂CH₃), 2.20 (s, 3 H, CH₃), 2.38 (m, 4 H, 2 × CH₂), 3.89 (s, 3 H, CH₃), 4.12 (q, J ₁ = J ₂ = 7.2 Hz, 2 H, CH₂CH₃), 5.00 (s, 1 H, CH), 5.40 (s, 1 H, OH), 5.76 (s, 1 H, NH), 6.74 (m, 2 H, ArH) 7.00 (d, 1 H, ArH). Anal. Calcd for C₂₂H₂₇NO₅: C, 68.55; H, 7.06; N, 3.63. Found: C, 68.53; H, 7.11; N, 3.51.