An Efficient One-Pot Synthesis of Pyrano- and Furoquinolines Employing Two Reusable Solid Acids as Heterogeneous Catalysts [1]

Abstract

Two solid acids, Fe³⁺-K-10 montmorillonite clay and HY-zeolite have been employed efficiently for single-step synthesis of pyrano- or furoquinolines in high yields and high diastereoselectivities by coupling of three components: anilines, benzaldehydes and 3,4-dihydro-2H-pyran or 2,3-dihydrofuran. Both the heterogeneous catalysts are recoverable and recyclable.

Pyrano- and furoquinolines - solid acids - multicomponent coupling - diastereoselectivity

References

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Part 41 in the series ‘Studies on Novel Synthetic Methodologies’.

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<A NAME="RD08104ST-7">7</A>

General Procedure for the Preparation of Pyrano- and Furoquinolines: To a solution of aniline (1 mmol), benzaldehyde (1 mmol) and 3,4-dihydro-2H-Pyran or 2,3-dihydrofuran (0.1 mL) in MeCN or CH₂Cl₂ (10 mL) Fe³⁺-K-10 clay or HY-zeolite (PQ Corporation, USA; 100 mg) was added. The mixture was stirred at r.t. with the first catalyst but refluxed with the second catalyst under N₂ atmosphere. The reaction was monitored by TLC. After completion of the reaction, the mixture was filtered. The concentrated filtrate was subjected to column chromatography over silica gel and the column was eluted with hexane-EtOAc (20:1) to afford the pyrano- or furoquinolines. Both the catalyst, Fe³⁺-K-10 clay and HY-zeolite were recovered by washing the residue of filtration with MeCN and CH₂Cl₂, respectively, activated and recycled.
All the prepared compounds are known. The spectral data of some representative pyrano and furoquinolines are given below. 4b: solid, mp 146-147 °C. ¹H NMR (200 MHz, CDCl₃): δ = 7.32 (2 H, d, J = 8.0 Hz), 7.18 (1 H, d, J = 8.0 Hz), 7.04 (1 H, t, J = 8.0 Hz), 6.84 (2 H, d, J = 8.0 Hz), 6.64 (1 H, t, J = 8.0 Hz), 6.45 (1 H, d, J = 8.0 Hz), 4.64 (1 H, d, J = 10.0 Hz), 4.36 (1 H, d, J = 2.5 Hz), 4.06 (1 H, m), 3.97 (1 H, d, J = 3.0 Hz), 3.82 (3 H, s), 3.63 (1 H, t, J = 10.0 Hz), 2.02 (1 H, m), 1.82 (1 H, m), 1.64 (1 H, m), 1.44 (1 H, m), 1.28 (1 H, m). MS-FAB: m/z = 296 [M⁺ + 1]. 5b: solid, mp 154-155 °C. ¹H NMR (200 MHz, CDCl₃): δ = 7.38 (1 H, d, J = 8.0 Hz), 7.30 (2 H, d, J = 8.0 Hz), 7.00 (1 H, m), 6.82 (2 H, d, J = 8.0 Hz), 6.77 (1 H, t, J = 8.0 Hz), 6.50 (1 H, d, J = 8.0 Hz), 5.26 (1 H, d, J = 3.0 Hz), 4.60 (1 H, d, J = 3.0 Hz), 3.84 (1 H, m), 3.82 (3 H, s), 3.58 (1 H, m), 3.22 (1 H, m), 2.04 (1 H, m), 1.58-1.30 (4 H, m). MS-FAB: m/z = 296 [M⁺ + 1]. 4c: semi-solid. ¹H NMR (200 MHz, CDCl₃): δ = 7.32 (4 H, s), 7.16 (1 H, d, J = 8.0 Hz), 7.04 (1 H, t, J = 8.0 Hz), 6.68 (1 H, t, J = 8.0 Hz), 6.48 (1 H, d, J = 8.0 Hz), 4.67 (1 H, d, J = 10.0 Hz), 4.92 (1 H, d, J = 2.5 Hz), 4.05 (1 H, m), 3.95 (1 H, br s), 3.68 (1 H, t, J = 10.0 Hz), 2.01 (1 H, m), 1.80 (1 H, m), 1.63 (1 H, m), 1.44 (1 H, m), 1.22 (1 H, m). MS-FAB: m/z = 300 [M⁺ + 1]. 5c: viscous. ¹H NMR (200 MHz, CDCl₃): δ = 7.38 (1 H, d, J = 8.0 Hz), 7.35 (4 H, s), 7.02 (1 H, t, J = 8.0 Hz), 6.74 (1 H, d, J = 8.0 Hz), 6.53 (1 H, d, J = 8.0 Hz), 5.24 (1 H, d, J = 8.0 Hz), 4.65 (1 H, d, J = 2.5 Hz), 3.72 (1 H, m), 3.55

(1 H, m), 3.40 (1 H, m), 2.08 (1 H, m), 1.57-1.32 (4 H, m). MS-FAB: m/z = 300 [M⁺ + 1]. 4d: solid, mp 152-153 °C. ¹H NMR (200 MHz, CDCl₃): δ = 7.18 (1 H, d, J = 8.0 Hz), 7.04 (1 H, t, J = 8.0 Hz), 6.92 (1 H, d, J = 2.5 Hz), 6.84-6.62 (3 H, m), 6.46 (1 H, d, J = 8.0 Hz), 5.96 (2 H, s), 4.62 (1 H, d, J = 10.0 Hz), 4.36 (1 H, d, J = 3.5 Hz), 4.10 (1 H, m), 3.98 (1 H, br s), 3.70 (1 H, m), 2.02 (1 H, m), 1.85-1.22 (4 H, m). MS-FAB: m/z = 310 [M⁺ + 1]. 5d: solid, mp 160-161 °C. ¹H NMR (200 MHz, CDCl₃): δ = 7.38 (1 H, d, J = 8.0 Hz), 7.04 (1 H, t, J = 8.0 Hz), 6.92-6.76 (4 H, m), 6.56 (1 H, d, J = 8.0 Hz), 5.96 (2 H, s), 5.24 (1 H, d, J = 6.0 Hz), 4.60 (1 H, d, J = 3.0 Hz), 3.78 (1 H, br s), 3.60-3.38 (2 H, m), 2.05 (1 H, m), 1.60-1.38 (4 H, m). MS-FAB: m/z = 310 [M⁺ + 1]. 4m: solid, mp 147-148 °C. ¹H NMR (200 MHz, CDCl₃): δ = 7.35 (4 H, s), 7.14 (1 H, d, J = 8.0 Hz), 7.05 (1 H, t, J = 8.0 Hz), 6.64 (1 H, d, J = 8.0 Hz), 6.42 (1 H, d, J = 8.0 Hz), 4.58 (1 H, d, J = 5.0 Hz), 4.08 (1 H, m), 3.85-3.42 (3 H, m), 2.45 (1 H, m), 2.00 (1 H, m), 1.72 (1 H, m). MS-FAB: m/z = 286 [M⁺ + 1]. 5m: solid, mp 152-153 °C. ¹H NMR (200 MHz, CDCl₃): δ = 7.40 (1 H, d, J = 8.0 Hz), 7.36 (4 H, s), 7.05 (1 H, t, J = 8.0 Hz), 6.68 (1 H, t, J = 8.0 Hz), 5.25 (1 H, d, J = 8.0 Hz), 4.65 (1 H, d, J = 3.0 Hz), 3.78 (1 H, br s), 3.62-3.40 (2 H, m), 2.18 (1 H, m), 1.62-1.50 (2 H, m). MS-FAB: m/z = 286 [M⁺ + 1].

<A NAME="RD08104ST-8">8</A> Laszlo P. Mathy A. Helv. Chim. Acta  1987,  70:  557