Montmorillonite K10 Clay Catalyzed Synthesis of 4-Aryltetrahydropyrans: A One-Pot, Multicomponent, Environmentally Friendly Prins–Friedel–Crafts-Type Reaction

Abstract

The Montmorillonite K10 clay catalyzed synthesis of 4-aryltetrahydropyrans is presented as a one-pot, multicomponent, environmentally friendly Prins–Friedel–Crafts-type reaction.

Key words

aldehydes - cyclization - green chemistry - hetero­geneous catalysis - multicomponent reaction

• References and Notes

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• 14 Typical Procedure for the Mont-K10-Catalyzed Prins–Friedel–Crafts Reaction for the Synthesis of 2a: In a 5-mL round-bottomed flask, equipped with a magnetic stir bar, the Mont-K10 clay (200 mg) and p-nitrobenzaldehyde (151 mg, 1 mmol) were combined with benzene (2 mL). Methanol (202 μL, 5 mmol) was added, followed by 3-buten-1-ol (94 μL, 1.1 mmol) and the reaction mixture was refluxed with vigorous stirring. Reaction progress was monitored by TLC (in 1:1 hexanes–EtOAc). When the reaction was complete, the mixture was allowed to cool to r.t. Then, the product mixture was vacuum filtered, washing with acetone, to separate the clay. The filtrate was concentrated under vacuum to give a pale yellow solid (255 mg, 90%). See ref. 15 for the experimental details and characteristic data.
• 15 Analytical Data for Compound 2a: ¹H NMR and ¹³C NMR spectra were recorded at 300 MHz and 100 MHz, respectively. The proton signal of residual, non-deuterated solvent (δ = 7.26 ppm for CHCl₃) was used as an internal reference for ¹H NMR spectra. ¹³C NMR chemical shifts are reported relative to the δ = 77.23 ppm resonance of CDCl₃. Coupling constants are reported in Hz. IR spectra were recorded as thin films on a Nicolet Avatar 360 instrument. GC analysis was performed on a Hewlett Packard 5890 Series II gas chromatograph with a 5971 Series mass selective detector. Tetrahydro-2-(4-nitrophenyl)-4-phenyl-2H-pyran (2a): IR (CDCl₃): 3029, 2942, 1849, 1602, 1517, 1345, 1130, 1106, 1085, 850, 744 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 8.20 (d, J = 8.8 Hz, 2 H), 7.57 (d, J = 8.8 Hz, 2 H), 7.23–7.33 (m, 5 H), 4.60 (dd, J = 11.2, 2.0 Hz, 1 H), 4.30–4.36 (m, 1 H), 2.75–3.83 (m, 1 H), 2.95–3.05 (m, 1 H), 2.10 (dq, J = 13.2, 2.0 Hz, 1 H), 1.85–1.90 (m, 2 H), 1.70 (q, J = 12.4 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 150.0, 145.5, 142.9, 128.3, 127.4, 126.7, 126.4, 125.7, 79.8, 68.5, 42.0, 41.5, 33.3. GC–MS (70 eV; t _R = 13.174 min): m/z (%) = 283 (28) [M⁺], 205 (88) [M – 78]⁺, 104 (100) [M – 179]⁺, 91 (68) [M – 192]⁺.