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Synlett 2011(14): 2017-2020  
DOI: 10.1055/s-0030-1261162
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Unmodified Nano-Powder Magnetite or Iron(III) Oxide Catalyze the Easy and Fast Synthesis of 4-Substituted-4H-Pyrans

Rafael Cano, Diego J. Ramón*, Miguel Yus
Departamento Química Orgánica and Instituto de Síntesis Orgánica, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
Fax: +34(96)5903549; e-Mail: djramon@ua.es;
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Publication History

Received 13 May 2011
Publication Date:
10 August 2011 (online)

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Abstract

Inexpensive and commercially available nano-power magnetite or iron(III) oxide can be used as catalyst in a new, straightforward, and fast protocol for the construction of 4-substituted-4H-pyrans. The reaction implies a tandem process, involving an aldol condensation, a Michael-type addition, and a dehydrating annulation.

Key words

annulation - heterocycles - heterogeneous catalysis - iron - pyrans

    References and Notes

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12

Representative Procedure for the Synthesis of Dimethyl 4-(4-Bromophenyl)-2,6-dimethyl-4 H -pyran-3,5-dicar-boxylate (4a) To a stirred solution of 4-bromobenzaldehyde (2a, 1 mmol) in toluene (3 mL) were added Fe3O4 (50 mg, 65 mol%), methyl 3-oxobutanoate (1a, 2.5 mmol), and AcCl (0.14 mL, 2 mmol). The resulting mixture was stirred at 25 ˚C during 3 h. The mixture was quenched with H2O (5 mL) and extracted with EtOAc (3 × 5 mL). The organic phases were dried over MgSO4, followed by evaporation under reduced pressure
to remove the solvent. The product was purified by chroma-tography on silica gel (hexane-EtOAc) to give the titled product; mp 96-100 ˚C(hexane). R f = 0.5 (hexane-EtOAc = 4:1). IR (KBr) : ν = 1721, 1671, 1629, 1584, 1296 cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 2.36 (6 H, d, J = 0.6 Hz, 2  CCH3), 3.64 (6 H, s, 2  CO2CH3), 4.72 (1 H, s, CH), 7.10 (2 H, d, J = 8.5 Hz, 2  BrCCHCH), 7.36 (2 H, d, J = 8.5 Hz, 2  BrCCH). ¹³C NMR (75 MHz, CDCl3): δ = 18.7 (2 C), 37.8, 51.4 (2 C), 107.7 (2 C), 120.4, 129.9 (2 C), 131.2 (2 C), 144.3, 158.7 (2 C), 166.9 (2 C). CG-MS: m/z (%) = 382 (11) [M+ + 2], 380 (11) [M+], 367 (14), 365 (13), 323 (14), 321 (14), 226 (11), 225 (100), 193 (11). HRMS:
m/z calcd for C17H17BrO5: 382.0259; found: 380.0256.