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DOI: 10.1055/s-0030-1261162
Unmodified Nano-Powder Magnetite or Iron(III) Oxide Catalyze the Easy and Fast Synthesis of 4-Substituted-4H-Pyrans
Publikationsverlauf
Publikationsdatum:
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
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References and Notes
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.