7110
G. Silvero et al. / Tetrahedron 61 (2005) 7105–7111
JZ8.0 Hz, N–CH2), 4.14 (s, 3H, N–CH3), 1.91 (m, 2H,
CH2), 1.31 (m, 6H, CH2), 0.88 (m, 3H, CH3). 13C NMR
(CDCl3, 100 MHz) d 137.11 (C2), 123.43 (C4), 121.61
(C5), 49.52 (C10), 36.06 (N–CH3), 30.60 (C20), 29.78 (C30),
25.38 (C40), 21.86 (C50), 13.46 (C60).
References and notes
1. Fringuelli, F.; Taticchi, A. The Diels–Alder Reaction In
Selected Practical Methods; Wiley: Chichester, 2002.
´
2. (a) Areces, P.; Avalos, M.; Babiano, R.; Cintas, P.; Gonzalez,
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L.; Hursthouse, M. B.; Jimenez, J. L.; Light, M. E.; Lopez, I.;
Palacios, J. C.; Silvero, G. Eur. J. Org. 2001, 2135. (b)
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Arevalo, M. J.; Avalos, M.; Babiano, R.; Cintas, P.; Hurst-
4.1.2. Preparation of 1-hexyl-3-methylimidazolium
tetrafluoroborate [HMI][BF4]: the Finkelstein
reaction.22 A solution of the [HMI][Cl] (1 equiv), NaBF4
(1 equiv) and water (14 equiv) is stirred at room temperature
for 48 h. The product is extracted into CH2Cl2 and the
organic phase is then washed with successive small portions
of deionised water, until no chloride ions are detected by
testing with AgNO3. The collected organic layer is dried
over MgSO4, filtered and CH2Cl2 is then removed on a
rotary evaporator. The ionic liquid is dried by heating under
vacuum for 48 h. The product is obtained in 79% yield. The
water content in the ionic liquid was determined using a
Karl–Fischer titrator (Aquapal(R) III, CSC Scientific Co.
Inc.) and showed a value of 1000 ppm for the melt used.23
Purity was examined using ion chromatography to check for
residual chloride ion impurities.21 The residual chloride
concentration was 217 ppm. IR (liquid film) nmax 3161,
3121, 2958, 2933, 2862, 1573, 1467, 1170, 1059 cmK1. 1H
NMR (CDCl3, 400 MHz) d 8.74 (s, 1H, H-2), 7.42 (s, 1H,
H-4), 7.38 (s, 1H, H-5), 4.17 (t, 2H, JZ7.6 Hz, N–CH2),
3.94 (s, 3H, N–CH3), 1.86 (m, 2H, CH2), 1.32 (m, 6H, CH2),
0.86 (m, 3H, CH3). 13C NMR (CDCl3, 100 MHz) d
135.84 (C2), 123.62 (C4), 122.13 (C5), 49.80 (C10), 35.93
(N–CH3), 30.81 (C20), 29.78 (C30), 25.56 (C40), 22.14 (C50),
13.70 (C60).
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house, M. B.; Jimenez, J. L.; Light, M. E.; Lopez, I.; Palacios,
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J. C. Tetrahedron Lett. 1999, 40, 8675. (c) Avalos, M.;
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Babiano, R.; Cintas, P.; Hursthouse, M. B.; Jimenez, J. L.;
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Light, M. E.; Lopez, I.; Palacios, J. C. Chem. Commun. 1999,
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1589. (d) Avalos, M.; Babiano, R.; Cintas, P.; Hursthouse,
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M. B.; Jimenez, J. L.; Light, M. E.; Lopez, I.; Palacios, J. C.;
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Silvero, G. Chem. Eur. J. 2001, 7, 3033. (e) Arevalo, M. J.;
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Avalos, M.; Babiano, R.; Cintas, P.; Hursthouse, M. B.;
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Babiano, R.; Cintas, P.; Hursthouse, M. B.; Jimenez, J. L.;
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4. Avalos, M.; Babiano, R.; Bravo, J. L.; Cintas, P.; Jimenez,
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J. L.; Palacios, J. C.; Silva, M. A. Green Chem. 2001, 3, 26.
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5. Avalos, M.; Babiano, R.; Bravo, J. L.; Cintas, P.; Jimenez,
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6. (a) Zhao, H.; Malhotra, S. V. Aldrichim. Acta 2002, 35, 75. (b)
Olivier-Bourbigou, H.; Magna, L. J. Mol. Catal. A: Chem.
2002, 419, 182–183. (c) Zhao, D.; Wu, M.; Kou, Y.; Min, E.
Catal. Today 2002, 74, 157. (d) Dupont, J.; de Souza, R. F.;
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C. M. Appl. Catal. A 2001, 222, 101. (f) Brennecke, J. F.;
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4.2. Typical procedure for cycloaddition reactions
A typical experimental procedure. In a flat-bottomed vial of
25 mL capacity, 2.2 mmol of freshly distilled cyclopenta-
diene and 2.0 mmol of dienophile were added to a mixture
of 2 mL of [HMI][BF4] and, if applicable, 0.2 or 0.5 mol%
catalyst. The reaction is stirred for a given reaction time. All
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1
processes were monitored by H NMR and/or TLC. After
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ether (5!4 mL). The ethereal solution was reduced to half
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gel bed, to avoid contamination of the ionic liquid. The final
adducts were isolated by evaporation of the crude mixture
and, if necessary, purified by chromatography or
crystallization.
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Acknowledgements
This work was made possible by the financial support from
´
the Ministerio de Ciencia y Tecnologıa of Spain (Grants
BQU2002-00015 and BQU2003-05946) and the Junta de
Extremadura—European Social Fund (Grant 2PR02-A016).
We would like to thank Prof. Pedro Cintas for helpful
discussions and Quill Research Centre, The Queen’s
University of Belfast, (UK), for water content analyses.
Referees are also acknowledged for invaluable
comments.