4
504
A. Fall et al. / Tetrahedron Letters 51 (2010) 4501–4504
Table 4
4
Recycling of IL-CLICK-TEMPO 2: oxidation of p-methoxybenzyl alcohol in [HMIM][BF ]
OH
BAIB (1.1 equiv), 2 (10 mol %)
O
MeO
[HMIM][BF4] , rt
MeO
Run
Time (h)
Yield (%)
1
2
3
4
5
1
1
1.25
12
48
94
94
92
88
36
methane. We were delighted to see that the reaction did proceed in
an ionic liquid medium to give good yields although the reaction
times were a bit longer (Table 3).
2. (a) Collins, J. C.; Hess, W. W.; Frank, F. J. Tetrahedron Lett. 1968, 3363–3366; (b)
Corey, E. J.; Suggs, J. W. Tetrahedron Lett. 1975, 2647–2650; (c) Corey, E. J.;
Schmidt, G. Tetrahedron Lett. 1979, 399–402; (d) Mancuso, A. J.; Swern, D.
Synthesis 1981, 165–185; (e) Tidwell, T. T. Synthesis 1990, 857–870.
[
HMIM][BF
4
] proved to be the solvent of choice for this reaction
3. (a) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155–4156; (b) Dess, D. B.;
Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277–7287; Ley, S. V.; Norman, J.;
Griffith, W. P.; Marsden, S. P. Synthesis 1994, 639–666; (c) Markó, I. E.; Giles, P.
R.; Tsukazaki, M.; Brown, S. M.; Urch, C. J. Science 1996, 274, 2044–2045; (d) de
Nooy, A. E. J.; Besemer, A. C.; van Bekkum, H. Synthesis 1996, 1153–1175; (e)
Markó, I. E.; Giles, P. R.; Tsukazaki, M.; Chellé-Regnaut, I.; Gautier, A.; Brown, S.
M.; Urch, C. J. J. Org. Chem. 1999, 64, 2433–2439; (f) Hallman, K.; Moberg, C. Adv.
Synth. Catal. 2001, 343, 260–263.
and was used to run the recycling experiments (Table 4).
Typical experimental procedure: To a solution of p-methoxy-
benzyl alcohol (90
l
l, 0.7 mmol) in [HMIM][BF
4
] (1 ml) were added
(34 mg,
.07 mmol, 0.1 equiv). The mixture was stirred at room tempera-
BAIB (262 mg, 0.8 mmol, 1.1 equiv) and catalyst
2
0
ture for 1 h (tlc), then Et
2
O (4 ml) was added and the ionic li-
4. (a) Anelli, P. L.; Biffi, C.; Montanari, F.; Quici, S. J. Org. Chem. 1987, 52, 2559–
2562; (b) Anelli, P. L.; Biffi, C.; Montanari, F.; Quici, S. J. Org. Chem. 1989, 54,
2970–2972; (c) Anelli, P. L.; Montanari, F.; Quici, S. Org. Synth. 1990, 69, 212–
219; (d) Einhorn, J.; Einhorn, C.; Ratajczak, F.; Pierre, J. L. J. Org. Chem. 1996, 61,
quid-phase was separated by decantation. The organic phase was
rotatory evaporated and the residue was chromatographed on sil-
ica gel (n-hexane/ethyl acetate 7/3) to afford p-methoxybenzylal-
dehyde (0.9 g, 94%). To the ionic liquid-phase containing catalyst
7452–7454; (e) De Mico, A.; Margarita, R.; Parlanti, L.; Vescovi, A.; Piancatelli, G.
J. Org. Chem. 1997, 62, 6974–6977; (f) Zhao, M.; Li, J.; Mano, E.; Song, Z.; Tschaen,
D. M.; Grabowski, E. J. J.; Reider, P. J. J. Org. Chem. 1999, 64, 2564–2566; (g)
Ferreira, P.; Phillips, E.; Rippon, D.; Tsang, S. C.; Hayes, W. J. Org. Chem. 2004, 69,
6851–6859; (h) Pozzi, G.; Cavazzini, M.; Quici, S.; Benaglia, M.; Dell’Anna, G. Org.
Lett. 2004, 6, 441–443.
2
were added the same quantities of BAIB and of p-methoxybenzyl
alcohol as mentioned above, to carry out the next run. From the re-
sults of Table 4, IL-CLICK-TEMPO 2 can be reused up to four times.
In conclusion, we have shown that the ionic liquid-supported
TEMPO 2 could be easily prepared via click chemistry and that 2
could be used in oxidation reactions in an ionic liquid medium,
affording excellent yields of carbonyl compounds. Additional
advantages of IL-CLICK-TEMPO 2 over free TEMPO are: simplified
workup procedure and easy recovery and recycling.
5
.
.
(a) Pozzi, G.; Cavazzini, M.; Holczknecht, O.; Quici, S.; Shepperson, I. Tetrahedron
Lett. 2004, 45, 4249–4251; (b) Wu, X.-E.; Ma, L.; Ding, M.-X.; Gao, L.-X. Synlett
2005, 607–610. and references cited therein; (c) Gheorghe, A.; Matsuno, A.;
Reiser, O. Adv. Synth. Catal. 2006, 348, 1016–1020; (d) Qian, W.; Jin, E.; Bao, W.;
Zhang, Y. Tetrahedron 2006, 62, 556–662; (e) Roy, M.-N.; Poupon, J.-C.; Charette,
A. B. J. Org. Chem. doi:10.1021/jo901509z.
For recent reviews on ionic liquids, see: (a) Welton, T. Chem. Rev. 1999, 99,
2071–2083; (b) Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39,
6
3772–3789; (c) Sheldon, R. Chem. Commun. 2001, 2399–2407; (d) Wilkes, J. S.
Green Chem. 2002, 4, 73–80; (e) Scammells, P. J.; Scott, J. L.; Singer, R. D. Aust. J.
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Acknowledgments
9
08; (g) Bica, K.; Gaertner, P. Eur. J. Org. Chem. 2008, 3235–3250.
Pérez-Sestelo, J.; Mascareñas, J. L.; Castedo, L.; Mouriño, A. J. Org. Chem. 1993, 58,
18–123.
(a) Huisgen, R.; Knorr, R.; Moebius, L.; Szeimies, G. Chem. Ber. 1965, 98, 4014–
4021; Huisgen, R. Pure Appl. Chem. 1989, 61, 613–628; (b) Kolb, H. C.; Finn,
M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004–2021; (c) Tomee,
C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67, 3057–3064; (d)
Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem., Int.
Ed. 2002, 41, 2596–2599; (e) Bock, V. D.; Hiemstra, H.; van Maarseveen, J.-H.
Eur. J. Org. Chem. 2006, 51–68; (f) Meldal, M.; Tornoe, C. W. Chem. Rev. 2008,
7
.
.
This work was financially supported by the Spanish Ministry of
Education and Science (CTQ2007-61788), the Spanish Ministry of
Foreign Affairs and Cooperation (PCI A/023040/09) and the Xunta
de Galicia (INCITE08PXIB314253PR, INCITE08ENA314019ES and
INCITE08PXIB314255PR). The work of the NMR and MS divisions
of the research support services of the University of Vigo (CACTI)
is also gratefully acknowledged. A. Fall and M. Sène thank Asiyla
Gum company SARL for research fellowships.
1
8
1
08, 2952–3015.
Selected spectral data for 2: mp: 44 °C; 1H NMR (acetone, 300 MHz) d: 9.48 (1H, s,
9
.
CH); 8.15, 7.98, 7.75 (1H, 3s, CH); 4.64 (2H, s, O–CH
CH –CH –N); 4.13 (3H, s, N–CH ); 2.64–2.67 (1H, m, CH); 1.92–2.07 (2H, m,
trans-3,5-H, CH ); 1.36–1.42 (2H, m, cis-3,5-H, CH ); 1.16, 1.17 (12H, 2s, cis-,
NMR (acetone) d: 145.38 (CH –C(N)@CH); 124.00
C(N)@CH–N); 61.48 (O–CH –N); 30.85 (CH –CH
); 44.60; 44.44 (2 Â CH
CH ); 137.38 (C-5); 123.63 (C-3); 122.76 (C-2); 36.26 (CH ); 54.83 (tert-C);
); 29.62; 20.09 (cis, trans-2,6-CH ); IR-(CDCl+
2 2
); 4.60, 3.83, 1.39 (N–CH –
References and notes
2
2
3
2
2
13
trans-2,6-CH
3
);
C
2
1
.
(a) Hudlick, M. Oxidations in Organic Chemistry; American Chemical Society:
Washington, DC, 1990; (b) Muzart, J. Chem. Rev. 1992, 92, 113–140; Larock, R. C.
Comprehensive Organic Transformations, 2nd ed.; Wiley-VCH: New York, 1999; (c)
Smith, M. B.; March, J. March’s Advanced Organic Chemistry: Reaction, Mechanism,
and Structure, 5th ed.; Wiley-Interscience: New York, 2001; (d) Choudhary, V. R.;
Chaudhari, P. A.; Narkhede, V. S. Catal. Commun. 2003, 4, 171–175.
(
2
2
2
2
–
2
3
4
m
8.98 (CH); 47.00; 46.68 (2 Â CH
2
3
3
,
À1
(cm )): 3419, 2938, 1571 (C@C), 1457, 1363, 1172, 1079, 752, 620; MS (FAB )
+
+
[
24 2
m/z, (%)]: 377 ([M+1] (63), 252 (66), 222 (34), 212 ([C13H O ] (100%).