954
G. Ragagnin, P. Knochel
LETTER
3993. (g) Ragagnin, G.; Betzemeier, B.; Quici, S.; Knochel,
P. Tetrahedron 2002, 58, 3985.
(7) (a) Pozzi, G.; Montanari, F.; Quici, S. Chem. Commun.
1997, 69. (b) Yamada, T.; Takai, T.; Rholde, O.;
Mukaiyama, T. Chem. Lett. 1991, 1. (c) Yamada, T.; Takai,
T.; Rholde, O.; Mukaiyama, T. Chem. Lett. 1991, 5.
(8) (a) Höger, S.; Bonrad, K.; Mourran, A.; Beginn, U.; Möller,
M. J. Am. Chem. Soc. 2001, 123, 5651. (b) Tsubata, Y.;
Suzuki, T.; Miyashi, T.; Yamashita, Y. J. Org. Chem. 1992,
57, 6749.
The complex of 1a with RuCl3 was also tested in the aer-
obic epoxidation of cyclooctene 2a, under the same con-
ditions as the ligand 1. Complete conversion to
cyclooctene oxide within 1 hour was achieved and no
leaching of catalyst in the organic phase was observed.
This shows that the presence of a spacer between the
benzimidazole ring and the fluorous ponytail does not
affect the reactivity of this catalyst.12
In summary, we have described an efficient ruthenium
catalyzed epoxidation of alkenes in a fluorous biphasic
system by using the novel fluorous ligand pyridine-benz-
imidazole Rf2Bimpy. Excellent conversions and reaction
rates could be achieved and the catalyst could be reused
for further reaction runs without loss of activity.
(9) Singh, M. P.; Sasmal, S.; Lu, W.; Chatterjee, M. N. Synthesis
2000, 1380.
(10) Main isomer 7: 1–5% of the 5,7-diiodo isomer was also
detected.
(11) Analytical data for C29H9N3F34 (1): 1H NMR (400 MHz,
CDCl3): d = 8.73 (d, J = 4 Hz, 1 H), 8.51 (d, J = 7.8 Hz, 1
H), 7.89 (td, J = 7.8 and 1.6 Hz, 1 H), 7.87 (s, 1 H), 7.73 (s,
1 H), 7.42 (m, 1 H), 4.40 (s, 3 H) ppm. 13C NMR (100 MHz,
CDCl3): d = 148.6, 147.7, 137.2, 136.1, 136.0, 122.0–
113.0(bm), 32.3, 28.7 ppm. 19F NMR (400 MHz, CDCl3): d
= –79.7 (s, 6 F), –107.4 (m, 4 F), –120.1 (s, 8 F), –120.7 (s,
8 F), –121.6 (s, 4 F), –125.0 (s, 4 F) ppm. IR (KBr, pellets):
3440 (m), 2922 (w), 2856 (w), 1635 (w), 1208 (s), 1150 (s),
666 (w) cm–1. MS (EI, 70 eV): m/e (rel. int.) = 1045 (100),
1025 (19), 967 (1), 706 (6), 676 (23), 626 (6), 338 (2), 307
(3), 258 (7), 168 (1). HRMS: calcd 1045.0254; found:
1045.0230. Mp 134 °C.
Acknowledgment
The European Union (contract HPRN-CT-2000-00002, ‘Develop-
ment of Fluorous Phase Technologies for Oxidation Processes’) is
gratefully acknowledged for financial support. The company
ATOFINA S.A. (Pierre-Benite, France) is acknowledged for the
generous gifts of chemicals.
References
Analytical data for C33H17N3F34 (1a): 1H NMR (400 MHz,
CDCl3): d = 8.68 (d, J = 3.6 Hz, 1 H), 8.37 (d, J = 6.0 Hz, 1
H), 7.84 (td, J = 5.4 and 0.9 Hz, 1 H), 7.34 (m, 1 H), 7.15 (s,
1 H), 6.98 (s, 1 H), 4.25 (s, 3 H), 3.37 (m, 2 H), 3.06 (m, 2
H), 2.73 (m, 2 H), 2.45 (m, 2 H) ppm. 13C NMR (75 MHz,
CDCl3): d = 149.7, 149.6, 147.5, 139.5, 136.7, 135.8, 133.7,
130.4, 123.9, 123.8, 122.6, 121.6, 122.0–108.0 (m), 107.0,
32.7 (t), 31.8, 30.5 (t), 28.7 ppm. 19F NMR (400 MHz,
CDCl3): d = –79.7 (s, 6 F), –113.4 (s, 4 F), –120.5 (s, 4 F), –
120.6 (s, 8 F), –120.8 (s, 4 F), –121.6 (s, 4 F), –122.3 (s, 4
F), –125.0 (s, 4 F). IR (KBr, pellets): 2961 (w), 1591 (w),
1470 (w), 1204 (s), 1150 (s), 724 (w), 659 (w) cm–1. MS (EI,
70 eV): m/e (rel. int.) = 1101 (100), 1082 (24), 732 (55), 682
(23), 668 (25), 355 (2), 334 (3), 281 (4), 207 (3). HRMS:
calcd.1101.088; found: 1101.044. Mp 104 °C.
(1) (a) Gerhartz, W.; Yamamoto, Y. S.; Kandy, L.; Rounsaville,
J. F.; Schulz, G. Ullmann’s Encyclopedia of Industrial
Chemistry, 5th ed., Vol. A9; Verlag Chemie: Weinheim,
1987, 531. (b) Rao, A. S. In Comprehensive Organic
Synthesis, Vol. 7; Trost, B. M.; Fleming, I.; Ley, S. V., Eds.;
Pergamon: Oxford, 1991, 357.
(2) (a) De Vos, D.; Bein, T. Chem. Commun. 1996, 917. (b) De
Vos, D. E.; Sels, B. F.; Reynaers, M.; Subba, R. a. o. Y. V.;
Jacobs, P. A. Tetrahedron Lett. 1998, 39, 3221.
(c) Wentzel, B. B.; Gosling, P. A.; Feiters, M. C.; Nolte, R.
J. M. J. Chem. Soc., Dalton Trans. 1998, 2241; and
references cited therein.
(3) (a) Groves, J. T.; Quinn, R. J. Am. Chem. Soc. 1985, 107,
5790. (b) Liu, C.-J.; Yu, W.-Y.; Che, C.-M.; Yeung, C.-H. J.
Org. Chem. 1999, 64, 7365. (c) Cheung, W.-H.; Yu, W.-Y.;
Yip, W.-P.; Zhu, N.-Y.; Che, C.-M. J. Org. Chem. 2002, 67,
7716; and references cited therein.
(4) (a) Horváth, I. T.; Rabái, J. Science 1994, 266, 72.
(b) Juliette, J. J. J.; Horváth, I. T.; Gladysz, J. A. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1610.
(5) For some excellent reviews on fluorous catalysis see:
(a) Cornils, B. Angew. Chem., Int. Ed. Engl. 1997, 36, 2057.
(b) Curran, D. P. Chemtracts Org. Chem. 1996, 9, 75.
(c) Horváth, I. T. Acc. Chem. Res. 1998, 31, 641. (d) de
Wolf, E.; van Koten, G.; Deelman, B.-J. Chem. Soc. Rev.
1999, 28, 37. (e) Betzemeier, B.; Knochel, P. Top. Curr.
Chem. 1999, 206, 61. (f) Fish, R. H. Chem.–Eur. J. 1999, 5,
1677. (g) Hope, E. G.; Stuart, A. M. J. Fluorine Chem. 1999,
100, 75. (h) Rocaboy, C.; Gladysz, J. A. Actualité Chimique
2000, 9, 47.
(6) For some examples of oxidations in FBC see: (a) Klement,
I.; Lütjens, H.; Knochel, P. Angew. Chem. 1997, 109, 1605.
(b) Betzemeier, B.; Lhermitte, F.; Knochel, P. Synlett 1999,
489. (c) Crich, D.; Neelamkavil, S. J. Am. Chem. Soc. 2001,
123, 7449. (d) Cavazzini, M.; Manfredi, A.; Montanari, F.;
Quici, S.; Pozzi, G. Eur. J. Org. Chem. 2001, 24, 4639.
(e) ten Brink, G.-J.; Vis, J. M.; Arends, I. W. C. E.; Sheldon,
R. A. Tetrahedron 2002, 58, 3977. (f) Legros, J.; Crousse,
B.; Bonnet-Delpon, D.; Bégué, J.-P. Tetrahedron 2002, 58,
(12) Typical Procedure: Preparation of cyclooctene oxide (3a):
A 50 mL Schlenk tube, equipped with a stirrer and a O2-inlet
was charged with the fluorous benzimidazole 1 (52.0 mg, 50
mmol, 2 mol%) dissolved in perfluorooctyl bromide (2.5
mL), and RuCl3·xH2O (36% Ru, 7 mg, 25 mmol, 1 mol%)
dissolved in a few drops of acetone leading to a red solution.
After stirring for 0.5 h, a solution of cis-cyclooctene (220
mg, 2.0 mmol) and i-PrCHO (288 mg, 4.0 mmol, 2 equiv) in
chlorobenzene (2 mL) was added. The biphasic reaction
mixture was stirred at 40 °C while a gentle stream of oxygen
from a balloon was passing. The color of the reaction
mixture changes from red to deep blue within 15 min. At the
end of the reaction, the mixture was cooled to 10 °C, the
organic layer was decanted and the fluorous phase was
washed with chlorobenzene (4 × 2 mL). The chlorobenzene
is removed in vacuo and the residue diluted with CH2Cl2 (20
mL). The organic phase is treated with cold NaOH (0.1 M,
20 mL) and washed with brine. After drying (MgSO4),
filtration and evaporation of the solvent in vacuo the crude
product was purified by flash chromatography (eluent:
Et2O–pentane), yielding 224 mg (89%) of analytically pure
cyclooctene oxide. The blue fluorous phase containing the
Ru-catalyst was used directly for further reaction runs
without loss of activity.
Synlett 2004, No. 6, 951–954 © Thieme Stuttgart · New York