A. L. Braga et al. / Tetrahedron Letters 43 (2002) 7329–7331
7331
Acknowledgements
10. Mugesh, G.; Singh, H. B. Acc. Chem. Res. 2002, 35,
226–236.
11. A stirred solution of 4-S-isopropyl-2-phenyloxazoline (1.3
g, 10 mmol) in dry ether (30 mL) under argon was treated
dropwise with a 1.7 M solution of n-BuLi (6.5 mL, 11
mmol) at 0°C. After stirring for 6 h at this temperature a
brown colored solution of the lithiated product was
obtained. To this solution, selenium powder (0.87 g, 11
mmol) was added at 0°C and stirring was continued for an
additional 2 h at this temperature. The reaction mixture
was quenched with cold aqueous NaHCO3 and O2 was
bubbled through it in a moderate rate for 15 min, followed
by extraction with dichloromethane. The organic phase
was dried with MgSO4 and concentrated under vacuum to
give a yellow oil which crystallizes upon slow evaporation
of ethanol. Yield: 30%. Mp 148.2–149.6°C. Anal. calcd for
C24H28O2N2Se2: C, 76.56; H, 7.50; N, 7.44. Found: C,
76.20; H, 7.60; N, 7.25%; [h]2D0 −28° (c 1.6 CHCl3); 1H
NMR (CDCl3, 200 MHz) l 1.04 (d, 3H, J=7.0 Hz), 1.12
(d, 3H, J=7.0 Hz), 1.81–1.89 (m, 1H), 4.14–4.22 (m, 1H),
4.24–4.28 (m, 1H), 4.45–4.53 (m, 1H), 7.26–7.81 (m, 4H);
13C NMR (CDCl3, 50 MHz) l 18.9, 19.0, 33.2, 70.6, 73.3,
125.5, 126.0, 129.4, 130.5, 131.3, 133.6, 162.9; IR (KBr,
cm−1): 1464, 1647, 2959, 3091.
12. A solution of 4-S-benzyl-2-(2%-bromophenyl)oxazoline
(0.82 g, 2.60 mmol) in 5 mL of THF was added dropwise
to a suspension of activated magnesium (0.062 g, 2.60
mmol) in THF (10 mL). The reaction mixture was stirred
for 8 h under reflux and then selenium powder (0.21 g, 2.60
mmol) was added. The resulting mixture was stirred under
reflux for an additional 6 h, and after this time cooled to
room temperature and diluted with ethyl ether. The organic
phase was washed with saturated NH4Cl, 2 M NaOH and
brine, dried with MgSO4. Removal of the solvent under
vacuum afforded a yellow oil which crystallizes upon slow
evaporation of ethanol. Yield: 35%. Mp 155.6–157.0°C.
Anal. calcd for C32H28O2N2Se2: C, 81.33; H, 5.97; N, 5.93.
Found: C, 81.30; H, 5.95; N, 5.90%; [h]2D0 −45° (c 2.1
CHCl3); 1H NMR (CDCl3, 200 MHz) l 2.77 (dd, 1H,
J=8.0 Hz, J=14.0 Hz), 3.18 (dd, 1H, J=6.0 Hz, J=14.0
Hz), 4.08 (dd, 1H, J=8.0 Hz, J=16.0 Hz), 4.32 (dd, 1H,
J=8.0 Hz, J=16.0 Hz), 4.64–4.72 (m, 1H), 7.12–7.78 (m,
9H); 13C NMR (CDCl3, 50 MHz) l 41.9, 68.1, 71.7, 125.5,
125.9, 126.4, 128.2, 128.4, 129.3, 129.6, 131.4, 133.4, 137.9,
163.4; IR (KBr, cm−1): 1361, 1464, 1653, 3026, 3061.
13. Typical procedure for the copper-catalyzed 1,4-addition: To
a suspension of diselenide 1 (53 mg, 0.1 mmol) and CuI
(19 mg, 0.1 mmol) in 10 mL THF under argon, 0.35 mL
(2 mmol) of HMPA was added. The resulting yellow
solution was cooled to −78°C. After addition of cyclo-
hexenone (1 mmol), 2 mL (1 mmol, 0.5 M in THF) of
i-PrMgCl was added at −78°C over a period of 2 h. The
reaction mixture was then stirred for an additional 4 h at
that temperature. After quenching with a saturated
aqueous NH4Cl solution, the mixture was warmed to room
temperature and extracted with CH2Cl2. The organic phase
was dried with MgSO4 and removal of the solvent under
vacuum followed by flash chromatography on silica with
hexanes/AcOEt (98:2) afforded the pure product. Yield:
80% ee: 60%. [h]D20 +45° (c 1.5 CHCl3); 1H NMR (CDCl3,
200 MHz) l 0.81 (d, 6H), 1.21–2.17 (m, 10H); 13C NMR
(CDCl3, 50 MHz) l 20.0, 25.4, 28.2, 32.4, 41.2, 45.2, 212.3;
IR (KBr, cm−1): 1713.
The authors wish to thank CAPES and the DAAD
(German Academic Exchange Service) for travel grants
as part of
a PROBRAL Program, CNPq and
FAPERGS for financial support. S.J.N.S. thanks
CAPES for a Ph.D. fellowship.
References
1. (a) Noyori, R. Asymmetric Catalysis in Organic Synthesis;
John Wiley & Sons: New York, 1994; (b) Comprehensive
Asymmetric Catalysis; Jacobsen, E. N.; Pfaltz, A.;
Yamamoto, H., Eds.; Springer: Berlin, 1999.
2. For reviews, see: (a) Rossiter, B. E.; Swingle, N. M. Chem.
Rev. 1992, 92, 771–806; (b) Alexakis, A. Organocopper
Reagents, A Practical Approach; Taylor R. J. K., Ed.;
Oxford University Press: Oxford, 1994; Chapter 8; (c)
Krause, N. Angew. Chem., Int. Ed. Engl. 1998, 37, 283–285;
(d) Leonard, J.; D´ıez-Barra, E.; Merino, S. Eur. J. Org.
Chem. 1998, 2051–2061; (e) Sibi, M. P.; Manyem, S.
Tetrahedron 2000, 56, 8033–8061.
3. (a) Zhou, Q.-L.; Pfaltz, A. Tetrahedron 1994, 50, 4467–
4478; (b) Lambert, F.; Knotter, D. M.; Janssen, M. D.; van
Klaveren, M.; Boersma, J.; van Koten, G. Tetrahedron:
Asymmetry 1991, 2, 1097–1100; (c) Cran, G. A.; Gibson,
C. L.; Handa, S.; Kennedy, A. R. Tetrahedron: Asymmetry
1996, 7, 2511–2514; (d) Nakagawa, Y.; Kanai, M.;
Nagaoka, Y.; Tomioka, K. Tetrahedron Lett. 1996, 37,
7805–7808; (e) Dieter, R. K.; Tokles, M. J. Am. Chem. Soc.
1987, 109, 2040–2046.
4. (a) Wessjohann, L.; Sinks, U. J. Prakt. Chem. 1998, 340,
189–203; (b) Wirth, T. Tetrahedron 1999, 55, 1–28.
5. (a) Fukuzawa, S.; Takahashi, K.; Kato, H.; Yamazaki, H.
J. Org. Chem. 1997, 62, 7711–7716; (b) Tomoda, S.;
Iwaoka, M. J. Chem. Soc., Chem. Commun. 1988, 1283–
1284; (c) Nishibayashi, Y.; Singh, J. D.; Fukuzawa, S.-I.;
Uemura, S. J. Chem. Soc., Perkin Trans. 1 1995, 2871–
2876.
6. (a) Tiecco, M.; Testaferri, L.; Santi, C.; Tomassini, C.;
Marini, F.; Bagnoli, L.; Temperini, A. Tetrahedron: Asym-
metry 2000, 11, 4645–4650; (b) Tiecco, M.; Testaferri, L.;
Marini, F.; Sternativo, S.; Santi, C.; Bagnoli, L.; Tem-
perini, A. Tetrahedron: Asymmetry 2001, 12, 3053–3059; (c)
Back, T. G.; Moussa, Z.; Parvez, M. J. Org. Chem. 2002,
67, 499–509.
7. (a) Nishibayashi, Y.; Singh, J. D.; Segawa, K.; Fukuzawa,
S.-I.; Uemura, S. J. Chem. Soc., Chem. Commun. 1994,
1375–1376; (b) Nishibayashi, Y.; Segawa, K.; Singh, J. D.;
Fukuzawa, S.-I.; Ohe, K.; Uemura, S. Organometallics
1996, 15, 370–379.
8. (a) Wirth, T. Tetrahedron Lett. 1995, 36, 7849–7852; (b)
Wirth, T.; Kulieke, K. J.; Fragale, G. Helv. Chim. Acta
1996, 79, 1957–1966; (c) Santi, C.; Wirth, T. Tetrahedron:
Asymmetry 1999, 10, 1019–1023.
9. (a) Braga, A. L.; Appelt, H. R.; Schneider, P. H.; Silveira,
C. C.; Wessjohann, L. A. Tetrahedron: Asymmetry 1999,
10, 1733–1738; (b) Braga, A. L.; Appelt, H. A.; Schneider,
P. H.; Rodrigues, O. E. D.; Silveira, C. C.; Wessjohann,
L. A. Tetrahedron 2001, 57, 3291–3295; (c) Braga, A. L.;
Vargas, F.; Silveira, C. C.; de Andrade, L. H. Tetrahedron
Lett. 2002, 43, 2335–2337.