9442
A. Saito et al. / Tetrahedron Letters 45 (2004) 9439–9442
8226; (c) Kawamura, M.; Kudo, K. Chirality 2002, 14,
(1.1 equiv)
(10 equiv)
1c
O
O
O
727–730.
H
H
H
4. Chiral cationic oxazaborolidine catalyzed Diels–Alder
reactions including an example of 5H-furan-2-one with
cyclopentadiene was reported, see: Ryu, D. H.; Lee, T. W.;
Corey, E. J. J. Am. Chem. Soc. 2002, 124, 9992–9993.
5. (a) Ikeda, T.; Yue, S.; Hutchinson, C. R. J. Org. Chem.
1985, 50, 5193–5199; (b) Drew, M. G. B.; Mann, J.;
Thomas, A. J. Chem. Soc., Perkin Trans. 1 1986, 2279–
2285; (c) Chen, Z.; Ortun˜o, R. M. Tetrahedron: Asymme-
try 1994, 5, 371–376; (d) Carretero, J. C.; Garcia Ruano, J.
L.; Martin Cabrejas, L. M. Tetrahedron 1997, 53, 14115–
14126.
O
O
O
toluene
H
5-exo
R
R
R
2
5-endo
Thermal reaction (ref. 8b)
2d: R = Me
Lewis acid mediated reaction
2d: R = Me
2e: R = CH2OTBS
80 °C
5d: 85%, endo/exo = 3.0:1
rt, 5 h
5d: 74%, endo/exo = 7.3:1
5e: 74%, endo/exo = 8.0:1
rt, 12 h
6. Total synthesis of natural product using Lewis acid
mediated Diels–Alder reaction, see: (a) Takadoi, M.;
Katoh, T.; Yamaguchi, K.; Terashima, S. Tetrahedron
Lett. 1999, 40, 3399–3402; (b) Shoji, M.; Kobayashi, E.;
Inomata, K.; Numazawa, M. J. Tohoku Pharm. Univ.
2000, 47, 47–53.
7. Branchadell, V.; Sodupe, M.; Ortun˜o, R. M.; Oliva, A.;
Gomez-Pardo, D.; Guingant, A.; DÕAngelo, J. J. Org.
Chem. 1991, 56, 4135–4141.
Scheme 2.
cyclopentadiene proceeded at 80°C with complete p-
facial selectivity to minimize steric influence of c-methyl
group, while the cycloadduct 5d was obtained as an
endo/exo mixture in a ratio of 3.0:1.8b The present biden-
tate Lewis acid 1c was also an effective catalyst for the
same reaction; that is, in the presence of 1c the reaction
of 2d with cyclopentadiene proceeded at room tempera-
ture within 5h to give the adduct 5d in 74% yield with
complete p-facial selectivity and a higher endo selectivity
(endo/exo = 7.3:1). Similar result was observed in the
reaction of c-silyloxymethyl derivative 2e with cyclo-
pentadiene catalyzed by 1c to give the adduct 5e (74%
yield, endo/exo = 8.0:1).
8. (a) Ortun˜o, R. M.; Corbera, J.; Font, J. Tetrahedron Lett.
1986, 27, 1081–1084; (b) Ortun˜o, R. M.; Batllori, R.;
´
Ballesteros, M.; Monsalvatje, M.; Corbera, J.; Sanchez-
Ferrando, F.; Font, J. Tetrahedron Lett. 1987, 28, 3405–
3408; (c) Ortun˜o, R. M.; Ballesteros, M.; Corbera, J.;
Sanchez-Ferrando, F.; Font, J. Tetrahedron 1988, 44,
1711–1719; (d) De Jong, J. C.; Van Bolhuis, F.; Feringa,
B. L. Tetrahedron: Asymmetry 1991, 2, 1247–1262.
9. (a) Gosselin, P.; Perrotin, A.; Mille, S. Tetrahedron 2001,
57, 733–738; (b) Birman, V. B.; Danishefsky, S. J. J. Am.
Chem. Soc. 2002, 124, 2080–2081.
10. (a) Saito, A.; Ito, H.; Taguchi, T. Org. Lett. 2002, 4, 4619–
4621(b) Saito, A.; Yanai, H.; Taguchi, T. Tetrahedron
2004, 60, in press.
11. (a) Nakanishi, H.; Fujita, H.; Yamamoto, O. Bull. Chem.
Soc. Jpn. 1978, 51, 214; (b) Parker, K. A.; Adamchuk, M.
R. Tetrahedron Lett. 1978, 1689–1692; (c) Toyota, M.;
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A. J. Org. Chem. 2001, 66, 6092–6095, and reference cited
therein.
In conclusion, we have shown that the Diels–Alder reac-
tions of a,b-unsaturated lactone derivatives including
their a-methylated substrate with acyclic dienes and
cyclopentadiene can be efficiently promoted by the bis-
aluminated triflic amide, TfN[Al(Me)Cl]2 and TfN[Al-
(iBu)2]2. Selection of these Lewis acids based on the ligand
on the aluminum should be crucial to obtain high yield
and high selectivity of the cycloadduct depending on the
combination of a,b-unsaturated lactone and 1,3-diene.
13. We conducted the reaction of 2c with isoprene in the
presence of 2.2equiv of monodentate Lewis acid Me2 AlCl
in toluene at 80°C, but the recovery of 2c was the result.
14. (a) Hanawa, H.; Maruoka, K. Tetrahedron Lett. 1999, 40,
5365–5368; (b) Hanawa, H.; Maekawa, N.; Maruoka, K.
Tetrahedron Lett. 1999, 40, 8379–8382.
References and notes
1. For reviews on the Diels–Alder reactions: (a) Oppolzer,
W. In Comprehensive Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 5,
Chapter 4.1, pp 315–399; (b) Kagan, H. B.; Riant, O.
Chem. Rev. 1992, 92, 1007–1019; (c) Dias, L. C. J. Braz.
Chem. Soc. 1997, 8, 289–322; (d) Evans, D. A.; Johnson, J.
S. In Comprehensive Asymmetric Catalysis; Jacobsen, E.
N., Pfaltz, A., Yamamoto, H., Eds.; Springer: Berlin,
1999; Vol. III, pp 1177–1235; (e) Corey, E. J. Angew.
Chem., Int. Ed. 2002, 41, 1650–1667.
15. Regarding the retro Diels–Alder reaction,16,17 we carried
out the reactions of 3b-endo under the similar conditions
(in toluene, rt, 4h) using the bidentate Lewis acid,
TfN[Al(Me)Cl]2, and TfN[Al(i-Bu)2]2, respectively. With
TfN[Al(Me)Cl]2,
a mixture of 3b-endo and 1b was
obtained in a ratio of 1.7:1, while with TfN[Al(i-Bu)2]2
the reaction proceeded more slowly (3b-endo:1b = 4.7:1).
In contrast, the exo adduct 3b-exo did not change at all by
mixing with TfN[Al(Me)Cl]2.
2. For a reference on synthetic applications of the Diels–
Alder reactions, see: Nicolaou, K. C.; Snyder, S. A.;
Montagnon, T.; Vassilikogiannakis, G. Angew. Chem.,
Int. Ed. 2002, 41, 1668–1698.
16. For a review on the retro Diels–Alder reaction, see:
Rickborn, B. Org. React. 1998, 52, 1–393.
3. For recent reports on the Diels–Alder reactions of acrylate
derivatives as dienophiles, see: (a) Ishihara, K.; Kobaya-
shi, J.; Inanaga, K.; Yamamoto, H. Synlett 2001, 394–396;
(b) Mathieu, B.; Ghosez, L. Tetrahedron 2002, 58, 8219–
17. (a) Marchand, A. P.; Vidyasagar, V. J. Org. Chem. 1988,
53, 4412; (b) Grieco, P. A.; Abood, N. J. Org. Chem. 1989,
54, 6008–6010; (c) Grieco, P. A.; Abood, N. J. Chem. Soc.,
Chem. Commun. 1990, 410–412.