Angewandte
Chemie
Reagents: A Practical Approach (Ed.: H. Yamamoto), Oxford
University Press, Oxford, 1999.
[12] For other highly enantioselective Diels–Alder reactions with less
than 1 mol% of chiral Lewis acid catalyst for the same
substrates, see: a) J. Bao, W. D. Wulff, A. L. Rheingold, J. Am.
Chem. Soc. 1998, 120, 8271 – 8272; b) ref. [4c].
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3808 – 3809; b) D. H. Ryu, T. W. Lee, E. J. Corey, J. Am. Chem.
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Hu, P. D. Rege, E. J. Corey, J. Am. Chem. Soc. 2004, 126, 5984 –
5986; g) D. H. Ryu, E. J. Corey, J. Am. Chem. Soc. 2004, 126,
8106 – 8107; h) Q.-Y. Hu, G. Zhou, E. J. Corey, J. Am. Chem. Soc.
2004, 126, 13708 – 13712.
[5] a) K. Ishihara, H. Yamamoto, J. Am. Chem. Soc. 1994, 116,
1561 – 1562; b) K. Ishihara, M. Miyata, K. Hattori, T. Tada, H.
Yamamoto, J. Am. Chem. Soc. 1994, 116, 10520 – 10524; c) K.
Ishihara, H. Kurihara, H. Yamamoto, J. Am. Chem. Soc. 1996,
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[6] a) M. Oishi, S. Aratake, H. Yamamoto, J. Am. Chem. Soc. 1998,
120, 8271 – 8272; b) K. Ishihara, J. Kobayashi, K. Inanaga, H.
Yamamoto, Synlett 2001, 394 – 396; c) G. Xia, K. Shibatomi, H.
Yamamoto, Synlett 2004, 2437 – 2439; for a similar activation of a
chiral boron Lewis acid by another Lewis acid, see: d) H.
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D. G. Hall, Synthesis 2004, 1290 – 1302.
[7] Lewis acid assisted Brønsted acid (LBA): a) K. Ishihara, M.
Kaneeda, H. Yamamoto, J. Am. Chem. Soc. 1994, 116, 11179 –
11180; b) K. Ishihara, S. Nakamura, M. Kaneeda, H. Yamamoto,
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K. Ishihara, H. Yamamoto, J. Am. Chem. Soc. 2000, 122, 8120 –
8130; f) S. Nakamura, K. Ishihara, H. Yamamoto, J. Am. Chem.
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Yamamoto, J. Am. Chem. Soc. 2001, 123, 1505 – 1506; h) K.
Ishihara, H. Ishibashi, H. Yamamoto, J. Am. Chem. Soc. 2002,
124, 3647 – 3655; i) K. Ishihara, D. Nakashima, Y. Hiraiwa, H.
Yamamoto, J. Am. Chem. Soc. 2003, 125, 24 – 25; j) K. Kuma-
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k) H. Ishibashi, K. Ishihara, H. Yamamoto, J. Am. Chem. Soc.
2004, 126, 11122 – 11123.
[13] The addition of more than one equivalent of water to 1a resulted
in a decrease in both reactivity and enantioselectivity. This
obstacle could be overcome by use of a larger amount of SnCl4
without dramatic loss of enantioselectivity.
[14] The physical and spectroscopic data for all cycloadducts were
identical to those reported previously for these compounds. 2a:
a) Y. Hayashi, J. J. Rohde, E. J. Corey, J. Am. Chem. Soc. 1996,
118, 5502 – 5503; 2b: b) S. Hashimoto, N. Komeshima, K. Koga,
J. Chem. Soc. Chem. Commun. 1979, 437 – 438 and ref. [5d]; 2c:
c) R. Kumareswaran, P. S. Vankar, M. V. R. Reddy, S. V. Pitre, R.
Roy, Y. D. Vankar, Tetrahedron 1999, 55, 1099 – 1110 and
ref. [4b]; 2d: d) M. E. Jung, W. D. Vaccaro, K. R. Buszek,
Tetrahedron Lett. 1989, 30, 1893 – 1896 and ref. [4b]; 2e: e) G.
Mehta, A. Srikrishna, A. V. Reddy, M. S. Nair, Tetrahedron 1981,
37, 4543 – 4559 and ref. [4c]; 2 f: f) S. Takano, T. Kamikubo, M.
Morita, K. Ogasawara, Synthesis 1994, 601 – 604, g) A. B.
Northrup, D. W. C. MacMillan, J. Am. Chem. Soc. 2002, 124,
2458 – 2459, and ref. [4b]; 3a: h) Z. Zhu, J. H. Espenson, J. Am.
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Lusch, J. Org. Chem. 1979, 44, 1923 – 1927; 4a: ref. [14i].
[15] The absolute configurations of 2a,[14b] 2c,[4b] 2e,[4c] and 2 f[4b] were
assigned by comparison with optical rotation values reported in
the literature. For 2b, the absolute configuration was assigned by
comparison with an authentic sample prepared separately, see
a) D. Sartor, J. Saffrich, G. Helmchen, Synlett 1990, 197 – 198.
The absolute configuration of 2d was assigned by comparison
with the optical rotation value of the corresponding alcohol, see:
b) O. Kitagawa, H. Izawa, K. Sato, A. Dobashi, T. Taguchi, J.
Org. Chem. 1998, 63, 2634 – 2640.
[16] The enantioselectivities of the cycloadducts were determined as
follows. 2a: a) K. Furuta, S. Shimizu, Y. Miwa, H. Yamamoto, J.
Org. Chem. 1989, 54, 1481 – 1483. For a general procedure for the
acetalization of Diels–Alder adducts with (À)-(2R,4R)-2,4-
pentanediol, see: b) K. Furuta, Q. Gao, H. Yamamoto, Org.
Synth. 1995, 72, 86 – 94; 2b: ref. [5d]; for 2c–f, see Supporting
Information; 3a: ref. [5d]; 4a: refs. [5d] and [16b].
[8] This mode of activation was speculated from the plausible active
species for CBS reduction. In this process, the coordination of
the electrophilic BH3 to the nitrogen atom of the oxazaboroli-
dine serves to increase the Lewis acidity of the endocyclic boron
atom strongly. For recent reviews, see: a) E. J. Corey, C. J. Helal,
Angew. Chem. 1998, 110, 2092 – 2118; Angew. Chem. Int. Ed.
1998, 37, 1986 – 2012; b) S. Itsuno in Comprehensive Asymmetric
Catalysis, Vol. 1 (Eds.: E. N. Jacobsen, A. Pfaltz, H. Yamamoto),
Springer, Berlin, 1999, pp. 290 – 315.
[9] Some chiral Lewis acid catalysts have been reported to be air-
stable, and even storable, see: a) S. Kobayashi, M. Ueno, S. Saito,
Y. Mizuki, H. Ishitani, Y. Yamashita, Proc. Natl. Acad. Sci. USA
2004, 101, 5476 – 5481; b) Y. S. Kim, S. Matsunaga, J. Das, A.
Sekine, T. Ohshima, M. Shibasaki, J. Am. Chem. Soc. 2000, 122,
6506 – 6507;
[10] For a chiral Lewis acid catalyzed Diels–Alder reaction in water,
see: a) S. Otto, G. Boccaletti, J. B. F. N. Engberts, J. Am. Chem.
Soc. 1998, 120, 4238 – 4239; b) S. Otto, J. B. F. N. Engberts, J. Am.
Chem. Soc. 1999, 121, 6798 – 6806.
[11] The use of other Lewis acids (BF3·Et2O, tris(pentafluorophen-
yl)boron, [Cp2TiCl2], ZnCl2) resulted in either poor reactivity or
lower enantioselectivity.
Angew. Chem. Int. Ed. 2005, 44, 1484 –1487
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