describe that a rhodium/chiral diene catalyst is highly
effective for asymmetric 1,4-addition of arylboronic acids
to â-silyl R,â-unsaturated carbonyl compounds, providing a
new and useful method for the construction of chiral
organosilicon compounds in high yield and enantioselectivity.
Table 1. Rh/(R,R)-Bn-bod*-Catalyzed Asymmetric
1,4-Addition of Arylboronic Acids to â-Phenyldimethylsilyl
Enones 1
In an initial investigation, we examined the effect of ligand
by employing â-phenyldimethylsilyl enone 1a as a model
substrate in the 1,4-addition of PhB(OH)2 with 3 mol % of
rhodium (eq 1). The use of (R)-binap8 as a ligand produced
1,4-adduct 2a in 82% yield with moderate ee of 72% (S).9
Change of the ligand to (S)-phosphoramidite10 (2.0 equiv to
rhodium) resulted in lower yield and enantioselectivity (54%
yield, 14% ee (S)). In contrast, the use of chiral diene ligands
proved to be more effective for this 1,4-addition reaction,
achieving higher yield and ee. Thus, the employment of
(R,R)-Ph-bod*11 as a ligand provided 2a in 90% yield with
97% ee (S), and the change of substituents on the olefins
from phenyl to benzyl ((R,R)-Bn-bod*)11-13 further improved
both yield and enantioselectivity (94% yield, 99% ee (S)).14
Under the optimized conditions with (R,R)-Bn-bod* as the
ligand, the scope of the substrate and the nucleophile is
(4) For reviews of palladium-catalyzed asymmetric hydrosilylations,
see: (a) Tang, J.; Hayashi, T. In Catalytic Hetero-functionalization; Togni,
A., Gru¨tzmacher, H., Eds.; Wiley-VCH: Weinheim, Germany, 2001; p 73.
(b) Tietze, L. F.; Ila, H.; Bell, H. P. Chem. ReV. 2004, 104, 3453 and the
references therein. See also: (c) Suginome, M.; Ohmura, T.; Miyake, Y.;
Mitani, S.; Ito, Y.; Murakami, M. J. Am. Chem. Soc. 2003, 125, 11174.
(5) For a review of asymmetric synthesis of allylsilanes by palladium-
catalyzed cross-coupling reactions, see: Hayashi, T. In ComprehensiVe
Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.;
Springer: New York, 1999; Vol. 2, Chapter 25.
(6) For examples of a palladium-catalyzed asymmetric 1,4-addition of
disilanes, see: (a) Hayashi, T.; Matsumoto, Y.; Ito, Y. J. Am. Chem. Soc.
1988, 110, 5579. (b) Matsumoto, Y.; Hayashi, T.; Ito, Y. Tetrahedron 1994,
50, 335.
a Ee was determined by chiral HPLC on a Chiralpak AD-H column with
hexane/2-propanol. b Ee was determined by chiral HPLC on a Chiralcel
OD-H column with hexane/2-propanol 90/10.
illustrated in Table 1.15 Thus, not only methyl enone, but
also ethyl or phenyl enone can be phenylated effectively in
excellent yield and ee (89-94% yield, 97-99% ee; entries
1-3). In addition, sterically and electronically diverse arrays
of aryl groups can be installed under the same conditions,
(7) For examples of palladium-catalyzed asymmetric allylic silylations,
see: (a) Matsumoto, Y.; Ohno, A.; Hayashi, T. Organometallics 1993, 12,
4051. (b) Hayashi, T.; Ohno, A.; Lu, S.; Matsumoto, Y.; Fukuyo, E.; Yanagi,
K. J. Am. Chem. Soc. 1994, 116, 4221.
(8) Takaya, H.; Mashima, K.; Koyano, K.; Yagi, M.; Kumobayashi, H.;
Taketomi, T.; Akutagawa, S.; Noyori, R. J. Org. Chem. 1986, 51, 629.
(9) (a) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N.
J. Am. Chem. Soc. 1998, 120, 5579. (b) For a review of rhodium-catalyzed
asymmetric 1,4-additions, see: Hayashi, T.; Yamasaki, K. Chem. ReV. 2003,
103, 2829.
(10) (a) Boiteau, J.-G.; Minnaard, A. J.; Feringa, B. L. J. Org. Chem.
2003, 68, 9481. (b) Feringa, B. L. Acc. Chem. Res. 2000, 33, 346.
(11) (a) Tokunaga, N.; Otomaru, Y.; Okamoto, K.; Ueyama, K.; Shintani,
R.; Hayashi, T. J. Am. Chem. Soc. 2004, 126, 13584. (b) Otomaru, Y.;
Okamoto, K.; Shintani, R.; Hayashi, T. J. Org. Chem. 2005, 70, 2503. (c)
Shintani, R.; Kimura, T.; Hayashi, T. Chem. Commun. 2005, 3213. (d)
Shintani, R.; Okamoto, K.; Hayashi, T. Chem. Lett. 2005, 1294.
(12) (a) Shintani, R.; Okamoto, K.; Otomaru, Y.; Ueyama, K.; Hayashi,
T. J. Am. Chem. Soc. 2005, 127, 54. (b) Shintani, R.; Tsurusaki, A.;
Okamoto, K.; Hayashi, T. Angew. Chem., Int. Ed. 2005, 44, 3909.
(13) For other chiral diene ligands in the literature, see: (a) Hayashi,
T.; Ueyama, K.; Tokunaga, N.; Yoshida, K. J. Am. Chem. Soc. 2003, 125,
11508. (b) Shintani, R.; Ueyama, K.; Yamada, I.; Hayashi, T. Org. Lett.
2004, 6, 3425. (c) Otomaru, Y.; Tokunaga, N.; Shintani, R.; Hayashi, T.
Org. Lett. 2005, 7, 307. (d) Otomaru, Y.; Kina, A.; Shintani, R.; Hayashi,
T. Tetrahedron: Asymmetry 2005, 16, 1673. (e) Fischer, C.; Defieber, C.;
Suzuki, T.; Carreira, E. M. J. Am. Chem. Soc. 2004, 126, 1628. (f) Defieber,
C.; Paquin, J.-F.; Serna, S.; Carreira, E. M. Org. Lett. 2004, 6, 3873. (g)
Paquin, J.-F.; Defieber, C.; Stephenson, C. R. J.; Carreira, E. M. J. Am.
Chem. Soc. 2005, 127, 10850. (h) Paquin, J.-F.; Stephenson, C. R. J.;
Defieber, C.; Carreira, E. M. Org. Lett. 2005, 7, 3821. (i) La¨ng, F.; Breher,
F.; Stein, D.; Gru¨tzmacher, H. Organometallics 2005, 24, 2997. (j) Grundl,
M. A.; Kennedy-Smith, J. J.; Trauner, D. Organometallics 2005, 24, 2831.
(14) The absolute configuration of compound 2a was determined to be
(S) by comparison of the optical rotation ([R]20 -9.3 (c 1.19, CHCl3))
D
with the reported value in ref 6a ([R]20 +9.2 in CHCl3 for (R)).
D
4758
Org. Lett., Vol. 7, No. 21, 2005