C O M M U N I C A T I O N S
Table 2. Asymmetric 1,4-Addition of Arylboronic Acids to
R,â-Unsaturated Carbonyl Compounds Catalyzed by Rh(l)/1a
References
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Catalytic Asymmetric Synthesis, 2nd ed.; Ojima, I., Ed.; Wiley-VCH: New
York, 2000; pp 1-110. (c) Brown, J. M. In ComprehensiVe Asymmetric
Catalysis; Jacobsen, E. N., Pfalz, A., Yamamoto, H., Eds.; Springer-
Verlag: Berlin, 1999; Vol. 1, pp 121-182. (d) Cre´py, K. V. L.; Imamoto,
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(2) For recent representative examples, see: (a) van den Berg, M.; Minnaard,
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Feringa, B. L. J. Am. Chem. Soc. 2000, 122, 11539-11540. (b) Reetz,
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Ostermeier, M.; Priess, J.; Helmchen, G. Angew. Chem., Int. Ed. 2002,
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Hoge, G.; Wu, H.-P.; Kissel, W. S.; Pflum, D. A.; Greene, D. J.; Bao, J.
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8160. (k) Wu, S.; Zhang, W.; Zhang, Z.; Zhang, X. Org. Lett. 2004, 6,
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(m) Imamoto, T.; Oohara, N.; Takahashi, H. Synthesis 2004, 1353-1358.
(n) Imamoto, T.; Cre´py, K. V. L.; Katagiri, K. Tetrahedron: Asymmetry
2004, 15, 2213-2218. (o) Cheng, X.; Zhang, Q.; Xie, J.-H.; Wang, L.-
X.; Zhou, Q.-L. Angew. Chem., Int. Ed. 2005, 44, 1118-1121. (p) Pa`mies,
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(3) Imamoto, T.; Watanabe, J.; Wada, Y.; Masuda, H.; Yamada, H.; Tsuruta,
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ee (%)
entry
enone
Ar
temp (
°
C)
time (h)
yield (%)b
(config)
1
2
3
4
5
5
5
5
6
7
Ph
40
40
50
50
40
1
1
12
12
1
93
97
92
90
97
98.2 (R)
93.9 (R)
99.4 (R)
96.2 (R)
99.1 (S)
4-MeOC6H4
4-CF3C6H4
Ph
Ph
a All reactions were performed with 0.3 mmol R,â-unsaturated carbonyl
compound, 0.6 mmol arylboronic acid, and 0.009 mmol rhodium catalyst
generated in situ from [RhCl(C2H4)2]2 (0.0045 mmol) and 1 (0.099 mmol).
b Isolated yield.
Table 3. Asymmetric Alkylative Ring Opening Catalyzed by
PdCl2(cod)/1a
(4) Gridnev, I. D.; Yamanoi, Y.; Higashi, N.; Tsuruta, H.; Yasutake, M.;
Imamoto, T. AdV. Synth. Catal. 2001, 343, 118-136.
ee (%)
(5) Yamanoi, Y.; Imamoto, T. J. Org. Chem. 1999, 64, 2988-2989.
(6) (a) Gridnev, I. D.; Higashi, N.; Asakura, K.; Imamoto, T. J. Am. Chem.
Soc. 2000, 122, 7183-7194. (b) Gridnev, I. D.; Yasutake, M.; Higashi,
N.; Imamoto, T. J. Am. Chem. Soc. 2001, 123, 5268-5276. (c) Gridnev,
I. D.; Imamoto, T. Acc. Chem. Res. 2004, 37, 633-644.
entry
R1
R2
time (h)
yield (%)b
(config)
1
2
3
H
H
F
Me
Et
Me
2
15
2
90
88
90
95.6 (1S,2S)
97.6 (1S,2S)
93.8 (1S,2S)
(7) Nagata, K.; Matsukawa, S.; Imamoto, T. J. Org. Chem. 2000, 65, 4185-
4188.
a All reactions were performed with 0.5 mmol of substrate and 0.025
(8) Both t-Bu-BisP* and t-Bu-MiniPhos afford excellent enantiomeric excesses
up to 99.7% only in the reductions of E-isomers. Yasutake, M.; Gridnev,
I. D.; Higashi, N.; Imamoto, T. Org. Lett. 2001, 3, 1701-1704.
(9) Gridnev, I. D.; Higashi, N.; Imamoto, T. J. Am. Chem. Soc. 2000, 122,
10486-10487.
mmol of in situ-prepared PdCl2(cod)/1. b Isolated yield.
In conclusion, we have prepared a new P-chiral phosphine ligand
1 by reacting enantiomerically pure tert-butylmethylphosphine-
borane with commercially available 2,3-dichloroquinoxaline. This
ligand, in contrast to most of the previously reported P-chiral
ligands, is an air-stable solid and exhibits excellent enantioselec-
tivities in both Rh-catalyzed asymmetric hydrogenations and Rh-
or Pd-catalyzed carbon-carbon bond-forming reactions. These
findings indicate its versatile utility in a wide variety of transition-
metal-catalyzed asymmetric reactions.
(10) Gridnev, I. D.; Yasutake, M.; Hogashi, N.; Imamoto, T. J. Am. Chem.
Soc. 2001, 123, 5268-5276.
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Acknowledgment. This work was supported by a Grant-in-Aid
for Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology, Japan.
Supporting Information Available: Synthesis and characterization
of phosphine ligand 1 and detailed experimental procedures of catalytic
asymmetric reactions using ligand 1. This material is available free of
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