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Catalytic Asymmetric Addition of Diethylzinc to N-(Diphenylphosphinoyl) Imines
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Chichester, 1997; pp. 225 244; for a review on catalytic
asymmetric addition to imines, see: b) S. Kobayashi, H.
Ishitani, Chem. Rev. 1999, 99, 1069 1094.
sulfur atom at d 64.988 in L7 was observed in the
presence of CuBF4 (see Supporting Information). This
result may indicate that CuBF4 can be potentially
coordinated by S, N atom in L7 ligand.
In conclusion, the catalytic asymmetric addition of
diethylzinc to N-(diphenylphosphinoyl) imines in gen-
erally good yields and enantioselectivities has been
achieved using Cu(OTf)2 and easily available, very
stable and recoverable axially chiral N-(binaphth-2-
yl)thiophosphoramide ligands. Efforts are underway to
elucidate the mechanistic details of this catalytic system
and to extend the scope and limitations of those novel
chiral ligands in other asymmetric C-C bond forming
processes.
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during our preparation of manuscript, we found that
Charette has reported the first example of catalytic
enantioselective addition of dialkylzinc to N-(diphenyl-
phosphinoyl) imines, see: A. A. Boezio, A. B. Charette, J.
Am. Chem. Soc. 2003, 125, 1692 1693.
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131 134.
Experimental Section
Typical Procedure for the Cu(II)-Catalyzed
Asymmetric Addition of Diethylzinc to N-
(Diphenylphosphinoyl) Imines
[6] T. Hayashi, M. Ishigedani, J. Am. Chem. Soc. 2000, 122,
976 977.
[7] a) K. Soai, T. Hatanaka, T. Miyazawa, J. Chem. Soc.
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New York, 1993; b) E. N. Jacobsen, A. Pfaltz, H.
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A solution of Cu(OTf)2 (5.4 mg, 0.015 mmol) and ligand 7
(8.4 mg, 0.018 mmol) in dry toluene (3mL) was stirred for 1 h
at room temperature under an argon atmosphere. N-(Diphe-
nylphosphinoyl) imine of benzaldehyde (92 mg, 0.3mmol) was
added and the solution was stirred for a further 10 min, then
Et2Zn (0.9 mL, 0.9 mmol, 1.0 M solution in hexane) was added
dropwise at 08C. The resulting mixture was stirred for about
48 h at the same temperature, saturated NH4Cl (10.0 mL) was
added. After extraction with ethyl acetate (3 Â 10.0 mL), the
combined organic layers were dried over MgSO4. The residue
obtained upon removal of volatiles under vacuum was purified
by column chromatography on silica gel (eluent: petroleum/
ethyl acetate 1:1) to afford the addition product N-(1-
phenylpropyl)-P,P-diphenylphosphinic amide as a colorless
solid; yield: 80 mg (80%).
The experimental procedures for the preparation of the
ligands and the spectroscopic and analytical data for the
ligands L1 L8 and products 2 shown in Table 2 are included in
the supporting information
[10] S. Miyano, M. Nawa, A. Mori, H. Hashimoto, Bull.
Chem. Soc. Jpn. 1984, 57, 2171 2176.
Acknowledgements
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G. A. More, J. Chem. Soc. Perkin Trans. 1 1984, 1357
1370.
[12] For selected X-ray structures of Cu complexes coordi-
nated by S,N ligands, see: a) D. M. Koten, D. M. Grove,
W. J. Smeets, A. L. Spek, G. van Koten, J. Am. Chem.
Soc. 1992, 114, 3400 3410; b) G. R. Brubaker, J. N.
Brown, M. K. Yoo, T. M. Kutchan, E. A. Mottel, Inorg.
Chem. 1979, 18, 299 302.
We thank the State Key Project of Basic Research (Project 973)
(No. G2000048007), Shanghai Municipal Committee of Science
and Technology, and the National Natural Science Foundation
of China (20025206 and 20272069) for financial support.
References and Notes
[1] a) H.-J. Federsel, A. N. Collins, G. N. Sheldrake, J.
Crosby, Chirality in Industry II, John Wiley & Sons,
Adv. Synth. Catal. 2003, 345, 971 973
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