LETTER
Asymmetric Transfer Hydrogenation by a New Ir(III) Catalyst in Water
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(3) (a) Wu, X.; Li, X.; Hems, W.; King, F.; Xiao, J. Org. Biomol.
Chem. 2004, 2, 1818. (b) Li, X.; Wu, X.; Chen, W.;
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2005, 23, 50.
(4) Blacker, J.; Martin, J. In Asymmetric Catalysis on an
Industrial Scale: Challenges, Approaches and Solutions;
Blaser, H. U.; Schmidt, E., Eds.; Wiley: New York, 2004,
201.
In summary, the camphor-modified 1,2-diphenylethyl-
enediamine, CsDPEN, is an efficient ligand for ATH of
aryl ketones in neat water. The Ir–CsDPEN catalyst is
shown to be particularly effective for the aqueous phase
reduction. It catalyzes the ATH of a wide range of aryl ke-
tones, furnishing high conversions at a S/C ratio of 1000
in a few hours for a number of substrates with ee of up to
98% in water with no organic solvent. The reduction ap-
pears to be more effective towards ketones without elec-
tron-donating substituents on the aryl rings.
(5) Reviews on ATH reactions: (a) Clapham, S. E.; Hadzovic,
A.; Morris, R. H. Coord. Chem. Rev. 2004, 248, 2201.
(b) Everaere, K.; Mortreux, A.; Carpentier, J.-F. Adv. Synth.
Catal. 2003, 345, 67. (c) Blaser, H.-U.; Malan, C.; Pugin,
B.; Spindler, F.; Steiner, H.; Studer, M. Adv. Synth. Catal.
2003, 345, 103. (d) Saluzzo, C.; Lemaire, M. Adv. Synth.
Catal. 2002, 344, 915. (e) Palmer, M. J.; Wills, M.
Tetrahedron: Asymmetry 1999, 10, 2045. (f) Noyori, R.;
Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97.
Preparation of the Precatalyst
The M–CsDPEN catalyst was prepared from [RuCl2(p-cymene)]2
(3.1 mg, 0.005 mmol), [Cp*RhCl2]2 (3.1 mg, 0.005 mmol), or
[Cp*IrCl2]2 (4.0 mg, 0.005 mmol), and (R,R,R)-CsDPEN (5.1 mg,
0.012 mmol) in H2O (8 mL). After stirring at 40 °C for 1 h, the
suspension was used for the following reduction.
(g) Zassinovich, G.; Mestroni, G.; Gladiai, S. Chem. Rev.
1992, 92, 1051.
Typical Procedure for Acetophenone Reduction
After preparing the precatalyst, HCOONa (3.40 g, 50.0 mmol) and
acetophenone (1.20 g, 10 mmol) were added to the solution. Fol-
lowing quick degassing (3 ×), the solution was allowed to react at
40 °C for a certain period of time. After cooling to r.t., the organic
phase was extracted with Et2O (3 × 2 mL) and passed through a
short silica gel column before being subjected to GC [Varian CP-
3380 equipped with a Chrompack Chirasil-Dex CB column (25
m × 0.25 mm)] or HPLC (GILSON UV/VIS-151 equipped with a
chiral OB-H column) analysis.
(6) Recent examples: (a) Vastila, P.; Wettergren, J.; Adolfsson,
H. Chem. Commun. 2005, 4039. (b) Yim, A. S. Y.; Wills,
M. Tetrahedron 2005, 61, 7994. (c) Hayes, A. M.; Morris,
D. J.; Clarkson, G. J.; Wills, M. J. Am. Chem. Soc. 2005,
127, 7318. (d) Guo, R.; Elpelt, C.; Chen, X.; Song, D.;
Morris, R. H. Chem. Commun. 2005, 3050. (e) Letondor,
C.; Humbert, N.; Ward, T. R. Proc. Natl. Acad. Sci. U.S.A.
2005, 102, 4683. (f) Sortais, J. B.; Ritleng, V.; Voelklin, A.;
Houluigue, A.; Smail, H.; Barloy, L.; Sirlin, C.; Verzijl, G.
K. M.; Boogers, J. A. F.; de Vries, A. H. M.; de Vries, J. G.;
Pfeffer, M. Org. Lett. 2005, 7, 1247. (g) Baratta, W.;
Herdtweck, E.; Siega, K.; Toniutti, M.; Rigo, P.
The ATH of other ketones with M-CsDPEN was carried out using
the same standard procedure as for acetophenone and the products
were routinely analyzed by comparing their GC/HPLC and NMR
(1H and 13C) data with the literature, and by MS and elemental ana-
lysis when necessary. The stereochemistry of products was assigned
by comparing the GC/HPLC retention time with literature data.
Organometallics 2005, 24, 1660. (h) Lennon, I. C.;
Ramsden, J. A. Org. Process Res. Dev. 2005, 9, 110.
(i) Tan, D.; Chan, K. Tetrahedron Lett. 2005, 46, 503.
(j) Chen, Y.; Wu, T.; Jiang, L.; Deng, J.; Liu, H.; Zhu, J.;
Jiang, Y. J. Org. Chem. 2005, 70, 1006. (k) Aboulaala, K.;
Goux-Henry, C.; Sinou, D.; Safi, M.; Soufiaoui, M. J. Mol.
Catal. A: Chem. 2005, 237, 259. (l) Liu, P.; Gu, P.; Deng, J.;
Tu, Y.; Ma, Y. Eur. J. Org. Chem. 2005, 3221. (m) Li, Y.;
Li, Z.; Li, F.; Wang, Q.; Tao, F. Org. Biomol. Chem. 2005,
3, 2513.
Acknowledgment
We gratefully acknowledge the Royal Society/FCO Chevening In-
ternational Fellowship (X. Li) and the DTI MMI Project for finan-
cial support (X. Wu).
(7) Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori,
R. J. Am. Chem. Soc. 1995, 117, 7562.
References
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Synlett 2006, No. 8, 1155–1160 © Thieme Stuttgart · New York