˚
evaporated, silica gel (1 g) was added to the residue, and the
rest of the solvent was evaporated to dryness. The latter silica
gel-adsorbed mixture was loaded onto a column of dry silica gel
(15 g) and eluted with a mixture of petroleum ether and ethyl
acetate (24 : 1 or 9 : 1) to afford pure amine 2a. For yields and
enantioselectivity, see Table 1.
Chem. Soc., 2006, 128, 12886; (d) J. B. Aberg, J. S. M. Samec and J.-E.
Ba¨ckvall, Chem. Commun., 2006, 2771. For an overview, see: (e) J. S. M.
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2006, 35, 237. For the kinetic resolution using transfer hydrogenation
combined with an enzymatic reaction, see: (f) J. Paetzold and J.-E.
Ba¨ckvall, J. Am. Chem. Soc., 2005, 127, 17620; (g) J. S. M. Samec,
´
˚
A. H. Ell, J. B. Aberg, T. Privalov, L. Eriksson and J.-E. Ba¨ckvall,
J. Am. Chem. Soc., 2006, 128, 14293; (h) T. Privalov, J. S. M. Samec
and J.-E. Ba¨ckvall, Organometallics, 2007, 26, 2840; (i) C. E. Hoben, L.
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(b) X. Verdaguer, U. E. W. Lange and S. L. Buchwald, Angew. Chem.,
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J. Am. Chem. Soc., 2001, 123, 12917; (g) B. H. Lipshutz and H. Shimizu,
Angew. Chem., Int. Ed., 2004, 43, 2228.
5 For enzymatic approaches, including reduction, see, e.g.: (a) M.
Alexeeva, A. Enright, M. J. Dawson, M. Mahmoidian and N. J. Turner,
Angew. Chem., Int. Ed., 2002, 41, 3177; (b) R. Carr, M. Alexeeva,
M. J. Dawson, V. Gotor-Ferna´ndez, C. E. Huphrey and N. J. Turner,
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General Procedure for the Asymmetric Reduction of 1a–f
Catalysed by 11c
Trichlorosilane (50 mL) was added to a solution of imine 1
(0.22 mmol) and catalyst 11c (0.022 mmol) in toluene (1.5 mL) at
0 ◦C and the mixture was stirred at room temperature overnight.
The mixture was then poured into rapidly stirred methanol
(50 mL), the resulting cloudy mixture was centrifuged, and the
clear supernatant was evaporated. The residue was treated with
chloroform (30 mL) and the resulting solution was washed with
aqueous saturated NaHCO3 (10 mL). The aqueous phase was
extracted with chloroform (30 mL), and the combined organic
solutions were dried over MgSO4 and evaporated. The crude
product was purified by chromatography on a column of silica gel
(10 g) using a mixture of petroleum ether and ethyl acetate (15 : 1)
to give the pure amine 2 (89%). For yields and enantioselectivity,
see Table 1. The amines thus obtained were identical to the
authentic samples prepared earlier by us.7
6 (a) S. Singh and U. K. Batra, Indian J. Chem, Sect. B, 1989, 28, 1;
(b) M. Rueping, E. Sugiono, C. Azap, T. Theissmann and M. Bolte,
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Theissmann, Angew. Chem., Int. Ed., 2006, 45, 3683; (d) M. Rueping,
A. P. Antonchik and T. Theissmann, Angew. Chem., Int. Ed., 2006, 45,
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Lett., 2004, 6, 2253; (b) A. V. Malkov, S. Stoncˇius, K. N. MacDougall,
A. Mariani, G. D. McGeoch and P. Kocˇovsky´, Tetrahedron, 2006, 62,
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P. Ko cˇovsky´, J. Org. Chem., 2008, 73, 3985; (f) A. V. Malkov, S. Stoncˇius,
K. Vrankova´, M. Arndt and P. Kocˇovsky´, Chem.–Eur. J., 2008, 14, 8082;
Acknowledgements
This work was supported by the EPSRC (grant Nos.
GR/S87294/01 and EP/E018211/1), the Royal Society of
Edinburgh, and AstraZeneca. We thank the University of Glasgow
for a graduate fellowship to M.F. A.S thanks TUBITAK (105S353)
and TUBA-GEBIP for financial support.
Notes and references
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