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Improved Methodology for the Preparation of Chiral Amines

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Reductive amination is a step powerful methodology <strong>for</strong> <strong>the</strong> syn<strong>the</strong>sis <strong>of</strong> α-chiral amines. The<br />

correct choice <strong>of</strong> Lewis acid is critical <strong>for</strong> efficient suppression <strong>of</strong> alcohols. The<br />

diastereoselectivity obtained with or without <strong>the</strong> use <strong>of</strong> Lewis acids was <strong>the</strong> same. No<br />

precedent <strong>of</strong> increasing diastereoselectivity in reductive amination with <strong>the</strong> use <strong>of</strong> achiral<br />

Lewis acid was ever reported. The use <strong>of</strong> Yb(OAc) 3 in reductive amination resulted in a<br />

significant increase in diastereoselectivities <strong>for</strong> different 2-alaknones. Diastereoselectivity <strong>of</strong><br />

2-octanone increased 15% compared to <strong>the</strong> highest reported result. Aromatic and cyclic<br />

ketones were not successfully reductively aminated using Yb(OAc) 3 . Ti(O i Pr) 4 proved to be<br />

<strong>the</strong> best Lewis acid in reductive amination <strong>of</strong> <strong>the</strong>se substrates.<br />

5.3. References:<br />

[1] a) H. Lebel, K. Huard, Org. Lett. 2007, 9, 639; b) M. Kim, J. V. Mulcahy, C. G. Espino, J.<br />

Du Bois, Org. Lett. 2005, 7, 4685; c) C. G. Espino, K. W, Fiori, M. Kim, J. Du Boisn, J. Am.<br />

Chem. Soc. 2004, 126, 15378.<br />

[2] a) J. Blacker, Innovations in Pharmaceutical Technology 2001, 1, 77; b) H. -U. Blaser, F.<br />

Spindler, A. Studer, App. Catal. Gen. 2001, 221, 119; c) H. -U. Blaser, M. Eissen, P. F.<br />

Fauquex. K. Hungerbuhler, E. Schmidt, G. Sedelmeier, M. Studer, Asymmetric Catalysis on<br />

Industrial Scale: Challenges, Approaches, and Solutions; H.-U. Blaser, E. Schmidt Eds.;<br />

Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2004.<br />

[3] T. C. Nugent, <strong>Chiral</strong> Amine Syn<strong>the</strong>sis - Strategies, Examples, and Limitations. In Process<br />

Chemistry in <strong>the</strong> Pharmaceutical Industry, Second Edition: Challenges in an Ever-Changing<br />

Climate, T. F. Braish, K. Gadamasetti Eds.; CRC Press-Taylor and Francis Group: New<br />

York, 2008.<br />

[4] a) L. Storace, L. Anzalone, P. N. Confalone, W. P. Davis, J. M. Fortunak, M.<br />

Giangiordano, J. J. Haley, Jr., K. Kamholz, H.-Y. Li, P. Ma, W. A. Nugent, R. L. Parsons, Jr.,<br />

P. J. Sheeran, C. E. Silverman, R. E. Waltermire, C. C. Wood, Org. Process Res. Dev. 2002,<br />

6, 54; b) E. Juaristi, J. L. León-Romo, A. Reyes, J. Escalante, Tetrahedron: Asymmetry 1999,<br />

10, 2441; c) G. Lauktien, F. -J. Volk, A. W. Frahm, Tetrahedron: Asymmetry 1997, 8, 3457;<br />

d) B. Speckenback, P. Bisel, A. W. Frahm, Syn<strong>the</strong>sis 1997, 1325.<br />

[5] a) T. C. Nugent, A. K. Ghosh, V. N. Wakchaure, R. R. Mohanty, Adv. Synth. Catal. 2006,<br />

348, 1289; b) T. C. Nugent, A. K. Ghosh, V. N. Wakchaure, R. R. Mohanty,<br />

116

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