LETTER
Thiourea-Catalyzed Transfer Hydrogenation of Aldimines
1457
(8) Kotke, M.; Schreiner, P. R. Tetrahedron 2006, 62, 434.
(9) Kleiner, C. M.; Schreiner, P. R. Chem. Commun. 2006,
4315.
(10) For reviews, see: (a) Schreiner, P. R. Chem. Soc. Rev. 2003,
32, 289. (b) Pihko, P. M. Angew. Chem. Int. Ed. 2004, 43,
2062. (c) Takemoto, Y. Org. Biomol. Chem. 2005, 3, 4299.
(d) Taylor, M. S.; Jacobsen, E. N. Angew. Chem. Int. Ed.
2006, 45, 1520.
References and Notes
(1) For a review of metal-catalyzed asymmetric reductive
amination, see: (a) Tararov, V. I.; Börner, A. Synlett 2005,
203. (b) For reviews of asymmetric reductions of imines,
see: Ohkuma, T.; Noyori, R. In Comprehensive Asymmetric
Catalysis, Suppl. 1; Jacobsen, E. N.; Pfaltz, A.; Yamamoto,
H., Eds.; Springer: New York, 2004.
(2) (a) Tang, W. J.; Zhang, X. M. Chem. Rev. 2003, 103, 3029.
(b) Blaser, H. U.; Malan, C.; Pugin, B.; Spindler, F.; Steiner,
H.; Studer, M. Adv. Synth. Catal. 2003, 345, 103.
(c) Noyori, R. Angew. Chem. Int. Ed. 2002, 41, 2008.
(d) Knowles, W. S. Angew. Chem. Int. Ed. 2002, 41, 1999.
(3) (a) Blaser, H. U.; Pugin, B.; Spindler, F. J. Mol. Catal. A:
Chem. 2005, 231, 1. (b) Blaser, H. U.; Buser, H. P.; Jalett,
H. P.; Pugin, B.; Spindler, F. Synlett 1999, 867.
(4) Palmer, M. J.; Wills, M. Tetrahedron: Asymmetry 1999, 10,
2045.
(5) (a) Wang, Z. Y.; Ye, X. X.; Wei, S. Y.; Wu, P. C.; Zhang, A.
J.; Sun, J. Org. Lett. 2006, 8, 999. (b) Onomura, O.;
Kouchi, Y.; Iwasaki, F.; Matsumura, Y. Tetrahedron Lett.
2006, 47, 3751. (c) Malkov, A. V.; Stoncius, S.;
MacDougall, K. N.; Mariani, A.; McGeoch, G. D.;
Kocovsky, P. Tetrahedron 2006, 62, 264. (d) Iwasaki, F.;
Onomura, O.; Mishima, K.; Kanematsu, T.; Maki, T.;
Matsumura, Y. Tetrahedron Lett. 2001, 42, 2525.
(6) (a) Storer, R. I.; Carrera, D. E.; Ni, Y.; MacMillan, D. W. C.
J. Am. Chem. Soc. 2006, 128, 84. (b) Rueping, M.; Sugiono,
E.; Azap, C.; Theissmann, T.; Bolte, M. Org. Lett. 2005, 7,
3781. (c) Hoffmann, S.; Seayad, A. M.; List, B. Angew.
Chem. Int. Ed. 2005, 44, 7424. (d) Rueping, M.; Azap, C.;
Sugiono, E.; Theissmann, T. Synlett 2005, 2367.
(11) Menche, D.; Hassfeld, J.; Li, J.; Menche, G.; Ritter, A.;
Rudolph, S. Org. Lett. 2006, 8, 741.
(12) Menche, D.; Arikan, F. Synlett 2006, 841.
(13) Since it is difficult to avoid the formation of carboxylic acids
generated from aldehydes during the reaction, 10 mol% of
NaHCO3 was added.
(14) General Procedure for the Thiourea-Catalyzed Transfer
Hydrogenation of Aldimines
In a typical experiment the aldimine 1 (1.0 mmol), thiourea
3 (1 mol%) and Hantzsch dihydropyridine 2 (1.1 equiv) were
suspended in anhyd CH2Cl2 (5 mL) in a flask. The resulting
mixture was allowed to stir at r.t. for 15 h. The solvent was
removed under reduced pressure and the residue was
purified by column chromatography on silica gel using
mixtures of PE and Et2O to afford the pure corresponding
amine 4. All compounds were fully characterized on the
basis of IR, 1H NMR, 13C NMR and HRMS.
Compound 4a: light yellow oil. IR (film): 3418, 1699, 1602,
1505, 1179, 1064 cm–1. 1H NMR (400 MHz, CDCl3):
d = 4.20 (s, 2 H), 6.50–6.52 (d, 2 H, J = 8.71 Hz), 6.59–6.63
(t, 1 H, J = 7.41 Hz), 7.04–7.09 (t, 2 H, J = 7.40 Hz), 7.14–
7.27 (m, 5 H). 13C NMR (100 MHz, CDCl3): d = 48.2, 112.8,
117.5, 127.1, 127.4, 128.5, 129.2, 139.4, 148.1. HRMS: m/z
calcd for C13H13N: 183.10425; found: 183.10347.
(7) (a) Wittkopp, A.; Schreiner, P. R. In The Chemistry of
Dienes and Polymers; Rappoport, Z., Ed.; Wiley:
Chichester, 2000. (b) Schreiner, P. R.; Wittkopp, A. Org.
Lett. 2002, 4, 217. (c) Wittkopp, A.; Schreiner, P. R. Chem.
Eur. J. 2003, 9, 407.
Synlett 2007, No. 9, 1455–1457 © Thieme Stuttgart · New York