LETTER
Switching Enantioface Selection in the Asymmetric Nitro-Mannich Reaction
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for high conversion, which suggests that the nitronate is
generated in the outer sphere and the PyBidine–CoCl2
complex act as a Lewis acid to activate the N-Ts imines.
The nitronate attacks the N-Ts imines coordinated to the
cobalt center from the second quadrant. To explain the S-
enriched formation of 2, the N-Ts imine must coordinate
to the cobalt center as shown in Scheme 3 (b).
References
(1) Reviews of enantiofacial switching: (a) Sibi, M. P.; Liu, M.
Curr. Org. Chem. 2001, 5, 719. (b) Zanoni, G.; Castronovo,
F.; Franzini, M.; Vidari, G.; Giannini, E. Chem. Soc. Rev.
2003, 32, 115. (c) Tanaka, T.; Hayashi, M. Synthesis 2008,
3361. (d) Bartók, M. Chem. Rev. 2010, 110, 1663.
(e) Escorihuela, J.; Burguete, M. I.; Luis, S. V. Chem. Soc.
Rev. 2013, 42, 5595.
For both reactions, hydrogen bonding using N–H on the
PyBidine ligand would contribute significantly because
pybox and pybim were not effective for the metal-cata-
lyzed nitro-Mannich reaction.
(2) Recent examples of enantiofacial switching: (a) Sohtome,
Y.; Yamaguchi, T.; Tanaka, S.; Nagawasa, K. Org. Biomol.
Chem. 2013, 11, 2780. (b) Garzan, A.; Jaganathan, A.;
Marzijarani, N. S.; Yousefi, R.; Whitehead, D. C.; Jackson,
J. E.; Borhan, B. Chem. Eur. J. 2013, 19, 9015. (c) Fukata,
Y.; Asano, K.; Matsubara, S. J. Am. Chem. Soc. 2013, 135,
12160.
In summary, switching the enantioface selection of imines
in the metal-catalyzed nitro-Mannich reaction was ac-
complished with the same enantiomer of the diamine-de-
rived bis(imidazolidine)pyridine (PyBidine) ligand. The
phenomenon of enantiofacial switching can be explained
by understanding the basicity and acidity of the metal salt
in the catalyst complex.
(3) Henry, L. Bull. Acad. R. Belg. 1896, 32, 33.
(4) Noble, A.; Anderson, J. C. Chem. Rev. 2013, 113, 2887.
(5) Marqués-López, E.; Merino, P.; Tejero, T.; Herrera, R. P.
Eur. J. Org. Chem. 2009, 2401; see also ref. 3.
(6) Yamada, K.-i.; Harwood, S. J.; Gröger, H.; Shibasaki, M.
Angew. Chem. Int. Ed. 1999, 38, 3504.
(7) Catalytic asymmetric nitro-Mannich reaction using Cu
complex: (a) Knudsen, K. R.; Risgaard, T.; Nishiwaki, N.;
Gothelf, K. V.; Jørgensen, K. A. J. Am. Chem. Soc. 2001,
123, 5843. (b) Nishiwaki, N.; Knudsen, K. R.; Gothelf, K.
V.; Jørgensen, K. A. Angew. Chem. Int. Ed. 2001, 40, 2992.
(c) Lee, A.; Kim, W.; Lee, J.; Hyeon, T.; Kim, B. M.
Tetrahedron: Asymmetry 2004, 15, 2595. (d) Knudsen, K.
R.; Rahbek, K.; Jørgensen, K. A. Org. Biomol. Chem. 2005,
3, 1362. (e) Anderson, J. C.; Howell, G. P.; Lawrence, R.
M.; Wilson, C. S. J. Org. Chem. 2005, 70, 5665. (f) Zhou,
H.; Peng, D.; Qin, B.; Hou, Z.; Liu, X.; Feng, X. J. Org.
Chem. 2007, 72, 10302. (g) Tan, C.; Liu, X.; Wang, L.;
Wang, J.; Feng, X. Org. Lett. 2008, 10, 5305. (h) Zhang, G.;
Yashima, E.; Woggon, W.-D. Adv. Synth. Catal. 2009, 351,
1255. (i) Blay, G.; Escamilla, A.; Hernández-Olmos, V.;
Pedro, J. R.; Sanz-Marco, A. Chirality 2012, 24, 441.
(j) Choudhary, M. K.; Das, A.; Kureshy, R. I.; Kumar, M.;
Khan, N. H.; Abdi, S. H. R.; Bajaj, H. C. Catal. Sci. Technol.
2014, 4, 548.
(8) Catalytic asymmetric nitro-Mannich reaction using Zn
complex: (a) Gao, F.; Zhu, J.; Tang, Y.; Deng, M.; Qian, C.
Chirality 2006, 18, 741. (b) Palomo, C.; Oiarbide, M.;
Halder, R.; Laso, A.; López, R. Angew. Chem. Int. Ed. 2006,
45, 117. (c) Trost, B. M.; Lupton, D. W. Org. Lett. 2007, 9,
2023.
(9) Catalytic asymmetric nitro-Mannich reaction using Ni
complex: Chen, Z.; Morimoto, H.; Matsunaga, S.; Shibasaki,
M. J. Am. Chem. Soc. 2008, 130, 2170.
General Procedure for PyBidine–CoCl2-Catalyzed Nitro-
Mannich Reaction of N-Ts-Imine
PyBidine (0.022 mmol) and CoCl2 (0.02 mmol) were added to a
two-necked round-bottomed flask under Ar. THF (0.60 mL) was
added to the flask, and the mixture was stirred for 6 h. To the result-
ing solution, MeNO2 (2.00 mmol), DIPEA (0.02 mmol), and azeo-
troped N-Ts imine (0.20 mmol) in THF (0.40 mL) were added at r.t.
After stirring, the reaction mixture was quenched using sat.
NaHCO3, extracted with CH2Cl2 and dried with Na2SO4. After re-
moval of the solvent under reduced pressure, the resulting crude
mixture was purified by silica gel column chromatography to give
the product.
General Procedure for PyBidine–Ni(OAc)2-Catalyzed Nitro-
Mannich Reaction of N-Boc-Imine
PyBidine (0.022 mmol) and Ni(OAc)2·4H2O (0.02 mmol) were
added to a two-necked round-bottomed flask under Ar. CH2Cl2
(1.00 mL) was added to the flask, and the mixture was stirred for 3
h. After removal of the solvent under reduced pressure, dioxane
(1.00 mL) was added as the reaction solvent. To the resulting solu-
tion, MeNO2 (2.00 mmol), DIPEA (0.02 mmol), and N-Boc imine
(0.20 mmol) were added at r.t. After stirring, the reaction mixture
was quenched using sat. NaHCO3, extracted with CH2Cl2, and dried
with Na2SO4. After removal of the solvent under reduced pressure,
the resulting crude mixture was purified by silica gel column chro-
matography to give the product.
(10) Catalytic asymmetric nitro-Mannich reaction using
heterobimetallic system: (a) Yamada, K.-I.; Moll, G.;
Shibasaki, M. Synlett 2001, 980. (b) Handa, S.;
Acknowledgment
This work was supported by a Grant-in-Aid for Challenging Explo-
ratory Research and for Scientific Research on Innovative Areas
‘Advanced Molecular Transformations by Organocatalysts’ from
The Ministry of Education, Culture, Sports, Science and Technolo-
gy, Japan, and by the Workshop on Chirality in Chiba University
(WCCU).
Gnanadesikan, V.; Matsunga, S.; Shibasaki, M. J. Am.
Chem. Soc. 2007, 129, 4900. (c) Nitabaru, T.; Kumagai, N.;
Shibasaki, M. Molecules 2010, 15, 1280. (d) Handa, S.;
Gnanadesikan, V.; Matsunga, S.; Shibasaki, M. J. Am.
Chem. Soc. 2010, 132, 4925.
(11) Representative examples of catalytic asymmetric nitro-
Mannich reaction using organocatalyst: (a) Okino, T.;
Nakamura, S.; Furukawa, T.; Takemoto, Y. Org. Lett. 2004,
6, 625. (b) Nugent, B. M.; Yoder, R. A.; Johnston, J. N.
J. Am. Chem. Soc. 2004, 126, 3418. (c) Yoon, T. P.;
Jacobsen, E. N. Angew. Chem. Int. Ed. 2005, 44, 466.
(d) Fini, F.; Sgarzani, V.; Pettersen, D.; Herrera, R. P.;
Bernardi, L.; Ricci, A. Angew. Chem. Int. Ed. 2005, 44,
7975. (e) Palomo, C.; Oiarbide, M.; Laso, A.; López, R.
J. Am. Chem. Soc. 2005, 127, 17622. (f) Singh, A.; Yoder, R.
Supporting Information for this article is available online
at
10.1055/s-00000083.SunpfgIpi
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© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1776–1780