Organic Letters
Letter
applied it in the asymmetrical hydrogenation of ketone 1a.
However, the coordination of L7 and manganese was
incomplete, giving a trace amount of the Mn−L7 species
and another unknown complex.27 We believe that the great
steric hindrance disrupts the coordination process, while the
imine group in L4 has a stronger capability of coordinating
with manganese than the amino group. Thus, the reaction with
L7 turned out to be unsuccessful, indicating that the imine
group is indispensable for achievement of high activity and
enantioselectivity. Furthermore, the imine group may play a
key role in the cleavage of H2 via addition of a molecule of H2
to the CN double bond. Then, the newly formed N−H
proton and the Mn−H hydride of the Mn−L4 complex add to
the carbonyl group of diaryl ketone via a six-membered ring
transition state, thus providing high activity and enantiose-
lectivity.28 The detailed mechanistic investigation is currently
underway.
In conclusion, we have described a new type of imidazole-
based chiral PNN tridentate ligand enabling the manganese
catalyzed asymmetrical hydrogenation of unsymmetrical
benzophenones with outstanding activity (up to 13 000
TON) and excellent enantioselectivity (up to >99% ee). The
utility of this manganese catalytic system has been demon-
strated by gram-scale experiments and formal synthesis of (S)-
neobenodine. Preliminary studies on reaction mechanism
revealed that the imine group of the catalyst might play a
key role in the cleavage of H2 and the activation of substrate.
Further applications of this methodology in asymmetrical
reductions of other unsaturated compounds are underway in
our lab.
REFERENCES
■
(1) (a) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40.
(b) Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029. (c) Mortreux,
A.; Karim, A. The handbook of homogeneous hydrogenation; de Vries, J.
G., Elsevier, C. J., Eds.; Wiley-VCH, Weinheim, 2007, 1165;. (d) Xie,
J.-H.; Zhou, Q.-L. Acc. Chem. Res. 2008, 41, 581. (e) Yang, G.-Q.;
Zhang, W.-B. Chem. Soc. Rev. 2018, 47, 1783. (f) Zhang, Z.-F.; Butt,
N. A.; Zhang, W.-B. Chem. Rev. 2016, 116, 14769. (g) Wang, Z.-H.;
Zhang, Z.-F.; Liu, Y.-G.; Zhang, W.-B. Youji Huaxue 2016, 36, 447.
(h) Yuan, Q.-J.; Zhang, W.-B. Youji Huaxue 2016, 36, 274. (i) Wang,
Y.-J.; Zhang, Z.-F.; Zhang, W.-B. Youji Huaxue 2015, 35, 528.
(2) Zhang, Z.; Butt, N. A.; Zhou, M.; Liu, D.; Zhang, W. Chin. J.
Chem. 2018, 36, 443.
(3) (a) Shimizu, H.; Igarashi, D.; Kuriyama, W.; Yusa, Y.; Sayo, N.;
Saito, T. Org. Lett. 2007, 9, 1655. (b) Junge, K.; Wendt, B.; Addis, D.;
Zhou, S.; Fleischer, S.; Das, S.; Beller, M. Chem. - Eur. J. 2011, 17,
101. (c) Krabbe, S. W.; Hatcher, M. A.; Bowman, R. K.; Mitchell, M.
B.; McClure, M. S.; Johnson, J. S. Org. Lett. 2013, 15, 4560.
(d) Zatolochnaya, O. V.; Rodríguez, S.; Zhang, Y.; Lao, K. S.;
Tcyrulnikov, S.; Li, G.; Wang, X.-J.; Qu, B.; Biswas, S.; Mangunuru, H.
P. R.; Rivalti, D.; Sieber, J. D.; Desrosiers, J.-N.; Leung, J. C.;
Grinberg, N.; Lee, H.; Haddad, N.; Yee, N. K.; Song, J. J.; Kozlowski,
M. C.; Senanayakea, C. H. Chem. Sci. 2018, 9, 4505.
(4) (a) Hamada, Y.; Koseki, Y.; Fujii, T.; Maeda, T.; Hibino, T.;
Makino, K. Chem. Commun. 2008, 6206. (b) Hibino, T.; Makino, K.;
Sugiyama, T.; Hamada, Y. ChemCatChem 2009, 1, 237.
̈
(5) (a) Berkessel, A.; Reichau, S.; von der Hoh, A.; Leconte, N.;
̈
Neudorfl, J.-M. Organometallics 2011, 30, 3880. (b) Gajewski, P.;
Renom-Carrasco, M.; Facchini, S. V.; Pignataro, L.; Lefort, L.; de
Vries, J. G.; Ferraccioli, R.; Forni, A.; Piarulli, U.; Gennari, C. Eur. J.
Org. Chem. 2015, 2015, 1887. (c) Hodgkinson, R.; Del Grosso, A.;
Clarkson, G. J.; Wills, M. Dalton Trans. 2016, 45, 3992.
(6) (a) Zhang, D.; Zhu, E.-Z.; Lin, Z.-W.; Li, Y.-Y.; Gao, J.-X. Asian
J. Org. Chem. 2016, 5, 1323. (b) Friedfeld, M. R.; Shevlin, M.; Hoyt, J.
M.; Krska, S. W.; Tudge, M. T.; Chirik, P. J. Science 2013, 342, 1076.
(c) Friedfeld, M. R.; Margulieux, G. W.; Schaefer, B.; Chirik, P. J. J.
Am. Chem. Soc. 2014, 136, 13178. (d) Chirik, P. J. Acc. Chem. Res.
2015, 48, 1687. (e) Friedfeld, M. R.; Zhong, H.; Ruck, R. T.; Shevlin,
M.; Chirik, P. J. Science 2018, 360, 888. (f) Monfette, S.; Turner, Z.
R.; Semproni, S. P.; Chirik, P. J. J. Am. Chem. Soc. 2012, 134, 4561.
(g) Friedfeld, M. R.; Shevlin, M.; Margulieux, G. W.; Campeau, L. C.;
Chirik, P. J. J. Am. Chem. Soc. 2016, 138, 3314. (h) Chen, J.; Chen, C.;
Ji, C.; Lu, Z. Org. Lett. 2016, 18, 1594.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
■
S
Experimental details, spectra data, copies of H and 13C
NMR spectra, and HPLC charts (PDF)
1
Accession Codes
(7) (a) Kallmeier, F.; Kempe, R. Angew. Chem., Int. Ed. 2018, 57, 46.
(b) Filonenko, G. A.; van Putten, R.; Hensen, E. J. M.; Pidko, E. A.
Chem. Soc. Rev. 2018, 47, 1459. (c) Garbe, M.; Junge, K.; Beller, M.
Eur. J. Org. Chem. 2017, 2017, 4344. (d) Maji, B.; Barman, M. K.
Synthesis 2017, 49, 3377.
CCDC 1902605 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(8) Widegren, M. B.; Harkness, G. J.; Slawin, A. M. Z.; Cordes, D.
B.; Clarke, M. L. Angew. Chem., Int. Ed. 2017, 56, 5825.
(9) Garbe, M.; Junge, K.; Walker, S.; Wei, Z.; Jiao, H.; Spannenberg,
A.; Bachmann, S.; Scalone, M.; Beller, M. Angew. Chem., Int. Ed. 2017,
56, 11237.
AUTHOR INFORMATION
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Corresponding Author
ORCID
(10) For examples of asymmetric transfer hydrogenation: (a) Zir-
̈
akzadeh, A.; de Aguiar, S. R. M. M.; Stoger, B.; Widhalm, M.;
Kirchner, K. ChemCatChem 2017, 9, 1744. (b) Wang, D.; Bruneau-
Voisine, A.; Sortais, J.-B. Catal. Commun. 2018, 105, 31. (c) Dem-
mans, K. Z.; Olson, M. E.; Morris, R. H. Organometallics 2018, 37,
4608.
Notes
(11) For an example of asymmetric hydrosilylation: Ma, X.; Zuo, Z.;
Liu, G.; Huang, Z. ACS Omega 2017, 2, 4688.
(12) For an example of asymmetric hydroboration: Vasilenko, V.;
Blasius, C. K.; Wadepohl, H.; Gade, L. H. Angew. Chem., Int. Ed. 2017,
56, 8393.
(13) (a) Schmidt, F.; Stemmler, R. T.; Rudolph, J.; Bolm, C. Chem.
Soc. Rev. 2006, 35, 454. (b) Devalia, J. L.; De Vos, C.; Hanotte, F.;
Baltes, E. Allergy 2001, 56, 50. (c) Corey, E. J.; Helal, C. J.
Tetrahedron Lett. 1996, 37, 4837.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We thank the National Natural Science Foundation of China
(Nos. 21676253 and 21706234) and the Natural Science
Foundation of Zhejiang Province of China (No.
LY19B060011) for financial support.
D
Org. Lett. XXXX, XXX, XXX−XXX