Ruthenium-catalyzed hydrogenation of carbocyclic aromatic amines: Access to chiral exocyclic amines

Article abstract of DOI:10.1021/acs.orglett.7b04060

The first highly enantioselective hydrogenation of carbocyclic aromatic amines has been successfully realized using in situ-generated chiral ruthenium complex as catalyst, affording facile access to chiral exocyclic amines with up to 98% ee.

Full text of DOI:10.1021/acs.orglett.7b04060

Letter
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Ruthenium-Catalyzed Hydrogenation of Carbocyclic Aromatic
Amines: Access to Chiral Exocyclic Amines
†
,§
†
†
,†,‡
Zhong Yan, Huan-Ping Xie, Hong-Qiang Shen, and Yong-Gui Zhou*
†State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People’s
Republic of China
§
University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
‡
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
*
S Supporting Information
ABSTRACT: The first highly enantioselective hydrogenation of carbocyclic
aromatic amines has been successfully realized using in situ-generated chiral
ruthenium complex as catalyst, affording facile access to chiral exocyclic amines
with up to 98% ee.
ecently, the homogeneous asymmetric hydrogenation of
heteroarenes with single and multiple heteroatoms, which
Scheme 1. Asymmetric Hydrogenation of Carbocyclic
Aromatic Compounds
R
provides an efficient method to structurally diverse heterocycles
with high stereoselectivity, has been intensively studied.
1
−3
Although considerable advances have been achieved in
heterogeneous and homogeneous achiral hydrogenation of
arenes in laboratory and industry, asymmetric hydrogenation
4
,5
of carbocyclic aromatics remains much less explored. Several
difficulties exist in this area, including the following: (a) the
inherent stability resulting from aromaticity; (b) lack of a
coordinating group makes stereoselectivity difficult to control;
and (c) the poor discrimination of enantiotopic face creates
another issue in diastereocontrol. Despite these difficulties,
synthetic chemists continue to make progress in this field. For
example, the selective hydrogenation of auxiliary-substituted
arenes using heterogeneous catalysts provides a convenient
strategy to the corresponding saturated compounds with high
4
e,6
diastereoselectivity.
Moreover, the hydrogenation of arenes
by using ruthenium nanoparticles modified with chiral N-donor
ligands has been tried, but no significant asymmetric induction
4
c,7
was observed.
Recently, asymmetric hydrogenation of
Since the aromatic stabilization of the second aromatic ring in
bicyclic aromatics is somewhat lower, hydrogenation of the
carbocyclic aromatics has been successfully realized using
homogeneous chiral catalysts. In 2011, Glorius’ group developed
the first homogeneous asymmetric hydrogenation of quinoxa-
lines that led to the selective hydrogenation of the carbocyclic
ring by using a chiral ruthenium NHC complex and up to 88% ee
5a,b
annulated ring is significantly facilitated.
We reasoned that
carbocyclic aromatics, such as phenanthrene and chrysene, might
be suitable substrates for asymmetric hydrogenation. In addition,
chiral amines are useful building blocks for construction of
10
8
biologically active molecules, as well as for the design of chiral
was obtained (see Scheme 1). Subsequently, as a breakthrough,
11
ligands. In view of the availability of carbocyclic aromatic
Kuwano and co-workers found that naphthalenes and quinoline
carbocycles could be successfully hydrogenated by a ruthenium-
PhTrap catalyst. In particular, 2-alkoxynaphthalene derivatives
were converted to the corresponding chiral tetralins with up to
12
amines, we envisioned to realize the synthesis of chiral amines
through asymmetric hydrogenation of carbocyclic aromatic
13
amines. Based on those successful experience of ruthenium-
8
,9
catalyzed asymmetric hydrogenation of carbocyclic aromatics
9
2% ee, despite the fact that harsh conditions were necessary (see
9
and our group’s longstanding work on asymmetric hydro-
Scheme 1). Given these impressive advances, a rejuvenation of
asymmetric hydrogenation of carbocyclic aromatics by exploring
general catalytic system and enriching the diversity of the
substrate is still challenging and highly desirable.
Received: December 30, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b04060
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
1
b,13,14
genation of N-containing heteroarenes,
herein, we
was established: Ru(COD)(methallyl) /L3/HBF as the cata-
2
4
describe the first highly enantioselective and diastereoselective
hydrogenation of carbocyclic aromatic amines using in situ-
generated chiral ruthenium complexes as catalysts (see Scheme
lyst, DCE as the solvent, hydrogen gas (1000 psi) and a reaction
temperature of 30 °C.
After establishing the optimal condition, we investigated the
substrate scope, and the results are summarized in Scheme 2.
1).
With the hypothesis in mind, N-(phenanthren-9-yl)acet-
amide (1a) was chosen as model substrate. We found that the
a
Scheme 2. Substrate Scope: Carbocyclic Aromatic Amines
treatment of 1.0 equiv of Ru(COD)(methallyl) and 1.1 equiv of
2
chiral bisphosphine ligands in various organic solvents with 2.0
equiv of HBF at ambient temperature for ∼30 min gave a
4
ruthenium catalyst that could be used directly for the
hydrogenation of 1a. The process was derived from procedures
1
5
̂
that were developed by Heiser’s group and Genet’s group.
Fortunately, when we tested the reaction with DuanPhos L1 as a
ligand in MeOH under hydrogen gas (600 psi) at 60 °C, 2a was
obtained with 92% ee and 42% yield (Table 1, entry 1). Notably,
a
Table 1. Evaluation of Reaction Parameters
b
c
entry
solvent
ligand
temp, t (°C)
yield (%)
ee (%)
1
2
3
4
5
6
7
8
9
MeOH
EtOH
L1
L1
L1
L1
L1
L1
L1
L1
L2
L3
L4
L5
L6
L7
L8
L3
L3
L3
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
30
30
42
51
48
44
44
47
39
92 (S)
91 (S)
88 (S)
79 (S)
91 (S)
88 (S)
73 (S)
i
PrOH
DCM
DCE
EtOAc
THF
toluene
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
a
Conditions: 1 (0.20 mmol), Ru(COD)(methallyl)
(10 mol %), H (1000 psi), DCE (2.0 mL), 30 °C,
4 h. Isolated yields. DCE (3.0 mL).
(5 mol %), L3
2
(5.5 mol %), HBF
2
4
2
b
49
88
88
84
95
55
68
95
95
95
82 (R)
86 (S)
56 (R)
06 (R)
41 (R)
52 (S)
83 (S)
84 (S)
88 (S)
93 (S)
10
11
12
13
14
15
16
17
18
Different substituents on the amide group were tested and linear
alkyl and aryl groups were suitable substituents, affording
moderate to excellent results, but sterically hindered tertiary
butyl was unfavorable (Scheme 2, 2a−2f). The electronic effect
of annulated ring displayed little concern with activities (Scheme
2, 2g−2i). Pleasingly, when the methoxy group was introduced at
the 7-position of the phenanthrene ring, 97% ee was obtained
(Scheme 2, 2h). Moreover, the effect of methyl position of
annulated ring was also screened (Scheme 2, 2j−2n). When the
methyl group was introduced at the 1-position of phenanthrene
ring, a slightly low ee value (85%) was obtained (Scheme 2, 2j).
The asymmetric hydrogenation of N-(chrysen-5-yl)acetamide
d
d
d
,
e
a
Conditions: 1a (0.10 mmol), Ru(COD)(methallyl)2 (2 mol %),
ligand (2.2 mol %), HBF (4.0 mol %), H (600 psi), solvent (2.0 mL),
0 °C, 24 h. Determined by H NMR, using 1,3,5-trimethoxybenzene
as an internal standard. Enantiomeric excess (ee), determined via
HPLC. Ru(COD)(methallyl) (5 mol %), L3 (5.5 mol %), HBF (10
4
2
b
1
6
c
d
1
o was also evaluated; the reaction also transformed completely
2
4
e
mol %). H (1000 psi). DCM = CH Cl , DCE = ClCH CH Cl.
and an excellent ee value (91%) was obtained (Scheme 2, 2o).
Next, asymmetric hydrogenation of more-challenging dis-
ubstituted carbocyclic aromatic amines was explored. Consider-
ing the difficulty in activity and stereocontrol, hydrogenation
conditions were further optimized. A survey of solvents indicated
2
2
2
2
2
the catalytic system was compatible with a series of solvents, but
deacetylation product was observed in alcoholic solvents (Table
, entries 1−7). In terms of enantioselectivity and yield,
dichloroethane (DCE) was chosen as the optimal solvent
Table 1, entry 5). Next, some commercially available chiral
bisphosphine ligands were evaluated. Electron-rich ligands were
favored and the best result was achieved with DuPhos L3 (88%
yield, 86% ee; see Table 1, entry 10). In order to enhance the
activity of the reaction, the catalyst loading was increased to 5
mol % with significantly improved activity and slightly reduced
enantioselectivity (Table 1, entry 16). To our delight, when
reaction temperature was decreased to 30 °C and hydrogen
pressure was increased to 1000 psi, 95% yield and 93% ee were
obtained (Table 1, entry 18). Therefore, the optimal condition
i
1
that PrOH was the best choice, albeit with low activity and
moderate enantioselectivity. It is noteworthy that excellent
diastereoselectivity was achieved, regardless of the solvent used
(Table 2, entries 1−5). To further improve the reaction
efficiency, an enhanced survey of the chiral bisphosphine ligands
was conducted; electron-rich JosiPhos L6 proved to be the most
favorable ligand, in terms of excellent yield, albeit with 77% ee see
(Table 2, entries 6−8). When we reduced the temperature to 30
°C, the ee value could be increased to 83% (Table 2, entry 9).
Therefore, the optimal reaction condition was established:
(
i
Ru(COD)(methallyl) /L6/HBF as the catalyst, PrOH as the
solvent, hydrogen gas (1000 psi), and a reaction temperature of
2
4
B
DOI: 10.1021/acs.orglett.7b04060
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Table 2. Optimization of Reaction Conditions
in CD OD, the D atoms were incorporated to the 9-position and
3
1
0-position with <5%, respectively (see Scheme 4). The above
Scheme 4. Deuterium Labeling Experiments
b
c
entry
solvent
ligand
yield (%)
ee (%)
1
2
3
4
5
6
7
8
MeOH
EtOH
L3
L3
L3
L3
L3
L2
L5
L6
L6
26
61 (S,S)
69 (S,S)
72 (S,S)
57 (S,S)
55 (S,S)
90 (R,R)
35 (R,R)
77 (R,R)
83 (R,R)
40
i
PrOH
46
DCM
DCE
44
38
i
PrOH
19
iPrOH
iPrOH
iPrOH
87
>99
>99
experiments suggested that the hydrogenation pathway is direct
hydrogenation of carbon−carbon double bond of enamide
moiety: the tautomerization process of enamide to ketimine
intermediate is not involved.
To demonstrate the practical utility of the above methodology,
scaleup of the asymmetric hydrogenation was tested and
conducted smoothly with retained enantioselectivity (see the
Supporting Information). Meanwhile, deacetylation reaction of
2a was carried out and furnished the chiral exocyclic amine 5 with
retained enantioselectivity and 94% yield (Scheme 5). The
d
9
a
Conditions: 3a (0.10 mmol), Ru(COD)(methallyl) (5 mol %), L
2
(
°
5.5 mol %), HBF (10 mol %), H (1000 psi), solvent (2.0 mL), 60
4 2
b c
1
C, 24 h. Isolated yields. Determined by H NMR. Determined by
d
HPLC. At 30 °C.
3
0 °C. The absolute configuration of product 4a (which could be
increased to 99% ee by a recrystallization with dichloromethane
and n-hexane) was unambiguously determined to be (R,R) by X-
ray crystallographic analysis (see the Supporting Information).
Having identified the optimal reaction conditions, we then
investigated the substrate scope and the results were depicted in
Scheme 3. Changing the methyl to ethyl group, 82% ee and 94%
Scheme 5. X-ray Structure of (S)-2a and Deacetylation
Scheme 3. Substrate Scope: ortho-Substituted Aromatic
a
Amines
absolute configuration of the product 2a (which could be
upgraded to 99% ee by a simple recrystallization with
dichloromethane and n-hexane) was unambiguously assigned
to be S by X-ray crystallographic analysis.
In summary, we have successfully realized the first highly
asymmetric hydrogenation of carbocyclic aromatic amines using
an in situ-generated chiral ruthenium as catalyst under mild
conditions, providing an efficient and facile access to chiral
exocyclic amines with up to 98% of enantioselectivity. Studies to
extend the strategy to various carbocyclic aromatic compounds
are ongoing in our laboratory.
a
Conditions: 3 (0.20 mmol), Ru(COD)(methallyl) (5 mol %), L6
2
i
(
5.5 mol %), HBF (10 mol %), H (1000 psi), PrOH (4.0 mL), 30
4
2
°C, 24 h. Isolated yields.
ASSOCIATED CONTENT
Supporting Information
yield was obtained (see 4b in Scheme 3). Fortunately, when we
introduced a methoxy group adjacent to amide group, excellent
enantioselectivity (93% ee) was obtained (see 4c in Scheme 3).
In addition, the electronic effect of annulated ring displayed little
concern with activities and enantioselectivities (see 4d−4f in
Scheme 3).
■
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.7b04060.
Experimental procedures, characterization data, and NMR
spectra (PDF)
To gain insight into the reaction process, two isotopic labeling
Accession Codes
experiments were carried out. When 1a was subjected to the
1
asymmetric hydrogenation with D , H NMR analysis of the
CCDC 1563447−1563448 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
2
crude hydrogenation product showed that one D atom was
incorporated into the 9-position with 91% and into 10-position
with >95%. When the asymmetric hydrogenation was carried out
C
DOI: 10.1021/acs.orglett.7b04060
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
50, 12526. (g) Shugrue, C. R.; Miller, S. J. Angew. Chem., Int. Ed. 2015,
5
4, 11173. (h) Wang, J.; Chen, M.-W.; Ji, Y.; Hu, S.-B.; Zhou, Y.-G. J.
Am. Chem. Soc. 2016, 138, 10413.
4) For reviews, see: (a) Dyson, P. J. Dalton Trans. 2003, 2964.
b) Maegawa, T.; Akashi, A.; Yaguchi, K.; Iwasaki, Y.; Shigetsura, M.;
Monguchi, Y.; Sajiki, H. Chem.Eur. J. 2009, 15, 6953. (c) Gual, A.;
Godard, C.; Castillon, S.; Claver, C. Dalton. Trans. 2010, 39, 11499.
d) Giustra, Z. X.; Ishibashi, J. S. A.; Liu, S.-Y. Coord. Chem. Rev. 2016,
1EZ, U.K.; fax: +44 1223 336033.
(
AUTHOR INFORMATION
Corresponding Author
E-mail: ygzhou@dicp.ac.cn.
■
*
(
́
(
ORCID
3
(
14, 134. (e) Gualandi, A.; Savoia, D. RSC Adv. 2016, 6, 18419.
5) For selected examples on homogeneous hydrogenation of benzene
Yong-Gui Zhou: 0000-0002-3321-5521
Notes
rings by using achiral catalysts, see: (a) Grey, R. A.; Pez, G. P.; Wallo, A.
J. Am. Chem. Soc. 1980, 102, 5948. (b) Borowski, A. F.; Sabo-Etienne, S.;
Donnadieu, B.; Chaudret, B. Organometallics 2003, 22, 1630. (c) Wei,
Y.; Rao, B.; Cong, X.; Zeng, X. J. Am. Chem. Soc. 2015, 137, 9250. (d) Li,
H.; Wang, Y.; Lai, Z.; Huang, K.-W. ACS Catal. 2017, 7, 4446.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(
3
e) Wiesenfeldt, M. P.; Nairoukh, Z.; Li, W.; Glorius, F. Science 2017,
57, 908.
6) For selected examples on diastereoselective hydrogenation of
We are grateful for the financial support from the National
Natural Science Foundation of China (Nos. 21532006,
(
21690074) and the Strategic Priority Program of Chinese
aromatics bearing a chiral auxiliary, see: (a) Besson, M.; Blanc, B.;
Academy of Sciences (No. XDB17020300) is acknowledged.
Champelet, M.; Gallezot, P.; Nasar, K.; Pinel, C. J. Catal. 1997, 170, 254.
(b) Besson, M.; Neto, S.; Pinel, C. Chem. Commun. 1998, 1431.
(
c) Ranade, V. S.; Prins, R. J. Catal. 1999, 185, 479. (d) Besson, M.;
REFERENCES
■
Delbecq, F.; Gallezot, P.; Neto, S.; Pinel, C. Chem.Eur. J. 2000, 6, 949.
e) Heitbaum, M.; Frohlich, R.; Glorius, F. Adv. Synth. Catal. 2010, 352,
57.
7) For selected examples on hydrogenation of arenes using ruthenium
nanoparticles modified with chiral ligands, see: (a) Jansat, S.; Picurelli,
D.; Pelzer, K.; Philippot, K.; Gomez, M.; Muller, G.; Lecante, P.;
(
1) For reviews, see: (a) Glorius, F. Org. Biomol. Chem. 2005, 3, 4171.
b) Zhou, Y.-G. Acc. Chem. Res. 2007, 40, 1357. (c) Kuwano, R.
(
3
̈
(
Heterocycles 2008, 76, 909. (d) Yu, Z.; Jin, W.; Jiang, Q. Angew. Chem.,
Int. Ed. 2012, 51, 6060. (e) Wang, D.-S.; Chen, Q.-A.; Lu, S.-M.; Zhou,
Y.-G. Chem. Rev. 2012, 112, 2557. (f) Chen, Q.-A.; Ye, Z.-S.; Duan, Y.;
Zhou, Y.-G. Chem. Soc. Rev. 2013, 42, 497. (g) Zhao, D.; Glorius, F.
Angew. Chem., Int. Ed. 2013, 52, 9616. (h) Ye, Z.-S.; Shi, L.; Zhou, Y.-G.
Synlett 2014, 25, 928. (i) He, Y.-M.; Song, F.-T.; Fan, Q.-H. Top. Curr.
Chem. 2013, 343, 145. (j) Balakrishna, B.; Nunez-Rico, J. L.; Vidal-
́
̃
Ferran, A. Eur. J. Org. Chem. 2015, 2015, 5293. (k) Zhao, D.; Candish,
L.; Paul, D.; Glorius, F. ACS Catal. 2016, 6, 5978.
(
́
Chaudret, B. New J. Chem. 2006, 30, 115. (b) Gual, A.; Axet, M. R.;
Philippot, K.; Chaudret, B.; Denicourt-Nowicki, A.; Roucoux, A.;
Castillon, S.; Claver, C. Chem. Commun. 2008, 2759.
(
8) Urban, S.; Ortega, N.; Glorius, F. Angew. Chem., Int. Ed. 2011, 50,
803.
9) (a) Kuwano, R.; Morioka, R.; Kashiwabara, M.; Kameyama, N.
3
(
(
2) For selected examples on metallocatalytic hydrogenation, see:
a) Kuwano, R.; Sato, K.; Kurokawa, T.; Karube, D.; Ito, Y. J. Am. Chem.
Angew. Chem., Int. Ed. 2012, 51, 4136. (b) Kuwano, R.; Ikeda, R.;
Hirasada, K. Chem. Commun. 2015, 51, 7558.
10) (a) Welch, W. M.; Kraska, A. R.; Sarges, R.; Koe, B. K. J. Med.
Chem. 1984, 27, 1508. (b) Ahlskog, J. E.; Muenter, M. D.; Bailey, P. A.;
Miller, P. M. Clin. Neuropharmacol. 1991, 14, 214. (c) Hohne, M.;
Bornscheuer, U. T. ChemCatChem 2009, 1, 42. (d) Nugent, T. C.; El-
Shazly, M. Adv. Synth. Catal. 2010, 352, 753.
11) (a) Irurre, J.; Riera, M.; Guixa,
S.-Z.; You, T.-P. Synth. Commun. 2009, 39, 4133.
12) (a) Benesch, L.; Bury, P.; Guillaneux, D.; Houldsworth, S.; Wang,
(
Soc. 2000, 122, 7614. (b) Wang, W.-B.; Lu, S.-M.; Yang, P.-Y.; Han, X.-
W.; Zhou, Y.-G. J. Am. Chem. Soc. 2003, 125, 10536. (c) Legault, C. Y.;
Charette, A. B. J. Am. Chem. Soc. 2005, 127, 8966. (d) Kaiser, S.; Smidt,
S. P.; Pfaltz, A. Angew. Chem., Int. Ed. 2006, 45, 5194. (e) Kuwano, R.;
Kashiwabara, M.; Ohsumi, M.; Kusano, H. J. Am. Chem. Soc. 2008, 130,
08. (f) Zhou, H.; Li, Z.; Wang, Z.; Wang, T.; Xu, L.; He, Y.; Fan, Q.-H.;
Pan, J.; Gu, L.; Chan, A. S. C. Angew. Chem., Int. Ed. 2008, 47, 8464.
g) Wang, D.-S.; Chen, Q.-A.; Li, W.; Yu, C.-B.; Zhou, Y.-G.; Zhang, X. J.
Am. Chem. Soc. 2010, 132, 8909. (h) Wang, D.-S.; Ye, Z.-S.; Chen, Q.-A.;
Zhou, Y.-G.; Yu, C.-B.; Fan, H.-J.; Duan, Y. J. Am. Chem. Soc. 2011, 133,
866. (i) Wang, T.; Zhuo, L.-G.; Li, Z.; Chen, F.; Ding, Z.; He, Y.; Fan,
Q.-H.; Xiang, J.; Yu, Z.-X.; Chan, A. S. C. J. Am. Chem. Soc. 2011, 133,
878. (j) Ortega, N.; Urban, S.; Beiring, B.; Glorius, F. Angew. Chem., Int.
Ed. 2012, 51, 1710. (k) Wang, T.; Chen, F.; Qin, J.; He, Y.-M.; Fan, Q.-
H. Angew. Chem., Int. Ed. 2013, 52, 7172. (l) Duan, Y.; Li, L.; Chen, M.-
W.; Yu, C.-B.; Fan, H.-J.; Zhou, Y.-G. J. Am. Chem. Soc. 2014, 136, 7688.
m) Zhang, J.; Chen, F.; He, Y.-M.; Fan, Q.-H. Angew. Chem., Int. Ed.
015, 54, 4622. (n) Wei, X.; Qu, B.; Zeng, X.; Savoie, J.; Fandrick, K. R.;
Desrosiers, J.-N.; Tcyrulnikov, S.; Marsini, M. A.; Buono, F. G.; Li, Z.;
Yang, B.-S.; Tang, W.; Haddad, N.; Gutierrez, O.; Wang, J.; Lee, H.; Ma,
S.; Campbell, S.; Lorenz, J. C.; Eckhardt, M.; Himmelsbach, F.; Peters,
S.; Patel, N. D.; Tan, Z.; Yee, N. K.; Song, J. J.; Roschangar, F.;
Kozlowski, M. C.; Senanayake, C. H. J. Am. Chem. Soc. 2016, 138, 15473.
o) Tosatti, P.; Pfaltz, A. Angew. Chem., Int. Ed. 2017, 56, 4579. (p) Li,
W.; Wiesenfeldt, M. P.; Glorius, F. J. Am. Chem. Soc. 2017, 139, 2585.
3) For selected examples on organocatalytic reduction of hetero-
(
̈
8
(
́
M. Chirality 2002, 14, 490. (b) Lin,
(
(
X.; Snieckus, V. Tetrahedron Lett. 1998, 39, 961. (b) Voth, S.; Hollett, J.
W.; McCubbin, J. A. J. Org. Chem. 2015, 80, 2545. (c) Yoshimura, F.;
Abe, T.; Tanino, K. Org. Lett. 2016, 18, 1630.
8
(13) For examples on enantioselective reduction of heteroaromatic
9
amines, quinolin-3-amines, see: (a) Cai, X.-F.; Huang, W.-X.; Chen, Z.-
P.; Zhou, Y.-G. Chem. Commun. 2014, 50, 9588. (b) Cai, X.-F.; Guo, R.-
N.; Feng, G.-S.; Wu, B.; Zhou, Y.-G. Org. Lett. 2014, 16, 2680. (c) Cai,
X.-F.; Guo, R.-N.; Chen, M.-W.; Shi, L.; Zhou, Y.-G. Chem.Eur. J.
(
2
2
014, 20, 7245.
(14) (a) Shi, L.; Ye, Z.-S.; Cao, L.-L.; Guo, R.-N.; Hu, Y.; Zhou, Y.-G.
Angew. Chem., Int. Ed. 2012, 51, 8286. (b) Ye, Z.-S.; Chen, M.-W.; Chen,
Q.-A.; Shi, L.; Duan, Y.; Zhou, Y.-G. Angew. Chem., Int. Ed. 2012, 51,
1
Y.-G. Angew. Chem., Int. Ed. 2013, 52, 3685. (d) Guo, R.-N.; Cai, X.-F.;
Shi, L.; Ye, Z.-S.; Chen, M.-W.; Zhou, Y.-G. Chem. Commun. 2013, 49,
8
0181. (c) Ye, Z.-S.; Guo, R.-N.; Cai, X.-F.; Chen, M.-W.; Shi, L.; Zhou,
(
537. (e) Huang, W.-X.; Yu, C.-B.; Shi, L.; Zhou, Y.-G. Org. Lett. 2014,
6, 3324. (f) Huang, W.-X.; Yu, C.-B.; Ji, Y.; Liu, L.-J.; Zhou, Y.-G. ACS
1
(
Catal. 2016, 6, 2368.
arenes, see: (a) Rueping, M.; Antonchick, A. P.; Theissmann, T. Angew.
Chem., Int. Ed. 2006, 45, 3683. (b) Rueping, M.; Antonchick, A. P.
Angew. Chem., Int. Ed. 2007, 46, 4562. (c) Guo, Q.-S.; Du, D.-M.; Xu, J.
Angew. Chem., Int. Ed. 2008, 47, 759. (d) Chen, Q.-A.; Wang, D.-S.;
Zhou, Y.-G.; Duan, Y.; Fan, H.-J.; Yang, Y.; Zhang, Z. J. Am. Chem. Soc.
(
15) (a) Genet, J. P.; Mallart, S.; Pinel, C.; Juge, S.; Laffitte, J. A.
̂
Tetrahedron: Asymmetry 1991, 2, 43. (b) Heiser, B.; Broger, E. A.;
Crameri, Y. Tetrahedron: Asymmetry 1991, 2, 51.
2
011, 133, 6126. (e) Chen, Q.-A.; Gao, K.; Duan, Y.; Ye, Z.-S.; Shi, L.;
Yang, Y.; Zhou, Y.-G. J. Am. Chem. Soc. 2012, 134, 2442. (f) Chen, M.-
W.; Cai, X.-F.; Chen, Z.-P.; Shi, L.; Zhou, Y.-G. Chem. Commun. 2014,
D
DOI: 10.1021/acs.orglett.7b04060
Org. Lett. XXXX, XXX, XXX−XXX