A new electronically deficient atropisomeric diphosphine ligand (S)-CF 3O-BiPhep and its application in asymmetric hydrogenation

Article abstract of DOI:10.1016/j.tetlet.2012.03.036

A new electronically deficient atropisomeric diphosphine ligand (S)-CF ₃O-BiPhep was synthesized from 1-bromo-3-(trifluoromethoxy)benzene in high yield. The key steps included oxidative coupling with anhydrous ferric chloride and optical resolution by (+)-DMTA. The ligand afforded high performance for Ir-catalyzed asymmetric hydrogenation of quinolines with ee up to 92% and TON up to 25,000. It was also successfully applied to the Pd-catalyzed asymmetric hydrogenation of simple indoles with ee up to 87% and Rh-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone with 97% ee.

Full text of DOI:10.1016/j.tetlet.2012.03.036

Tetrahedron Letters 53 (2012) 2556–2559
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A new electronically deficient atropisomeric diphosphine ligand
(S)-CF3O-BiPhep and its application in asymmetric hydrogenation
De-Yang Zhang a,b, Chang-Bin Yu b, Min-Can Wang a, , Kai Gao b, Yong-Gui Zhou b,
⇑
⇑
a Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052, China
b State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new electronically deficient atropisomeric diphosphine ligand (S)-CF3O-BiPhep was synthesized from
1-bromo-3-(trifluoromethoxy)benzene in high yield. The key steps included oxidative coupling with
anhydrous ferric chloride and optical resolution by (+)-DMTA. The ligand afforded high performance
for Ir-catalyzed asymmetric hydrogenation of quinolines with ee up to 92% and TON up to 25,000. It
was also successfully applied to the Pd-catalyzed asymmetric hydrogenation of simple indoles with ee
up to 87% and Rh-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone with
97% ee.
Received 19 January 2012
Revised 1 March 2012
Accepted 9 March 2012
Available online 16 March 2012
Keywords:
Asymmetric catalysis
Fluorinated diphosphine ligands
Quinolines
Ó 2012 Elsevier Ltd. All rights reserved.
Indoles
Chiral bidentate phosphine ligands play an important role in
various homogeneous transition metal-catalyzed reactions.1 There-
fore, design and synthesis of new chiral diphosphine ligands with
new scaffold and/or electronic properties were still an attractive
area of research.2 Recently, several studies revealed that electroni-
cally deficient atropisomeric diphosphine ligands could often lead
to a dramatic variation of the reactivity and enantioselectivity for
some transition metal-mediated asymmetric reactions.3 For exam-
ple, in 2004, Genêt and co-workers synthesized the DifluorPhos li-
gand which displayed better reactivity and enantioselectivity
than electron-rich diphosphine ligands for several transition me-
tal-catalyzed reactions.4,5 In 2009, Korenaga group synthesized an
electron poor chiral diphosphine ligand MeO-F28-BiPhep which
was found to greatly improve the catalytic activity for Rh-catalyzed
1,4-addition at room temperature.6 Afterward, they found the
ligand gave very good catalytic activity in the reaction with TOF
up to 53,000 hꢀ1 and TON up to 320,000.7 In the research field of
Ir-catalyzed asymmetric hydrogenation of quinolines, the electron-
ically deficient atropisomeric diphosphine ligands also showed very
high catalytic activities, such as P-Phos and the aforementioned
DifluorPhos.8 Recently, our group also synthesized a series of elec-
tronically deficient atropisomeric bisphosphine ligands based on
(S)-MeO-BiPhep and studied the effectiveness in the Ir-catalyzed
asymmetric hydrogenation of quinolines. We found that these
O
F
F
O
O
PPh2
PPh2
MeO
MeO
PAr2
PAr2
F
F
O
Ar = 3,4,5-F3-C6H2
(S)-MeO-F26-BiPhep
(S)-DifluorPhos
TfO
TfO
PPh2
PPh2
F3CO
F3CO
PPh2
PPh2
(S)-TfO-BiPhep
(S)-CF3O-BiPhep
Scheme 1. Electronically deficient atropisomeric diphosphine ligands.
electron-poor chiral diphosphine ligands gave much better
catalytic activities than MeO-BiPhep, and the introduction of more
electron-withdrawing groups in the biaryl backbone could dramat-
ically improve the catalyst activity. When using the ligand (S)-TfO-
BiPhep, we achieved the highest 95% ee and TON could be up to
14,600 (Scheme 1).9 It was known to us that most of the catalytic
system for quinoline hydrogenation suffered from low catalytic
activity because of the deactivation of iridium catalyst by the
formation of catalytically unreactive dimers and trimers through
hydride-bridged bonds under hydrogen atmosphere. So we
⇑
Corresponding authors. Tel./fax: +86 371 67769024 (M.-C.W.); tel./fax: +86 411
84379220 (Y.-G.Z.).
E-mail addresses: wangmincan@zzu.edu.cn (M.-C. Wang), ygzhou@dicp.ac.cn
(Y.-G. Zhou).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.03.036

D.-Y. Zhang et al. / Tetrahedron Letters 53 (2012) 2556–2559
2557
hypothesized that the using of the electronically deficient atropiso-
meric diphosphine ligands might inhibit the formation of inactive
dimmers or trimers and thus the productivity of the catalyst might
be enhanced dramatically. Herein, we designed and synthesized a
novel electronically deficient atropisomeric diphosphine ligand
bearing a trifluoromethoxy at the 6- and 60-positions of the biaryl
backbone. Following the nomenclature for MeO-BiPhep, the ligand
was named as CF3O-BiPhep [2,20-bis(diphenylphosphino)-6,60-
ditrifluoromethoxy-1,10-biphenyl].
Our synthetic approach to enantiopure ligand (S)-CF3O-BiPhep
was shown in Scheme 2 and the (R)-CF3O-BiPhep was also obtained
in the sameway.10 In the firststep, treatmentofthe Grignard reagent
of commercially available 1-bromo-3-(trifluoromethoxy)benzene
(1) with chlorodiphenylphosphine followed by the addition of
H2O2 to afford the phosphine oxide 2 in 91% yield was performed.
ortho-Lithiation of 2 by LDA at ꢀ78 °C in THF and further oxidative
coupling with anhydrous ferric chloride provided the racemic
diphosphine dioxide 3 in 56% yield. Effective optical resolution of
the rac-3 was achieved by using (+)-di-p-methoxybenzoyl-D-tartaric
acid [(+)-DMTA] as a resolving agent. Recrystallization of the mix-
ture by a mixed solvent of CHCl3/EtOAc (2:3) gave a complex of
(ꢀ)-4 and (+)-DMTA. Treatment of the tartrate complex with aque-
ous base provided enantiomerically pure (ꢀ)-4 (ee >99%) in 78%
yield, based onthe amount of(ꢀ)-4 in rac-3. Finally, HSiCl3 reduction
of compound (ꢀ)-4 in the presence of N,N-diisopropyl-ethylamine
afforded the enantiomerically pure ligand in 83% yield (Scheme 2).11
The absolute configuration of (ꢀ)-4 was determined by X-ray
analysis of the complex of (ꢀ)-4 with (+)-DMTA which was recrys-
tallized from MeOH as a colorless crystal. From the internal
comparison with (+)-DMTA, the absolute configuration of (ꢀ)-4
was defined to be S (Fig. 1). Therefore, the ligand reduced from
(ꢀ)-4 was assigned as (S)-CF3O-BiPhep.
Figure 1. X-ray structure of compound (S)-(ꢀ)-4ꢁ(+)-DMTA.
Table 1
Asymmetric hydrogenation of quinoline derivativesa
With the ligand in hand, its catalytic performance in the Ir-cat-
alyzed asymmetric hydrogenation of quinolines was firstly investi-
gated.12,13 Having established the optimal conditions, a variety of
substituted quinoline derivatives were tested to explore the scope
of the reaction (the S/C molar ratio was 1000/1). As summarized in
Table 1, high yields and good enantioselectivities were obtained for
several 2-alkyl substituted quinolines and the reaction was rela-
tively insensitive to the length of the alkyl group (Table 1, entries
1–5). It was noted that the C@C double bond in the side chain of
5d was also completely hydrogenated (Table 1, entry 4). When hy-
droxyl groups at the side chain, the yield was very excellent but
R1
R1
[Ir((COD)Cl]2/(S)-L/I2, THF
N
H
R2
H
2 (700 psi), rt, 22 h
N
R2
5
6
Entry
R1/R2
Yieldb (%)
eec (%)
1
2
3
4
5
6
7
8
9
10
H/Me (6a)
H/Et (6b)
H/n-Pr (6c)
H/3-Butenyl (6d)
H/n-Pentyl (6e)
H/Me2C(OH)CH2–(6f)
H/C6H5(CH2)2–(6g)
Me/Me (6h)
98
93
97
97
99
98
98
88
95
98
91 (S)
92 (S)
90 (S)
87 (S)
88 (S)
70 (R)
86 (S)
79 (S)
81 (S)
60 (R)
1) Mg, THF, Reflux
F/Me (6i)
H/Ph (6j)
F3CO
Br
F3CO
P(O)Ph2
2) Ph2PCl, then H2O2
91%
a
Conditions: 5 (1 mmol), [Ir(COD)Cl]2 (0.0005 mmol), (S)-L (0.0011 mmol), I2
(0.0050 mmol), H2 (700 psi), THF (2 mL), rt, 22 h.
1
2
b
Isolated yields.
Determined by HPLC.
c
1) LDA, THF, -78 o
C
(+)-DMTA
F3CO
F3CO
P(O)Ph2
P(O)Ph2
2) FeCl3, THF
56%
CHCl3/EtOAc (2/3)
78%
only moderate enantioselectivity was obtained (Table 1, entry 6).
With 2-phenethyl substituted quinoline, slightly lower enantiose-
lectivity was obtained (Table 1, entry 7). For the 6-substituted
quinolines, the enantioselectivities decreased significantly (Table
1, entries 8 and 9). Replacing the alkyl at 2-position with phenyl
group still gave high yield but the enantioselectivity was moderate
(Table 1, entry 10).
rac-3
HSiCl3, (i-Pr)2NEt
F3CO
F3CO
P(O)Ph2
P(O)Ph2
F3CO
F3CO
PPh2
PPh2
PhMe, Reflux
83%
To evaluate the catalytic efficiency of the system [Ir(COD)Cl]2/L/
I2 in asymmetric hydrogenation of quinolines, we investigated the
effect of the substrate-to-catalyst (S/C) molar ratio on the conver-
sion and enantioselectivity of this reaction. 2-Methylquinoline was
selected as substrate and the results were shown in the Table 2. It
4
L
(S)-
(S)-(-)-
Scheme 2. Synthesis of the ligand (S)-CF3O-BiPhep.

2558
D.-Y. Zhang et al. / Tetrahedron Letters 53 (2012) 2556–2559
Table 2
We also applied our ligand in the Rh-catalyzed asymmetric 1,4-
The effect of the S/C on conversion and enantioselectivitya
addition of phenylboronic acid to 2-cyclohexenone.16 Gratifyingly,
the reaction proceeded well with 97% ee and 92% yield. (Scheme 4)
In summary, we have developed a new electronically deficient
atropisomeric diphosphine ligand CF3O-BiPhep. The ligand affor-
ded high activity in the Ir-catalyzed asymmetric hydrogenation
of quinolines with ee up to 92% and TON up to 25,000. It showed
again that the electronically deficient atropisomeric diphosphine
ligand had good catalytic performance in the Ir-catalyzed asym-
metric hydrogenation of quinolines. The CF3O-BiPhep ligand was
also successfully applied in the Pd-catalyzed asymmetric hydroge-
nation of simple indoles and Rh-catalyzed asymmetric 1,4-addition
of phenylboronic acid to 2-cyclohexenone with up to 97% ee. Fur-
ther study on the detailed reason for the good performance of elec-
tronically deficient diphosphine ligand in the Ir-catalyzed
asymmetric hydrogenation of quinolines is underway and will be
disclosed in due course.
[Ir((COD)Cl]2/(S)-L/I2, THF
H2 (700 psi), rt
N
N
H
6a
5a
Entry
S/C
I2 (mol %)
Time (h)
Convn.b (%)
eec (%)
1
2
3
1000/1
5000/1
10,000/1
20,000/1
50,000/1
0.5
1.0
1.0
1.0
2.0
22
36
36
72
72
>95
>95
>95
>95
50
91 (S)
93 (S)
92 (S)
93 (S)
91 (S)
4
5d
a
b
c
Conditions: 5a (1 mmol), [Ir(COD)Cl]2/L (0.5/1.1), H2 (700 psi), THF (2 mL), rt.
Determined by 1H NMR.
Determined by HPLC.
5 mmol 5a, 3 mL THF.
d
Acknowledgments
-L
Pd(OCOCF3)2/(S) /EtSO3H
R
R
We are grateful to the financial support from National Science
Foundation of China (21125208 & 21032003), National Basic
Research Program (2010CB833300) and Chinese Academy of
Sciences.
DCM/TFE (1/1), H2 (700 psi)
rt, 24 h
N
H
N
H
8
7
Entry
R
Yield (%)
Ee (%)
CH3
Bn
8a
87 (
98 (
60 (
82 (
)
75 (S)
87 (S)
83 (R)
82 (R)
1
2
3
4
8b
)
)
Supplementary data
Cyclopentyl
Cyclohexyl
8c
8d
)
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.03.036.
Scheme 3. Asymmetric hydrogenation of simple indoles.
References and notes
O
O
[RhCl(C2H4)2]2 (1 mol%)
1. (a) Noyori, R. In Asymmetric Catalysis in Organic Synthesis; Wiley & Sons: New
York, 1994; pp 342–437; (b) Ohkuma, T.; Kitamura, M.; Noyori, R. In Catalysis
Asymmetric Synthesis; Ojima, I., Ed., second ed.; John Wiley & Sons: New York,
2000; pp 1–110.
2. For reviews, see: (a) McCarthy, M.; Guiry, P. J. Tetrahedron 2001, 57, 3809; (b)
Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029.
3. For reviews, see: (a) Flanagan, P. S.; Guiry, P. J. J. Organomet. Chem. 2006, 691,
2125; (b) Pollock, C. L.; Saunders, G. C.; Smyth, E. C. M. S.; Sorokin, V. I. J.
Fluorine Chem. 2008, 129, 142.
L
(S)- (2.2 mol%)
PhB(OH)2
+
KOH (50 mol%)
Toluene/H2O (10/1)
50 °C, 17 h
Ph
Yield: 92%
Ee: 97%
Scheme 4. The addition of phenylboronic acid to cyclohexenone.
4. Jeulin, S.; Duprat de Paule, S.; Ratovelomanana-Vidal, V.; Genêt, J.-P.;
Champion, N.; Dellis, P. Angew. Chem., Int. Ed. 2004, 43, 320.
was noteworthy that the enantioselectivity changed slightly when
the S/C ratio was increased (91–93% ee). When the S/C ratio was
increased from 5000/1 to 20,000/1, prolonging the reaction time
would facilitate the reaction with full conversion (Table 2, entries
2–4). When S/C ratio further increased to 50,000/1, 50% conversion
was observed, providing a high TON value of 25,000 (Table 2, entry
5). It was obvious that our ligand afforded excellent performance
for Ir-catalyzed asymmetric hydrogenation of quinolines. It
revealed again that the electronically deficient atropisomeric
diphosphine ligand showed good catalytic performance in the
Ir-catalyzed asymmetric hydrogenation of quinolines.
5. Selected examples on transition metal-catalyzed asymmetric reactions using
DifluorPhos ligand, see: (a) Yamamoto, Y.; Yamamoto, H. Angew. Chem., Int. Ed.
2005, 44, 7082; (b) Wadamoto, M.; Yamamoto, H. J. Am. Chem. Soc. 2005, 127,
14556; (c) Oisaki, K.; Zhao, D.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2007,
129, 7439; (d) Deport, C.; Buchotte, M.; Abecassis, K.; Tadaoka, H.; Ayad, T.;
Ohshima, T.; Genêt, J.-P.; Mashima, K.; Ratovelomanana-Vidal, V. Synlett 2007,
2743; (e) Liao, X.; Weng, Z.; Hartwig, J. F. J. Am. Chem. Soc. 2008, 130, 195; (f)
Du, L.; Xu, L.-W.; Shimizu, Y.; Oisaki, K.; Kanai, M.; Shibasaki, M. J. Am. Chem.
Soc. 2008, 130, 16146; (g) Navarre, L.; Martinez, R.; Genêt, J.-P.; Darses, S. J. Am.
Chem. Soc. 2008, 130, 6159; (h) Tadaoka, H.; Cartigny, D.; Nagano, T.; Gosavi, T.;
Ayad, T.; Genêt, J.-P.; Ohshima, T.; Ratovelomanana-Vidal, V.; Mashima, K.
Chem. -Eur. J. 2009, 15, 9990; (i) Cartigny, D.; Nagano, T.; Ayad, T.; Genêt, J.-P.;
Ohshima, T.; Mashima, K.; Ratovelomanana-Vidal, V. Adv. Synth. Catal. 2010,
352, 1886.
To further investigate the effectiveness of the ligand in other
reactions, we also applied it in the Pd-catalyzed asymmetric hydroge-
nation of indoles. In contrast to quinolines, the asymmetric hydroge-
nation of indoles was much less studied, especially the asymmetric
hydrogenation of unprotected indoles.12,14 Very recently, our group
developed the first highly enantioselective hydrogenation of unpro-
tected indoles using Pd-H8-BINAP with a Brønsted acid as an activa-
tor.15 Herein, we also applied our ligand in the Pd-catalyzed
asymmetric hydrogenation of simple indoles using a Brønsted acid
as an activator. To our delight, the ligand also proceeded well in this
reaction and the results were shown in Scheme 3. 2-Methyl and 2-
benzyl substituted indoles could be hydrogenated smoothly with
75% and 87% ee, respectively (Scheme 3, entries 1 and 2). With the
2-cyclopentyl and 2-cyclohexyl substituted indoles, 83% and 82%
ees were obtained, respectively (Scheme 3, entries 3 and 4).
6. Korenaga, T.; Osaki, K.; Maenishi, R.; Sakai, T. Org. Lett. 2009, 11, 2325.
7. Korenaga, T.; Maenishi, R.; Hayashi, K.; Sakai, T. Adv. Synth. Catal. 2010, 352,
3247.
8. (a) Tang, W.-J.; Tan, J.; Xu; L, -J.; Lam, K.-H.; Fan, Q.-H.; Chan, A. S. C. Adv. Synth.
Catal. 2010, 352, 1055; (b) Tang, W.-J.; Sun, Y.-W.; Xu, L.-J.; Wang, T.-L.; Fan, Q.-
H.; Lam, K.-H.; Chan, A. S. C. Org. Biomol. Chem. 2010, 8, 3464.
9. Zhang, D.-Y.; Wang, D.-S.; Wang, M.-C.; Yu, C.-B.; Gao, K.; Zhou, Y.-G. Synthesis
2011, 2796.
10. (a) Saito, T.; Yokozawa, T.; Ishizaki, T.; Moroi, T.; Sayo, N.; Miura, T.;
Kumobayashi, H. Adv. Synth. Catal. 2001, 343, 264; (b) Pai, C.-C.; Li, Y.-M.;
Zhou, Z.-Y.; Chan, A. S. C. Tetrahedron Lett. 2002, 43, 2789; (c) Duprat de Paule,
S.; Jeulin, S.; Ratovelomanana-Vidal, V.; Genêt, J.-P.; Champion, N.; Dellis, P.
Tetrahedron Lett. 2003, 44, 823; (d) Raghunath, M.; Zhang, X. Tetrahedron Lett.
2005, 46, 8213; (e) Chen, Q.-A.; Dong, X.; Chen, M.-W.; Wang, D.-S.; Zhou, Y.-
G.; Li, Y.-X. Org. Lett. 2010, 12, 1928.
11. Characterization data of (S)-CF3O-BiPhep: White solid. Mp 194–195 °C.
½ ꢂ
a 2D7 = 87.0 (c 0.97, CHCl3). 1H NMR (400 MHz, CDCl3): d 7.25–7.35 (m, 14H),
7.14–7.20 (m, 8H), 7.11 (d, J = 8.2 Hz, 2H), 6.99–7.06 (m, 2H). 13C NMR
(100 MHz, CDCl3): d 134.5, 134.3, 134.2, 133.6, 133.5, 133.4, 131.7, 129.7,

D.-Y. Zhang et al. / Tetrahedron Letters 53 (2012) 2556–2559
2559
129.0, 128.6, 128.5, 128.4, 117.4, 110.2. 31P NMR (162 MHz, CDCl3): d = ꢀ13.6.
19F NMR (376 MHz, CDCl3): d = ꢀ57.1.
3014; (o) Wang, D.-S.; Zhou, J.; Wang, D.-W.; Guo, Y.-L.; Zhou, Y.-G.
Tetrahedron Lett. 2010, 51, 525; (p) Tang, W.-J.; Tan, J.; Xu, L.-J.; Lam, K.-H.;
Fan, Q.-H.; Chan, A. S. C. Adv. Synth. Catal. 2010, 352, 1055.
12. For recent reviews on asymmetric hydrogenation of aromatic compounds, see:
(a) Dyson, P. J. Dalton Trans. 2003, 2964; (b) Glorius, F. Org. Biomol. Chem. 2005,
3, 4171; (c) Lu, S.-M.; Han, X.-W.; Zhou, Y.-G. Chin. J. Org. Chem. 2005, 25, 634;
(d) Zhou, Y.-G. Acc. Chem. Res. 2007, 40, 135; (e) Kuwano, R. Heterocycles 2008,
76, 909; (f) Wang, D.-S.; Chen, Q.-A.; Lu, S.-M.; Zhou, Y.-G. Chem. Rev. 2012.
http://dx.doi.org/10.1021/cr200328h.
14. (a) Kuwano, R.; Sato, K.; Kurokawa, T.; Karube, D.; Ito, Y. J. Am. Chem. Soc. 2000,
122, 7614; (b) Kuwano, R.; Kaneda, K.; Ito, T.; Sato, K.; Kurokawa, T.; Ito, Y. Org.
Lett. 2004, 6, 2213; (c) Kuwano, R.; Kashiwabara, M. Org. Lett. 2006, 8, 2653; (d)
Kuwano, R.; Kashiwabara, M.; Sato, K.; Ito, T.; Kaneda, K.; Ito, Y. Tetrahedron:
Asymmetry 2006, 17, 521; (e) Baeza, A.; Pfaltz, A. Chem. -Eur. J. 2010, 16, 2036;
´
13. Selected examples on asymmetric hydrogenation of quinolines using chiral
diphosphine ligands: (a) Wang, W.-B.; Lu, S.-M.; Yang, P.-Y.; Han, X.-W.; Zhou,
Y.-G. J. Am. Chem. Soc. 2003, 125, 10536; (b) Xu, L.-J.; Lam, K.-H.; Ji, J.-X.; Wu, J.;
Fan, Q.-H.; Lo, W.-H.; Chan, A. S. C. Chem. Commun. 2005, 1390; (c) Lu, S.-M.;
Wang, Y.-Q.; Han, X.-W.; Zhou, Y.-G. Angew. Chem., Int. Ed. 2006, 45, 2260; (d)
Reetz, M. T.; Li, X.-G. Chem. Commun. 2006, 2159; (e) Qiu, L.; Kwong, F. Y.; Wu,
J.; Lam, W.-H.; Chan, S.; Yu, W.-Y.; Li, Y.-M.; Guo, R.; Zhou, Z.; Chan, A. S. C. J.
Am. Chem. Soc. 2006, 128, 5955; (f) Yamagata, T.; Tadaoka, H.; Nagata, M.;
Hirao, T.; Kataoka, Y.; Ratovelomanana-Vidal, V.; Genêt, J. P.; Mashima, K.
Organometallics 2006, 25, 2505; (g) Jahjah, M.; Alame, M.; Pellet-Rostaing, S.;
Lemaire, M. Tetrahedron: Asymmetry 2007, 18, 2305; (h) Wang, D.-W.; Zeng,
W.; Zhou, Y.-G. Tetrahedron: Asymmetry 2007, 18, 1103; (i) Chan, S.-H.; Lam, K.-
H.; Li, Y.-M.; Xu, L.-J.; Tang, W.-J.; Lam, F.-L.; Lo, W.-H.; Yu, W.-Y.; Fan, Q.-H.;
Chan, A. S. C. Tetrahedron: Asymmetry 2007, 18, 2625; (j) Wang, X.-B.; Zhou,
Y.-G. J. Org. Chem. 2008, 73, 5640; (k) Wang, D.-W.; Wang, X.-B.; Wang,
D.-S.; Lu, S.-M.; Zhou, Y.-G.; Li, Y.-X. J. Org. Chem. 2009, 74, 2780; (l)
Gou, F.-R.; Li, W.; Zhang, X.; Liang, Y.-M. Adv. Synth. Catal. 2010, 352,
2441; (m) Wang, D.-W.; Wang, D.-S.; Chen, Q.-A.; Zhou, Y.-G. Chem. Eur.
J. 2010, 16, 1133; (n) Wang, D.-S.; Zhou, Y.-G. Tetrahedron Lett. 2010, 51,
(f) Mršic, N.; Jerphagnon, T.; Minnaard, A. J.; Feringa, B. L.; de Vries, J. G.
Tetrahedron: Asymmetry 2010, 21, 7; (g) Maj, A. M.; Suisse, I.; Méliet, C.;
Agbossou-Niedercorn, F. Tetrahedron: Asymmetry 2010, 21, 2010; (h) Wang, D.-
S.; Tang, J.; Zhou, Y.-G.; Chen, M.-W.; Yu, C.-B.; Duan, Y.; Jiang, G.-F. Chem. Sci.
2011, 2, 803.
15. Wang, D.-S.; Chen, Q.-A.; Li, W.; Yu, C.-B.; Zhou, Y.-G.; Zhang, X. J. Am. Chem.
Soc. 2010, 132, 8909.
16. For reviews on Rh-catalyzed asymmetric 1,4-addition, see: (a) Hayashi, T.;
Yamasaki, K. Chem. Rev. 2003, 103, 2829; (b) Fagnou, K.; Lautens, M. Chem. Rev.
2003, 103, 169; (c) Ewards, H. J.; Hargrave, J. D.; Penrose, S. D.; Frost, C. G. Chem.
Soc. Rev. 2010, 39, 2093; Selected examples, see: (d) Takaya, Y.; Ogasawara, M.;
Hayashi, T.; Sakai, M.; Miyaura, N. J. Am. Chem. Soc. 1998, 120, 5579; (e)
Hayashi, T.; Takahashi, M.; Takaya, Y.; Ogasawara, M. J. Am. Chem. Soc. 2002,
124, 5052; (f) Kuriyama, M.; Nagai, K.; Yamada, K.; Miwa, Y.; Taga, T.; Tomioka,
K. J. Am. Chem. Soc. 2002, 124, 8932; Feng, C.-G.; Wang, Z.-Q.; Shao, -C.; Xu, M.-
H.; Lin, G.-Q. Org. Lett. 2008, 10, 4101; (g) Gendrineau, T.; Chuzel, O.; Eijsberg,
H.; Genêt, J.-P.; Darses, S. Angew. Chem., Int. Ed. 2008, 47, 7669; (h) Chen, J.;
Chen, J.; Lang, F.; Zhang, X.; Cun, L.; Zhu, J.; Deng, J.; Liao, J. J. Am. Chem. Soc.
2010, 132, 4552.