Iridium-catalyzed asymmetric transfer hydrogenation of quinolines with Hantzsch esters

Article abstract of DOI:10.1016/j.tetasy.2007.04.028

The iridium-catalyzed enantioselective transfer hydrogenation of quinolines with Hantzsch esters was developed with up to 88% ee using [Ir(COD)Cl]₂/(S)-SegPhos/I₂ as a catalyst.

Full text of DOI:10.1016/j.tetasy.2007.04.028

Tetrahedron: Asymmetry 18 (2007) 1103–1107
Iridium-catalyzed asymmetric transfer hydrogenation
of quinolines with Hantzsch esters
Da-Wei Wang, Wei Zeng and Yong-Gui Zhou*
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, PR China
Received 22 March 2007; accepted 25 April 2007
Available online 1 June 2007
Abstract—The iridium-catalyzed enantioselective transfer hydrogenation of quinolines with Hantzsch esters was developed with up to
88% ee using [Ir(COD)Cl]2/(S)-SegPhos/I2 as a catalyst.
Ó 2007 Published by Elsevier Ltd.
1. Introduction
was produced in this reaction.8 As a result, we explored
the iridium-catalyzed asymmetric transfer hydrogenation
of quinolines using Hantzsch esters as hydrogen source
by combination of the above two reactions (Scheme 1). A
mild asymmetric transfer hydrogenation of quinolines
was realized smoothly using [Ir(COD)Cl]2/(S)-SegPhos/I2
in the presence of Hantzsch esters.
Recently, the biomimetic highly enantioselective organo-
catalyzed transfer hydrogenation of a,b-unsaturated car-
bonyl compounds and imines has been realized by List,
MacMillan, and Rueping using Hantzsch esters as the
hydrogen source.1 A copper-catalyzed asymmetric hydro-
genation of a-ketoesters was reported with up to 94% ee
by List et al. using Hantzsch esters,2 which avoided some
of the technical and safety concerns associated with using
compressed hydrogen gas. In 2006, Rueping extended this
strategy to the asymmetric transfer hydrogenation of het-
eroaromatic compounds, quinolines, and realized the first
example of a metal-free reduction of heteroaromatic
compounds.3 The catalysts are sterically congested chiral
phosphoric acids derived from BINOL. Excellent enantio-
selectivities (87–>99% ee) were obtained for 2-substituted
quinolines.
R'
R'
[Ir(COD)Cl]2 / (S)-MeO-Biphep
N
H
R
N
H
R
H
2 (600psi), I2, Toluene, RT
Ee: 72-96%
H
[Ir(COD)Cl]2
EtO2C
+
CO2Et
EtO2C
CO2Et
rac-MeO-Biphep
I2, Toluene, 80 o
H2
C
N
N
H
Hantzsch ester
H
H
MeO2C
CO2Me
Recently, we developed the highly enantioselective Ir-cata-
lyzed asymmetric hydrogenation of quinoline derivatives
using [Ir(COD)Cl]2/MeO-BiPhep as a catalyst in the pres-
ence of iodine,4–6 and this methodology has been success-
fully applied to the synthesis of tetrahydroquinoline
alkaloids.7 Furthermore, over the course of studying the
quinoline hydrogenation mechanism, we found that the
dehydroaromatization reactions of 1,4-dihydropyridines
(Hantzsch esters) could be realized when using the above
asymmetric hydrogenation catalytic system, hydrogen gas
R'
R'
N
H
N
R
[Ir(COD)Cl]2 / (S)-SegPhos
N
R
H
Scheme 1. Asymmetric transfer hydrogenation of quinolines.
2. Results and discussion
In our initial investigation, we found the [Ir(COD)Cl]2/
(S)-SynPhos/I2 system could catalyze the transfer hydrogena-
tion of 2-methylquinoline in THF with moderate activity
and enantioselectivity (Table 1, entry 1). To evaluate the
effect of solvents and other factors, 2-methylquinoline 1a
*
Corresponding author. Tel./fax: +86 411 84379220; e-mail: ygzhou@
dicp.ac.cn
0957-4166/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.tetasy.2007.04.028

1104
D.-W. Wang et al. / Tetrahedron: Asymmetry 18 (2007) 1103–1107
Table 1. Ir-catalyzed asymmetric transfer hydrogenation of 2-methylquinolinea
H
H
RO2C
CO2R
N
H
N
H
[Ir(COD)Cl]2 / L*/ I2, Solvent, RT
N
1a
2a
Entry
R
Ligand
Solvent
Time (h)
Yieldb (%)
eec (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Et
Et
Et
Et
Et
Et
Et
Et
(S)-SynPhos
(S)-SynPhos
(S)-SynPhos
(S)-SynPhos
(S)-SynPhos
(S)-BINAP
(S)-MeO-BiPhep
(R,R)-Me-DuPhos
(R)-Cl-MeOBiPhep
(S)-SegPhos
THF
CH2Cl2
DME
22
21
30
5
53
80
38
71
43
96
77
73
92
96
97
97
90
68
86
52
2
49
8
Toluened
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Toluene
24
42
20
20
40
42
20
20
24
90
42
68
54
78
4
79
79
82
59
23
91
87
Et
Et
Me
i-Pr
t-Bu
Me
Me
(S)-SegPhos
(S)-SegPhos
(S)-SegPhos
(S)-SegPhos
(S)-SegPhos
Toluene/dioxane (2/1)
Cl
O
O
O
MeO
MeO
PPh2
PPh2
MeO
MeO
PPh2
PPh2
O
O
PPh2
PPh2
PPh2
PPh2
PPh2
PPh2
P
P
O
O
O
Cl
(S)-MeO-BiPhep
(S)-SegPhos
(S)-SynPhos
(R,R)-Me-DuPhos (R)-Cl-MeOBiPhep
(S)-BINAP
a Conditions: 0.25 mmol quinoline, [Ir(COD)Cl]2 (1 mol %), ligand (2.2 mol %), I2 (5 mol %), 2.5 mL solvent, Hantzsch ester (2.0 equiv).
b Isolated yields based on 2-methylquinoline.
c Determined by HPLC analysis using a chiralpak OJ-H column.
d The reaction was carried out at 60 °C.
was chosen as the model substrate. First, the effect of sol-
vents on reactivity and enantioselectivity were studied; this
reaction is highly solvent dependent. For dichloromethane,
the reactivity is high and the enantioselectivity is very low
(2% ee, entry 2). For dioxane, high enantioselectivity and
low reactivity were obtained. Moderate reactivity and
enantioselectivity were obtained in THF and DME. For
our previously developed Ir-catalyzed asymmetric hydroge-
nation of quinolines in the presence of iodine, toluene is the
best solvent; the reaction was carried out in toluene at
room temperature. The reactivity was very low, when the
temperature was raised to 60 °C; a very low enantioselec-
tivity was obtained (8% ee, entry 4). Next, the effect of
chiral ligands was also investigated using dioxane as sol-
vent. Some commercially available ligands (Table 1, entries
5–10) were screened: (S)-MeO-BiPhep (78% ee), (R,R)-Me-
DuPhos (4% ee), (S)-BINAP (54% ee), (R)-Cl-MeOBiPhep
(79% ee), (S)-SegPhos (79% ee), (R)-Cl-MeOBiPhep,
and (S)-SegPhos gave the best results (79% ee, entries
9 and 10).
at room temperature (82% ee, entry 11). This can be ex-
plained by the relative size of the ester moieties.1e Subse-
quently, we reevaluated the solvent effect using the
dimethyl Hantzsch ester as a hydrogen source. Gratify-
ingly, the transfer hydrogenation can proceed in toluene
with 91% ee, but the reactivity is moderate (entry 14).
For the above optimized conditions, high enantioselectivity
was obtained in toluene, while high reactivity was obtained
in dioxane. To obtain better activity and enantioselectivity,
we screened the effect of the toluene/dioxane mixed sol-
vents on the reactivity and enantioselectivity; the results
showed that toluene/dioxane ratio (2/1) is the best conclu-
sion. It should be noted that transfer hydrogenation cannot
take place in the absence of iodine.
Having established the optimal conditions, we explored the
scope of this new Ir-catalyzed asymmetric transfer hydro-
genation of quinolines, the results are summarized in
Table 2. 2-Alkyl substituted quinolines were hydrogenated
smoothly with good yields, although, enantioselectivities
were obviously influenced by the length of the side chain
(Table 2, entries 1–4). Substrates with a short chain gave
better enantioselectivities. The reactions were sensitive to
the substituents at the 6-position (Table 2, entries 5–7),
A survey of various Hantzsch esters (entries 10–13) for the
transfer hydrogenation revealed that dimethyl Hantzsch es-
ter provided the highest reaction rate and enantioselectivity

D.-W. Wang et al. / Tetrahedron: Asymmetry 18 (2007) 1103–1107
Table 2. Ir-catalyzed asymmetric transfer hydrogenation of quinolinesa
1105
H
H
MeO2C
CO2Me
R'
R'
N
H
N
H
2a-l
R
[Ir(COD)Cl]2 / (S)-SegPhos, I2,
Toluene / Dioxane = 2 / 1, RT
N
R
1a-l
Entry
R0/R
Yieldb (%)
Time (h)
eec (%)
Config.
1
2
3
4
5
6
7
8
9
H/Me
H/Et
86 (2a)
92 (2b)
98 (2c)
94 (2d)
90 (2e)
82 (2f)
43 (2g)
88 (2h)
87 (2i)
92 (2j)
76 (2k)
90 (2l)
42
42
42
45
45
56
74
45
46
46
79
69
87
87
81
68
86
86
81d
87
87
88
78
10
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(R)
(R)
H/n-Bu
H/n-Pentyl
F/Me
Me/Me
MeO/Me
H/Phenethyl
H/3,4-Methylenedioxyphenethyl
H/3,4-(MeO)2C6H3(CH2)2–
H/Ph2CH(OH)CH2–
H/Ph
10
11
12
a Conditions: 0.25 mmol quinoline, [Ir(COD)Cl]2 (1 mol %), ligand (2.2 mol %), I2 (5 mol %), 2.5 mL solvents, Hantzsch ester (2.0 equiv).
b Isolated yields based on 1.
c Determined by HPLC.
d 48% recovered starting material.
with low reactivity being obtained for substrates with elec-
tron-donating groups, which is probably attributable to the
electronic effect. 2-(2-Arylethyl)-substituted quinolines can
also be hydrogenated with good asymmetric induction
(Table 2, entries 8–10). Interestingly, this transfer hydro-
genation system can tolerate a hydroxyl group, and
moderate enantioselectivity can be achieved for 1k (Table
2, entry 11). For 2-aryl substituted quinoline (entry 12),
only 10% enantioselectivity was obtained, although the
reason for this is unclear.
performed on silica gel (200–300 mesh). All reactions were
monitored by TLC analysis. Transfer hydrogenation reac-
tions were performed in a Schlenk tube.
4.2. Experimental data for the tetrahydroquinoline deriva-
tives 2a–2l
Typical procedure: A mixture of [Ir(COD)Cl]2 (1.7 mg,
0.0025 mmol) and (S)-SegPhos (3.4 mg, 0.0055 mmol) in
solvent (1 mL) was stirred at room temperature for
10 min in a Schlenk tube, after which I2 (3.2 mg,
0.0125 mmol) was added and stirred for another 10 min,
the substrate (0.25 mmol) and Hantzsch dihydropyridine
(0.50 mmol) were then added. The resulting mixture was al-
lowed to stir at rt for 20–90 h. The solvent was removed
under reduced pressure. The enantiomeric excesses were
determined by chiral HPLC (OJ-H, OD-H, or AS-H) after
the purification by column chromatography on silica gel
(ethyl acetate/hexane).
3. Conclusions
In conclusion, we have developed the asymmetric transfer
hydrogenation of quinolines with the [Ir(COD)Cl]2/(S)-
SegPhos/I2 system under mild reaction conditions, and
up to 88% ee was obtained. This system provides an effi-
cient and convenient route to synthesize tetrahydroquino-
lines and their derivatives. Further investigation on the
mechanism and the range of substrates is currently in
progress.
4.2.1. 2-Methyl-1,2,3,4-tetrahydroquinoline 2a. (Known
RT
compound, see Ref. 4). 87% ee, ½aꢀD ¼ ꢁ73:2 (c 0.56,
1
CHCl3); H NMR (400 MHz, CDCl3) 1.21 (t, J = 6.2 Hz,
4. Experimental
4.1. General
3H), 1.60 (m, 1H), 1.93 (m, 1H), 2.75 (m, 1H), 2.81 (m,
1H), 3.40 (m, 1H), 3.68 (br, 1H), 6.47 (d, J = 8.5 Hz,
1H), 6.60 (m, 1H), 6.95 (m, 2H); HPLC (OJ-H, elute: hex-
anes/i-PrOH = 95/5, detector: 254 nm, flow rate: 1.0 mL/
min), (S) t1 = 10.6 min, (R) t2 = 11.8 min.
Commercially available reagents were used without further
purification. Solvents were treated prior to use according to
1
the standard methods. H NMR and 13C NMR spectra
were recorded at room temperature in CDCl3 on Bruker
DRX 400 instrument with tetramethylsilane (TMS) as the
internal standard. Enantiomeric excesses were determined
by HPLC analysis, using a Chiral column described below
in detail. Optical rotations were measured with JASCO
P-1020 polarimeter. Flash column chromatography was
4.2.2. 2-Ethyl-1,2,3,4-tetrahydroquinoline 2b. (Known
RT
compound, see Ref. 4). 87% ee, ½aꢀD ¼ ꢁ70:9 (c 0.66,
1
CHCl3); H NMR (400 MHz, CDCl3) 0.98 (t, J = 7.5 Hz,
3H), 1.52 (m, 3H), 1.95 (m, 1H), 2.76 (m, 2H), 3.15 (m,
1H), 3.75 (br, 1H), 6.46 (d, J = 7.9 Hz, 1H), 6.59 (t,
J = 7.3 Hz, 1H), 6.95 (m, 2H); HPLC (OJ-H, elute:

1106
D.-W. Wang et al. / Tetrahedron: Asymmetry 18 (2007) 1103–1107
hexanes/i-PrOH = 95/5, detector: 254 nm, flow rate:
0.6 mL/min), (S) t1 = 15.0 min, (R) t2 = 16.4 min.
(br, 1H), 5.92 (s, 2H), 6.46 (d, J = 7.8 Hz, 1H), 6.60 (m,
2H), 6.70 (m, 2H), 6.95 (m, 2H); HPLC (AS-H, elute: hex-
anes/i-PrOH = 97/3, detector: 254 nm, flow rate: 0.8 mL/
min), (S) t1 = 16.7 min, (R) t2 = 20.3 min.
4.2.3. 2-Butyl-1,2,3,4-tetrahydroquinoline 2c. (Known
RT
compound, see Ref. 4). 81% ee, ½aꢀD ¼ ꢁ72:2 (c 0.92,
1
CHCl3); H NMR (400 MHz, CDCl3) 0.95 (t, J = 6.9 Hz,
4.2.10.
2-(30,40-Dimethoxyphenethyl)-1,2,3,4-tetrahydro-
3H), 1.36 (m, 4H), 1.50 (m, 3H), 1.96 (m, 1H), 2.75 (m,
2H), 3.22 (m, 2H), 3.76 (br, 1H), 6.48 (d, J = 7.6 Hz,
1H), 6.59 (m, J = 7.3 Hz, 1H), 6.95 (m, 2H); HPLC (OJ-
H, elute: hexanes/i-PrOH = 95/5, detector: 254 nm, flow
rate 0.6 mL/min), (S) t1 = 11.9 min, (R) t2 = 13.7 min.
quinoline 2j. (Known compound, see Ref. 4). 88% ee,
RT
½aꢀD ¼ ꢁ43:8 (c 1.34, CHCl3); 1H NMR (400 MHz,
CDCl3) 1.68 (m, 1H), 1.81 (m, 2H), 1.98 (m, 1H), 2.69
(m, 2H), 2.79 (m, 2H), 3.30 (m, 1H), 3.86 (s, 3H), 3.87 (s,
3H), 6.45 (d, J = 7.7 Hz, 1H), 6.60 (m, 1H), 6.74 (m,
3H), 6.96 (m, 2H); HPLC (AS-H, elute: hexanes/i-
PrOH = 90/10, detector: 254 nm, flow rate 0.8 mL/min),
(R) t1 = 9.9 min, (S) t2 = 10.5 min.
4.2.4. 2-Pentyl-1,2,3,4-tetrahydroquinoline 2d. (Known
RT
compound, see Ref. 4). 68% ee, ½aꢀD ¼ ꢁ41:3 (c 0.92,
1
CHCl3); H NMR (400 MHz, CDCl3) 0.91 (t, J = 6.7 Hz,
3H), 1.42 (m, 8H), 1.48 (m, 1H), 1.95 (m, 1H), 2.76 (m,
2H), 3.23 (m, 1H), 3.74 (br, 1H), 6.47 (d, J = 7.5 Hz,
1H), 6.59 (t, J = 7.3 Hz, 1H), 6.95 (m, 2H); HPLC
(OJ-H, elute: hexanes/i-PrOH = 95/5, detector: 254 nm,
flow rate 0.6 mL/min), (S) t1 = 11.2 min, (R) t2 = 12.2 min.
4.2.11. 1,1-Diphenyl-2-(1,2,3,4-tetrahydroquinolin-2-yl)-eth-
anol 2k. (Known compound, see Ref. 4). 78% ee,
RT
½aꢀD ¼ ꢁ82:6 (c 1.18, CHCl3); 1H NMR (400 MHz,
CDCl3) 0.87 (m, 1H), 1.71 (m, 2H), 2.46 (m, 2H), 2.69
(m, 2H), 3.29 (m, 2H), 4.41 (br, 1H), 6.38 (d, J = 7.8 Hz,
1H), 6.60 (m, 1H), 6.91 (m, 2H), 7.24 (m, 2H), 7.33 (m,
4H), 7.45 (m, 4H); HPLC (OD-H, elute: hexanes/i-
PrOH = 94/6, detector: 254 nm, flow rate: 1.0 mL/min),
(S) t1 = 11.3 min, (R) t2 = 13.4 min.
4.2.5. 6-Fluoro-2-methyl-1,2,3,4-tetrahydroquinoline 2e.
RT
(Known compound, see Ref. 4). 86% ee, ½aꢀD ¼ ꢁ54:4 (c
0.70, CHCl3); 1H NMR (400 MHz, CDCl3) 1.20 (d,
J = 6.2 Hz, 3H), 1.55 (m, 1H), 1.91 (m, 1H), 2.72 (m,
1H), 2.80 (m, 1H), 3.35 (m, 1H), 3.75 (br, 1H), 6.40 (m,
1H), 6.67 (m, 2H); HPLC (OD-H, elute: hexanes/i-
PrOH = 95/5, detector: 254 nm, flow rate: 0.8 mL/min),
(S) t1 = 6.6 min, (R) t2 = 7.9 min.
4.2.12. 2-Phenyl-1,2,3,4-tetrahydroquinoline 2l. (Known
RT
compound, see Ref. 3a). 10% ee, ½aꢀD ¼ þ7:6 (c 0.88,
1
CHCl3); H NMR (400 MHz, CDCl3) 1.99 (m, 1H), 2.12
(m, 1H), 2.75 (m, 1H), 2.90 (m, 1H), 4.01 (br, 1H), 4.43
(m, 1H), 6.38 (d, J = 7.9 Hz, 1H), 6.88 (m, 1H), 6.90 (m,
2H), 7.35 (m, 6H), 7.41 (m, 4H); HPLC (AS-H, elute:
hexanes/i-PrOH = 94/6, detector: 254 nm, flow rate
1.0 mL/min), (S) t1 = 5.2 min, (R) t2 = 11.9 min.
4.2.6. 2,6-Dimethyl-1,2,3,4-tetrahydroquinoline 2f. (Known
RT
compound, see Ref. 4). 87% ee, ½aꢀD ¼ ꢁ65:3 (c 0.62,
1
CHCl3); H NMR (400 MHz, CDCl3) 1.20 (d, J = 6.2 Hz,
3H), 1.58 (m, 2H), 1.92 (m, 1H), 2.20 (s, 3), 2.70 (m, 1),
2.78 (m, 1), 3.35 (m, 1H), 3.56 (br, 1H), 6.41 (d,
J = 7.8 Hz, 1H), 6.78 (m, 2H); HPLC (OJ-H, elute:
hexanes/i-PrOH = 95/5, detector: 254 nm, flow rate:
1.0 mL/min), (S) t1 = 13.1 min, (R) t2 = 16.3 min.
Acknowledgment
We are grateful for the financial support from the National
Science Foundation of China (20302005).
4.2.7. 6-Methoxy-2-methyl-1,2,3,4-tetrahydroquinoline 2g.
RT
(Known compound, see Ref. 4). 81% ee, ½aꢀD ¼ ꢁ63:5 (c
0.36, CHCl3); 1H NMR (400 MHz, CDCl3) 1.21 (t,
J = 6.2 Hz, 3H), 1.57 (m, 1H), 1.93 (m, 1H), 2.73 (m,
1H), 2.83 (m, 1H), 3.33 (m, 1H), 3.73 (s, 3H), 6.46 (d,
J = 8.3 Hz, 1H), 6.60 (m, 2H); HPLC (OJ-H, elute: hex-
anes/i-PrOH = 90/10, detector: 254 nm, flow rate:
1.0 mL/min), (S) t1 = 14.7 min, (R) t2 = 17.8 min.
References
1. (a) Yang, J. W.; Hechavarria Fonseca, M. T.; List, B. J. Am.
Chem. Soc. 2005, 127, 15036–15037; (b) Huang, Y.; Walji, A.
M.; Larsen, C. H.; MacMillan, D. W. C. J. Am. Chem. Soc.
2005, 127, 15051–15053; (c) Ouellet, S. G.; Tuttle, J. B.;
MacMillan, D. W. C. J. Am. Chem. Soc. 2005, 127, 32–33; (d)
Yang, J. W.; Hechavarria Fonseca, M. T.; Vignola, N.; List, B.
Angew. Chem., Int. Ed. 2005, 44, 108–110; (e) Tuttle, J. B.;
Ouellet, S. G.; MacMillan, D. W. C. J. Am. Chem. Soc. 2006,
128, 12622–12623; (f) Mayer, S.; List, B. Angew. Chem, Int. Ed.
2006, 45, 4193–4195; (g) Martin, N. J. A.; List, B. J. Am.
Chem. Soc. 2006, 128, 13368–13369; (h) Hoffmann, S.; Seayad,
A. M.; List, B. Angew. Chem., Int. Ed. 2005, 44, 7424–7427; (i)
Rueping, M.; Sugiono, E.; Azap, C.; Theissmann, T.; Bolte,
M. Org. Lett. 2005, 7, 3781–3783; (j) Hoffmann, S.; Nicoletti,
M.; List, B. J. Am. Chem. Soc. 2006, 128, 13074–13075.
2. Yang, J. W.; List, B. Org. Lett. 2006, 8, 5653–5655.
4.2.8. 2-Phenethyl-1,2,3,4-tetrahydroquinoline 2h. (Known
RT
compound, see Ref. 4). 87% ee, ½aꢀD ¼ ꢁ67:2 (c 1.14,
1
CHCl3); H NMR (400 MHz, CDCl3) 1.68 (m, 1H), 1.83
(m, 2H), 1.98 (m, 1H), 2.78 (m, 4H), 3.29 (m, 1H), 3.74
(br, 1H), 6.45 (d, J = 7.4 Hz, 1H), 6.60 (t, J = 7.3 Hz,
1H), 6.95 (m, 2H), 7.21 (m, 3H), 7.30 (m, 2H); HPLC
(AS-H, elute: hexanes/i-PrOH = 94/6, detector: 254 nm,
flow rate 0.8 mL/min), (S) t1 = 6.4 min, (R) t2 = 7.0 min.
4.2.9. 2-(30,40-Methylenedioxyphenethyl)-1,2,3,4-tetrahydro-
quinoline 2i. (Known compound, see Ref. 4). 87% ee,
RT
½aꢀD ¼ ꢁ50:0 (c 1.19, CHCl3); 1H NMR (400 MHz,
3. (a) Rueping, M.; Antonchick, A. P.; Theissmann, T. Angew.
Chem., Int. Ed. 2006, 45, 3683–3686; (b) Rueping, M.;
Theissmann, T.; Antonchick, A. P. Synlett 2006, 7, 1071–1074.
CDCl3) 1.21 (m, 1H), 1.66 (m, 1H), 1.76 (m, 2H), 1.98
(m, 1H), 2.65 (m, 2H), 2.78 (m, 2H), 3.27 (m, 1H), 3.75

D.-W. Wang et al. / Tetrahedron: Asymmetry 18 (2007) 1103–1107
1107
4. For our recent work on asymmetric hydrogenation of quin-
olines and isoquinolines, see: (a) Wang, W.-B.; Lu, S.-M.;
Yang, P.-Y.; Han, X.-W.; Zhou, Y.-G. J. Am. Chem. Soc.
2003, 125, 10536–10537; (b) Lu, S.-M.; Han, X.-W.; Zhou,
Y.-G. Adv. Synth. Catal. 2004, 346, 909–912; (c) Lu, S.-M.;
Wang, Y.-Q.; Han, X.-W.; Zhou, Y.-G. Angew. Chem., Int.
Ed. 2006, 45, 2260–2263; (d) Zhao, Y.-J.; Wang, Y.-Q.; Zhou,
Y.-G. Chin. J. Catal. 2005, 26, 737–739; For other group’s
work on asymmetric hydrogenation of quinolines, see: (e) Xu,
L. J.; Lam, K. H.; Ji, J. X.; Fan, Q-H.; Lo, W.-H.; Chan, A. S.
C. Chem. Commun. 2005, 1390–1392; (f) Lam, K. H.; Xu, L. J.;
Feng, L. C.; Fan, Q. H.; Lam, F. L.; Lo, W.-H.; Chan, A. S. C.
Adv. Synth. Catal. 2005, 347, 1755–1758; (g) Yamagata, T.;
Tadaoka, H.; Nagata, M.; Hirao, T.; Kataoka, Y.; Ratovelo-
manana-Vidal, V.; Genet, J. P.; Mashima, K. Organometallics
2006, 25, 2505–2513; (h) Reetz, M. T.; Li, X. G. Chem.
Commun. 2006, 2159–2160; (i) Wu, J.; Chan, A. S. C. Acc.
Chem. Res. 2006, 39, 711–720; (j) Tang, W.-J.; Zhu, S.-F.; Xu,
L.-J.; Zhou, Q.-L.; Fan, Q.-H.; Zhou, H.-F.; Lam, K.; Chan,
A. S. C. Chem. Commun. 2007, 613–615; (k) 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,
5955–5965; (l) Wang, Z.-J.; Deng, G.-J.; Li, Y.; He, Y.-M.;
Tang, W.-J.; Fan, Q.-H. Org. Lett. 2007, 9, 1243–1246.
Karube, D.; Ito, Y. J. Am. Chem. Soc. 2000, 122, 7614–7615;
(b) Kuwano, R.; Kaneda, K.; Ito, T.; Sato, K.; Kurokawa, T.;
Ito, Y. Org. Lett. 2004, 6, 2213–2215; (c) Kuwano, R.;
Kashiwabara, M. Org. Lett. 2006, 8, 2653–2655; (d) Kuwano,
R.; Kashiwabara, M.; Sato, K.; Ito, T.; Kaneda, K.; Ito, Y.
Tetrahedron: Asymmetry 2006, 17, 521–535; For the asymmet-
ric hydrogenation of quinoxalines: (e) Bianchini, C.; Barbaro,
P.; Scapacci, G.; Farnetti, E.; Graziani, M. Organometallics
1998, 17, 3308–3310; (f) Henschke, J. P.; Burk, M. J.; Malan,
C. G.; Herzberg, D.; Peterson, J. A.; Wildsmith, A. J.; Cobley,
C. J.; Casy, G. Adv. Synth. Catal. 2003, 345, 300–307; For the
asymmetric hydrogenation of pyridine derivatives: (g) Glorius,
F.; Spielkamp, N.; Holle, S.; Goddard, R.; Lehmann, C. W.
Angew. Chem., Int. Ed. 2004, 43, 2850–2852; (h) Legault, C.
Y.; Charette, A. B. J. Am. Chem. Soc. 2005, 127, 8966–8967; (i)
Lei, A.-W.; Chen, M.; He, M.-S.; Zhang, X.-M. Eur. J. Org.
Chem. 2006, 4343–4347; (j) Studer, M.; Wedemeyer-Exl, C.;
Spindler, F.; Blaser, H.-U. Monatsh. Chem. 2000, 131, 1335–
1343; (k) Blaser, H.-U.; Honig, H.; Studer, M.; Wedemeyer-
Exl, C. J. Mol. Catal. A: Chem. 1999, 139, 253–257; (l)
Raynor, S. A.; Thomas, J. M.; Raja, R.; Johnson, B. F. G.;
Bell, R. G.; Mantle, M. D. Chem. Commun. 2000, 1925–1926;
For the asymmetric hydrogenation of furans: (m) Kaiser, S.;
Smidt, S. P.; Pfaltz, A. Angew. Chem., Int. Ed. 2006, 45, 5194–
5197; (n) Feiertag, P.; Albert, M.; Nettekoven, U.; Spindler, F.
Org. Lett. 2006, 8, 4133–4135.
5. For recent reviews on hydrogenation of aromatic compounds,
see: (a) Glorius, F. Org. Biomol. Chem 2005, 3, 4171–4175; (b)
Lu, S.-M.; Han, X.-W.; Zhou, Y.-G. Chin. J. Org. Chem. 2005,
25, 634–640; (c) Dyson, P. J. Dalton Trans. 2003, 2964–2974.
6. For some examples on asymmetric hydrogenation of indole
derivatives, see: (a) Kuwano, R.; Sato, K.; Kurokawa, T.;
7. Yang, P.-Y.; Zhou, Y.-G. Tetrahedron: Asymmetry 2004, 15,
1145–1149.
8. Lu, S.-M.; Wang, Y.-Q.; Han, X.-W.; Zhou, Y.-G. Chin. J.
Catal. 2005, 26, 287–290.