Synthesis of electronically deficient atropisomeric bisphosphine ligands and their application in asymmetric hydrogenation of quinolines

Article abstract of DOI:10.1055/s-0030-1260129

A series of electronically deficient atropisomeric bisphosphine ligands have been synthesized from (S)-MeO-BiPhep. The introduction of electron-withdrawing groups in the ligands had a dramatic influence on both the enantioselectivity and the activity of catalyst. The iridium complex of the MeO-BiPhep-based ligand bearing a trifluoromethanesulfonyl group was successfully applied in the asymmetric hydrogenation of quinolines with ee values of up to 95% and turnover numbers (TON) of up to 14,600. Georg Thieme Verlag Stuttgart, New York.

Full text of DOI:10.1055/s-0030-1260129

2796
PAPER
Synthesis of Electronically Deficient Atropisomeric Bisphosphine Ligands and
Their Application in Asymmetric Hydrogenation of Quinolines
E
lectron-Deficient
e
A
tropisom
-
e
ric Bisp
Y
hosphine
L
igandsang Zhang,a,b Duo-Sheng Wang,b Min-Can Wang,*a Chang-Bin Yu,b Kai Gao,b Yong-Gui Zhou*b
a
Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052, P. R. of China
Fax +86(371)67769024; E-mail: wangmincan@zzu.edu.cn
b
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road,
Dalian 116023, P. R. of China
Fax +86(411)84379220; E-mail: ygzhou@dicp.ac.cn
Received 9 May 2011; revised 2 June 2011
chiral BINAP derivatives and applied them in the iridium-
catalyzed asymmetric hydrogenation of quinolines, how-
ever, the enantioselectivity and activity were unsatisfacto-
ry.10 Recently, Xu et al. found that air-stable, electroni-
Abstract: A series of electronically deficient atropisomeric bisphos-
phine ligands have been synthesized from (S)-MeO-BiPhep. The
introduction of electron-withdrawing groups in the ligands had a
dramatic influence on both the enantioselectivity and the activity of
catalyst. The iridium complex of the MeO-BiPhep-based ligand cally deficient P-Phos and DifluorPhos showed high ac-
bearing a trifluoromethanesulfonyl group was successfully applied
tivity in the hydrogenation of quinolines with TON up to
43,000.11
in the asymmetric hydrogenation of quinolines with ee values of up
to 95% and turnover numbers (TON) of up to 14,600.
Encouraged by the above results, we envisioned that the
catalytic activity might be improved by introducing elec-
tron-withdrawing substituents to the backbone of atrop-
isomeric bisphosphine ligands. Commercially available
Key words: iridium, asymmetric hydrogenation, electron-deficient
ligands, quinolines
MeO-BiPhep (L1) was thought to be a suitable candidate
The direct asymmetric hydrogenation of quinoline deriv-
because of its readily modifiable substituents at the 6- and
atives provides a convenient route to chiral tetrahydro-
6¢-positions of the biaryl backbone. Hence, this compound
quinolines, which are useful intermediates and building
was chosen as the starting material to synthesize electron-
blocks for the construction of a variety of alkaloids and
ically deficient atropisomeric bisphosphine ligands
biologically active compounds.1 Since our group’s pio-
(Scheme 1).
neering work on the asymmetric hydrogenation of quino-
lines using the iridium/bisphosphine/iodine catalyst
system with high enantioselectivities and yields,2 exciting
advances have been achieved in this field.3–7 Most effort
MeO
MeO
PPh2
PPh2
RO
RO
PPh2
PPh2
has focused on developing effective ligands for higher
enantioselectivity and catalytic activity, especially the lat-
ter. Thus far, several bisphosphine ligands with high cata-
lytic activity have been developed with the iridium-
catalyzed system. Fan and co-workers employed BINAP-
cored dendrimers as ligands in iridium-catalyzed asym-
metric hydrogenation of quinolines with turnover num-
bers (TON) up to 43,000.8 The authors proposed that the
formation of inactive species was reduced by the encapsu-
lation of the iridium complex into a dendrimer framework
and, thus, the activity of the catalyst was enhanced. Very
recently, our group also found that the introduction of
bulky groups on the coordination phosphorous atoms of
P,P- and P,N-ligands could improve the catalytic activity
with a substrate-to-catalyst (S/C) ratio of up to 25,000 and
ee values up to 93%.9 For the above work, the steric hin-
drance of the matrix ligands were modified to improve
their activities. Furthermore, the electronic properties of
the ligands were also investigated. In 2007, Lemaire and
co-workers synthesized several electronically enriched
(S)-MeO-BiPhep L1
R = electron-withdrawing
group
low activity and ee
high activity and ee
Scheme 1 Design of electronically deficient bisphosphine ligands
These ligands were easily obtained through condensation
of (S)-OH-BiPhep with the corresponding acyl chloride or
PhNTf2 (Scheme 2) with 45–89% yields.12
method A or B
HO
HO
PPh2
PPh2
RO
RO
PPh2
PPh2
45–89%
(S)-L2a–e and L3
L2a R = CyCO
L2b R = PhCO
L2c R = 4-MeOC6H4CO
L2d R = 3,5-CF3C6H3CO
L2e R = C6F5CO
L3 R = Tf
SYNTHESIS 2011, No. 17, pp 2796–2802
Advanced online publication: 21.07.2011
DOI: 10.1055/s-0030-1260129; Art ID: H48111SS
x
x.
x
x
.
2
0
1
1
Scheme 2 Synthesis of bisphosphine ligands. Reagents and condi-
tions: Method A (for L2a–e): acyl chloride, t-BuOK, CH2Cl2; Method
B (for L3): NaH, PhNTf2, THF.
© Georg Thieme Verlag Stuttgart · New York

PAPER
Electron-Deficient Atropisomeric Bisphosphine Ligands
2797
With these electronically deficient ligands in hand, iridi- those achieved with tetrahydrofuran, but gave lower
um-catalyzed asymmetric hydrogenation of quinolines yields (entries 2 and 3). The use of dichloromethane and
was investigated. Initially, 2-methylquinoline was chosen 2-propanol resulted in much lower yields and enantiose-
as a model substrate and the catalysts were prepared in lectivities (entries 4 and 5). Slightly lower yield and enan-
situ from [Ir(cod)Cl]2 and the ligands in tetrahydrofuran. tioselectivity were obtained in ethyl acetate (entry 6).
The hydrogenation reaction was run on a S/C molar ratio Ethereal solvents were more effective than other solvents
of 1000, with molecular iodine (0.5 mol%) as additive; the (entries 1 and 7), and the highest enantioselectivity was
results are summarized in Table 1. After 22 hours, full obtained in tetrahydrofuran (entry 1; 95%). Thus, tetrahy-
conversions were obtained for all ligands. The lowest ee drofuran was the best choice in terms of both yield and
value was obtained (entry 1; 78%) for the matrix ligand enantioselectivity.
MeO-BiPhep (L1), which was also lower than that ob-
It was noticed that the catalytic performance was also re-
tained with a catalyst loading of 100 (78 vs 94% ee).2
lated to the amount of additive iodine. In the absence of
Gratifyingly, the enantioselectivity was enhanced dramat-
iodine, very low yield and enantioselectivity were ob-
ically with the introduction of electron-withdrawing ester
served (entry 11). Increasing the amount of iodine to 1
groups on the ligand (entries 2–7). For the commercially
mol%, or decreasing the amount to 0.25 mol% had no ob-
available ligand L2a, with a cyclohexanecarbonyl instead
vious effect on either the yield or enantioselectivity (en-
of a methyl group, 86% ee was obtained (entry 2). When
tries 8 and 9), but the ee value decreased significantly with
more electron-withdrawing aroyl groups were introduced,
0.125 mol% iodine (entry 10). Either reducing the pres-
the enantioselectivities were further increased (entries 3–
sure or increasing the temperature gave full conversions
6; 89–91% ee). It is noteworthy that the highest enantiose-
but slightly lower enantioselectivities (entries 12 and 13).
lectivity was achieved for L3, with an electron-withdraw-
Thus, the optimized reaction conditions were:
[Ir(cod)Cl]2, L3, and iodine (0.5 mol%) in tetrahydrofuran
under a hydrogen atmosphere (700 psi) at room tempera-
ing trifluoromethanesulfonyl group (entry 7; 95% ee),
which was consistent with our initial expectation. Based
on the above results, it was clear that the ligands with elec-
ture.
tronically deficient substituents showed excellent perfor-
mance in iridium-catalyzed asymmetric hydrogenation of
2-methylquinoline, with high enantioselectivity and activ-
ity being achieved.
Table 2 Optimization of Reaction Conditionsa
[Ir(cod)Cl]2/L3, I2
Table 1 Asymmetric Hydrogenation of 2-Methylquinolinea
solvent, H2, 22 h
N
N
H
[Ir(cod)Cl]2/L*, I2, THF
2 (700 psi), r.t., 22 h
1a
2a
H
N
N
Entry
Solvent
THF
I2 (mol%)
0.5
Yield (%)b ee (%)c
H
1a
2a
1
2
99
19
46
10
15
91
98
98
98
97
19
99
99
95 (S)
94 (S)
93 (S)
71 (S)
41 (S)
90 (S)
94 (S)
95 (S)
94 (S)
91 (S)
6 (S)
Entry
Ligand
L1
Yield (%)b
ee (%)c
78 (S)
86 (S)
90 (S)
91 (S)
89 (S)
91 (S)
95 (S)
toluene
benzene
CH2Cl2
i-PrOH
EtOAc
dioxane
THF
0.5
1
2
3
4
5
6
7
98
98
99
98
98
98
99
3
0.5
L2a
L2b
L2c
L2d
L2e
L3
4
0.5
5
0.5
6
0.5
7
0.5
8
1.0
9
THF
0.25
0.125
–
a Reaction conditions: 1a (1 mmol), [Ir(cod)Cl]2 (0.0005 mmol),
ligand (0.0011 mmol), I2 (0.0050 mmol), THF (2 mL), r.t., 22 h.
b Isolated yield.
10
11
12d
13e
THF
THF
c Determined by HPLC analysis.
THF
0.5
94 (S)
93 (S)
With these promising results in hand, the effect of solvent,
amount of iodine, hydrogen pressure, and temperature on
the activity and enantioselectivity was further studied us-
ing iridium complexes of L3 as the catalyst; the results are
summarized in Table 2. Solvent screening trials indicated
that the reaction was strongly solvent-dependent. The use
of toluene and benzene gave similar enantioselectivities to
THF
0.5
a Reaction conditions: 1a (1 mmol), [Ir(cod)Cl]2 (0.0005 mmol), L3
(0.0011 mmol), H2 (700 psi), solvent (2 mL), r.t., 22 h.
b Isolated yield.
c Determined by HPLC analysis.
d H2 (300 psi), r.t.
e H2 (700 psi), 50 °C.
Synthesis 2011, No. 17, 2796–2802 © Thieme Stuttgart · New York

2798
D.-Y. Zhang et al.
PAPER
Table 4 Effect of S/C Ratio on the Conversion and Enantioselectiv-
Having established the optimal conditions, a variety of 2-
substituted quinoline derivatives were tested to explore
the scope of the reaction. As summarized in Table 3, sev-
eral 2-alkyl substituted quinolines were hydrogenated
with high yields and excellent enantioselectivities, regard-
less of the length of side chain (entries 1–5; >93% ee). Re-
markably, the carbon–carbon double bond in the side
chain of the substrate was also hydrogenated (entry 4).
Slightly lower enantioselectivity was obtained with hy-
droxyl groups on the side chain (entry 6). It was noted that
excellent yields and good enantioselectivities were also
observed for 2-arylethyl substituted quinolines (entries 7
itya
[Ir(cod)Cl]2/L3, I2, THF
H
2 (700 psi), r.t., 22 h
N
N
H
1a
2a
S/C
1000
>95
95
5000d
>95
95
10000d,e
20000d,e
73
Conv. (%)b
Ee (%)c
>95
95
95
a Reaction conditions: 1a (1 mmol), [Ir(cod)Cl]2/L3 (0.5/1.1), I2
and 8). For substrates possessing a substituent on the 6- (0.0050 mmol), H2 (700 psi), THF (2 mL), r.t., 22 h.
b Determined by 1H NMR analysis.
position, the yields were also excellent, but slightly lower
enantioselectivities were observed (entries 9 and 10).
c Determined by HPLC analysis.
d I2 (0.0100 mmol) was used.
Moreover, it was found that the presence of an electron-
withdrawing group at the 6-position of the substrate gave
better results than those with an electron-donating substit-
uent (92 versus 87% ee). The yield was also excellent with
2-aryl-substituted quinoline, but the enantioselectivity
was only moderate (entry 11).
e Reaction time: 36 h.
It was notable that the enantioselectivity remained un-
changed (95% ee) when the S/C ratio was increased.
When the S/C ratio was raised to 5000:1, the reaction pro-
ceeded smoothly with complete conversion. When the S/
C ratio was increased to 10000:1, prolonging the reaction
time could facilitate the reaction to full conversion. How-
ever, when the S/C ratio was increased to 20000:1, the
conversion decreased to 73%.
Table 3 Asymmetric Hydrogenation of Quinoline Derivativesa
R1
R1
[Ir(cod)Cl]2/L3, I2, THF
2 (700 psi), r.t., 22 h
H
N
R2
N
R2
H
In conclusion, a series of electronically deficient atropiso-
meric bisphosphine ligands were conveniently synthe-
sized and successfully applied in the asymmetric
hydrogenation of quinoline derivatives; up to 95% ee was
obtained and TON reached 14,600. More importantly, we
have shown that the introduction of electron-withdrawing
groups to (S)-MeO-BiPhep had a dramatic effect on the
enantioselectivity and the activity of catalyst. Our future
work will focus on designing other ligands and extending
the catalytic system to other hydrogenation reactions.
1
2
Entry R1
R2
Product Yield ee
(%)b (%)c
1
2
H
H
H
H
H
H
H
H
Me
F
Me
Et
2a
2b
2c
2d
2e
2f
99
93
97
95
98
99
99
96
96
97
95
95 (S)
95 (S)
94 (S)
94 (S)
94 (S)
87 (R)
93 (S)
93 (S)
87 (S)
92 (S)
60 (R)
3
n-Pr
4
3-butenyl
5
n-pentyl
All reactions were performed under N2 in dried flasks using Schlenk
techniques. Commercially available reagents were used without
further purification. Solvents were dried and distilled under N2 be-
fore use. 1H, 13C and 31P NMR spectra were recorded at r.t. in CDCl3
with a 400 MHz Bruker DRX-400 spectrometer. Enantiomeric ex-
cesses were determined by HPLC analysis with an Agilent 1100 in-
strument fitted with a chiral column as described below. Optical
rotations were measured with a JASCO P-1010 polarimeter. All re-
actions were monitored by TLC analysis. Flash column chromatog-
raphy was performed on either silica gel (particle size 200–300
mesh) or Al2O3 gel (particle size 200–300 mesh).
6
Me2C(OH)CH2-
7
3,4-(MeO)2C6H3(CH2)2-
2g
8
3-BnO-4-MeOC6H3(CH2)2- 2h
9
Me
Me
Ph
2i
10
11
2j
2k
H
a Reaction conditions: 1 (1 mmol), [Ir(cod)Cl]2 (0.0005 mmol), L3
(0.0011 mmol), I2 (0.0050 mmol), H2 (700 psi), THF (2 mL), r.t., 22 h.
b Isolated yield.
Bisphosphine Ligands (S)-L2a–e; General Procedure A12a
Under an N2 atmosphere, to a solution of (S)-OH-BiPhep4f (1.0
equiv) in anhydrous CH2Cl2 (10 mL), was added t-BuOK (2.4
equiv) and the mixture was stirred at r.t. for 30 min. Acyl chloride
a–e (2.4 equiv) was added and the solution was stirred at r.t. for an
additional 2 h. Degassed H2O (10 mL) was added, the organic layer
separated, and the aqueous layer was extracted with CH2Cl2 (3 × 10
mL). The combined organic layers were washed with brine (10
mL), dried over anhydrous Na2SO4 and concentrated under reduced
pressure. The crude product was purified by either recrystallization
or column chromatography.
c Determined by HPLC analysis.
To further evaluate the catalytic efficiency of the
[Ir(cod)Cl]2, L3, and iodine system in asymmetric hydro-
genation, the effect of the S/C molar ratio on the conver-
sion and enantioselectivity of this reaction was
investigated. 2-Methylquinoline was selected as substrate
and the results are shown in Table 4.
Synthesis 2011, No. 17, 2796–2802 © Thieme Stuttgart · New York

PAPER
Electron-Deficient Atropisomeric Bisphosphine Ligands
2799
(S)-6,6¢-Bis(diphenylphosphino)-1,1¢-biphenyl-2,2¢-diylbis(cy-
clohexanecarboxylate) (L2a)13
13C NMR (101 MHz, CDCl3): d = 161.2, 148.8, 148.7, 141.4, 141.3,
137.9, 137.8, 137.7, 135.2, 135.1, 135.0, 133.9, 133.7, 133.5, 133.0,
132.9, 132.8, 132.5, 132.2, 132.1, 131.8, 131.6, 131.5, 130.3, 129.5,
129.4, 128.6, 128.5, 128.4, 126.7, 126.6, 124.3, 122.4, 121.6.
31P NMR (162 MHz, CDCl3): d = –15.00 (s).
HRMS: m/z [M + Na]+ calcd for C54H32F12O4P2Na: 1057.1482;
Obtained following General Procedure A, with (S)-OH-BiPhep (83
mg, 0.15 mmol), t-BuOK (40 mg, 0.36 mmol), and cyclohexanecar-
bonyl chloride a (53 mg, 0.36 mmol). The crude product was puri-
fied by column chromatography on silica gel (PE–EtOAc,
30:1→25:1) to give compound L2a.
found: 1057.1479.
Yield: 67 mg (58%); white solid; mp 234–235 °C; Rf = 0.82 (PE–
EtOAc, 5:1); [a]D23 –92.2 (c 0.67, CHCl3).
(S)-6,6¢-Bis(diphenylphosphino)-1,1¢-biphenyl-2,2¢-diyl-
bis(2,3,4,5,6-pentafluorobenzenecarboxylate) (L2e)
Obtained following General Procedure A, with (S)-OH-BiPhep
(110 mg, 0.20 mmol), t-BuOK (54 mg, 0.48 mmol), and 2,3,4,5,6-
pentafluorobenzoyl chloride e (111 mg, 0.48 mmol). The crude
product was purified by column chromatography on silica gel (PE–
EtOAc, 50:1→30:1) to give L2e.
1H NMR (400 MHz, CDCl3): d = 7.42–7.23 (m, 12 H), 7.15–7.23
(m, 6 H), 7.03–7.14 (m, 8 H), 1.77–1.94 (m, 2 H), 1.18–1.69 (m,
10 H), 0.93–1.18 (m, 9 H), 0.74–0.93 (m, 1 H).
(S)-6,6¢-Bis(diphenylphosphino)-1,1¢-biphenyl-2,2¢-diylbis(ben-
zenecarboxylate) (L2b)
Obtained following General Procedure A, with (S)-OH-BiPhep
(110 mg, 0.20 mmol), t-BuOK (54 mg, 0.48 mmol), and benzoyl
chloride b (68 mg, 0.48 mmol). The crude product was purified by
recrystallization (CH2Cl2–n-hexane) to give compound L2b.
Yield: 157 mg (83%); white solid; mp 68–69 °C; Rf = 0.76 (PE–
EtOAc, 5:1); [a]D23 –86.4 (c 0.73, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.44 (t, J = 7.9 Hz, 2 H), 7.19–
7.31 (m, 14 H), 7.12–7.19 (m, 6 H), 7.09 (t, J = 7.4 Hz, 4 H).
Yield: 97 mg (64%); white solid; mp 195–196 °C; Rf = 0.64 (PE–
EtOAc, 5:1); [a]D23 –38.6 (c 0.70, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.41–7.53 (m, 6 H), 7.33–7.40 (m,
4 H), 7.10–7.30 (m, 22 H), 7.03 (t, J = 7.3 Hz, 4 H).
13C NMR (100 MHz, CDCl3): d = 163.9, 149.4, 149.3, 140.4, 138.4,
138.3, 136.2, 136.1, 134.8, 134.7, 134.6, 133.3, 133.2, 133.1, 131.7,
130.3, 129.6, 129.0, 128.9, 128.5, 128.4, 128.2, 128.1, 123.0.
31P NMR (162 MHz, CDCl3): d = –15.28 (s).
13C NMR (100 MHz, CDCl3): d = 156.7, 148.7, 148.6, 146.8, 146.7,
146.6, 144.9, 144.8, 144.7, 144.3, 144.2, 144.0, 142.4, 142.2, 142.0,
141.3, 141.2, 139.0, 138.8, 138.7, 137.7, 137.6, 136.5, 136.3, 136.2,
136.0, 135.9, 135.2, 135.0, 134.9, 134.8, 134.6, 134.3, 134.1, 133.9,
133.2, 133.1, 133.0, 132.8, 129.5, 128.9, 128.5, 128.3, 128.1, 128.0,
122.8.
31P NMR (162 MHz, CDCl3): d = –14.84 (s).
HRMS: m/z [M + H]+ calcd for C50H26F10O4P2: 943.1225; found:
HRMS: m/z [M + Na]+ calcd for C50H36O4P2Na: 785.1987; found:
943.1248.
785.1988.
(S)-6,6¢-Bis(diphenylphosphino)-1,1¢-biphenyl-2,2¢-diylbis(tri-
fluoromethylsulfonate) (L3)12b
(S)-6,6¢-Bis(diphenylphosphino)-1,1¢-biphenyl-2,2¢-diylbis(4-
methoxybenzenecarboxylate) (L2c)
To a suspension of NaH (60% in mineral oil, 10 mg, 0.24 mmol) in
THF (7 mL) under argon, was carefully added a solution of (S)-OH-
BiPhep (55 mg, 0.10 mmol) in THF (8 mL) at 0 °C, and the result-
ing mixture was stirred at r.t. for 30 min. After cooling to 0 °C,
PhNTf2 (86 mg, 0.24 mmol) was added and the mixture was stirred
at r.t. for an additional 2 h. The mixture was cooled to 0 °C and de-
gassed H2O (10 mL) was added. The resulting mixture was diluted
with CH2Cl2 (40 mL) and the organic layer was washed with de-
gassed H2O (10 mL) and brine (10 mL), dried over anhydrous
Na2SO4 and concentrated under reduced pressure. The crude prod-
uct was purified by column chromatography on silica gel (PE–
EtOAc, 20:1→10:1) to give L3.
Obtained following General Procedure A, with (S)-OH-BiPhep
(110 mg, 0.20 mmol) and t-BuOK (54 mg, 0.48 mmol), and 4-meth-
oxybenzoyl chloride c (82 mg, 0.48 mmol). The crude product was
purified by column chromatography on Al2O3 gel (PE–EtOAc,
10:1→5:1) to give L2c.
Yield: 74 mg (45%); white solid; mp 161–162 °C; Rf = 0.36 (PE–
EtOAc, 5:1); [a]D23 –8.0 (c 0.67, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.41 (d, J = 8.8 Hz, 4 H), 7.35 (d,
J = 4.4 Hz, 4 H), 7.15–7.31 (m, 16 H), 7.09–7.15 (m, 2 H), 7.05 (t,
J = 7.4 Hz, 4 H), 6.73 (d, J = 8.9 Hz, 4 H), 3.81 (s, 6 H).
13C NMR (100 MHz, CDCl3): d = 163.6, 149.4, 134.8, 134.7, 134.6,
133.3, 133.2, 133.1, 132.4, 131.5, 128.9, 128.4, 128.1, 123.0, 122.1,
113.5, 55.6.
31P NMR (162 MHz, CDCl3): d = –15.23 (s).
HRMS: m/z [M + Na]+ calcd for C52H40O6P2Na: 845.2198; found:
Yield: 71 mg (87%); white solid; mp 159–160 °C; Rf = 0.70 (PE–
EtOAc, 5:1); [a]D23 +12.2 (c 0.97, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.44 (t, J = 8.0 Hz, 2 H), 7.25–
7.36 (m, 8 H), 7.14–7.25 (m, 12 H), 6.98–7.07 (m, 4 H).
13C NMR (100 MHz, CDCl3): d = 148.7, 148.6, 142.5, 142.4, 136.7,
136.6, 136.5, 135.2, 135.1, 134.7, 134.5, 134.4, 134.3, 134.1, 133.7,
133.5, 133.4, 133.3, 133.1, 132.9, 130.7, 129.4, 128.8, 128.6, 120.6,
119.9, 116.7.
31P NMR (162 MHz, CDCl3): d = –14.47 (s).
HRMS: m/z [M + Na]+ calcd for C38H26F6O6P2S2Na: 841.0448;
845.2175.
(S)-6,6¢-Bis(diphenylphosphino)-1,1¢-biphenyl-2,2¢-diylbis(3,5-
bistrifluoromethylbenzenecarboxylate) (L2d)
Obtained following General Procedure A, with (S)-OH-BiPhep
(110 mg, 0.20 mmol), t-BuOK (54 mg, 0.48 mmol), and 3,5-bis(tri-
fluoromethyl)benzoyl chloride d (133 mg, 0.48 mmol). The crude
product was purified by column chromatography on silica gel (PE–
EtOAc, 50:1→30:1) to give L2d.
found: 841.0454.
Iridium-Catalyzed Asymmetric Hydrogenation of Quinoline
Derivatives: General Procedure B
Yield: 185 mg (89%); white solid; mp 76–77 °C; Rf = 0.82 (PE–
A mixture of [Ir(cod)Cl]2 (1.0 mg, 0.0015 mmol) and L3 (2.7 mg,
0.0033 mmol) in THF (3.0 mL) was stirred at r.t. for 10 min in a
glovebox. I2 (1.3 mg, 0.0050 mmol) and substrate (1.0 mmol) in
THF (1.0 mL) were placed in a stainless steel autoclave and the cat-
alyst solution (1.0 mL) was added by using a syringe. The hydroge-
nation was performed at r.t. under H2 (700 psi) for 22 h. After
EtOAc, 5:1); [a]D23 –11.8 (c 0.70, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.96 (s, 2 H), 7.76 (s, 4 H), 7.37–
7.53 (m, 4 H), 7.24–7.34 (m, 12 H), 7.16–7.23 (m, 4 H), 7.08 (t,
J = 7.4 Hz, 2 H), 6.97 (t, J = 7.5 Hz, 4 H).
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D.-Y. Zhang et al.
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carefully releasing the hydrogen, the reaction mixture was concen-
trated to afford the crude product. Purification was performed by
silica gel column chromatography (PE–EtOAc) to give the pure
product. The enantiomeric excesses were determined by chiral
HPLC with chiral columns (OJ-H, OD-H, or AS-H).
(R)-2-Methyl-1-(1,2,3,4-tetrahydroquinolin-2-yl)propan-2-ol
(2f)2
Yield: 99%; white solid; 87% ee; [a]D23 –52.0 (c 0.70, CHCl3).
1H NMR (400 MHz, CDCl3): d = 6.96 (t, J = 7.7 Hz, 2 H), 6.59 (t,
J = 7.3 Hz, 1 H), 6.49 (d, J = 7.9 Hz, 1 H), 3.51–3.63 (m, 1 H),
2.82–2.95 (m, 1 H), 2.67–2.79 (m, 1 H), 1.80–1.90 (m, 1 H), 1.55–
1.77 (m, 3 H), 1.32 (d, J = 5.2 Hz, 6 H).
13C NMR (100 MHz, CDCl3): d = 144.8, 129.4, 126.9, 121.1, 116.9,
114.6, 72.2, 49.0, 48.6, 33.0, 30.0, 28.0, 26.8.
(S)-2-Methyl-1,2,3,4-tetrahydroquinoline (2a)2
Yield: 99%; yellow oil; 95% ee; [a]D22 –82.8 (c 0.87, CHCl3).
1H NMR (400 MHz, CDCl3): d = 6.95–7.04 (m, 2 H), 6.59–6.70 (m,
1 H), 6.45–6.56 (m, 1 H), 3.68 (br, 1 H), 3.29–3.51 (m, 1 H), 2.82–
2.94 (m, 1 H), 2.70–2.84 (m, 1 H), 1.91–2.01 (t, J = 12.3 Hz, 1 H),
1.54–1.69 (t, J = 21.4 Hz, 1 H), 1.24 (dd, J = 6.2, 3.0 Hz, 3 H).
HPLC (OD-H; n-hexane–i-PrOH, 90:10; 254 nm; 0.8 mL/min):
tR = 8.1 [(S) minor], 9.4 [(R) major] min.
13C NMR (100 MHz, CDCl3): d = 145.0, 129.4, 126.9, 121.3, 117.1,
(S)-2-(3¢,4¢-Dimethoxyphenethyl)-1,2,3,4-tetrahydroquinoline
(2g)2
114.2, 47.3, 30.3, 26.8, 22.8.
HPLC (OJ-H; n-hexane–i-PrOH, 95:5; 254 nm; 0.8 mL/min):
tR = 13.8 [(S) major], 15.4 [(R) minor] min.
Yield: 99%; yellow oil; 93% ee; [a]D23 –75.3 (c 0.73, CHCl3).
1H NMR (400 MHz, CDCl3): d = 6.93–7.02 (m, 2 H), 6.80–6.84 (m,
1 H), 6.73–6.79 (m, 2 H), 6.62 (t, J = 7.3 Hz, 1 H), 6.46 (d,
J = 8.1 Hz, 1 H), 3.89 (s, 3 H), 3.88 (s, 3 H), 3.79 (br, 1 H), 3.29–
3.35 (m, 1 H), 2.74–2.89 (m, 2 H), 2.66–2.74 (m, 2 H), 1.95–2.06
(m, 1 H), 1.77–1.88 (m, 2 H), 1.61–1.76 (m, 1 H).
13C NMR (100 MHz, CDCl3): d = 149.1, 147.4, 144.7, 134.6, 129.4,
126.9, 121.5, 120.3, 117.2, 114.3, 111.8, 111.4, 56.1, 56.0, 51.4,
38.6, 32.0, 28.2, 26.4.
(S)-2-Ethyl-1,2,3,4-tetrahydroquinoline (2b)2
Yield: 93%; yellow oil; 95% ee; [a]D23 –83.1 (c 1.00, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.00 (t, J = 7.2 Hz, 2 H), 6.63 (t,
J = 7.3 Hz, 1 H), 6.51 (d, J = 8.0 Hz, 1 H), 3.80 (br, 1 H), 3.13–3.26
(m, 1 H), 2.66–2.96 (m, 2 H), 1.90–2.13 (m, 1 H), 1.47–1.76 (m,
3 H), 1.03 (t, J = 7.4 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 144.9, 129.4, 126.9, 121.6, 117.0,
114.2, 53.2, 29.6, 27.8, 26.6, 10.2.
HPLC (AS-H; n-hexane–i-PrOH, 95:5; 254 nm; 0.8 mL/min):
tR = 14.5 [(R) minor], 15.4 [(S) major] min.
HPLC (OJ-H; n-hexane–i-PrOH, 90:10; 254 nm; 0.8 mL/min):
tR = 9.8 [(S) major], 10.8 [(R) minor] min.
(S)-2-(3¢-Benzyloxy-4¢-methoxyphenethyl)-1,2,3,4-tetrahydro-
quinoline (2h)4b
(S)-2-Propyl-1,2,3,4-tetrahydroquinoline (2c)2
Yield: 96%; yellow oil; 93% ee; [a]D23 –49.2 (c 0.80, CHCl3).
Yield: 97%; yellow oil; 94% ee; [a]D23 –72.6 (c 0.70, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.42–7.47 (m, 2 H), 7.33–7.39 (m,
2 H), 7.27–7.32 (m, 1 H), 6.92–7.00 (m, 2 H), 6.83 (d, J = 8.5 Hz,
1 H), 6.73–6.79 (m, 2 H), 6.60 (t, J = 7.2 Hz, 1 H), 6.44 (d,
J = 7.8 Hz, 1 H), 5.15 (s, 2 H), 3.88 (s, 3 H), 3.71 (br, 1 H), 3.14–
3.28 (m, 1 H), 2.67–2.84 (m, 2 H), 2.60–2.67 (m, 2 H), 1.89–2.00
(m, 1 H), 1.71–1.80 (m, 2 H), 1.53–1.70 (m, 1 H).
13C NMR (100 MHz, CDCl3): d = 148.2, 148.1, 144.6, 137.3, 134.4,
129.3, 128.6, 127.9, 127.4, 126.8, 121.3, 121.0, 117.1, 114.7, 114.2,
112.1, 71.1, 56.2, 51.0, 38.3, 31.7, 28.0, 26.3.
1H NMR (400 MHz, CDCl3): d = 7.00 (t, J = 7.2 Hz, 2 H), 6.63 (t,
J = 7.3 Hz, 1 H), 6.50 (d, J = 8.4 Hz, 1 H), 3.78 (br, 1 H), 3.23–3.33
(m, 1 H), 2.58–2.99 (m, 2 H), 1.94–2.04 (m, 1 H), 1.57–1.70 (m,
1 H), 1.38–1.56 (m, 4 H), 0.89–1.12 (m, 3 H).
13C NMR (100 MHz, CDCl3): d = 144.9, 129.4, 126.9, 121.5, 117.0,
114.2, 51.5, 39.1, 28.3, 26.6, 19.1, 14.4.
HPLC (OJ-H; n-hexane–i-PrOH, 90:10; 254 nm; 0.8 mL/min):
tR = 9.1 [(S) major], 11.2 [(R) minor] min.
HPLC (AS-H; n-hexane–i-PrOH, 97:3; 254 nm; 0.5 mL/min):
tR = 30.1 [(R) minor], 32.2 [(S) major] min.
(S)-2-Butyl-1,2,3,4-tetrahydroquinoline (2d)2
Yield: 95%; yellow oil; 94% ee; [a]D22 –82.8 (c 1.07, CHCl3).
(S)-2,6-Dimethyl-1,2,3,4-tetrahydroquinoline (2i)2
1H NMR (400 MHz, CDCl3): d = 6.97 (t, J = 7.3 Hz, 2 H), 6.61 (t,
J = 7.3 Hz, 1 H), 6.49 (d, J = 8.2 Hz, 1 H), 3.78 (br, 1 H), 3.12–3.43
(m, 1 H), 2.61–2.99 (m, 2 H), 1.88–2.12 (m, 1 H), 1.56–1.68 (m,
1 H), 1.46–1.55 (m, 2 H), 1.26–1.45 (m, 4 H), 0.92–0.99 (m, 3 H).
13C NMR (100 MHz, CDCl3): d = 144.9, 129.4, 126.9, 121.6, 117.1,
114.2, 51.8, 36.6, 28.3, 28.1, 26.6, 23.0, 14.3.
Yield: 96%; yellow solid; 87% ee; [a]D22 –68.1 (c 0.73, CHCl3).
1H NMR (400 MHz, CDCl3): d = 6.79–6.81 (m, 2 H), 6.43 (d,
J = 7.9 Hz, 1 H), 3.58 (br, 1 H), 3.32–3.43 (m, 1 H), 2.78–2.90 (m,
1 H), 2.66–2.76 (m, 1 H), 2.23 (s, 3 H), 1.88–1.98 (m, 1 H), 1.53–
1.66 (m, 1 H), 1.22 (d, J = 6.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 142.6, 130.0, 127.4, 126.4, 121.4,
114.4, 47.5, 30.5, 26.8, 22.8, 20.6.
HPLC (OJ-H; n-hexane–i-PrOH, 90:10; 254 nm; 0.8 mL/min):
tR = 8.1 [(S) major], 9.3 [(R) minor] min.
HPLC (OJ-H; n-hexane–i-PrOH, 90:10; 254 nm; 0.8 mL/min):
tR = 13.5 [(S) major], 16.7 [(R) minor] min.
(S)-2-Pentyl-1,2,3,4-tetrahydroquinoline (2e)2
Yield: 98%; yellow oil; 94% ee; [a]D23 –75.1 (c 0.73, CHCl3).
(S)-6-Fluoro-2-methyl-1,2,3,4-tetrahydroquinoline (2j)2
Yield: 97%; yellow solid; 92% ee; [a]D23 –80.7 (c 0.73, CHCl3).
1H NMR (400 MHz, CDCl3): d = 6.65–6.72 (m, 2 H), 6.36–6.44 (m,
1 H), 3.57 (br, 1 H), 3.30–3.40 (m, 1 H), 2.77–2.90 (m, 1 H), 2.66–
2.75 (m, 1 H), 1.89–1.97 (m, 1 H), 1.51–1.63 (m, 1 H), 1.21 (d,
J = 6.3 Hz, 3 H).
1H NMR (400 MHz, CDCl3): d = 7.00 (t, J = 7.5 Hz, 2 H), 6.65 (t,
J = 7.4 Hz, 1 H), 6.57 (d, J = 7.8 Hz, 1 H), 4.26 (br, 1 H), 3.23–3.33
(m, 1 H), 2.71–2.89 (m, 2 H), 1.90–2.05 (m, 1 H), 1.24–1.72 (m,
9 H), 0.94 (t, J = 6.7 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 144.2, 129.5, 126.9, 122.0, 117.7,
114.7, 52.0, 36.6, 32.1, 28.1, 26.5, 25.6, 22.8, 14.3.
13C NMR (100 MHz, CDCl3): d = 156.8, 154.5, 141.2, 122.7, 122.6,
115.7, 115.5, 114.9, 114.8, 113.4, 113.2, 47.5, 30.1, 26.9, 22.7.
HPLC (OJ-H; n-hexane–i-PrOH, 90:10; 254 nm; 0.8 mL/min):
tR = 7.4 [(S) major], 8.0 [(R) minor] min.
HPLC (OD-H; n-hexane–i-PrOH, 95:5; 254 nm; 0.8 mL/min):
tR = 6.8 [(R) minor], 8.1 [(S) major] min.
Synthesis 2011, No. 17, 2796–2802 © Thieme Stuttgart · New York

PAPER
Electron-Deficient Atropisomeric Bisphosphine Ligands
2801
(R)-2-Phenyl-1,2,3,4-tetrahydroquinoline (2k)6a
Vidal, V.; Genet, J. P.; Mashima, K. Organometallics 2006,
25, 2505. (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) Deport, C.; Buchotte, M.; Abecassis, K.; Tadaoka, H.;
Ayad, T.; Ohshima, T.; Genet, J.-P.; Mashima, K.;
Yield: 95%; yellow solid; 60% ee; [a]D23 +19.1 (c 1.00, CHCl3).
1H NMR (400 MHz, CDCl3): d = 7.28–7.49 (m, 5 H), 6.97–7.10 (m,
2 H), 6.69 (t, J = 7.3 Hz, 1 H), 6.57 (d, J = 7.9 Hz, 1 H), 4.47 (dd,
J = 9.3, 2.9 Hz, 1 H), 4.06 (br, 1 H), 2.89–3.02 (m, 1 H), 2.71–2.84
(m, 1 H), 2.10–2.22 (m, 1 H), 1.96–2.09 (m, 1 H).
Ratovelomanana-Vidal, V. Synlett 2007, 2743. (k) Li,
Z.-W.; Wang, T.-L.; He, Y.-M.; Wang, Z.-J.; Fan, Q.-H.;
Pan, J.; Xu, L.-J. Org. Lett. 2008, 10, 5265. (l) Zhou, H.-F.;
Li, Z.-W.; Wang, Z.-J.; Wang, T.-L.; Xu, L.-J.; He, Y.-M.;
Fan, Q.-H.; Pan, J.; Gu, L.-Q.; Chan, A. S. C. Angew. Chem.
Int. Ed. 2008, 47, 8464. (m) Lu, S.-M.; Bolm, C. Adv. Synth.
Catal. 2008, 350, 1101. (n) Mršić, N.; Lefort, L.; Boogers, J.
A. F.; Minnaard, A. J.; Feringa, B. L.; de Vries, J. G. Adv.
Synth. Catal. 2008, 350, 1081. (o) Eggenstein, M.; Thomas,
A.; Theuerkauf, J.; Franciò, G.; Leitner, W. Adv. Synth.
Catal. 2009, 351, 725. (p) Wang, C.; Li, C.-Q.; Wu, X.-F.;
Pettman, A.; Xiao, J.-L. Angew. Chem. Int. Ed. 2009, 48,
6524. (q) Tadaoka, H.; Cartigny, D.; Nagano, T.; Gosavi, T.;
Ayad, T.; Genet, J.-P.; Ohshima, T.; Ratovelomanana-Vidal,
V.; Mashima, K. Chem. Eur. J. 2009, 15, 9990. (r) Wang,
Z.-J.; Zhou, H.-F.; Wang, T.-L.; He, Y.-M.; Fan, Q.-H.
Green Chem. 2009, 11, 767. (s) Parekh, V.; Ramsden, J. A.;
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2010, 352, 2441.
13C NMR (100 MHz, CDCl3): d = 145.0, 144.9, 129.5, 128.8, 127.6,
127.1, 126.7, 121.0, 117.3, 114.1, 56.4, 31.2, 26.6.
HPLC (AS-H; n-hexane–i-PrOH, 95:5; 254 nm; 0.8 mL/min):
tR = 7.1 [(R) major], 21.5 [(S) minor] min.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals /toc/synthesis.
Acknowledgment
We are grateful for financial support from the National Science
Foundation of China (21032003 & 20921092), the National Basic
Research Program (2010CB833300) and the Chinese Academy of
Sciences.
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