Asymmetric hydrogenation and allylic substitution reaction with novel chiral pinene-derived N,P-ligands

Article abstract of DOI:10.1016/j.tetasy.2009.05.020

A series of new chiral tetrahydroquinoline ligands, derived from chiral α-pinene, were successfully synthesized. Iridium and palladium complexes of these ligands were proven to be efficient catalysts for enantioselective hydrogenation and allylic substitution reactions with moderate to excellent enantioselectivities (90-95% ee) and high yields.

Full text of DOI:10.1016/j.tetasy.2009.05.020

Tetrahedron: Asymmetry 20 (2009) 1402–1406
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Asymmetric hydrogenation and allylic substitution reaction with novel
chiral pinene-derived N,P-ligands
*
Xiangyan Meng, Xinsheng Li , Dongcheng Xu
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new chiral tetrahydroquinoline ligands, derived from chiral a-pinene, were successfully syn-
Received 7 April 2009
Accepted 18 May 2009
Available online 24 June 2009
thesized. Iridium and palladium complexes of these ligands were proven to be efficient catalysts for
enantioselective hydrogenation and allylic substitution reactions with moderate to excellent enantiose-
lectivities (90–95% ee) and high yields.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
bearing a chiral pinene moiety, in asymmetric hydrogenations
with moderate to good enantioselectivities and conversions
Transition-metal-catalyzed asymmetric transformations in the
presence of chiral ligands have proven to be one of the most
efficient methods for the construction of enantioenriched com-
pounds.1 Therefore, the design and synthesis of novel chiral ligands
have been of a great interest in organic and organometallic chem-
istries over the past few decades. Among these, phosphorus- and
nitrogen-based chiral ligands have been the most extensively
investigated.2 Crabtree reported the first homogenous achiral irid-
ium hydrogenation catalysts in 1977,3 while in 1997, Pfaltz et al.
developed the first chiral iridium catalysts with chiral oxazoli-
dine–phosphine ligands.4 Since then, several highly efficient chiral
N,P-ligands have been developed and used for iridium-catalyzed
asymmetric hydrogenation and allylic substitution reactions.5
Although chiral phosphine–oxazolidines have been extensively re-
searched, the aza-heterocycle-phosphine ligands have scarcely
been developed. Typical efficient iridium complexes based on
thiazole 16 and pyridines 27 and 38 were developed by several
(Fig. 1).12 Taking into consideration that the formation of a
six-membered ring when ligands 4 complexes with iridium may
reduce the enantiocontrol of the chiral environment, we developed
a series of new N,P-ligands that form five-membered rings in the
metal complex and applied them to the Ir-catalyzed hydrogenation
of olefins and Pd-catalyzed allylic alkylations.
2. Results and discussion
2.1. Preparation of chiral Ir complexes 8
Afterdeprotonation of5 with n-BuLiat ꢀ78 °C, thereactionswere
quenched with either chlorodiarylphosphine or chlorodicyclohexyl-
phosphine and borane–dimethylsulfide to afford only one isomer of
phosphine–borane 6 in 80–92% yields. The crystal structure of com-
pound 6a was determined by X-ray analysis (Fig. 2).13 After removal
of the BH3 with diethylamine, the resulting pyridine–phosphines 7
reacted with an iridium complex and NaBArF (NaBArF: sodium
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) to provide chiral
iridium complex catalysts 8 in high yields (Scheme 1).
research groups (Fig. 1). The derivatives of
a-pinene, bearing a
pyridine ring, have been used in asymmetric additions,9 cycloprop-
anations10, and allylic oxidation and substitution reactions.11
Recently, Andersson et al. reported the iridium complexes of 4,
2.2. Ir-catalyzed asymmetric hydrogenation
PPh2
N
PPh2
N
PPh2
N
PPh2
N
2-Methyl-3-phenylallyl acetate 9a was chosen as a model sub-
strate to test the efficiency of catalysts 8a–8g. The hydrogenation
was carried out with a pressure of 50 bar of H2 in CH2Cl2 at room
temperature for 4 h. As shown in Table 1, all catalysts 8a–8g were
effective for the reaction as high conversions and moderate enanti-
oselectivities were obtained (Table 1, entries 1–7). The results
show that the electronic nature of the aromatic ring of the Ar2P
moiety has an important influence on the enantioselectivities of
the reaction. For example, the aryl ring of the Ar2P moiety with
an electron-withdrawing substituent reduced enantioselectivities
X
O
Ph
R
S
4a
4b
X = CH2
X = O
1
2
3
Figure 1.
* Corresponding author. Tel.: +86 579 82283702; fax: +86 579 82282610.
E-mail address: sky33@zjnu.cn (X. Li).
0957-4166/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2009.05.020

X. Meng et al. / Tetrahedron: Asymmetry 20 (2009) 1402–1406
1403
Table 1
The results of asymmetric hydrogenation with 0.5 mol % 8 as a catalyst
0.5 mol % 8a-8g,
50 bar H2
*
Ph
OAc
Ph
OAc
CH2Cl2, rt
10a
9a
CO2CH3
Ph
O
Ph
CO2Me
R
OH
Ph
Ph
R
OPPh2
NHAc
9b
9c
9d
9e R = C6H5
9f R = p-CH3C6H4
9g R = p-FC6H4
9h R = C6H5
9i R = p -CH3C6H4
9j R = p-BrC6H4
Entry
Sub.
Cat.
Con.a (%)
eeb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
9a
9a
9a
9a
9a
9a
9a
9b
9c
9d
9e
9f
8a
8b
8c
8d
8e
8f
8g
8c
8c
8c
8c
8c
8c
8c
8c
8c
99
77
99
99
99
75
65
93
99
99
99
99
99
99
92
99
28 (S)
14 (S)
51 (S)
20 (S)
47 (S)
29 (S)
16 (S)
37 (S)c
42 (S)c
52 (R)d
59 (S)
47e
Figure 2. Molecular structure of 6a.
9g
9h
9i
42e
90 (S)f
86 (S)f
70 (S)f
1) n-BuLi
9j
HNEt2
Ph
N
Ph
N
2) Ar2PCl
a
Ph
N
PAr2
Determined by GC.
PAr2
6a-6g
3) BH3·SMe2
H3B
b
Determined by GC using a chiral CP-Chirasil-Dex CB column.6b The absolute
5
7a-7g
configurations of the products were determined by comparison of the retention
times with literature data.
c
Determined by HPLC using a chiral Chiracel OJ-H column.6b,14
d
Determined by GC using a chiral Chiralsil-L-Val column.7
a: Ar = Ph,
b: Ar = o -CH3C6H4
e
1) [Ir(cod)Cl]2
2) NaBArF
Compounds 10f and 10g were converted to corresponding acetic esters and
Ph
N
c
: Ar =p -CH3C6H4
compared with literature data.15
BHArF
d: Ar = o-CH3OC6H4
e: Ar = p-CH3OC6H4
f : Ar = cyclohexyl
r
Determined by HPLC using a chiral Chiracel AD-H column.16
f
I
PAr2
8a-8g
Scheme 1. Preparation of Ir complexes.
g
: Ar = 3,5-(CF3)2C6H3
ity of hydrogenation. This phenomenon was supported by the re-
sults of hydrogenation.
2.3. Pd-catalyzed asymmetric allylic alkylation of 1,3-
diphenylallyl acetate
(Table 1, entry 7). The activities and enantioselectivities of cata-
lysts 8c and 8e with (p-Tol)2P and (p-anisole)2P group were slightly
superior to those of the other corresponding catalysts (Table 1, en-
tries 3 and 5). This indicated that the position of the substituent of
the aromatic ring of the Ar2P moiety can also strongly influence the
enantioselectivities of the catalysts. Electron-donating groups at
the para-positions of the aryl ring led to higher activities and
enantioselectivities (Table 1, entries 3 and 5), while substituents
on the ortho-positions gave lower enantioselectivities (Table 1,
entries 2 and 4).
With the new ligands in hand, the asymmetric allylic alkylation
of racemic 1,3-diphenylallyl acetate with dimethyl malonate was
tested in the presence of the catalyst formed in situ from
2.5 mol % of [Pd(p-C3H5)Cl]2 and 6 mol % of ligands 7 at room tem-
perature. The results are listed in Table 2. All ligands 7a–7g pro-
vided the substituted products in high yields (Table 2, entries 1–
7). Ligand 7d, which afforded the product with quantitative yield
(>99%) and good enantiomeric excess (84% ee), was found to be
the ligand of choice (Table 2, entry 4).
Other substrates, including diphenylpropene, methyl 3-phenyl-
but-2-enoate, dehydrogen amino acid ester, phenylallyl alcohols,
and vinyl phosphinates, were also hydrogenated in the presence
of catalyst 8c (0.5 mol % cat.; 50 bar H2), and the desired reduced
products were obtained in high yields and with moderate to good
enantioselectivities (Table 1, entries 8–16). Vinyl phosphinates,
terminal olefins with a small steric hindrance, gave much better
enantioselectivities than other substrates. Substrates 9e–9j,
regardless of whether they contained electron-withdrawing or
electron-donating groups at the para-position of phenyl ring, were
observed to give reduced enantioselectivities (Table 1, entries
11–15). These results show that these bulkier ligands are both less
active and selective than those of ligands 3. While catalyst 8 gave
higher activities than 4, the enantioselectivities of 8c lies between
4a and 4b. Repulsion between the pinene moiety and a phosphorus
phenyl group may result in a conformational change that produces
a more crowded active site which may reduce the enantioselectiv-
The effect of the base, solvent, and palladium precursor on the
catalytic activity and enantioselectivity was investigated in the
presence of 7d as the ligand. The representative results are sum-
marized in Table 3. The results showed that these factors strongly
affect the activities and enantioselectivities of the allylic alkylation.
The best result (up to 99% yield and 92% ee) was obtained with
Cs2CO3 as a base in CH2Cl2 (Table 3, entry 3). Stronger bases, such
as NaH and n-BuLi, and weaker BSA led to reduced ee values (Table
3, entries 2, 4, and 1). Other solvents, including toluene and THF,
gave slightly lower enantioselectivities (Table 3, entries 5 and 6).
Furthermore, Pd(PhCN)2Cl2, Pd(CH3CN)2Cl2, and Pd2(bda)3 were
examined as palladium precursors and enantioselectivities were
obtained that were lower than [Pd(p-C3H5)Cl]2 (Table 3, entries
7–9).
To extend the scope of nucleophiles of the allylic substitution
catalyzed by the [Pd( -C3H5)Cl]2 complex of ligand 7d, some other
p

1404
X. Meng et al. / Tetrahedron: Asymmetry 20 (2009) 1402–1406
Table 2
Table 4
a
Enantioselective allylic alkylation of 1,3-diphenylallyl acetate with dimethyl
Enantioselective allylic alkylation of 1,3-diphenylallyl acetate in CH2Cl2
malonatea
OAc
Nu
[Pd( -C H )Cl] /7d
π
3
5
2
CH(CO2Me)2
Ph
OAc
+
Nu-H
7a-7g
[Pd(π-C3H5)Cl]2/
Ph
Ph
Ph
Ph
Cs2CO3, CH2Cl2, rt
+ CH2(CO2Me)2
Ph
Ph
Ph
BSA/KOAc, CH2Cl2, rt
Entry
Nu-H
Time
Yieldb (%)
eec (%)
Entry
Ligand
Time (h)
Yieldb (%)
eec (%)
1
2
3
4
5
CH2(CO2Me)2
CH2(CO2Et)2
CH3CH(CO2Me)2
CH3CH(CO2Et)2
CNCH2CN
8
8
8
8
8
>99
98
85
72
85
92 (R)
90 (R)
95 (R)
94 (R)
64 (R)
1
2
3
4
5
6
7
7a
7b
7c
7d
7e
7f
2
2
2
2
2
2
2
95
90
88
>99
76
75
66 (R)
56 (R)
62 (R)
84 (R)
65 (R)
56 (R)
30 (R)
a
All reactions were conducted with ligand 7d (6% equiv), [Pd(
p
-C3H5)Cl]2
(2.5% equiv), Cs2CO3 (3 equiv) in CH2Cl2 at room temperature.
7g
69
b
Isolated yield.
a
c
All reactions were conducted with ligand (6% equiv), [Pd(
(2.5% equiv), BSA-AcOK (3 equiv) in CH2Cl2 at room temperature.
p
-C3H5)Cl]2
Determined by chiral HPLC using Chiralcel AD-H column or OJ-H column. The
absolute configurations were determined by comparison of the retention times
with literature data.17
b
Isolated yield.
c
Determined by chiral HPLC analysis with a Chiralcel AD-H column. The absolute
configurations were determined by comparison of the retention times with litera-
ture data.17
tivities (up to 90% ee) and the substituted products with high
enantioselectivities (up to 95% ee). Further studies on the modifica-
tions of ligands and their applications to other asymmetric reac-
tions are currently in progress in our laboratory.
4. Experimental
Table 3
The effect of various base, solvents, and Pd precursors in allylic alkylation with 7d as a
liganda
4.1. General methods
CH(CO2Me)2
OAc
Pd /7d
Melting points were measured on a Yanagimoto micro appara-
tus and are uncorrected. Optical rotations were measured with
WZZ-2B digital polarimeter. The ee value was determined by HPLC
+ CH2(CO2Me)2
Ph
Ph
Ph
Ph
Entry
Pd precursor
Base
Solvent
Time
Yieldb (%)
eec (%)
TM
using Chiralcel AD-H, OD-H, OB-H, and OJ-H column with 2-pro-
1
2
3
4
5
6
7
8
9
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
[Pd(
Pd(PhCN)2Cl2
Pd(CH3CN)2Cl2
Pd2(bda)3
p
p
p
p
p
p
-C3H5)Cl]2
BSA
NaH
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Toluene
THF
CH2Cl2
CH2Cl2
CH2Cl2
2
8
8
0.5
8
8
8
8
8
>99
77
>99
98
95
92
85
88
95
84 (R)
77 (R)
92 (R)
65 (R)
85 (R)
85 (R)
50 (R)
73 (R)
78 (R)
panol–hexane as the eluent. The conversion was determined on
an Agilent 6820 or a Bruker AV-400 MHz spectrometer. NMR spec-
tra were recorded on a Bruker AV-400 MHz instrument using TMS
as internal standard for 1H NMR and 13C NMR and 85% H3PO4 as
external referencing for 31P NMR in CDCl3. Elemental analyses
were performed on Elementar Vario EL III CHNS Foss-instrument.
All reactions were carried out in dry glassware under nitrogen.
-C3H5)Cl]2
-C3H5)Cl]2
-C3H5)Cl]2
-C3H5)Cl]2
-C3H5)Cl]2
Cs2CO3
n-BuLi
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
a
All reactions were conducted with ligand 7d (6% equiv), Pd complexes
4.2. Synthesis of phosphine–borane ligand 6
(2.5% equiv), base (3 equiv) at room temperature.
b
Isolated yield.
c
Determined by chiral HPLC analysis with a Chiralcel AD-H column. The absolute
A colorless stirred solution of 5 (0.30 g, 1.20 mmol) in Et2O
(6 mL) under nitrogen was cooled to ꢀ78 °C. To this mixture was
added n-BuLi (0.58 mL, 1.44 mmol). After stirring at ꢀ78 °C for
0.5 h, the orange reaction mixture was transferred to an ice bath
and stirred for a further 0.5 h. The resulting solution was cooled
to ꢀ78 °C again and PAr2C1 (0.28 mL, 1.56 mmol) was added. The
reaction mixture was allowed to warm to room temperature
slowly for 3 h. Borane–dimethylsulfide (2 M in THF, 0.78 mL,
1.56 mmol) was added to the mixture. The solution was stirred un-
der nitrogen for a further 2 h and quenched with water. After
extraction of the mixture with ethyl acetate, the combined organic
layers were washed with brine, and dried over sodium sulfate, fil-
tered, and the solvent was removed under reduced pressure. The
crude phosphine–borane was purified by flash chromatography
to yield 6 as a colorless solid.
configurations were determined by comparison of the retention times with litera-
ture data.17
nucleophiles were applied in the catalytic system. The results of
the allylic substitution under the optimum conditions are listed
in Table 4. The results showed that all nucleophiles could offer
the desired products with high yields and enantiomeric excesses
(Table 4, entries 2–5). When CH2(CO2Et)2 was used as a nucleo-
phile, the enantiomeric excess of the product was slightly reduced
to 90% ee (Table 4, entry 2). A bulky substituent of nucleophiles
such as CH3CH(COOMe)2 or CH3CH(COOEt)2, could increase the
enantioselectivities to 95% ee and 94% ee, respectively (Table 4, en-
tries 3 and 4). Moderate enantiomeric excess was obtained with
CNCH2CN as the nucleophile (Table 4, entry 5).
Compound 6a: Yield 90%, mp 215–217 °C. ½a2D0 ¼ þ118 (c 0.72,
CHCl3); 1H NMR (CDCl3) d 0.52–1.18 (br m, 3H, BH3), 0.73 (s, 3H),
1.21 (d, J = 10 Hz, 1H),1.40 (s, 3H), 2.43–2.46 (m, 1H), 2.65 (t,
J = 4.8 Hz, 1H), 2.76–2.77 (m, 1H), 4.42 (d, J = 13.6 Hz, 1H), 7.19–
7.28 (m, 6H), 7.35–7.46 (m, 3H), 7.48–7.49 (m, 4H), 7.71–7.75
(m, 2H), 7.83–7.85 (m, 2H); 13C NMR (CDCl3) d 20.9, 26.0, 28.4,
42.4, 42.5, 42.8, 45.7, 117.1, 126.2, 128.2, 128.3, 128.4, 128.5,
130.2, 131.0, 131.4, 132.5, 132.6, 134.3, 134.4, 134.5, 138.5,
140.8, 153.1, 153.4; 31P NMR (CDCl3) d 27.2. Anal. Calcd for
3. Conclusion
In conclusion, a series of new chiral tetrahydroquinoline li-
gands, derived from the chiral a-pinene, were successfully synthe-
sized and evaluated in the Ir-catalyzed asymmetric hydrogenation
and Pd-catalyzed asymmetric allylic substitution reactions, which
afforded the hydrogenated products with moderate enantioselec-

X. Meng et al. / Tetrahedron: Asymmetry 20 (2009) 1402–1406
1405
C30H31BNP: C, 80.54; H, 6.98; N, 3.13. Found: C, 80.51; H, 6.97; N,
3.12.
117.1, 126.2, 128.2, 128.3, 128.4, 128.5, 130.2, 131.0, 131.4,
132.5, 132.6, 134.3, 134.4, 134.5, 138.5, 140.8, 153.1, 153.4; 31P
NMR (CDCl3) d 20.3. Anal. Calcd for C34H27BF12NP: C, 56.77; H,
3.78; N, 1.95. Found: C, 56.76; H, 3.76; N, 1.92.
Compound 6b: Yield 89%, mp 204–206 °C. ½a2D0 ¼ ꢀ19:1 (c 1.2,
CHCl3); 1H NMR (CDCl3) d 0.56–1.20 (br m, 3H, BH3), 0.77 (s, 3H),
1.32 (s, 3H), 1.76 (d, J = 10 Hz, 1H), 1.97–1.99 (m, 1H), 2.18 (s,
3H), 2.46 (s, 3H), 2.52–2.60 (m, 1H), 2.76 (t, J = 5.6 Hz, 1H), 4.32
(d, J = 13.6 Hz, 1H), 7.10–7.28 (m, 11H), 7.43–7.50 (m, 3H), 8.10–
8.12 (m, 1H); 13C NMR (CDCl3) d 21.2, 21.5, 26.2, 26.7, 40.8, 42.4,
42.6, 43.0, 46.7, 116.2, 125.3, 126.0, 126.4, 128.1, 128.2, 128.4,
129.8, 133.4, 136.1, 139.0, 140.1, 142.3, 142.6, 143.4, 143.7,
153.7, 157.8; 31P NMR (CDCl3) d ꢀ28.4. Anal. Calcd for C32H35BNP:
C, 80.84; H, 7.42; N, 2.95. Found: C, 80.82; H, 7.42; N, 2.96.
Compound 6c: Yield 87%, mp 206–208 °C. ½a2D0 ¼ þ58:9 (c 0.56,
CHCl3); 1H NMR (CDCl3) d 0.53–1.11 (br m, 3H, BH3), 0.72 (s, 3H),
1.21 (d, J = 10 Hz, 1H), 1.40 (s, 3H), 2.31 (s, 3H), 2.41–2.43 (m,
1H), 2.45 (s, 3H), 2.64 (t, J = 5.6 Hz, 1H), 2.76–2.78 (m, 1H), 4.36
(d, J = 13.6 Hz, 1H), 7.06 (d, J = 4.8 Hz, 2H), 7.18–7.25 (m, 6H),
7.28 (d, J = 8 Hz, 2H), 7.36 (d, J = 8.4 Hz, 1H), 7.57 (t, J = 4.8 Hz,
2H), 7.71 (t, J = 4.8 Hz, 2H); 13C NMR (CDCl3) d 20.9, 21.5, 26.0,
28.3, 42.3, 42.4, 42.7, 43.0, 45.8, 117.0, 124.9, 126.3, 128.2, 128.3,
129.0, 129.1, 129.2, 129.3, 132.4, 132.5, 134.2, 134.4, 138.6,
140.3, 140.8, 141.4, 153.4; 31P NMR (CDCl3) d 25.6. Anal. Calcd
for C32H35BNP: C, 80.84; H, 7.42; N, 2.95. Found: C, 80.81; H,
7.43; N, 2.94.
4.3. General procedure for the preparation of iridium
complexes 8
The borane-protected phosphine ligand 6 (0.2 mmol) was trea-
ted with neat diethylamine (1 mL), under argon and warmed to
50 °C. The reaction mixture was stirred with monitoring by TLC.
After the TLC showed the disappearance of the starting material,
the reaction mixture was cooled to RT. Removal of diethylamine
and the diethylamine–borane complex under reduced pressure
gave ligand 7 as an air-sensitive foam. Ligand 7 (0.2 mmol), [Ir(-
cod)Cl]2 (67.2 mg, 0.1 mmol), and CH2Cl2 (5 mL) were added to a
flask under N2. The solution was stirred at room temperature for
about 2 h until TLC indicated that the ligand had been consumed.
Next, NaBArF (0.22 g, 0.25 mmol) was added followed by H2O
(5 mL), and the resulting two-phase mixture was stirred vigorously
for 30 min. The organic layer was separated, and the aqueous layer
was extracted with CH2Cl2. The combined organic phase was
washed with H2O (5 mL) and dried over anhydrous Na2SO4. After
removing solvent under reduced pressure, the residue was purified
by column chromatography to afford yellow or red complexes.
Compound 8a: Yield 91%, mp 66–68 °C. ½a2D0 ¼ þ100:8 (c 1.05,
CHCl3); 1H NMR (CDCl3) d 0.94 (d, J = 17.2 Hz, 3H), 1.21 (d,
J = 10 Hz, 1H), 1.26–1.27 (m, 1H, COD), 1.40 (d, J = 10 Hz, 3H),
1.61–1.70 (m, 2H, COD), 1.90–2.20 (m, 5H, COD), 2.21–2.29 (m,
1H, COD), 2.61 (m, 1H), 2.65 (t, J = 4.8 Hz, 1H), 2.75 (m, 1H),
3.38–3.46 (m, 1H, COD), 4.23–4.79 (m, 2H, COD), 5.39 (dd,
J = 10.4 Hz, J = 416 Hz, 1H), 7.28–7.43 (m, 6H), 7.46–7.49 (m, 1H),
7.50 (s, 4H, BArF-H), 7.52–7.68 (m, 7H), 7.70 (sbr, 8H, BArF-H),
7.75–7.91 (m, 2H), 8.10–7.15 (m, 1H); 31P NMR (CDCl3) d 44.4.
Anal. Calcd for C70H52BF24IrNP: C, 52.64; H, 3.28; N, 0.88. Found:
C, 52.66; H, 3.24; N, 0.84.
Compound 6d: Yield 85%, mp 178–179 °C. ½a2D0 ¼ ꢀ23:8 (c 0.55,
CHCl3); 1H NMR (CDCl3) d 0.60–1.18 (br m, 3H, BH3), 0.74 (s, 3H),
1.33 (d, J = 10 Hz, 1H),1.37 (s, 3H), 2.24–2.29 (m, 1H), 2.53–2.60
(m, 1H), 2.69 (t, J = 5.6 Hz, 1H), 3.10 (s, 3H), 3.73 (s, 3H), 4.97 (d,
J = 16.8 Hz, 1H), 6.71–6.72 (m, 1H), 6.95–7.49 (m, 13H), 8.20–
8.24 (m, 1H); 13C NMR (CDCl3) d 21.1, 21.9, 27.6, 28.9, 40.3, 41.8,
45.4, 53.9, 55.0, 109.8, 111.2, 119.8, 119.9, 120.0, 125.9, 127.2,
127.4, 131.1, 132.7, 133.4, 136.4, 136.5, 138.7, 139.2, 153.0,
154.7, 160.8, 161.1; 31P NMR (CDCl3) d 25.7. Anal. Calcd for
C32H35BNO2P: C, 75.75; H, 6.95; N, 2.76. Found: C, 77.74; H, 6.93;
N, 2.75.
Compound 6e: Yield 82%, mp 180–181 °C. ½a2D0 ¼ þ72 (c 0.72,
CHCl3); 1H NMR (CDCl3) d 0.62–1.23 (br m, 3H, BH3), 0.75 (s, 3H),
1.33 (d, J = 10 Hz, 1H),1.37 (s, 3H), 2.24–2.29 (m, 1H), 2.53–2.60
(m, 1H), 2.69 (t, J = 5.6 Hz, 1H), 3.10 (s, 3H), 3.73 (s, 3H), 4.97 (d,
J = 16.8 Hz, 1H), 6.72 (dd, J = 2.8 Hz, J = 5.6 Hz, 2H), 7.14–7.23 (m,
6H), 7.35 (d, J = 8.0 Hz, 1H), 7.42 (d, J = 8.4 Hz, 1H), 7.64 (t,
J = 4.8 Hz, 2H), 7.79 (t, J = 4.8 Hz, 2H), 8.18–8.22 (m, 1H); 13C
NMR (CDCl3) d 20.9, 21.5, 25.4, 28.7, 42.3, 43.8, 45.4, 54.5, 55.2,
108.3, 113.2, 120.8, 120.9, 124.0, 126.9, 129.2, 129.4, 132.1,
133.7, 134.4, 138.4, 138.5, 140.7, 153.2, 162.8, 163.1; 31P NMR
(CDCl3) d 27.4. Anal. Calcd for C32H35BNO2P: C, 75.75; H, 6.95; N,
2.76. Found: C, 77.73; H, 6.94; N, 2.76.
Compound 8b: Yield 89%, mp 86–88 °C. ½a2D0 ¼ þ148:9 (c 0.68,
CHCl3); 1H NMR (CDCl3) d 0.94 (s, 3H), 1.26–1.31 (m, 1H, COD),
1.44 (d, J = 10 Hz, 1H), 1.47 (s, 3H), 1.54–1.56 (m, 1H), 1.61–1.70
(m, 2H, COD), 1.80 (s, 3H), 1.81 (s, 3H), 1.90–2.00 (m, 2H, COD),
2.13–2.25 (m, 2H, COD), 2.40–2.58 (m, 2H, COD), 2.70–2.74 (m,
1H), 2.78 (t, J = 5.6 Hz, 1H), 3.03–3.05 (m, 1H, COD), 4.66–4.78
(m, 2H, COD), 5.10 (d, J = 9.6 Hz, 1H), 6.90–7.12 (m, 5H), 7.27–
7.29 (m, 2H), 7.42–7.47 (m, 4H), 7.48 (s, 4H, BArF-H), 7.59–7.68
(m, 3H), 7.70 (sbr, 8H, BArF-H), 8.00–8.05 (m, 1H); 31P NMR (CDCl3)
d 36.1. Anal. Calcd for C72H56BF24IrNP: C, 53.21; H, 3.47; N, 0.86.
Found: C, 53.27; H, 3.40; N, 0.82.
Compound 6f: Yield 90%, mp 208–210 °C. ½a2D0 ¼ þ17:8 (c 1.0,
CHCl3); 1H NMR (CDCl3) d 0.30–0.70 (br m, 3H, BH3), 0.63–0.65
(m, 1H), 0.66 (s, 3H), 0.72–0.78 (m, 1H), 1.06–1.08 (m, 2H), 1.20–
1.43 (m, 8H), 1.45 (s, 3H),1.54 (d, J = 10 Hz, 1H), 1.62–1.72 (m,
2H), 1.74–1.78 (m, 2H), 1.81–1.91 (m, 2H), 2.16–2.27 (m, 3H),
2.62 -2.78 (m, 4H), 3.65 (d, J = 13.2 Hz, 1H), 7.29 (d, J = 8.0 Hz,
1H), 7.41 (d, J = 8.0 Hz, 1H), 7.46–7.53 (m, 3H), 8.04 (d, J = 5.6 Hz,
2H); 13C NMR (CDCl3) d 20.9, 25.9, 26.1, 26.2, 26.6, 26.9, 27.0,
27.1, 27.3, 29.1, 29.5, 31.1, 33.2, 33.4, 37.0, 37.2, 41.2, 43.3, 45.5,
117.2, 126.4, 128.6, 128.7, 134.3, 139.2, 140.5, 153.9, 154.1; 31P
NMR (CDCl3) d 36.6. Anal. Calcd for C30H43BNP: C, 78.42; H, 9.43;
N, 3.05. Found: C, 78.40; H, 9.40; N, 3.04.
Compound 8c: Yield 92%, mp 72–74 °C. ½a2D0 ¼ þ102:3 (c 0.9,
CHCl3); 1H NMR (CDCl3) d 0.89 (s, 3H), 1.05–1.15 (m, 1H, COD),
1.39 (d, J = 10 Hz, 1H), 1.41 (s, 3H), 1.45–1.62 (m, 2H, COD),
1.63–1.82 (m, 2H, COD), 1.97–2.05 (m, 2H, COD), 2.08–2.19 (m,
2H, COD), 2.28–2.30 (m, 1H), 2.35 (s, 3H), 2.49 (s, 3H), 2.62–2.64
(m, 1H), 2.74 (t, J = 5.6 Hz, 1H), 3.16–3.23 (m, 1H, COD), 3.34–
3.38 (m, 1H, COD), 4.59–4.62 (m, 1H, COD), 5.81 (dd, J = 10.4 Hz,
J = 416 Hz, 1H), 7.07 (d, J = 4.8 Hz, 2H), 7.18–7.28 (m, 4H), 7.32–
7.40 (m, 2H), 7.46 (s, 4H, BArF-H), 7.50–7.60 (m, 3H), 7.70 (sbr,
8H, BArF-H), 7.72–7.80 (m, 3H), 8.10–8.15 (m, 1H); 31P NMR
(CDCl3) d 44.8. Anal. Calcd for C72H56BF24IrNP: C, 53.21; H, 3.47;
N, 0.86. Found: C, 53.25; H, 3.39; N, 0.81.
Compound 6g: Yield 84%, mp 217–219 °C. ½a2D0 ¼ ꢀ61:3 (c 0.72,
CHCl3); 1H NMR (CDCl3) d 0.70–1.32 (br m, 3H, BH3), 0.71 (s, 3H),
1.21 (d, J = 10 Hz, 1H),1.41 (s, 3H), 2.46 (m, 1H), 2.66 (t,
J = 4.8 Hz, 1H), 2.76 (m, 1H), 4.52 (d, J = 13.6 Hz, 1H), 7.29 (d,
J = 8.0 Hz, 1H), 7.42 (d, J = 8.0 Hz, 1H), 7.48–7.55 (m, 3H), 8.01 (d,
J = 5.6 Hz, 2H), 8.03–8.05 (m, 2H), 8.27–8.29 (m, 2H), 8.64–8.67
(m, 2H); 13C NMR (CDCl3) d 20.9, 26.0, 28.4, 42.4, 42.5, 42.8, 45.7,
Compound 8d: Yield 88%, mp 62–64 °C. ½a2D0 ¼ þ63:0 (c 0.9,
CHCl3); 1H NMR (CDCl3) d 0.95 (s, 3H), 1.13–1.21 (m, 1H, COD),
1.35 (d, J = 10 Hz, 1H), 1.50 (s, 3H), 1.60–1.75 (m, 2H, COD), 1.98–
2.13 (m, 3H, COD), 2.20–2.34 (m, 2H, COD), 2.42–2.52 (m, 1H,
COD), 2.83–2.84 (m, 1H), 2.98–3.10 (m, 1H, COD), 3.33 (s, 3H),
3.35 (s, 3H), 3.49–3.50 (m, 1H), 3.73–3.83 (m, 1H, COD), 4.03 (t,
J = 5.6 Hz, 1H), 4.61 (d, J = 16.8 Hz, 1H), 4.83–4.94 (m, 1H, COD),

1406
X. Meng et al. / Tetrahedron: Asymmetry 20 (2009) 1402–1406
6.84–7.49 (m, 11H), 7.52 (s, 4H, BArF-H),7.60–7.74 (m, 3H), 7.77
(sbr, 8H, BArF-H), 8.20–8.24 (m, 1H); 31P NMR (CDCl3) d 46.1. Anal.
Calcd for C72H56BF24IrNO2P: C, 52.18; H, 3.41; N, 0.85. Found: C,
52.26; H, 3.35; N, 0.87.
time. After the reaction was concentrated under vacuum, the crude
residue was purified by flash column chromatography with 15%
ethyl acetate in hexane.
Compound 8e: Yield 85%, mp 68–70 °C. ½a2D0 ¼ þ94:7 (c 0.35,
CHCl3); 1H NMR (CDCl3) d 0.88 (d, J = 10 Hz, 1H), 0.92 (s, 3H),
1.08–1.12 (m, 1H, COD), 1.40 (s, 3H), 1.50–1.57 (m, 2H, COD),
1.65–1.72 (m, 2H, COD), 2.01–2.07 (m, 3H, COD), 2.08–2.14 (m,
1H, COD), 2.18–2.21 (m, 1H), 2.58–2.60 (m, 1H), 2.75 (t,
J = 5.6 Hz, 1H), 3.18–3.24 (m, 1H, COD), 3.35–3.40 (m, 1H, COD),
3.76 (s, 3H), 3.89 (s, 3H), 4.56–4.60 (m, 1H, COD), 5.76 (d,
J = 16.8 Hz, 1H), 6.90 (dd, J = 2.8 Hz, J = 5.6 Hz, 2H), 7.16–7.25 (m,
5H), 7.38 (d, J = 8.0 Hz, 1H), 7.44 (d, J = 8.4 Hz, 1H), 7.50 (s, 4H,
BArF-H),7.67 (t, J = 4.8 Hz, 3H), 7.71 (sbr, 8H, BArF-H), 7.82 (t,
J = 4.8 Hz, 2H), 8.08–8.12 (m, 1H); 31P NMR (CDCl3) d 44.2. Anal.
Calcd for C72H56BF24IrNO2P: C, 52.18; H, 3.41; N, 0.85. Found: C,
52.23; H, 3.38; N, 0.79.
Acknowledgments
This project was supported by the National Natural Science
Foundation of China (No. 20672101) and Natural Science Founda-
tion of Zhejiang Province (Y405013). Dr Jianwu Xie and Gangguo
Zhu are thanked for the useful discussions, and Ms Chua Pei Juan
of CBC-SPMS Nanyang Technological University is thanked for
the revision of this paper.
References
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1.33 (d, J = 10 Hz, 1H), 1.48 (s, 3H), 1.40–1.44 (m, 2H, COD), 1.82–
1.95 (m, 2H, COD), 2.38 (m, 1H), 2.46–2.78 (m, 3H, COD), 2.84–
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6.96 (t, J = 8.0 Hz, 2H), 7.05–7.09 (m, 1H), 7.22 (d, J = 7.2 Hz, 2H),
7.31–7.40 (m, 3H), 7.49 (s, 4H, BArF-H),7.56 (d, J = 8.0 Hz, 2H),
7.69 (sbr, 8H, BArF-H), 7.87–7.94 (m, 2H), 8.08–8.10 (m, 1H); 31P
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4.4. General procedure for the hydrogenation of olefins using
0.5 mol % iridium complexes 6a–6g
Enantioselective hydrogenation of olefins: olefin 9 (0.5 mmol)
and iridium complexes 8 (0.0025 mmol) in 2 mL dry degassed
CH2Cl2 were added to the autoclave under inert atmosphere. The
autoclave was sealed immediately and pressurized to 50 bar H2.
The mixture was stirred for 5 h. The CH2Cl2 was removed and the
crude product was passed through a short silica-gel column with
10% ethyl acetate in hexane as eluent. After evaporation of the sol-
vent, 10 was obtained and analyzed for conversion (GC) and ee
(HPLC).
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4.5. General experimental procedure for the Pd-catalyzed
asymmetric allylic alkylation
To a Schlenk tube containing Pd complexes (0.005 mmol) and
chiral ligands 7a–7g (0.012 mmol) were added dry solvents
(2 mL), and the mixture was stirred at room temperature for 1 h.
Then 1,3-diphenylallyl acetate (50 mg, 0.2 mmol) was added and
the mixture was stirred for further 10 min, nucleophiles
(0.6 mmol) was added to the reaction mixture followed by base
(0.6 mmol). The resultant mixture was stirred for an appropriate