Chiral quaternary alkylammonium ionic liquid [Pro-dabco][BF4]: As a recyclable and highly efficient organocatalyst for asymmetric Michael addition reactions

Article abstract of DOI:10.1016/j.tetasy.2010.10.009

A novel series of chiral quaternary ammonium ionic liquids have been synthesized and shown to be very effective catalysts for the asymmetric Michael addition reactions of ketones and aldehydes to nitroolefins with excellent yields (up to 100%), diastereos

Full text of DOI:10.1016/j.tetasy.2010.10.009

Tetrahedron: Asymmetry 21 (2010) 2530–2534
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Chiral quaternary alkylammonium ionic liquid [Pro-dabco][BF ]: as a
4
recyclable and highly efficient organocatalyst for asymmetric Michael addition
reactions
⇑
Da-Zhen Xu, Yingjun Liu, Sen Shi, Yongmei Wang
Department of Chemistry, State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of chiral quaternary ammonium ionic liquids have been synthesized and shown to be very
effective catalysts for the asymmetric Michael addition reactions of ketones and aldehydes to nitroolefins
with excellent yields (up to 100%), diastereoselectivities (syn/anti = 99:1), and enantioselectivities (up to
Received 6 September 2010
Accepted 7 October 2010
Available online 4 November 2010
97%). The catalytic system, an ionic liquid organocatalyst in [Bmim][BF
4
], could be reused five times with-
out a significant loss in catalytic activity or stereoselectivity.
Ó 2010 Elsevier Ltd. All rights reserved.
1
. Introduction
and high thermal stability.8 They have served as effective reac-
tion media for a wide variety of organic reactions and other
applications in chemistry. Among the various ionic liquids, chiral
9
The Michael reaction is widely recognized as one of the most
important carbon–carbon bond-forming procedures, and it plays
an important role in organic synthesis. The development of organ-
ionic liquids are particularly attractive and important owing to
their potential applications to chiral discrimination, such as
asymmetric synthesis and the resolution of racemates.10 Chiral
ionic liquids with functional groups have also been applied as
soluble and recyclable organocatalysts for asymmetric reaction
by attachment of catalytically active chiral groups onto the side
chains of ionic liquids. Recently, some functionalized chiral ionic
liquids have been designed and used effectively as catalysts for
1
ocatalysts that promote asymmetric Michael reactions is an attrac-
2
tive area of research. Over the past few years, there has been a
tremendous increase in research activities concerning the develop-
ment of organocatalysts for asymmetric carbon–carbon bond-
3
4
forming reactions, especially for the Michael addition reactions.
Among the various organocatalysts, proline and its derivatives
have been demonstrated to make up a successful class of organo-
catalysts in enamine chemistry.5,6 Some of them have been devel-
oped for asymmetric Michael reactions of ketones to nitroolefins
with high enantioselectivity and diastereoselectivity. Most
recently, we have also reported a new class of proline based cata-
lysts, which were very effective catalysts for asymmetric Michael
1
1
asymmetric reactions, such as Michael additons, Aldol reac-
12
13
tions, and borane reductions. There have been cases where
imidazolium ionic liquids have been used most successfully for
asymmetric Michael reactions with high enantioselectivities. For
1
1a–c
11d–f
11i–k
example, Luo et al.,
Headley et al.,
Wang et al.,
and
other teams have reported excellent chiral imidazolium ionic li-
quid catalysts for asymmetric Michael reactions to nitroolefins.
We have also reported an efficient procedure for asymmetric Mi-
chael additions of cyclohexanone to chalcones catalyzed by an
7
addition reactions of ketones with nitroolefins and chalcones;
however, a major disadvantage is that they cannot be easily recov-
ered and recycled. As a result, the design and development of envi-
ronmentally friendly chiral organocatalysts, which could be easily
recovered and recycled for asymmetric Michael reactions with
high enantioselectivity remain a major challenge in synthetic
organic chemistry.
Over the past decade, room-temperature ionic liquids have
received broad attention due to their favorable properties, such
as non-inflammability, negligible vapor pressure, reusability,
1
1m
imidazolium ionic liquid.
However, nearly all chiral ionic li-
quid catalysts are based on imidazolium, only one example in
which chiral pyridinium ionic liquids have been used as catalyst
1
4
for asymmetric reactions. The application of chiral quaternary
alkylammonium ionic liquids as catalysts to achieve asymmetric
products has not been reported for Michael addition between
nitroolefins with ketones and aldehydes. Herein, we report the
design and synthesis of a novel class of chiral quaternary alky-
lammonium ionic liquids, which are very effective organocata-
lysts for highly enantioselective Michael additions of cyclic
ketones to nitroolefins; in addition, they are easily recovered
from the reaction mixture.
⇑
Corresponding author. Fax: +86 22 2350 2654.
E-mail address: ymw@nankai.edu.cn (Y. Wang).
0
957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.10.009

D.-Z. Xu et al. / Tetrahedron: Asymmetry 21 (2010) 2530–2534
2531
2
. Results and discussion
yields (Table 1, entries 4 and 5). When the reaction was carried
out in a protic solvent, such as MeOH, C OH, i-PrOH, and t-BuOH,
2 5
H
A series of pyrrolidine–DABCO-type chiral ionic liquids were
prepared from the ‘‘chiral pool” using N-Boc-L-prolinol as the start-
moderate to good enantioselectivities were obtained (Table 1, en-
tries 6–9). However, when using water as the solvent, no product
ing material (Scheme 1). The synthetic procedures were straight-
forward: (S)-N-Boc 2-bromomethylpyrrolidine was prepared in
6
was obtained (Table 1, entry 10). The use of [Bmim][PF ] led to a
slight decrease in both activity and enantioselectivity with 83%
yield and 88% ee value being obtained (Table 1, entry 11). Pyrroli-
two steps from N-Boc-L-prolinol, which was then treated with
DABCO at room temperature in ethyl acetate. Anion metathesis
4
dine–DABCO tetrafluoroborate in [Bmim][BF ] gave the best per-
of 3 with either AgBF
4
or KPF
6
afforded 4a or 4b.
formances with quantitative yield and high diastereoselectivity
(syn/anti = 96:4) and enantioselectivity (91% ee).
The recyclability and reusability of the catalyst chiral ionic li-
4
quid 4a and the solvent [Bmim][BF ] were examined for the reac-
a, b
OH
c
Br
N
N
tion of cyclohexanone to trans-b-nitrostyrene under standard
reaction conditions. After the reaction was complete, the reaction
mixture was concentrated and the residue was extracted three
times with ether. Removal of the solvent and purification by
column chromatography gave the Michael adduct 7a. The catalyst
N
Boc
N
Boc
N
Boc Br
1
2
4
chiral ionic liquid 4a remained in the solvent [Bmim][BF ]. The cat-
d
e
N
N
N
N
alyst and the solvent were easily recovered in more than 90% yield.
After drying, they were reused for the next run of the reaction. As
shown in Table 2, catalyst 4a could be recycled and reused at least
five more times without any loss of stereoselectivity (ee >90%; syn/
anti >93:7) but a slight decrease in activity was observed in cycles
2–6.
N
N
H
H
4a: X = BF4
b: X = PF6
Br
X
4
3
4
Scheme 1. Synthesis of functionalized chiral ionic liquids. Reagents and conditions:
(
(
a) TsCl, CH
d) HBr, NaHCO
2
Cl
2
88%; (b) LiBr, acetone, reflux, 91%; (c) DABCO, ethyl acetate, rt, 62%;
(aq), 95%; (e) AgBF or KPF , C OH, 100%.
3
4
6
2 5
H
Table 2
Recycling studies of ionic liquid [Pro-dabco][BF
cyclohexanone to trans-b-nitrostyrene
4
] catalyzed Michael addition of
a
Initially, we used these chiral ionic liquids for the direct
asymmetric Michael addition of cyclohexanone 5a to trans-b-
nitrostyrene 6a to afford the Michael adduct 7a using ILs
O
Ph
O
[
Pro-dabco][BF4]
NO2
[
4
Bmim][BF ] as reaction media. As shown in Table 1, all of the
NO2
+
Ph
catalysts tested exhibited good catalytic activity with the corre-
sponding products, which were obtained in good to excellent
chemical yields (Table 1, entries 1–3). Catalyst 4a was superior
to 3 and 4b, which promoted the Michael addition reaction with
higher diastereoselectivity and enantioselectivity (Table 1, entry
[Bmim][BF4], r.t.
5
a
6a
7a
Cycle
t (h)
Yieldb (%)
drc (syn/anti)
eed (%)
2
). Catalyst 4a was used as the catalyst of choice and evaluated
1
2
3
4
5
6
22
29
35
41
43
62
100
97
95
88
93
90
96:4
96:4
93:7
95:5
96:4
95:5
91
91
90
92
91
91
in different solvents (Table 1, entries 4–11). The yields and enanti-
oselectivities of the product differed significantly. When THF and
CHCl
3
were used as the solvent, the product was obtained in low
a
4
All reactions were conducted in [Bmim][BF ] (0.5 mL) using 5a (0.1 mL,
Table 1
1.0 mmol) and 6a (15 mg, 0.1 mmol) in the presence of 20 mol % of the catalyst.
a
b
Optimization of the reaction conditions
Isolated yield.
c
Determined by 1H NMR spectroscopy.
d
Determined by HPLC analysis (chiralcel AD-H column).
O
O
Ph
cat. ( 20 mol%)
solvent
NO2
+
NO2
Having established the standard reaction conditions for the
Michael addition of cyclohexanone to trans-b-nitrostyrene, we then
examined the reactions of other nitroolefins to establish a general
scope of this asymmetric transformation. The results are shown
in Table 3. High isolated yields were obtained for all of the six-
membered ring ketones, which can efficiently undergo Michael
reactions with different aryl-substituted nitroolefins in the pres-
Ph
5a
6a
Solvent
7a
Entry
Cat.
t (h)
Yieldb (%)
drc (syn/anti)
eed (%)
1
2
3
4
5
6
7
8
9
3
[Bmim][BF
[Bmim][BF
[Bmim][BF
THF
4
4
4
]
]
]
48
22
48
96
96
48
48
96
48
96
54
95
100
85
<5
<5
88
84
61
83
0
88:12
96:4
92:8
—
85
91
90
—
4a
4b
4a
4a
4a
4a
4a
4a
4a
4a
4
ence of 20 mol % of catalyst 4a in [Bmim][BF ] at room temperature
to give the Michael adducts 7a–7l in high yields and with excellent
enantioselectivities (87–97% ee) and diastereoselectivities (syn/anti
ratio up to 99:1). Other ketones, such as cyclopentanone and
acetone, were also examined in the 4a-catalyzed Michael addition
reaction with 6a. The reaction with cyclopentanone occurred
smoothly and showed moderate diastereoselectivity and enanti-
oselectivity for the syn product (Table 3, entry 13). Acetone worked
well to give the desired products in good yield but with low enanti-
oselectivity (40% ee) (Table 3, entry 14). The Michael addition of
isobutyraldehyde to trans-b-nitrostyrene was obtained in moder-
ate yield but with good enantioselectivity (81% ee) (Table 3, entry
15).
CHCl
MeOH
OH
3
—
—
76:24
79:21
78:22
75:25
—
74
79
81
78
—
2 5
C H
i-PrOH
t-BuOH
H O
2
1
1
0
1
[Bmim][PF
6
]
83
94:6
88
a
All reactions were conducted in a solvent (0.5 mL) using 5a (0.1 mL, 1.0 mmol)
and 6a (15 mg, 0.1 mmol) in the presence of 20 mol % of the catalyst.
b
Isolated yield.
c
Determined by 1H NMR spectroscopy.
d
Determined by HPLC analysis (chiralcel AD-H column).

2
532
D.-Z. Xu et al. / Tetrahedron: Asymmetry 21 (2010) 2530–2534
Table 3 (continued)
Table 3
Asymmetric Michael addition reactions of ketones and nitrostyrenea
Entry
Product
t (h)
Yieldb (%)
drc (syn/anti)
eed (%)
O
Ar
O
O
O
cat. 4a ( 20 mol%)
Bmim][BF4], r.t.
NO2
NO2
R1
R1
+
Ar
[
R2
9
NO2
NO2
28
97
93:7
90
R2
5
6
7
7
i
Entry
Product
t (h)
Yieldb (%)
100
drc (syn/anti)
eed (%)
S
O
O
Ph
1
0
1
60
17
93
96:4
99:1
90
96
NO2
1
22
96:4
91
7
j
7a
Me
O
1
100
NO2
NO2
NO2
O
O
2
68
94
99:1
93
NO2
NO2
O
O
7
k
7
Cl
b
1
1
2
3
48
22
96
95
91:9
87
79
S
3
20
87
98:2
93
7l
7
c
O
75:25
Cl
7
m
O
O
4
5
36
20
98
97:3
99:1
87
97
NO2
O
7d
14
90
96
81
41
—
—
40
81
NO2
NO2
7
n
Cl
NO2
100
O
H
15
7e
NO2
7
o
a
All reactions were conducted in solvent (0.5 mL) using 5 (1.0 mmol) and 6
(
0.1 mmol) in the presence of 20 mol % of the catalyst.
O
b
c
6
20
95
94:6
91
Isolated yield.
Determined by 1H NMR spectroscopy.
Determined by HPLC analysis (chiralcel AD-H or OD-H column).
NO2
d
7f
OMe
The stereochemistries of the major products 7 were determined
to be (2S,3R) by comparison of their specific rotations with other
5
–7
previous studies.
The absolute stereochemical results can be ex-
O
O
OMe
NO2
7
96
92
97:3
92
plained by an acyclic synclinal transition state, as proposed by See-
bach and Golinski.
15
7g
3
. Conclusions
In conclusion, we have designed and prepared the first example
of an asymmetric Michael reaction in which chiral quaternary
alkylammonium ionic liquids have been used as highly efficient
asymmetric organocatalysts. The chiral ionic liquid catalysts were
8
72
91
98:2
97
NO2
7h
easily prepared from commercially available L-prolinol. They are
capable of catalyzing highly enantioselective and diastereoselec-
tive nitro-Michael addition reactions. Moreover, the catalyst and

D.-Z. Xu et al. / Tetrahedron: Asymmetry 21 (2010) 2530–2534
2533
1
the solvent were readily recovered and reused for at least five
times without a significant loss of catalytic activity or stereoselec-
tivity. Further investigation into the applications of this recyclable
catalyst in asymmetric catalysis is currently in progress and will be
reported in due course.
compound was obtained as a colorless oil (2.33 g, 62%). H NMR
(300 MHz, D O): d (ppm) 1.12–1.30 (m, 2H), 1.42 (s, 9H), 1.57–
2
1.67 (m, 2H), 1.99–2.21 (m, 1H), 2.71–2.82 (m, 2H), 3.02 (t, 6H,
J = 6.9 Hz), 3.33 (t, 6H, J = 8.0 Hz), 3.45–3.56 (m, 3H); 13C NMR
2
(75 MHz, D O): d (ppm) 22.68, 28.53, 34.64, 46.55, 50.90, 52.68,
2
D
0
5
7.80, 69.39, 79.42, 154.56; ½
aꢁ
¼ ꢂ12:0 (c 0.80, CH
3
OH); HRMS
þ
+
4
4
. Experimental section
calcd for C16
H
30
N
3
O
2
M 296.2333, found 296.2335.
0
.1. General
4.2.3. 1-[(S)-2 -Methylpyrrolidine]-4-aza-1-
azoniabicyclo[2.2.2]octane bromide 3
All the solvents were purified according to standard procedures.
To a solution of [Boc-pro-dabco][Br] 2 (752 mg, 2 mmol) in
Cl (5 mL) was added dropwise HBr (5 mL) at 0 °C. The mixture
was warmed to room temperature and stirred overnight. After re-
1
13
The H NMR spectra were recorded at 300 MHz, C NMR was re-
CH
2
2
1
13
corded at 75 MHz. H and C NMR chemical shifts were calibrated
to tetramethylsilane as an external reference. Coupling constants
are given in Hertz. The following abbreviations are used to indicate
the multiplicity: s, singlet; d, doublet: t, triplet; q, quartet; m, mul-
tiplet; HRMS were recorded on an IonSpec FT-ICR mass spectrom-
eter with ESI resource. Melting points were measured on a RY-I
apparatus and are reported uncorrected. Optical rotations were
measured on a Perkin–Elmer 341 Polarimeter at 20 °C. HPLC anal-
ysis was performed on Shimadzu CTO-10AS by using a Chiralpak
AD-H or OD-H column purchased from Daicel Chemical Industries.
moval of the organic solvents in vacuo, the residue was dissolved
in CH
(15 mL) for 1 h at room temperature. The aqueous layer was
extracted three times with CH Cl
(3 ꢀ 5 mL) and the combined
extracts were dried over anhydrous Na SO . Concentration in
vacuo after filtration gave the catalyst [Pro-dabco][Br] 3 524 mg
2 2 3
Cl (5 mL) and then treated with saturated NaHCO solution
2
2
2
4
1
2
(95% yield). H NMR (300 MHz, D O): d (ppm) 1.02–1.07 (m, 1H),
1.24–1.36 (m, 1H), 1.53–1.69 (m, 2H), 1.94–2.14 (m, 1H), 2.70–
2.78 (m, 2H), 3.11 (t, 6H, J = 6.9 Hz), 3.38 (t, 6H, J = 8.0 Hz), 3.48–
1
3
3
2
.55 (m, 3H); C NMR (75 MHz, D O): d (ppm) 24.38, 31.48,
2
D
0
4
.2. General procedure for the preparation of ionic liquid
catalyst
46.35, 51.80, 53.01, 57.54, 69.28; ½
aꢁ
¼ þ20:5 (c 0.80, CH
3
OH);
þ
22
H N
3
+
HRMS calcd for C11
M 196.1808, found 196.1809.
0
4
1
.2.1. (S)-tert-Butyl 2-(bromomethyl)pyrrolidine-1-carboxylate
4.2.4. 1-[(S)-2 -Methylpyrrolidine]-4-aza-1-azoniabicyclo[2.2.2]
octane tetrafluoroborate 4a
1
6
In a 50 mL round-bottomed flask, N-Boc-
mmol) was dissolved in 25 mL CH Cl , 7.5 mL of pyridine was
added and cooled down to 0 °C. Then, p-toluenesulfonyl chloride
2.96 g, 15.6 mmol) was added and the mixture was stirred at
room temperature for 24 h. After this time, the reaction mixture
was diluted with 50 mL of CH Cl and washed with water, 1 M
HCl, saturated NaHCO and, finally, brine. The organic layer was
dried with sodium sulfate, filtered, and concentrated under re-
duced pressure, to yield a colorless oil. The crude product was puri-
fied by flash chromatography through deactivated silica eluting
with petroleum ether–ethyl acetate 8:1. After evaporation of the
solvents, colorless oil was obtained (3.91 g, 88%). A solution of
the colorless oil O-tosyl-N-Boc-prolinol (3.55 g, 10 mmol) and lith-
ium bromide (2.58 g, 30 mmol) in acetone (20 mL) was heated at
reflux for 6 h during which time the formation of a fine precipitate
was observed. On cooling, the volatiles were removed in vacuo and
the residual material was partitioned between dichloromethane
L
-prolinol (2.52 g, 12.5
To a solution of product 3 (276 mg, 1 mmol) in ethanol (10 mL),
was added AgBF (195 mg, 1 mmol) solution (in ethanol). The mix-
4
ture was vigorously stirred at room temperature for 30 min. Fil-
tered to remove the inorganic salts and the filtrate was
2
2
(
concentrated in vacuo to afford a pale yellow and clear liquid 4a
1
283 mg (100% yield). H NMR (300 MHz, D
2
O): d (ppm) 1.05–1.12
2
2
(m, 1H), 1.27–1.39 (m, 1H), 1.49–1.60 (m, 2H), 1.91–2.10 (m,
1H), 2.71–2.80 (m, 2H), 3.01–3.16 (m, 6H), 3.29–3.38 (m, 6H),
3
1
3
3.50–3.56 (m, 3H);
C NMR (75 MHz, D
2
O): d (ppm) 24.79,
2
0
31.68, 46.39, 51.88, 53.11, 58.54, 68.25; ½
a
ꢁ
¼ þ34:4 (c 0.80,
D
þ
+
CH
3
OH); HRMS calcd for C11
H
22
N
M 196.1808, found 196.1811.
3
0
4.2.5. 1-[(S)-2 -Methylpyrrolidine]-4-aza-1-azoniabicyclo[2.2.2]
octane hexafluoro-phosphate 4b
To a solution of product 3 (276 mg, 1 mmol) in acetonitrile and
acetone (15 mL, 9:1), was added well-sieved KPF
6
(920 mg,
5.0 mmol). The mixture was vigorously stirred at room tempera-
ture for 2 days and then filtered to remove the inorganic salts.
(
20 mL) and distilled water (20 mL) and further extracted with
dichloromethane (2 ꢀ 20 mL). The combined organic portions were
washed with brine (15 mL), dried (magnesium sulfate), filtered,
and concentrated in vacuo to yield a colorless oil. The crude prod-
uct was purified by flash chromatography through deactivated
silica eluting with petroleum ether–ethyl acetate 7:1. After evapo-
6
The filtrate was triturated with AgPF solution (in acetonitrile) un-
til no precipitation was formed and then filtered again and concen-
trated. The combined organic layer was concentrated in vacuo to
1
afford a pale clear yellow liquid 4b 341 mg (100% yield). H NMR
2
(300 MHz, D O): d (ppm) 1.03–1.11 (m, 1H), 1.29–1.43 (m, 1H),
ration of the solvents, the title compound was obtained as a color-
1.43–1.56 (m, 2H), 1.93–2.15 (m, 1H), 2.74–2.83 (m, 2H), 2.92–
1
13
less liquid (2.4 g, 91%). H NMR (300 MHz, CDCl
3
): d (ppm) 1.47 (s,
3.13 (m, 6H), 3.24–3.36 (m, 6H), 3.51–3.59 (m, 3H); C NMR
9
3
H), 1.79–1.90 (m, 2H), 1.94–2.04 (m, 2H), 3.19–3.51 (m, 3H),
(75 MHz, D
2
O): d (ppm) 25.56, 30.82, 45.71, 52.09, 53.14, 59.06,
.58–3.63 (m, 1H), 3.91–4.13 (m, 1H); 13C NMR (75 MHz, CDCl
,):
20
þ
67.32; ½
a
ꢁ
3
22
¼ þ27:6 (c 0.80, CH OH); HRMS calcd for C11H N
3
3
D
+
d (ppm) 22.62, 28.45, 30.11, 34.84, 46.94, 57.84, 79.70, 154.19;
M 196.1808, found 196.1803.
2
D
0
½
a
ꢁ
¼ ꢂ40:5 (c 0.80, CHCl
3
).
4
.3. Typical experimental procedure for the asymmetric Michael
0
0
4
.2.2. 1-[(S)-tert-Butyl 2 -methyl pyrrolidine-1 -carboxylate]-4-
addition to nitroolefins
aza-1-azoniabicyclo[2.2.2]octane bromide 2
In a 100 mL round-bottomed flask, DABCO (3.36 g, 30 mmol)
was added to a solution of compound 1 (2.64 g, 10 mmol) in AcOEt
To a mixture of catalyst 4a (6 mg, 0.02 mmol) in [Bmim][BF4]
(0.5 mL) and cyclohexanone (104 lL, 1.0 mmol), trans-b-nitrosty-
(
50 mL) at room temperature. The mixture was stirred for 5 days
rene (15 mg, 0.1 mmol) was added at room temperature under
air. After stirring at room temperature for 22 h, the reaction mix-
ture was extracted with ether and the organic layer was concen-
trated under reduced pressure. The product was purified by flash
and concentrated in vacuo. The residue was purified by flash chro-
matography through deactivated silica eluting with petroleum
ether–ethyl acetate 1:1. After evaporation of the solvents, the title

2
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D.-Z. Xu et al. / Tetrahedron: Asymmetry 21 (2010) 2530–2534
chromatography on silica gel (EtOAc/hexane = 1:5) to afford the
7. (a) Xu, D.-Z.; Shi, S.; Wang, Y. Eur. J. Org. Chem. 2009, 4848–4853; (b) Xu, D.-Z.;
Shi, S.; Wang, Y. Tetrahedron 2009, 65, 9344–9349.
Michael adduct 7a (24.8 mg, 100%) as a white solid: syn/anti = 98:2
8.
For reviews see: (a) Welton, T. Chem. Rev. 1999, 99, 2071–2083; (b)
Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772–3789; (c)
Jain, N.; Kumar, A.; Chauhan, S.; Chauhan, S. M. S. Tetrahedron 2005, 61, 1015–
1060; (d) Winkel, A.; Reddy, P. V. G.; Wilhelm, R. Synthesis 2008, 999–1016; (e)
Patil, M. L.; Sasai, H. Chem. Rec. 2008, 8, 98–108.
1
(
by H NMR), The ee was determined by HPLC analysis (Chiralpak
AD-H, k = 254 nm, i-PrOH/hexane = 10:90, 0.5 mL/min, 254 nm, t
R
25
(
(
[
minor) = 21.8 min, t
c 0.80, CHCl
Bmim][BF ] was reused for the next run of the reaction.
R
(major) = 27.0 min), 96% ee; ½
a
ꢁ
¼ ꢂ35:8
D
3
). After drying, the catalytic system of catalyst 4a in
9.
For reviews see: (a) Zhao, D.; Wu, M.; Kou, Y.; Min, E. Catal. Today 2002, 74,
157–189; (b) Dupont, J.; de Souza, R. F.; Suarez, P. A. Z. Chem. Rev. 2002, 102,
4
3667–3692; (c) Handy, S. T. Chem. Eur. J. 2003, 9, 2938–2944; (d) Dalko, P. I.;
Moisan, L. Angew. Chem., Int. Ed. 2004, 43, 5138–5175; (e) Miao, W.; Chan, T. H.
Acc. Chem. Res. 2006, 39, 897–908; (f) Muzart, J. Adv. Synth. Catal. 2006, 348,
Acknowledgments
275–295; (g) Lee, S. Chem. Commun. 2006, 1049–1063; (h) Shamsi, S. A.;
Danielson, N. D. J. Sep. Sci. 2007, 30, 1729–1750; (i) Domínguez de María, P.
Angew. Chem., Int. Ed. 2008, 47, 6960–6968; (j) Martins, M. A. P.; Frizzo, C. P.;
Moreira, D. N.; Zanatta, N.; Bonacorso, H. G. Chem. Rev. 2008, 108, 2015–2050;
(k) Gua, Y.; Lia, G. Adv. Synth. Catal. 2009, 351, 817–847; (l) Toma, Š.; Me cˇ iarová,
M.; Šebesta, R. Eur. J. Org. Chem. 2009, 321–327.
This work was financially supported by National Basic Research
Program of China (973 Program) (No. 2010CB833301) and the Re-
search Fund for the Doctoral Program of Higher Education (No.
2
0090031110019). We also thank the Nankai University State
1
0. For reviews see: (a) Baudequin, C.; Brégeon, D.; Levillain, J.; Guillen, F.;
Key Laboratory of Elemento-Organic Chemistry for support.
Plaquevent, J.-C.; Gaumont, A.-C. Tetrahedron: Asymmetry 2005, 16, 3921–
3945; (b) Baudequin, C.; Baudoux, J.; Levillain, J.; Cahard, D.; Gaumont, A.-C.;
References
Plaquevent, J.-C. Tetrahedron: Asymmetry 2003, 14, 3081–3093; (c) Bica, K.;
Gaertner, P. Eur. J. Org. Chem. 2008, 3235–3250; (d) Luo, S.; Zhang, L.; Cheng, J.-
P. Chem. Asian J. 2009, 4, 1184–1195.
1
.
.
Perlmutter, P. Conjugate Addition Reactions in Organic Synthesis; Pergamon:
Oxford, 1992.
(a) Krause, N.; Hoffmann-Röder, A. Synthesis 2001, 171–196; (b) Jha, S. C.; Joshi,
N. N. ARKIVOC 2002, vii, 167–196; (c) Berner, O. M.; Tedeschi, L.; Enders, D. Eur.
J. Org. Chem. 2002, 1877–1894; (d) Christoffers, J.; Baro, A. Angew. Chem., Int. Ed.
1
1. (a) Luo, S.; Mi, X.; Zhang, L.; Liu, S.; Xu, H.; Cheng, J.-P. Angew. Chem., Int. Ed.
2006, 45, 3093–3097; (b) Luo, S.; Zhang, L.; Mi, X.; Qiao, Y.; Cheng, J.-P. J. Org.
2
Chem. 2007, 72, 9350–9352; (c) Luo, S.; Mi, X.; Liu, S.; Xu, H.; Cheng, J.-P. Chem.
Commun. 2006, 3687–3689; (d) Ni, B.; Zhang, Q. Y.; Headley, A. D. Green Chem.
2007, 9, 737–739; (e) Zhang, Q.; Ni, B.; Headley, A. D. Tetrahedron 2008, 64,
2
003, 42, 1688–1690; (e) Xie, J.-W.; Chen, W.; Li, R.; Zeng, M.; Du, W.; Yue, L.;
5091–5097; (f) Ni, B.; Zhang, Q.; Dhungana, K.; Headley, A. D. Org. Lett. 2009,
Chem, Y.-C.; Wu, Y.; Zhu, J.; Deng, J.-G. Angew. Chem., Int. Ed. 2007, 46, 389–392.
Tietze, L. F. Pure Appl. Chem. 2004, 76, 1967–1983.
Freeman, F. Chem. Rev. 1981, 80, 329–350.
1
2
1, 1037–1040; (g) Xu, D.; Luo, S.; Yue, H.; Wang, L.; Liu, Y.; Xu, Z. Synlett 2006,
569–2572; (h) Wu, L.-Y.; Yan, Z.-Y.; Xie, Y.-X.; Niu, Y.-N.; Liang, Y.-M.
3.
4.
5.
Tetrahedron: Asymmetry 2007, 18, 2086–2090; (i) Li, P.; Wang, L.; Zhang, Y.;
Wang, G. Tetrahedron 2008, 64, 7633–7638; (j) Li, P.; Wang, L.; Wang, M.;
Zhang, Y. Eur. J. Org. Chem. 2008, 1157–1160; (k) Miao, T.; Wang, L.; Li, P.; Yan,
J. Synthesis 2008, 3828–3834; (l) Yacob, Z.; Shah, J.; Leistner, J.; Liebscher, J.
Synlett 2008, 2342–2344; (m) Qian, Y.; Xiao, S.; Liu, L.; Wang, Y. Tetrahedron:
Asymmetry 2008, 19, 1515–1518; (n) Maltsev, O. V.; Kucherenko, A. S.; Zlotin, S.
G. Eur. J. Org. Chem. 2009, 5134–5137.
For reviews see: (a) Mukherjee, S.; Yang, J. W.; Hoffmann, S.; List, B. Chem. Rev.
2
007, 107, 5471–5569; (b) List, B. Acc. Chem. Res. 2004, 37, 548–557; (c) Notz,
W., ; Tanaka, F., III; Barbas, C. F. Acc. Chem. Res. 2004, 37, 580–591; (d) Duthaler,
R. O. Angew. Chem., Int. Ed. 2003, 42, 975–978; (e) List, B. Tetrahedron 2002, 58,
5
573–5590; (f) Groger, H.; Wilken, J. Angew. Chem., Int. Ed. 2001, 40, 529–532.
6
.
For examples see: (a) Xu, D.-Q.; Yue, H.-D.; Luo, S.-P.; Xia, A.-B.; Zhang, S.; Xu,
Z.-Y. Org. Biomol. Chem. 2008, 6, 2054–2057; (b) Xu, D.-Q.; Wang, L.-P.; Luo, S.-
P.; Wang, Y.-F.; Zhang, S.; Xu, Z.-Y. Tetrahedron 2008, 64, 1049–1057; (c) Xiong,
Y.; Wen, Y.; Wang, F.; Gao, B.; Liu, X.; Huang, X.; Feng, X.-M. Adv. Synth. Catal.
1
2. (a) Miao, W.; Chan, T. H. Adv. Synth. Catal. 2006, 348, 1711–1718; (b) Lombardo,
M.; Pasi, F.; Easwar, S.; Trombini, C. Adv. Synth. Catal. 2007, 349, 2061–2065; (c)
Lombardo, M.; Easwar, S.; Pasi, F.; Trombini, C. Adv. Synth. Catal. 2009, 351,
2
007, 349, 2156–2166; (d) Xu, D.-Q.; Luo, S.-P.; Wang, Y.-F.; Xia, A.-B.; Yue, H.-
276–282; (d) Lombardo, M.; Easwar, S.; Marco, A. D.; Trombini, F. P. C. Org.
D.; Wang, L.-P.; Xu, Z.-Y. Chem. Commun. 2007, 4393–4395; (e) Alza, E.;
Cambeiro, X. C.; Jimeno, C.; Pericas, M. A. Org. Lett. 2007, 9, 3717–3720; (f) Cao,
C.-L.; Ye, M.-C.; Sun, X.-L.; Tang, Y. Org. Lett. 2006, 8, 2901–2904; (g) Chen, J.-R.;
Lu, H.-H.; Li, X.-Y.; Cheng, L.; Wan, J.; Xiao, W.-J. Org. Lett. 2005, 7, 4543–4545;
Biomol. Chem. 2008, 6, 4224–4229; (e) Lombardo, M.; Easwar, S.; Pasi, F.;
Trombini, C.; Dhavale, D. D. Tetrahedron 2008, 64, 9203–9207; (f) Zhou, L.;
Wang, L. Chem. Lett. 2007, 35, 628–629; (g) Luo, S.; Mi, X.; Zhang, L.; Liu, S.; Xu,
H.; Cheng, J.-P. Tetrahedron 2007, 63, 1923–1930; (h) Zhang, L.; Luo, S.; Mi, X.;
Liu, S.; Qiao, Y.; Xu, H.; Cheng, J.-P. Org. Biomol. Chem. 2008, 6, 567–576; (i) Hu,
S.; Jiang, T.; Zhang, Z.; Zhu, A.; Han, B.; Song, J.; Xie, Y.; Li, W. Tetrahedron Lett.
(
h) Tang, Z.; Yang, Z.-H.; Chen, X.-H.; Cun, L.-F.; Mi, A.-Q.; Jiang, Y.-Z.; Gong, L.-
Z. J. Am. Chem. Soc. 2005, 127, 9285–9289; (i) Hayashi, Y.; Gotoh, H.; Tamura, T.;
Yamaguchi, H.; Masui, R.; Shoji, M. J. Am. Chem. Soc. 2005, 127, 16028–16029;
2
007, 48, 5613–5617.
3. Yang, S.-D.; Shi, Y.; Sun, Z.-H.; Zhao, Y.-B.; Liang, Y.-M. Tetrahedron: Asymmetry
006, 17, 1895–1900.
(
j) Itagaki, N.; Kimura, M.; Sugahara, T.; Iwabuchi, Y. Org. Lett. 2005, 7, 4185–
1
4
188; (k) Tokuda, O.; Kano, T.; Gao, W.-G.; Ikemoto, T.; Maruoka, K. Org. Lett.
2
2
005, 7, 5103–5105; (l) Kano, T.; Yamaguchi, Y.; Tokuda, O.; Maruoka, K. J. Am.
1
1
1
4. Ni, B.; Zhang, Q.; Headley, A. D. Tetrahedron Lett. 2008, 49, 1249–1252.
5. Seebach, D.; Golinski, J. Helv. Chim. Acta 1981, 64, 1413–1423.
6. Davies, S. G.; Dixon, D. J.; Doisneau, G. J.-M.; Prodger, J. C.; Sanganee, H. J.
Tetrahedron: Asymmetry 2002, 13, 647–658.
Chem. Soc. 2005, 127, 16408; (m) Cordova, A.; Zou, W.; Ibrahem, I.; Reyes, E.;
Engqvist, M.; Liao, W.-W. Chem. Commun. 2005, 3586–3588; (n) Samanta, S.;
Liu, J.; Dodda, R.; Zhao, C.-G. Org. Lett. 2005, 7, 5321–5323; (o) Terakado, D.;
Takano, M.; Oriyama, T. Chem. Lett. 2005, 34, 962–963.