Synthesis of binaphthyl sulfonimides and their application in the enantioselective Michael addition of ketones to nitroalkenes

Article abstract of DOI:10.1002/ejoc.201000818

Novel types of L-proline-based binaphthyl sulfonimides and sulfonamides were found to be efficient organocatalysts for the asymmetric Michael addition of ketones to nitroalkenes to provide optically active γ-nitroketone derivatives of synthetic and biolog

Full text of DOI:10.1002/ejoc.201000818

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201000818
Synthesis of Binaphthyl Sulfonimides and Their Application in the
Enantioselective Michael Addition of Ketones to Nitroalkenes
Shurong Ban,[a,b] Da-Ming Du,* Han Liu, and Wen Yang
[a]
[c]
[a]
Keywords: Sulfonamides / Organocatalysis / Enantioselectivity / Michael addition / Alkenes
Novel types of
L
-proline-based binaphthyl sulfonimides and
thetic and biological importance. After the fine optimization
of solvents, temperature, and additive, good to excellent
enantioselectivities and diastereoselectivities (71–96%ee, up
to Ͼ99:1dr) can be achieved.
sulfonamides were found to be efficient organocatalysts for
the asymmetric Michael addition of ketones to nitroalkenes
to provide optically active γ-nitroketone derivatives of syn-
Introduction
ported. Herein, we report the synthesis of novel -proline-
based binaphthyl sulfonimides and sulfonamides (3a–d) and
their application in the asymmetric Michael addition of
ketones to nitroalkenes to give the desired adducts in mod-
erate to high yields with excellent enantioselectivities and
diastereoselectivities (up to 97% yield, 96%ee, Ͼ99:1dr)
under mild conditions.
In recent years, considerable attention has been focused
on the development of efficient and operationally simple
protocols for the formation of carbon–carbon bonds for the
construction of valuable molecules. The Michael addition
reaction is one of the most general and versatile methods
for the construction of new carbon–carbon bonds in or-
ganic synthesis. The organocatalytic asymmetric Michael
addition of ketones to trans-β-nitrostyrene, which provides
optically active nitroalkane derivatives of synthetic and bio-
Results and Discussion
The synthetic route towards binaphthyl sulfonimides and
sulfonamides 3a–d is shown in Scheme 1. Our original re-
[1]
[2]
logical importance, was pioneered by List and Barbas
independently, and since then great effort has been devoted search project is the synthesis of binaphthyl sulfonamide
to the development of more selective and efficient catalytic compounds 3b and 3d and their application in asymmetric
[
3,4]
systems for this synthetically useful transformation.
De- Michael additions. However, the unexpected binaphthyl
spite the excellent results that have been achieved by these sulfonimides were obtained firstly and showed better cata-
systems, the design and development of novel backbones lytic performance.
and efficient chiral organocatalysts remain major challenges
in synthetic organic chemistry. During the past several years fonyl dichloride (1)
sulfonamide derivatives as organocatalysts or ligands have tyl 2-(aminomethyl)pyrrolidine-1-carboxylate (2)
Initially, one equivalent of (R)-1,1Ј-binaphthyl-2,2Ј-disul-
[
12,13]
and two equivalents of (S)-tert-bu-
[
14,15]
were
been successfully applied in asymmetric Michael ad- stirred in CH Cl . A new spot was observed by TLC (petro-
2
2
[
5]
[6]
ditions, asymmetric Aldol reactions, asymmetric alk- leum ether/ethyl acetate, 2:1; R = 0.3) after 12 h; thus, the
asymmetric diethylzinc ad- mixture was purified by column chromatography and
ditions, asymmetric cyclopropanations, asymmetric re- treated with TFA. Other than the expected binaphthyl sulf-
f
[7]
ynylations of aldehydes,
[
8]
[9]
[10]
duction of ketones,
Kishi reactions,
and asymmetric Nozaki–Hiyama– onamide catalyst, the new compound was determined to be
but to the best of our knowledge, the sulfonimide compound through NMR spectroscopy
[
11]
sulfonimide-catalyzed asymmetric reactions are rarely re- and MS characterization. Then, the mmol ratio of starting
materials was adjusted to 1:1 and an improved yield of bi-
naphthyl sulfonimide (3a) could be achieved. In our further
[
a] School of Chemical Engineering and Environment, Beijing
Institute of Technology,
experiments, when the amount of starting material 2 was
increased to 3.6 equiv., the formation of a new product with
significantly higher polarity could be observed (petroleum
Beijing 100081, People’s Republic of China
Fax: +86-10-68914985
E-mail: dudm@bit.edu.cn
[
[
b] School of Pharmaceutical Science, Shanxi Medical University,
Taiyuan 030001, People’s Republic of China
c] Beijing National Laboratory for Molecular Sciences (BNLMS),
College of Chemistry and Molecular Engineering, Peking
University,
ether/ethyl acetate, 1:1; R = 0.1). After deprotection of the
f
N-Boc group with TFA, binaphthyl sulfonamide 3b was ob-
tained in pure form. Catalysts 3c and 3d were prepared in
similar ways. The detailed experimental procedures and the
spectroscopic data are provided in the Experimental Sec-
tion.
Beijing 100871, People’s Republic of China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201000818.
View this journal online at
wileyonlinelibrary.com
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 5160–5164

Binaphthyl Sulfonimides in Enantioselective Michael Additions
Almost the same levels of enantioselectivity and diastereo-
selectivity were observed for solvent-free (Table 1, Entry 1;
97:3dr, 92%ee), toluene (Table 1, Entry 2; 97:3dr, 92%ee),
EtOH (Table 1, Entries 3; 96:4dr, 91%ee), and dichloro-
methane (Table 1, Entry 4; 97:3dr, 92%ee). Considering
both the reaction rate and atom economy, DCM is the best
choice and was selected as the reaction solvent in the fol-
lowing reactions. Moreover, the additive carboxylic acid
was found to be an essential factor to this reaction. In the
absence of any carboxylic acid or in the presence of
CF COOH, no product was obtained (Table 1, Entries 5
3
and 7). Almost the same level of enantioselectivity was ob-
served for substituted benzoic acids such as o-nitrobenzoic
acid (Table 1, Entry 4; 92%ee), p-bromobenzoic acid
(Table 1, Entry 6; 92%ee), benzoic acid (Table 1, Entry 8;
9
9
3%ee), and p-methylbenzoic acid (Table 1, Entry 9;
3%ee). Benzoic acid is the suitable choice because of the
higher diastereoselectivity and reaction rate. We also found
that the stereoselectivity was increased by decreasing the
reaction temperature from 20 to 0 °C (Table 1, Entry 10;
9
9:1dr, 95%ee).
Other chiral catalysts 3b–d were screened by employing
these optimized conditions (Table 1, Entry 10), and the re-
sults are summarized in Table 2. Catalysts 3a–d facilitated
the asymmetric Michael addition of cyclohexanone to ni-
trostyrene with good to excellent stereoselectivities and
Scheme 1. Synthesis of binaphthyl sulfonimides and sulfonamides yields. Sulfonimides 3a and 3c exhibited significantly higher
3a–d.
enantioselectivities than sulfonamides 3b and 3d. (S)-1,1Ј-
Binaphthyl-derived catalysts 3c and 3d demonstrated slight
With the desired catalysts in hand, we immediately began higher catalytic activity. Catalyst 3c was the best catalyst
to optimize the reaction conditions. Using 3a as the cata- and was selected in the following reactions.
lyst, a number of parameters were screened in the model
With the optimized reaction conditions in hand, we next
asymmetric Michael addition of cyclohexanone to β-nitro- examined other nitroalkenes to expand the substrate scope
styrene. The results are summarized in Table 1. Initially, the of catalyst 3c, and the results are summarized in Table 3.
conjugate addition was examined in a few solvents at room Various styrene-type nitroalkenes reacted smoothly with cy-
temperature with o-nitrobenzoic acid as additive. In terms clohexanone to provide the corresponding adducts in mod-
of enantioselectivity and diastereoselectivity, a variety of erate to excellent yields with excellent diastereoselectivities
solvents were tolerated in this Michael addition reaction. and enantioselectivities (Table 3, Entries 1–10). Excellent
Table 1. Optimization of solvents, reaction temperature, and additive.[a]
Entry
Additive
Solvent
Temp. [°C]
Time [h]
Yield [%][b]
dr [syn/anti][c]
ee [%][d]
1
2
3
4
5
6
7
8
9
o-NO
o-NO
o-NO
o-NO
2
2
2
2
PhCO
PhCO
PhCO
PhCO
–
2
2
2
2
H
H
H
H
–
20
20
20
20
20
20
20
20
20
0
12
12
12
12
12
12
12
12
12
24
97
92
81
97
0
94
0
97
74
97
97:3
97:3
96:4
97:3
–
97:3
–
98:2
97:3
99:1
92
92
91
92
–
92
–
93
93
95
toluene
EtOH
DCM
DCM
DCM
DCM
DCM
DCM
DCM
p-BrPhCO
CF CO
PhCO
p-CH PhCO
PhCO
2
H
3
2
H
2
H
3
2
H
10
2
H
[
a] All reactions were carried out with cyclohexanone (4; 100 mg, 1.0 mmol) and nitrostyrene (5a; 18.7 mg, 0.13 mmol) in the presence of
catalyst 3a (10 mol-%) in DCM (0.2 mL). [b] Yield of the isolated product after chromatography on silica gel. [c] Determined by chiral
HPLC on a Chiracel AS-H column with n-hexane and 2-propanol as eluents. [d] Determined by chiral HPLC analysis.
Eur. J. Org. Chem. 2010, 5160–5164
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5161

S. Ban, D.-M. Du, H. Liu, W. Yang
SHORT COMMUNICATION
Table 2. Screening of catalysts.[a]
Cyclopentanone and acetone were subsequently exam-
ined in the 3c-catalyzed Michael addition with nitrostyrene
(5a). Unfortunately, as depicted in Scheme 2, the results
were not satisfactory. Cyclopentanone gave low yield and
moderate enantioselectivities, and no product was obtained
for acetone.
Entry Catalyst Time [h] Yield [%][b] dr [syn/anti][c] ee [%][d]
1
2
3
4
3a
3b
3c
3d
24
24
24
24
97
94
97
95
99:1
97:3
99:1
98:2
95.1
88.0
95.3
93.0
[
1
a] All reactions were carried out with cyclohexanone (4; 100 mg,
.0 mmol) and nitrostyrene (5a; 18.7 mg, 0.13 mmol) in the pres-
ence of catalyst 3 (10 mol-%) and benzoic acid (10 mol-%) in DCM
0.2 mL). [b] Yield of the isolated product after chromatography on
(
silica gel. [c] Determined by chiral HPLC. [d] Determined by chiral
HPLC analysis.
Scheme 2. Michael addition of ketones to 5a.
diastereoselectivities (up to 99:1dr) and enantioselectivities
(93–96%ee) were observed regardless of the electronic na-
On the basis of the configuration of the product, the pos-
ture of the aromatic substituent R, whereas the nature of sible transition state for the 3c-catalyzed Michael addition
the substituent on the benzene ring exhibited a slight influ- is illustrated in Figure 1. The pyrrolidine ring will first react
ence on the reaction activity. When an electron-donating with the carbonyl compound to form an enamine with the
substituent was introduced at the para position of the ben- aid of the acidic cocatalyst. Subsequently, the oxygen atom
zene ring, only low to moderate yields were obtained of the sulfonimide as well as the Brønsted acid additive will
(Table 3, Entries 5 and 8), and this may be ascribed to the orientate the nitro group through a hydrogen bonding inter-
lower reactivity of these substrates as no other side reac- action so that the enamine will nucleophilically attack the
tions were observed. In addition, aliphatic-aldehyde-derived nitrooalkene from the Re face to give the highly enantio-
nitroalkenes do not appear to be good candidates for this and diastereoselective product.
asymmetric Michael addition reaction (Table 3, Entry 11;
syn/anti, 67:33; 71%ee for syn isomer).
Table 3. Catalytic asymmetric Michael addition of cyclohexanone
[
a]
to nitroalkenes.
dr
Entry
R
Time [h] Yield [%][b]
ee [%][d]
Figure 1. Possible transition state.
[
c]
[
syn/anti ]
1
2
3
4
5
6
7
Ph
24
24
24
36
48
48
48
97
87
81
57
47
88
50
99:1
Ͼ99:1
Ͼ99:1
99:1
Ͼ99:1
98:2
95
96
96
96
95
96
94
2-MeOC
2-ClC
4-ClC
4-MeC
3-NO
2-furyl
,4-(MeO)
6 4
H
H
4
6
6
H
4
Conclusions
6
H
4
[e]
2
C
6 4
H
In conclusion, we have developed new -proline-based
binaphthyl sulfonimides and sulfonamides 3 as highly ef-
ficient and stereoselective organocatalysts for the asymmet-
ric Michael addition of ketones to nitroalkenes. Moderate
to excellent diastereoselectivities and enantioselectivities
were obtained for the addition of cyclohexanone to a vari-
99:1
3
8[e]
96
42
99:1
96
2 6 3
C H
9
2-thienyl
4-FC
PhCH
70
70
70
63
78
30
98:2
99:1
67:33
93
96
71
1
0
6 4
H
11
2
CH
2
[
1
a] All reactions were carried out with cyclohexanone (4; 100 mg, ety of nitroalkenes under the catalysis of 3c. The presence
.0 mmol) and nitroalkene 5 (0.13 mmol) in the presence of catalyst of a brønsted acid with proper acidity, such as PhCO H,
2
3
c (10 mol-%) and benzoic acid (10 mol-%) in DCM (0.2 mL).
proved to be critical for the excellent performance of this
[
[
b] Yield of the isolated product after chromatography on silica gel.
c] Determined by chiral HPLC. [d] Determined by chiral HPLC
catalyst system. The application of this new type of organo-
catalyst in other asymmetric reactions is underway in our
laboratory.
[4]
analysis, the configuration was assigned according to ref. [e] Re-
action at room temperature.
5162
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Eur. J. Org. Chem. 2010, 5160–5164

Binaphthyl Sulfonimides in Enantioselective Michael Additions
ArH), 8.00 (d, J = 8.2 Hz, 2 H, ArH), 7.63 (t, J = 6.4 Hz, 2 H,
ArH), 7.35 (d, J = 6.5 Hz, 4 H, ArH), 3.88 (dd, J = 6.5 Hz, J =
Experimental Section
N-{[(S)-Pyrrolidin-2-yl]methyl}-(R)-1,1Ј-binaphthyl-2,2Ј-disulfon-
imide (3a): To a solution of (R)-1,1Ј-binaphthyl-2,2Ј-disulfonyl di-
chloride (197 mg, 0.44 mmol) in dichloromethane was added drop-
wise a mixture of (S)-tert-butyl 2-(aminomethyl)pyrrolidine-1-carb-
oxylate (105 mg, 0.52 mmol) and triethylamine (2 mL). The reac-
tion mixture was stirred at room temperature overnight. The mix-
ture was separated directly by silica gel column chromatography
1
4.9 Hz, 1 H, CH
2
), 3.73 (dd, J = 6.6 Hz, J = 15.0 Hz, 1 H, CH
+ NH), 1.65–1.91
): δ = 135.5, 134.4,
31.4, 130.8, 129.4, 128.6, 128.2, 128.0, 122.9, 58.1, 50.2, 46.0, 28.6,
2
),
3.58–3.65 (m, 1 H, CH), 2.90–3.05 (m, 3 H, CH
2
13
2 3
(m, 4 H, CH ) ppm. C NMR (75 MHz, CDCl
1
2
4
+
4.6 ppm. HRMS (ESI): calcd. for C25
79.10938; found 479.10907.
23 2 4 2
H N O S [M + H]
N,NЈ-{[(S)-Pyrrolidin-2-yl]methyl}-(S)-1,1Ј-binaphthyl-2,2Ј-disulfon-
amide (3d): Compound 3d was prepared according to the method
outlined for 3b by using (S)-1,1Ј-binaphthyl-2,2Ј-disulfonyl dichlo-
ride (140 mg, 0.31 mmol) and (S)-tert-butyl 2-(aminomethyl)pyr-
rolidine-1-carboxylate (224 mg, 1.12 mmol). A white solid (55 mg,
(
dichloromethane) to give a white solid, which was then dissolved
in a mixture of trifluoroacetic acid (0.28 mL) and dichloromethane
10 mL). The mixture was stirred for 4 h at room temperature. The
pH of the mixture was adjusted to about 8 with saturated
NaHCO . The mixture was extracted with dichloromethane
3ϫ20 mL) and dried with anhydrous Na SO . After removal of
the solvent, the product was obtained as a white solid (133 mg,
(
3
2
0
3
1% yield) was obtained. M.p. 181–183 °C. [α]
D
= –208.0 (c = 0.5,
(
2
4
DMSO). IR (KBr): ν˜ = 3434, 3060, 2922, 2871, 1646, 1586, 1502,
1
6
8
7
8
2
2
1
4
407, 1321, 1258, 1171, 1136, 1083, 1025, 952, 906, 819, 750, 698,
82, 638 cm . H NMR (300 MHz, [D ]DMSO): δ = 8.17 (d, J =
6
.5 Hz, 2 H, ArH), 8.02 (d, J = 8.4 Hz, 4 H, ArH), 7.54 (t, J =
.0 Hz, 2 H, ArH), 7.28 (t, J = 7.2 Hz, 2 H, ArH), 6.80 (d, J =
4% yield). M.p. Ͼ270 °C. [α]2
0
6
D 2 2
= –4.2 (c = 0.5, CH Cl ). IR (KBr):
–
1 1
ν˜ = 3457, 3060, 2951, 2868, 1584, 1504, 1449, 1340, 1281, 1182,
–1 1
1
(
138, 1106, 1027, 877, 820, 776, 751, 728, 671, 656 cm . H NMR
300 MHz, CDCl ): δ = 8.22 (s, 4 H, ArH), 8.04 (d, J = 8.2 Hz, 2
H, ArH), 7.67 (t, J = 7.4 Hz, 2 H, ArH), 7.26–7.41 (m, 4 H, ArH),
.91 (dd, J = 7.8 Hz, J = 15.0 Hz, 1 H, CH ), 3.74 (dd, J = 5.1 Hz,
J = 15.1 Hz, 1 H, CH ), 3.60–3.66 (m, 1 H, CH), 3.05–3.11 (m, 1
H, CH), 2.92–3.00 (m, 1 H, CH ), 2.82 (br. s, 1 H, NH), 1.67–1.99
m, 3 H, CH ), 1.52–1.61 (m, 1 H, CH
) ppm. 13C NMR (75 MHz,
CDCl ): δ = 135.3, 135.2, 134.0, 131.2, 130.5, 129.1, 128.4, 127.9,
27.8, 122.8, 58.4, 49.7, 45.5, 28.4, 24.1 ppm. HRMS (ESI): calcd.
3
.2 Hz, 2 H, ArH), 4.79 (br. s, 4 H, NH), 2.91–2.93 (m, 2 H, CH
.61–2.71 (m, 8 H, CH + CH), 1.49–1.60 (m, 6 H, CH ), 1.18 (s,
) ppm. C NMR (75 MHz, [D ]DMSO): δ = 137.1, 134.6,
33.7, 132.8, 128.9, 128.0, 127.9, 127.3, 126.9, 123.9, 57.4, 47.2,
5.5, 28.7, 24.7 ppm. HRMS (ESI): calcd. for C30 [M +
2
),
2
2
3
2
1
3
H, CH
2
6
2
2
35 4 4 2
H N O S
(
2
2
+
H] 579.20942; found 579.20969.
3
1
General Procedure for 3-Catalyzed Asymmetric Michael Addition of
Ketone to Nitroalkenes: A solution of catalyst 3 (0.013 mmol) and
cyclohexanone (0.1 mL, 0.1 mmol) in DCM (0.2 mL) was stirred at
room temperature for 30 min. Then, benzoic acid (1.5 mg,
+
23 2 4 2
for C25H N O S [M + H] 479.10938; found 479.10908.
N,NЈ-{[(S)-Pyrrolidin-2-yl]methyl}-(R)-1,1Ј-binaphthyl-2,2Ј-disulfon-
amide (3b): To a solution of (S)-tert-butyl 2-(aminomethyl)pyrroli-
dine-1-carboxylate (300 mg, 1.50 mmol) and triethylamine (3 mL)
in dichloromethane (10 mL) was added dropwise (R)-1,1Ј-binaph-
thyl-2,2Ј-disulfonyl dichloride (188 mg, 0.42 mmol). The reaction
mixture was stirred at room temperature overnight. The mixture
was separated directly by silica gel column chromatography (petro-
leum ether/ethyl acetate, 1:1) to give a white solid, which was dis-
solved in a mixture of trifluoroacetic acid (0.50 mL) and dichloro-
methane (10 mL). The mixture was then stirred for 4 h at room
temperature. The pH of the mixture was adjusted to about 8 with
0
1
.013 mmol) was added, and the reaction mixture was stirred for
5 min. To the resulting mixture was added the nitroalkene
(
0.13 mmol) at the required temperature. Upon completion of the
reaction (monitored by TLC), the mixture was purified by column
chromatography on silica gel (200–300 mesh; petroleum ether/ethyl
acetate, 10:1) to afford the pure product.
Supporting Information (see footnote on the first page of this arti-
1
13
cle): General remarks; H NMR, C NMR, IR, and mass spectra
of the new organocatalysts; spectra data and HPLC diagrams for
the Michael addition adducts.
saturated NaHCO
ane (3ϫ30 mL) and dried with anhydrous Na
of the solvent, the product was obtained as a white solid (100 mg,
3
. The mixture was extracted with dichlorometh-
2
SO . After removal
4
4
1% yield). M.p. 172–173 °C. [α]2
0
= +221.2 (c = 0.5, CH Cl ). IR
D 2 2
Acknowledgments
(
1
KBr): ν˜ = 3425, 3060, 2960, 2873, 1588, 1503, 1424, 1330, 1170,
149, 1135, 1123, 879, 817, 752, 697, 683 cm–1
1
We are grateful to the National Natural Science Foundation of
China (Grant No. 20772006) and the Development Program for
Distinguished Young and Middle-Aged Teachers of Beijing Insti-
tute of Technology for financial support.
. H NMR
3
(300 MHz, CDCl ): δ = 8.08 (s, 4 H, ArH), 7.94 (d, J = 8.1 Hz, 2
H, ArH), 7.55 (t, J = 7.4 Hz, 2 H, ArH), 7.29 (t, J = 7.3 Hz, 2 H,
ArH), 7.02 (d, J = 8.5 Hz, 2 H, ArH), 4.22 (br. s, 4 H, NH), 3.12–
3
2
.16 (m, 2 H, CH
.77–2.85 (m, 6 H, CH
) ppm. 13C NMR (75 MHz, CDCl
34.3, 133.3, 129.3, 128.2, 128.1, 127.5, 124.4, 57.9, 47.3, 46.0, 28.8,
2
), 2.99 (dd, J = 4.5 Hz, J = 12.3 Hz, 2 H, CH
+ CH), 1.58–1.77 (m, 6 H, CH
): δ = 136.2, 134.8,
2
),
),1.24–1.33 [1] B. List, P. Pojarliev, H. J. Martin, Org. Lett. 2001, 3, 2423–
2
2
(m, 2 H, CH
2
3
2425.
[
2] K. Sakthivel, W. Notz, T. Bui, C. F. Barbas, J. Am. Chem. Soc.
2001, 123, 5260–5267.
3] For recent reviews on asymmetric Michael additions, see: a)
O. M. Berner, L. Tedeschi, D. Enders, Eur. J. Org. Chem. 2002,
1877–1894; b) R. Ballini, G. Bosica, D. Fiorini, A. Palmieri,
M. Petrini, Chem. Rev. 2005, 105, 933–971; c) S. Mukherjee,
J. W. Yang, S. Hoffmann, B. List, Chem. Rev. 2007, 107, 5471–
1
2
5
35 4 4 2
H N O S
[M + H]+
5.3 ppm. HRMS (ESI): calcd. for C30
79.20942; found 579.20957.
[
N-{[(S)-Pyrrolidin-2-yl]methyl}-(S)-1,1Ј-binaphthyl-2,2Ј-disulfon-
imide (3c): Compound 3c was prepared according to the method
outlined for 3a by using (S)-1,1Ј-binaphthyl-2,2Ј-disulfonyl dichlo-
ride (201 mg, 0.45 mmol) and (S)-tert-butyl 2-(aminomethyl)pyr-
5569; d) S. Sulzer-Mosse, A. Alexakis, Chem. Commun. 2007,
3123–3135; e) S. B. Tsogoeva, Eur. J. Org. Chem. 2007, 1701–
1716; f) J. L. Vicario, D. Badía, L. Carrillo, Synthesis 2007,
2065–2092.
rolidine-1-carboxylate (107 mg, 0.53 mmol). A white solid (88 mg,
1% yield) was obtained. M.p. 249–251 °C. [α]2
0
= –30.2 (c = 0.5,
4
D
CH
2
Cl
2
). IR (KBr): ν˜ = 3448, 3058, 2955, 2874, 1718, 1623, 1584,
[
4] For selected examples of the organocatalyzed asymmetric
Michael addition of ketones to nitroalkenes, see: a) Z. G. Yang,
J. Liu, X. H. Liu, Z. Wang, X. M. Feng, Z. S. Su, C. W. Hu,
1
7
504, 1450, 1341, 1280, 1182, 1138, 1106, 1028, 877, 821, 781, 750,
28, 672, 656 cm . H NMR (300 MHz, CDCl ): δ = 8.18 (s, 4 H,
3
–1 1
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Received: June 8, 2010
Published Online: July 27, 2010
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Eur. J. Org. Chem. 2010, 5160–5164