Sugar-based pyrrolidine as a highly enantioselective organocatalyst for asymmetric michael addition of ketones to nitrostyrenes

Article abstract of DOI:10.1002/adsc.201000162

A modular sugar-based pyrrolidine (3) was prepared and was found to be a highly enantioselective organocatalyst for the asymmetric Michael addition of ketones to nitrostyrenes. In the presence of 10 mol% of 3, a pyrrolidine unit anchored to a natural D-gl

Full text of DOI:10.1002/adsc.201000162

FULL PAPERS
DOI: 10.1002/adsc.201000162
Sugar-Based Pyrrolidine as a Highly Enantioselective
Organocatalyst for Asymmetric Michael Addition of Ketones to
Nitrostyrenes
Lei Wang,a,c,* Jie Liu,a Tao Miao,a Wei Zhou,a Pinhua Li,a Kai Ren,a
and Xiuli Zhangb,c,*
a
Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, Peopleꢀs Republic of China
Fax : (+86)-561-3090-518; phone: (+86)-561-3802-069; e-mail: leiwang@chnu.edu.cn
College of Science, Anhui Agricultural University, Hefei, Anhui 230036, Peopleꢀs Republic of China
b
Fax : (+86)-551-5786-121; phone: (+86)-551-5786-791; e-mail: zhxiuli@163.com
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
c
Sciences, Shanghai 200032, Peopleꢀs Republic of China
Received: March 2, 2010; Revised: July 15, 2010; Published online: September 30, 2010
Abstract: A modular sugar-based pyrrolidine (3) was ducts in good yields (up to 98%), high enantioselec-
prepared and was found to be a highly enantioselec- tivities (up to >99% ee) and excellent diastereose-
tive organocatalyst for the asymmetric Michael addi- lectivities (up to >99:1 dr) under solvent-free reac-
tion of ketones to nitrostyrenes. In the presence of tion conditions.
10 mol% of 3, a pyrrolidine unit anchored to a natu-
ral d-glucose backbone through click chemistry, the Keywords: asymmetric Michael addition; d-glucose;
Michael additions of ketones to nitrostyrenes pro- nitrostyrenes; organocatalysts; pyrrolidine unit; sol-
ceeded smoothly to generate the corresponding ad- vent-free reaction conditions
Introduction
amine bifunctional catalysts.[23–29] Currently, asymmet-
ric organocatalysis has attracted considerable atten-
The asymmetric Michael addition of a carbon nucleo- tion as a new, powerful, and environmentally friendly
phile to a nitroalkene plays a particularly important methodology for the catalytic production of enantio-
role among the numerous carbon-carbon bond form- merically pure organic compounds and also as one of
ing reactions since it represents a very useful synthetic the most rapidly growing and competitive research
method for the preparation of chiral nitroalkanes areas in synthetic organic chemistry. Therefore, the
with at least two vicinal stereogenic centers in a single design of new effective organocatalysts for asymmet-
step.[1–6] Chiral nitroalkanes are valuable building ric synthesis is of great importance.
blocks in organic synthesis because they can be trans-
With their configurations being assigned as the d-
formed into a wide variety of different functional family, natural carbohydrates which are the most
groups such as amines, carboxylic acids, nitrile oxides, abundant class of organic compounds found in living
etc.[7,8] Their versatile utility in organic synthesis has organisms among the natural products perform nu-
stimulated tremendous research interest in the devel- merous roles. Besides, natural amino acids with the l-
opment of asymmetric Michael catalysts, especially configuration found within proteins convey a vast
metal-free organo-catalysts. In 2001, Barbas[9] and array of chemical versatility and play central roles
List[10] independently reported that l-proline could both as building blocks of proteins and as intermedi-
catalyze the asymmetric Michael addition of ketone ates in metabolism. Recently carbohydrate-based bi-
to trans-b-nitrostyrene, but the natural catalysts, such dentate ligands have been successfully used in some
as l-proline failed to demonstrate good enantioselec- enantioselective reactions.[30–34] In this context, a mod-
tivity (0–23% ee). Since then, a variety of asymmetric ular and more efficient approach constructs the sugar-
organocatalysts have been explored for the Michael based pyrrolidine through a click reaction, which in-
addition of ketones or aldehydes to nitroolefins, such troduces a chiral pyrrolidine moiety into a common
as pyrrolidine-based diamines,[11–17] chiral di- and inexpensive carbohydrate. Sugar-based pyrroli-
ACHTUNGTRENNUNG
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Scheme 1. We were pleased to find that the newly de-
signed organocatalyst 3 catalyzed the reaction of cy-
clohexanone to arylnitroolefins smoothly to generate
the corresponding adducts in good yields (up to
98%), high enantioselectivities (up to >99% ee) and
excellent diastereoselectivities (up to >99:1 dr) under
solvent-free reaction conditions.
In comparison with the above-mentioned similar
pyrrolidine-based organocatalysts used in the asym-
metric Michael addition to nitrostyrenes,[16] this sugar-
based pyrrolidine organocatalyst 3 showed particular
advantages: (i) high yields attained; (ii) excellent
enantioselectivities (up to >99% ee) and diastereose-
lectivities (up to >99:1 dr) obtained; (iii) solvent-free
reaction conditions without any organic solvent in the
reaction; (iv) free of TFA as additive in the reaction;
and (v) simple and easy experimental operation. In
this paper, we will describe our experimental results.
Results and Discussion
Organocatalysts 1 and 2 were prepared according to
the literature,[16c] and the synthesis of sugar-based pyr-
rolidine catalyst 3 (or 4) is illustrated in Scheme 2. It
was readily prepared through a three-step procedure
for the synthsis of 3 (or 4). Diacetone-d-glucose 5 in
dry THF reacted with propargyl bromide in the pres-
ence of NaH (60% dispersion in mineral oil) and tet-
raethylammonium iodide (TEAI, 20 mol%) at room
temperature and 708C for 20 h to afford 6 as pale
yellow oil in 76% yield.[35] The obtained 6 reacted
with 7, obtained according to the synthetic route[36] in
the presence of DIPEA and CuI (20 mol%) in the
mixed solvent (CHCl3/EtOH/H2O=9/1/1) at room
temperature for 16 h to form the corresponding 8 as a
pale yellow oil, followed by deprotection of the Fmoc
Scheme 1. Sugar-based pyrrolidine 3 as catalyst and screened
organocatalysts 1–4 for the asymmetric Michael addition.
Scheme 2. Typical synthesis route to sugar-based pyrrolidine 3.
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Sugar-Based Pyrrolidine as a Highly Enantioselective Organocatalyst
group in DMF/piperidine (v/v 8/2) at room tempera- important to note that 4 derived from l-glucose
ture with shaking for 0.5 h. The desired 3 was ob- showed lower enantioselectivity than 3 derived from
tained as a colorless oil in 78% yield.[37] When diace- d-glucose (Table 1, entry 3 vs. 4). The reason for the
tone-l-glucose was used as starting material through difference of this type of catalyst is unclear at present,
the same synthetic procedure, the corresponding 4 but the size of substituted group on the 1,2,3-triazole
was obtained as a colorless oil.
and stereochemistry mating of the substituted group
For optimization of the reaction conditions and the on the 1,2,3-triazole with the pyrrolidine unit derived
identification of the best organocatalyst, solvent and from l-proline have a certain effect on its activity and
reaction temperature, a model reaction of cyclohexa- stereoselectivity. In the following reaction, 3 was
none with trans-b-nitrostyrene was chosen. The results chosen as catalyst considering its high activity, high
are summarized in Table 1. Initially, organocatalysts stereoselectivity and the low cost of natural d-glucose.
with different skeletons were explored. As shown in Next, various solvents were examined on the model
Table 1, when the model reactions were carried out in reaction at room temperature using 10 mol% of 3 as a
the presence of organocatalysts 1–4 (10 mol%) re- catalyst. As shown in Table 1, in polar or non-polar
spectively in EtOH at room temperature for 24 h, 3 solvents, such as EtOH, CH3CN, DMF, H2O, CHCl3,
was found to be the most effective one in reaction ac- THF, hexane or toluene, the model Michael addition
tivity and stereoselectivity (Table 1, entries 1–4). It is reaction proceeded smoothly to give the product in
moderate to good yields with high diastereoselectivi-
ties and enantioselectivities (Table 1, entries 3, and 5–
11). To our delight, almost quantitative isolated yield
and excellent diastereoselectivity and enantioselectivi-
ty were obtained when the model reaction was carried
out under solvent-free reaction conditions (Table 1,
entry 12). With respect to the catalyst loading, when
less than 10 mol% of 3 was used, the reaction did not
go to completion, but that a higher loading (up to
10 mol%) of the catalyst 3 gave a very good result
(Table 1, entries 13 and 12). However, with an in-
creased loading of the catalyst 3 up to 15 mol%, there
was no increase in the isolated yield of the product
(Table 1, entry 14). In addition, a slightly higher enan-
tioselectivity and almost same diastereoselectivity
were achieved when the reaction temperature was
down to 108C without a significant decrease of the re-
action rate (Table 1, entry 15). Interestingly, the addi-
tion of a catalytic amount of organic acid, such as
TFA, could reduce the reaction rate along with loss of
enantiomeric excess (Table 1, entry 16). In addition, it
was also found that the reaction was accomplished as
the reaction was carried out for more than 24 h
(Table 1, entries 17 and 18).
Under the optimized Michael additions of nitroole-
fins with ketones the reaction involved the use of
10 mol% of 3 as catalyst in the absence of solvent at
room temperature for 24 h. The reactions of a variety
of nitroolefins with different substituents and ketones
were investigated, and the results are summarized in
Table 2. Various styrene-type nitroolefins reacted
smoothly with cyclohexanone in high yields with ex-
cellent diastereoselectivities and enantioselectivities
(Table 2, entries 1–14). Generally, substituents on the
aryl groups in nitroolefins slightly influenced the dia-
stereoselectivities and enantioselectivities, as well as
the yields. For example, phenyl rings in nitroolefins
bearing both electron-withdrawing and electron-do-
nating groups gave the desired Michael addition prod-
ucts with high stereoselectivities (up to >99:1 dr and
Table 1. Optimization of the reaction conditions.[a]
Entry Catalyst Solvent Yield[b] [%] ee[c] [%] dr[d]
1
2
3
4
5
6
7
8
1
2
3
4
3
3
3
3
3
3
3
3
3
3
3
3
3
3
EtOH
EtOH
EtOH
EtOH
CH3CN 86
DMF
H2O
CHCl3
THF
hexane
82
75
88
87
91
90
99
85
98
99
99
99
98
98
99
99
99
99
>99
97
99
99
49:1
24:1
99:1
49:1
98:2
98:2
99:1
99:1
99:1
98:2
98:2
99:1
99:1
99:1
99:1
99:1
99:1
99:1
85
73
78
80
87
9
10
11
12
13[e]
14[f]
15[g]
16[h]
17[i]
18[j]
toluene 83
neat
neat
neat
neat
neat
neat
neat
98
64
98
90
78
86
98
[a]
Nitrostyrene (1.0 mmol), cyclohexanone (2.0 mmol), or-
ganocatalyst 1, 2, 3, or 4 (0.10 mmol), in solvent (2.0 mL)
or under solventless reaction condition at room tempera-
ture for 24 h.
Isolated yields.
Enantiomeric excess, ee, determined by HPLC using chir-
alpak AD-H column.
[b]
[c]
[d]
Diasteromeric ratio, dr (syn/anti), determined by
1H NMR spectroscopy.
[e]
[f]
[g]
[h]
[i]
5 mol% of 3 was used in the reaction.
15 mol% of 3 was used in the reaction.
The reaction temperature was 108C for 36 h.
5 mol% of TFA was added in the reaction.
The reaction time was 12 h.
[j]
The reaction time was 36 h.
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Table 2. Michael additions of ketones to trans-b-nitrostyr-
enes catalyzed by 3.[a]
Table 2. (Continued)
Entry Product
Yield[b] [%] ee[c] [%] dr[d]
13
14
91
86
>99
>99:1
Entry Product
1
Yield[b] [%] ee[c] [%] dr[d]
99
99:1
98
96
97
98
95
99
99:1
2
3
4
5
>99
99
>99:1
99:1
15
16
75
89
87
93
95
98
94:6
99:1
99:1
>99
99
>99:1
99:1
17
18
95
93
85; 83
63
34:66
–
19
6
7
8
90
93
97
93
98
96
98:2
99:1
99:1
[a]
Nitroolefin
(1.0 mmol),
ketone
(2.0 mmol),
3
(0.10 mmol), under solvent-free reaction conditions at
room temperature for 24 h.
[b]
[c]
Isolated yields.
Enantiomeric excess, ee, determined by HPLC using chir-
alpak AS-H and AD-H columns.
Diasteromeric ratio, dr (syn/anti), determined by
[d]
1H NMR spectroscopy.
9
94
90
99
91
98:2
99:1
up to >99% ee) in excellent yields. However, an aver-
age yield but good enantioselectivity of product was
obtained when aliphatic substituted nitroolefin was
used as one of the reaction substrate (Table 2,
entry 15). Moreover, the Michael reactions were eval-
uated with other ketones and we found that tetrahy-
drothiopyran-4-one and tetrahydro-4H-pyran-4-one
were also suitable substrates as Michael donors
(Table 2, entries 16 and 17). However, cyclopentanone
and acetone served as efficient Michael donors and
generated the desired adducts with excellent yield,
but moderate to good diastereoselectivity and enan-
tioselectivity were observed (Table 2, entries 18 and
19).
10
11
12
84
90
99
99:1
>99
>99:1
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Sugar-Based Pyrrolidine as a Highly Enantioselective Organocatalyst
28.2, 23.3, À1.47; anal. calcd. for C10H20N4Si: C 53.53, H
Conclusions
8.98, N 24.97; found: C 53.81, H 8.76, N 24.85.
In summary, we have developed a new type of sugar-
based pyrrolidine organocatalyst, which is capable of
catalyzing Michael addition reaction of ketones to ni-
trostyrenes, a remarkably better catalytic performance
Procedure for the Preparation of Sugar-Based
Pyrrolidine 3 (or 4)
was provided by the reactions in terms of productivity Sodium hydride (800 mg, 60% dispersion in mineral oil,
20 mmol) was added to a solution of diacetone-d-glucose 5
(5.0 g, 19 mmol) in dry THF (20.0 mL) at room temperature
and the mixture was stirred and heated up to 708C for 2 h.
Tetraethylammonium iodide (1.0 g, 3.8 mmol) and propargyl
bromide (4.0 g, 27 mmol) in toluene (6.0 mL) were then
added to the mixture and stirred at room temperature for
16 h. After the reaction was complete, the reaction mixture
was diluted with Et2O (100.0 mL) and washed with water.
The organic layer was separated and dried with MgSO4. The
filtrate was concentrated under reduced pressure and the
residue was purified by column chromatography (SiO2,
hexane/ethyl acetate 70/30 v/v) to afford 6 as a pale yellow
oil; yield: 4.3 g (76%).[35] 1H NMR (400 MHz, CDCl3): d=
5.85 (d, J=4.0 Hz, 1H, CH), 4.62 (d, J=3.6 Hz, 1H, CH),
4.60–4.23 (m, 3H, CH2 and CH), 4.13–4.05 (m, 3H, CH2 and
CH), 3.98–3.94 (m, 1H, CH), 2.56 (s, 1H, CH), 1.48 (s, 3H,
CH3), 1.41 (s, 3H, CH3), 1.33 (s, 3H, CH3), 1.31 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): d=111.5, 108.6, 104.9,
82.6, 81.3, 80.7, 79.1, 74.9, 72.2, 66.9, 57.8, 26.5, 26.0, 25.1.
To a reaction vessel, 6 (142.2 mg, 0.5 mmol), 7 (174.2 mg,
0.5 mmol) obtained according to the reported synthetic
route,[36] DIPEA (64.5 mg, 0.5 mmol), CuI (10 mg,
0.1 mmol) and the mixed solvent (5.0 mL, CHCl3/EtOH/
H2O=9/1/1) were added and stirred vigorously at room
temperature for 16 h. After completion of the reaction, the
solvent was removed under reduced pressure. The residue
was purified by column chromatography (with hexane/ethyl
acetate 70/30 v/v) and 8 was obtained as a pale yellow oil.
The obtained yellow oil 8 was dissolved in DMF/piperidine
(5.0 mL, 8/2 v/v) at room temperature and shaken for 0.5 h.
After the reaction was completed (TLC monitoring), H2O
(15.0 mL) was added. The mixture was extracted with ethyl
acetate (10.0 mLꢂ3), and the combined organic phase was
dried over Na2SO4 and concentrated. The residue was puri-
fied by flash chromatography to afford the desired 3 as a
colorless oil; yield: 172 mg (78%).[37] 1H NMR (400 MHz,
CDCl3): d=7.76 (s, 1H, C=CH), 5.88 (s, 1H, CH), 4.81–4.79
(m, 2H, CH), 4.60 (s, 1H, CH), 4.40–4.38 (m, 2H, CH),
4.31–3.99 (m, 5H, CH), 3.63–3.60 (m, 1H, CH), 2.97–2.93
(m, 2H, CH), 2.10 (s, 1H, CH), 1.97–1.94 (m, 1H, CH),
1.79–1.73 (m, 2H, CH), 1.49 (s, 3H, CH3), 1.42 (s, 3H, CH3),
1.36 (s, 3H, CH3), 1.31 (s, 3H, CH3); 13C NMR (100 MHz,
CDCl3): d=144.4, 123.3, 111.8, 108.9, 105.2, 82.6, 81.6, 81.0,
72.4, 67.3, 64.0, 57.8, 55.4, 46.5, 29.0, 26.7, 26.2, 25.4; anal.
calcd. for C20H32N4O6: C 56.59, H 7.60, N 13.20; found: C
56.78, H 7.46, N 13.41.
(up to 98%), diastereoselectivity (syn/anti 99:1), enan-
tioselectivity (up to 99%) under solvent-free reaction
conditions at room temperature. Further investiga-
tions on the application of this kind of organocatalyst
in asymmetric catalysis are still underway in our labo-
ratory.
Experimental Section
General Remarks
All reactions were carried out under an air atmosphere. All
reagents were purchased from commercial suppliers and
used after further purification. Products were purified by
flash chromatography on 230–400 mesh silica gel, SiO2. All
1H NMR, 13C NMR spectra were measured on a Bruker
Avance NMR spectrometer (400 MHz or 100 MHz, respec-
tively) with CDCl3 as solvent and recorded in ppm relative
to internal tetramethylsilane standard.
Typical Procedure for Sugar-Based Pyrrolidine 3 as
Organocatalyst for Asymmetric Michael Addition of
Ketones to Nitrostyrenes
A 5.0-mL of reaction tube was charged with organocatalyst
3
(44 mg, 0.10 mmol), trans-b-nitrostyrene (150 mg,
1.0 mmol), cyclohexanone (2.0 mmol). The mixture was
stirred at room temperature (258C) for 24 h, and then
washed with ethyl acetate (3.0 mLꢂ3), the combined ethyl
acetate fraction was concentrated. Flash chromatography
(hexane:ethyl acetate=3:1, v/v) furnished the corresponding
(S)-2-[(R)-2-nitro-1-phenylethyl]cyclohexanone as colorless
crystals; yield: 242 mg (98%).
Procedure for the Preparation of Pyrrolidine-Type
Organocatalyst 1 (or 2)
Organocatalyst 1 was prepared according to synthetic proce-
dure shown in the literature[16c] as a pale yellow solid; over-
all yield: 90%. 1H NMR (400 MHz, CDCl3): d=8.07 (s,
1H), 7.63 (t, J=6.8 Hz, 2H), 7.35–7.26 (m, 3H), 4.94–4.89
(dd, J=8.8, 6.0, 8.4 Hz, 1H), 4.68–4.63 (dd, J=4.8, 10.0,
4.8 Hz, 1H), 4.23–4.16 (m, 1H), 3.40–3.24 (m, 2H), 2.23–
2.15 (m, 1H), 2.12–1.82 (m, 3H); 13C NMR (100 MHz,
CDCl3): d=147.7, 129.7, 128.8, 128.4, 125.5, 121.4, 59.2, 50.3,
45.5, 28.1, 23.3.
Organocatalyst 4 was obtained through the same synthetic
procedure from diacetone-l-glucose as starting material as a
colorless oil; overall yield: 61%. 1H NMR (400 MHz,
CDCl3): d=7.78 (s, 1H, C=CH), 5.87 (s, 1H, CH), 4.83–4.80
(m, 2H, CH), 4.61 (s, 1H, CH), 4.43–4.39 (m, 2H, CH),
4.30–3.95 (m, 5H, CH), 3.64–3.60 (m, 1H, CH), 2.99–2.95
(m, 2H, CH), 2.12 (s, 1H, CH), 1.98–1.94 (m, 1H, CH),
1.80–1.74 (m, 2H, CH), 1.49 (s, 3H, CH3), 1.41 (s, 3H, CH3),
1.37 (s, 3H, CH3), 1.32 (s, 3H, CH3); 13C NMR (100 MHz,
Organocatalyst 2 was prepared also according to synthetic
procedure shown in the literature[16c] as a pale yellow oil;
1
overall yield: 91%. H NMR (400 MHz, CDCl3): d=7.74 (s,
1H), 4.94–4.88 (dd, J=8.0, 6.4, 8.0 Hz, 1H), 4.67–4.62 (dd,
J=4.8, 9.6, 4.8 Hz, 1H), 4.20–4.18 (m, 1H), 3.36–3.29 (m,
2H), 2.17–2.11 (m, 1H), 2.05–1.78 (m, 3H), 0.15 (s, 9H);
13C NMR (100 MHz, CDCl3): d 146.8, 130.7, 59.1, 49.7, 45.5,
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CDCl3): d=144.5, 123.4, 111.9, 108.9, 105.2, 82.8, 81.7, 81.1,
72.4, 67.4, 64.1, 57.9, 55.5, 46.7, 29.1, 26.8, 26.2, 25.5; anal.
calcd. for C20H32N4O6: C 56.59, H 7.60, N 13.20; found: C
56.81, H 7.38, N 13.52.
4H, 2ꢂCH2), 1.30–1.17 (m, 1H, CH); 13C NMR (100 MHz,
CDCl3): d=210.8, 148.4, 140.2, 134.6, 129.9, 122.8, 78.2, 52.0,
43.4, 42.5, 33.3, 28.2, 25.0; HPLC (Chiralpak AD-H, 2-prop-
anol/hexane=10/90, flow rate 1.0 mLminÀ1, l=254 nm):
(S)-2-[(R)-2-Nitro-1-phenylethyl]cyclohexanone:[38]
tminor =11.92 min, tmajor =18.67 min; dr (syn/anti)=99:1; ee=
1H NMR (400 MHz, CDCl3): d=7.34–7.23 (m, 3H, ArH),
7.16 (d, J=7.3 Hz, 2H, ArH), 4.92 (dd, J=4.5, 12.3 Hz, 1H,
CH), 4.66 (dd, J=9.9, 12.0 Hz, 1H, CH), 3.75 (dt, J=4.5,
9.9 Hz, 1H, CH), 2.70–2.67 (m, 1H, CH), 2.49–2.45 (m, 1H,
CH), 2.43–2.36 (m, 1H, CH), 2.14–2.05 (m, 1H, CH), 1.78–
1.60 (m, 4H, 2ꢂCH2), 1.28–1.21 (m, 1H, CH); 13C NMR
(100 MHz, CDCl3): d=211.6, 137.5, 128.9, 128.3, 127.6, 78.8,
52.4, 43.9, 42.9, 33.1, 28.4, 25.2; HPLC (Chiralpak AD-H, 2-
propanol/hexane=10/90, flow rate 1.0 mLminÀ1, l=
254 nm): tminor =10.34 min, tmajor =13.23 min; dr (syn/anti)=
99:1; ee=99%; [a]2D5: À23.2 (c 1.2, CHCl3).
99%; [a]25: À28.2 (c 1.2, CHCl3).
(S)-2-[D(R)-1-(3-Bromophenyl)-2-nitroethyl]cyclohexa-
none:[39] 1H NMR (400 MHz, CDCl3): d=7.41 (d, J=7.7 Hz,
1H, ArH), 7.38 (s, 1H, ArH), 7.20 (t, J=7.9 Hz, 1H, ArH),
7.12 (d, J=7.2 Hz, 1H, ArH), 4.93 (dd, J=4.5, 12.7 Hz, 1H,
CH), 4.62 (dd, J=10.0, 12.7 Hz, 1H, CH), 3.77–3.71 (m, 1H,
CH), 2.64–2.58 (m, 1H, CH), 2.48–2.37 (m, 2H, CH2), 2.07–
2.04 (m, 1H, CH), 1.78–1.55 (m, 4H, 2ꢂCH2), 1.31–1.21 (m,
1H, CH); 13C NMR (100 MHz, CDCl3): d=211.1, 140.2,
131.2, 130.8, 130.5, 126.8, 122.7, 78.2, 52.2, 43.7, 42.7, 33.1,
28.4, 25.1; HPLC (Chiralpak AD-H, 2-propanol/hexane=
10/90, flow rate 1.0 mLminÀ1, l=254 nm): tminor =9.41 min,
(S)-2-[(R)-1-(4-Methylphenyl)-2-nitroethyl]cyclohexa-
none:[38] 1H NMR (400 MHz, CDCl3): d=7.12 (d, J=8.2 Hz,
2H, ArH), 7.03 (d, J=8.0 Hz, 2H, ArH), 4.90 (dd, J=4.7,
12.0 Hz, 1H, CH), 4.62 (dd, J=9.3, 11.9 Hz, 1H, CH), 3.73
(dt, J=4.6, 10.0 Hz, 1H, CH), 2.64–2.58 (m, 1H, CH), 2.46–
2.43 (m, 1H, CH), 2.39–2.35 (m, 1H, CH) 2.32 (s, 3H, CH3),
1.78–1.76 (m, 1H, CH), 1.76–1.55 (m, 4H, 2ꢂCH2), 1.24–
1.21(m, 1H, CH); 13C NMR (100 MHz, CDCl3): d=212.1,
137.5, 134.6, 129.6, 128.0, 79.2, 52.6, 43.7, 42.5, 33.4, 28.5,
25.1, 21.0; HPLC (Chiralpak AD-H, 2-propanol/hexane=
10/90, flow rate 1.0 mLminÀ1, l=254 nm): tminor =8.99 min,
t
major =10.35 min; dr (syn/anti)=98:2; ee=93%; [a]2D5: À31.5
(c 1.2, CHCl3).
(S)-2-[(R)-1-(2-Bromophenyl)-2-nitroethyl]cyclohexa-
none:[28] 1H NMR (400 MHz, CDCl3): d=7.59 (d, J=8.2 Hz,
1H, ArH), 7.31–7.20 (m, 2H, ArH), 7.14–7.12 (m, 1H,
ArH), 4.88 (d, J=8.0 Hz, 2H, CH2), 4.31 (dd, J=6.3, 6.8 Hz,
1H, CH), 2.91–2.85 (m, 1H, CH), 2.48–2.34 (m, 2H, CH2),
2.12–2.06 (m, 1H, CH), 1.82–1.57 (m, 4H, 2ꢂCH2), 1.40–
1.22 (m, 1H, CH); 13C NMR (100 MHz, CDCl3): d=211.4,
137.3, 133.4, 129.2, 127.8, 77.2, 52.4, 43.1, 42.5, 41.8, 32.7,
28.4, 25.2; HPLC (Chiralpak AD-H, 2-propanol/hexane=
10/90, flow rate 1.0 mLminÀ1, l=254 nm): tminor =10.34 min,
t
major =12.34 min; dr (syn/anti)> 99:1; ee>99%; [a]2D5: À25.8
(c 1.2, CHCl3).
(S)-2-[(R)-1-(4-Methoxyphenyl)-2-nitroethyl]cyclohexa-
none:[14] 1H NMR (400 MHz, CDCl3): d=7.06 (d, J=8.3 Hz,
2H, ArH), 6.82 (d, J=8.9 Hz, 2H, ArH), 4.94 (dd, J=4.5,
12.2 Hz, 1H, CH), 4.56 (dd, J=10.2, 12.3 Hz, 1H, CH), 3.77
(s, 3H, OCH3), 3.72 (dt, J=4.8, 10.4 Hz, 1H, CH), 2.65–2.63
(m, 1H, CH), 2.54–2.43 (m, 1H, CH), 2.44–2.36 (m, 1H,
CH), 2.13–2.06 (m, 1H, CH), 1.82–1.57 (m, 4H, 2ꢂCH2),
1.25–1.20 (m, 1H, CH); 13C NMR (100 MHz, CDCl3): d=
212.2, 137.4, 134.6, 129.6, 128.2, 79.0, 52.6, 43.5, 42.6, 33.4,
28.5, 25.1, 21.0; HPLC (Chiralpak AD-H, 2-propanol/
t
major =18.06 min; dr (syn/anti)=99:1; ee=98%; [a]2D5: À51.8
(c 1.2, CHCl3).
(S)-2-[(R)-1-(4-Fluorophenyl)-2-nitroethyl]cyclohexa-
none:[38] 1H NMR (400 MHz, CDCl3): d=7.14 (d, J=8.2 Hz,
2H, ArH), 7.02 (d, J=8.5 Hz, 2H, ArH), 4.93 (dd, J=4.5,
12.6 Hz, 1H, CH), 4.57 (dd, J=10.0, 12.4 Hz, 1H, CH),
3.81–3.73 (m, 1H, CH), 2.64–2.60 (m, 1H, CH), 2.48–2.38
(m, 2H, CH2), 2.09–2.07 (m, 1H, CH), 1.79–1.58 (m, 4H, 2ꢂ
CH2), 1.24–1.21 (m, 1H, CH); 13C NMR (100 MHz, CDCl3):
d=211.5, 133.4, 129.6, 129.4, 124.7, 124.6, 116.5, 115.3, 78.9,
52.3, 43.1, 42.7, 33.0, 28.4, 25.2; HPLC (Chiralpak AD-H, 2-
propanol/hexane=10/90, flow rate 1.0 mLminÀ1, l=
254 nm): tminor =16.45 min, tmajor =25.57 min; dr (syn/anti)=
99:1; ee=96%; [a]2D5: À32.6 (c 1.2, CHCl3).
hexane=10/90, flow rate 1.0 mLminÀ1, l=254 nm): tminor
=
11.99 min, tmajor =15.75 min; dr (syn/anti)=99:1; ee=99%;
[a]25: À21.8 (c 1.2, CHCl3).
(DS)-2-[(R)-1-(4-Trifluoromethylphenyl)-2-nitroethyl]cyclo-
hexanone:[14] 1H NMR (400 MHz, CDCl3): d=7.61 (d, J=
8.0 Hz, 2H, ArH), 7.30 (d, J=8.0 Hz, 2H, ArH), 4.97 (dd,
J=12.8, 4.5 Hz, 1H, CH), 4.65 (dd, J=12.8, 10.0 Hz, 1H,
CH), 3.87 (dt, 1H, J=10.0, 4.5 Hz, ArCH), 2.73–2.65 (m,
1H, CH), 2.50–2.49 (m, 1H, CH), 2.41–2.33 (m, 1H, CH),
2.15–2.05 (m, 1H, CH), 1.82–1.75 (m, 1H, CH), 1.75–1.66
(m, 2H, CH2), 1.64–1.56 (m, 1H, CH), 1.29–1.20 (m, 1H,
CH); 13C NMR (100 MHz, CDCl3): d=212.3, 149.2, 148.7,
130.2, 120.5, 111.8, 79.4, 56.2, 52.6, 43.8, 42.6, 33.4, 28.5, 27.6,
25.1; HPLC (Chiralpak AD-H, 2-propanol/hexane=5/95,
(S)-2-[(R)-1-(4-Chlorophenyl)-2-nitroethyl]cyclohexa-
none:[38] 1H NMR (400 MHz, CDCl3): d=7.31 (d, J=8.3 Hz,
2H, ArH), 7.16 (d, J=8.4 Hz, 2H, ArH), 4.92 (dd, J=4.6,
12.5 Hz, 1H, CH), 4.64 (dd, J=10.0, 12.6 Hz, 1H, CH),
3.78–3.72 (m, 1H, CH), 2.73–2.64 (m, 1H, CH), 2.46–2.36
(m, 2H, CH2), 2.12–2.04 (m, 1H, CH), 1.77–1.56 (m, 4H, 2ꢂ
CH2), 1.26–1.23 (m, 1H, CH); 13C NMR (100 MHz, CDCl3):
d=211.4, 136.3, 133.4, 129.7, 129.1, 122.8, 78.4, 52.4, 43.2,
42.6, 33.4, 29.5, 28.4, 25.2; HPLC (Chiralpak AD-H, 2-prop-
anol/hexane=10/90, flow rate 1.0 mLminÀ1, l=254 nm):
flow rate 1.0 mLminÀ1, l=254 nm): tminor =16.78 min, tmajor
=
tminor =27.41 min, tmajor =41.83 min; dr (syn/anti)=98:2; ee=
36.24 min; dr (syn/anti)>99:1; ee>99%; [a]2D5: À20.6 (c 1.2,
99%; [a]25: À38.1 (c 1.2, CHCl3).
CHCl3).
(S)-2-[D(R)-1-(2-Chlorophenyl)-2-nitroethyl]cyclohexa-
none:[38] 1H NMR (400 MHz, CDCl3): d 7.36 (d, J=8.0 Hz,
1H, ArH), 7.27–7.21 (m, 3H, ArH), 4.94–4.88 (m, 2H,
CH2), 4.31–4.25 (m, 1H, CH), 2.96–2.90 (m, 1H, CH), 2.46–
2.38 (m, 2H, CH2), 2.12–2.07 (m, 1H, CH), 1.82–1.57 (m,
4H, 2ꢂCH2), 1.27–1.23 (m, 1H, CH); 13C NMR (100 MHz,
CDCl3): d=211.4, 135.5, 134.4, 130.3, 129.3, 128.7, 127.2,
(S)-2-[(R)-1-(4-Bromophenyl)-2-nitroethyl]cyclohexa-
none:[38] 1H NMR (400 MHz, CDCl3): d=7.46 (d, J=8.7 Hz,
2H, ArH), 7.05 (d, J=8.4 Hz, 2H, ArH), 4.93 (dd, J=4.5,
12.6 Hz, 1H, CH), 4.62 (dd, J=9.9, 12.6 Hz, 1H, CH), 3.76
(dt, J=4.5, 9.9 Hz, 1H, CH), 2.68–2.57 (m, 1H, CH), 2.53–
2.30 (m, 2H, CH2), 2.14–2.05 (m, 1H, CH), 1.82–1.53 (m,
2576
asc.wiley-vch.de
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2010, 352, 2571 – 2578

Sugar-Based Pyrrolidine as a Highly Enantioselective Organocatalyst
77.2, 51.6, 42.8, 41.2, 33.4, 28.6, 25.2; HPLC (Chiralpak AD-
H, 2-propanol/hexane=10/90, flow rate 1.0 mLminÀ1, l=
254 nm): tminor =23.34 min, tmajor =39.63 min; dr (syn/anti)=
99:1; ee=91%; [a]25: À21.8 (c 1.1, CHCl3).
4.15 (m, 1H, PhCH), 3.89–3.79 (m, 2H, CH2), 3.73 (dd, J=
11.0, 5.3 Hz, 1H, CH), 3.31 (dd, J=11.0, 8.8 Hz, 1H, CH),
2.94–2.89 (m, 1H, CH), 2.72–2.67 (m, 1H, CH), 2.62–2.58
(m, 1H, CH); 13C NMR (100 MHz, CDCl3): d=209.2, 136.4,
129.2, 128.4, 128.1, 78.7, 54.6, 44.7, 43.4, 35.1, 31.6; HPLC
(Chiralpak AS-H, 2-propanol/hexane=30/70, flow rate
(S)-2-[(R)-1-(BeDnzo[d]
ACTHNUGRTENUNG[1,3]dioxol-5-yl)-2-nitroethyl]cyclo-
hexanone:[28] 1H NMR (400 MHz, CDCl3): d=6.75 (d, J=
7.9 Hz, 1H, ArH), 6.63–6.62 (m, 2H, ArH), 5.95 (s, 2H,
CH2), 4.92 (dd, J=4.5, 12.4 Hz, 1H, CH), 4.56 (dd, J=4.5,
10.0 Hz, 1H, CH), 3.67 (dt, J=4.5, 9.9 Hz, 1H, CH), 2.64–
2.57 (m, 1H, CH), 2.52–2.36 (m, 2H, CH2), 2.14–2.06 (m,
1H, CH), 1.78–1.56 (m, 4H, 2ꢂCH2), 1.35–1.24 (m, 1H,
CH); 13C NMR (100 MHz, CDCl3): d 211.6, 148.2, 147.2,
131.5, 121.7, 108.4, 108.0, 101.3, 78.8, 52.3, 43.4, 42.5, 33.2,
28.3, 25.2; HPLC (Chiralpak AD-H, 2-propanol/hexane=
10/90, flow rate 1.0 mLminÀ1, l=254 nm): tminor =16.56 min,
1.0 mLminÀ1,
l=254 nm):
t
minor =11.63 min,
tmajor =
16.93 min; dr (syn/anti)>99/1; ee=95%; [a]2D5: À34.7 (c 1.2,
CHCl3).
(R)-Tetrahydro-3-[(R)-2-nitro-1-phenylethyl]thiopyran-4-
one:[14] 1H NMR (400 MHz, CDCl3): d=7.36–7.33 (m, 2H,
ArH), 7.33–7.29 (m, 1H, ArH), 7.19 (d, J=6.5 Hz, 2H,
ArH), 4.73 (dd, J=12.7, 4.5 Hz, 1H, CH), 4.63 (dd, J=12.7,
10.0 Hz, 1H, CH), 3.98 (dt, J=10.0, 4.5 Hz, 1H, PhCH),
3.07–3.00 (m, 1H, CH), 3.00–2.94 (m, 2H, CH2), 2.88–2.84
(m, 1H, CH), 2.84–2.77 (m, 1H, CH), 2.61 (ddd, J=2.0, 4.0,
13.8 Hz, 1H, CH), 2.45 (dd, J=13.8, 9.7 Hz, 1H, CH);
13C NMR (100 MHz, CDCl3): d=208.4, 136.6, 129.3, 128.5,
127.7, 78.9, 71.8, 69.2, 53.4, 43.2, 41.4; HPLC (Chiralpak AS-
H, 2-propanol/hexane=30/70, flow rate 1.0 mLminÀ1, l=
254 nm): tminor =11.85 min, tmajor =17.63 min; dr (syn/anti)=
99/1; ee=98%; [a]2D5: À40.4 (c 1.2, CHCl3).
t
major =18.72 min; dr (syn/anti)=99:1; ee=99%; [a]2D5: À45.3
(c 1.2, CHCl3).
(S)-2-[(R)-1-(3,4-Dimethoxyphenyl)-2-nitroethyl]cyclo-
hexanone:[40] 1H NMR (400 MHz, CDCl3): d=6.80 (d, J=
8.2 Hz, 1H, ArH), 6.67–6.63 (m, 2H, ArH), 4.92 (dd, J=4.6,
7.8 Hz, 1H, CH), 4.63 (dd, J=2.4, 9.9 Hz, 1H, CH), 3.88 (s,
6H, 2ꢂCH3), 3.72–3.64 (m, 1H, CH), 2.65–2.63 (m, 1H,
CH), 2.48–2.43 (m, 1H, CH), 2.42–2.36 (m, 1H, CH), 2.06–
2.03 (m, 1H, CH), 1.80–1.62 (m, 4H, 2ꢂCH2), 1.27–1.24 (m,
1H, CH); 13C NMR (100 MHz, CDCl3): d=212.1, 149.3,
148.4, 130.0, 120.4, 111.6, 79.1, 56.1, 52.6, 43.8, 42.6, 33.4,
28.5, 27.4, 25.2; HPLC (Chiralpak As-H, 2-propanol/
(S)-2-[(R)-2-Nitro-1-phenylethyl]cyclopentanone:[41]
1H NMR (400 MHz, CDCl3): d=7.27–7.20 (m, 3H, ArH),
7.15–7.05 (m, 2H, ArH), 5.31–5.24 (m, 1H, CH), 4.97 (dd,
J=9.9, 12.8 Hz, 1H, CH), 3.69–3.62 (m, 1H, CH), 2.36–2.28
(m, 2H, CH2), 2.13–2.09 (m, 1H, CH), 1.87–1.75 (m, 2H,
CH2), 1.70–1.68 (m, 1H, CH), 1.56–1.39 (m, 1H, CH);
13C NMR (100 MHz, CDCl3): d=218.6, 137.5, 137.3, 128.9,
128.5, 127.8, 78.3, 50.5, 44.2, 38.7, 28.1, 25.2; HPLC (Chiral-
hexane=30/70, flow rate 1.0 mLminÀ1, l=254 nm): tminor
=
12.35 min, tmajor =23.37 min; dr (syn/anti)>99:1; ee>99%;
[a]25: À29.3 (c 1.2, CHCl3).
(DS)-2-[(R)-2-(Naphthalen-1-yl)-2-nitroethyl)cyclohexa-
none:[14] 1H NMR (400 MHz, CDCl3): d=7.82–7.78 (m, 2H,
ArH), 7.63 (s, 1H, ArH), 7.50–7.45 (m, 2H, ArH), 7.28 (dd,
J=8.5, 2.0 Hz, 2H, ArH), 5.01 (dd, J=12.0, 4.7 Hz, 1H,
CH), 4.74 (dd, J=12.0, 10.0 Hz, 1H, CH), 3.95 (dt, J=10.0,
4.7 Hz, 1H, ArCH), 2.81–2.75 (m, 1H, CH), 2.52–2.48 (m,
1H, CH), 2.44–2.37 (m, 1H, CH), 2.10–2.04 (m, 1H, CH),
1.78–1.61 (m, 4H, 2ꢂCH2), 1.31–1.23 (m, 1H, CH);
13C NMR (100 MHz, CDCl3): d=212.1, 134.5, 128.9, 128.1,
126.3, 125.7, 125.1, 123.5, 122.4, 78.6, 53.5, 42.7, 36.5, 33.1,
28.5, 25.1; HPLC (Chiralpak AS-H, 2-propanol/hexane=30/
70, flow rate 1.0 mLminÀ1, l=254 nm): tminor =10.17 min,
pak
AD-H,
2-propanol/hexane=10/90,
flow
rate
=
1.0 mLminÀ1, l=254 nm): syn:
t
major =9.96 min, tminor
11.42 min, anti: tminor =12.90 min, tmajor =17.32 min; dr (syn/
anti)=34:66; ee=83%, 85%; [a]2D5: À40.6 (c 1.2, CHCl3).
(S)-2-[(S)-3-Methyl-1-nitrobutan-2-yl]cyclohexanone:[39]
1H NMR (400 MHz, CDCl3): d=4.61 (dd, J=5.8, 12.9 Hz,
1H), 4.39 (dd, J=5.3, 13.3 Hz, 1H), 2.69–2.61 (m, 1H),
2.45–2.29 (m, 3H), 2.16–2.07 (m, 2H), 1.99–1.88 (m, 2H),
1.74–1.54 (m, 3H), 0.95 (d, J=6.7 Hz, 3H), 0.91 (d, J=
6.8 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=211.8, 76.8,
50.8, 43.3, 41.9, 32.1, 28.4, 26.2, 25.3, 19.8; HPLC (Chiralpak
AD-H, 2-propanol/hexane=10/90, flow rate 1.0 mLminÀ1,
l=254 nm): tmajor =6.63 min, tminor =7.95 min; dr (syn/anti)=
94/6; ee=93%; [a]2D5: À30.2 (c 1.2, CHCl3).
t
major =16.22 min; dr (syn/anti)>99:1; ee>99%; [a]2D5: À65.7
(c 1.2, CHCl3).
(R)-5-Nitro-4-phenylpentan-2-one:[28] 1H NMR (400 MHz,
CDCl3): d=7.36–7.15 (m, 5H), 4.71–4.58 (m, 2H), 4.02–3.97
(m, 1H), 2.91 (d, J=6.8 Hz, 2H), 2.11 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=205.3, 138.9, 129.2, 127.9, 127.2,
109.1, 79.5, 46.2, 39.0, 30.5; HPLC (Chiralpak AD-H, 2-
propanol/hexane=10/90, flow rate 1.0 mLminÀ1, l=
254 nm): tminor =9.12 min, tmajor =11.05 min; ee=63%; [a]2D5:
À8.9 (c 1.2, CHCl3).
(S)-2-[(R)-1-(Naphthalen-1-yl)-2-nitroethyl]cyclohexa-
none:[14] 1H NMR (400 MHz, CDCl3): d=8.16 (s, 1H, ArH),
7.84 (d, J=7.7 Hz, 1H, ArH), 7.75 (d, J=8.2 Hz, 1H, ArH),
7.56–7.43 (m, 3H, ArH), 7.36 (d, J=7.2 Hz, 1H, ArH), 5.07
(dd, J=12.5, 4.5 Hz, 1H, CH2), 4.72 (br, t, 1H, J=12.5 Hz,
CH), 4.74–4.73 (br, m, 1H, CH), 2.87 (s, 1H, CH), 2.53–2.46
(m, 1H, CH), 2.44–2.34 (m, 1H, CH), 2.08–2.04 (m, 1H,
CH), 1.76–1.58 (m, 4H, 2ꢂCH2), 1.30–1.22 (m, 1H, CH);
13C NMR (100 MHz, CDCl3): d=211.7, 135.2, 133.4, 132.7,
128.9, 127.9, 127.7, 126.4, 126.2, 125.2, 78.8, 76.6, 52.6, 44.1,
42.4, 33.3, 28.5, 25.0; HPLC (Chiralpak AD-H, 2-propanol/
hexane=30/70, flow rate 1.0 mLminÀ1, l=254 nm): tminor
=
8.83 min, tmajor =14.45 min; dr (syn/anti)=99:1; ee=99%;
[a]25: À97.6 (c 1.2, CHCl3).
Acknowledgements
(DR)-Tetrahydro-3-[(R)-2-nitro-1-phenylethyl]pyran-4-
one:[14] 1H NMR (400 MHz, CDCl3): d=7.39–7.31 (m, 3H,
ArH), 7.21 (d, J=7.4 Hz, 2H, ArH), 4.96 (dd, J=12.5,
4.7 Hz, 1H, CH), 4.68 (dd, J=12.5, 10.0 Hz, 1H, CH), 4.20–
We gratefully acknowledge financial support by the National
Natural Science Foundation of China (No. 20972057,
20772043).
Adv. Synth. Catal. 2010, 352, 2571 – 2578
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2577

Lei Wang et al.
FULL PAPERS
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2578
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Adv. Synth. Catal. 2010, 352, 2571 – 2578