Chiral squaramide-catalyzed enantioselective conjugate michael addition of various thiols to α,β-unsaturated n-acylated oxazolidin-2-ones

Article abstract of DOI:10.1002/ejoc.201100403

A highly enantioselective sulfa-Michael addition (SMA) of various thiols to α,β-unsaturated N-acylated oxazolidinones has been achieved with a chiral squaramide catalyst under very mild reaction conditions. In addition, the conversion of the β-thio-substi

Full text of DOI:10.1002/ejoc.201100403

FULL PAPER
DOI: 10.1002/ejoc.201100403
Chiral Squaramide-Catalyzed Enantioselective Conjugate Michael Addition of
Various Thiols to α,β-Unsaturated N-Acylated Oxazolidin-2-ones
Le Dai,[a] Hongjun Yang,[a] and Fener Chen*[a]
Keywords: Michael addition / Enantioselectivity / Organocatalysis / Asymmetric catalysis / Sulfur
A highly enantioselective sulfa-Michael addition (SMA) of
various thiols to α,β-unsaturated N-acylated oxazolidinones
has been achieved with a chiral squaramide catalyst under
very mild reaction conditions. In addition, the conversion of
the β-thio-substituted adduct to the corresponding methyl β-
tosylbutanoate was demonstrated in high yield through a
methanolysis/oxidation sequence.
We envisioned that α,β-unsaturated N-acylated oxazolidin-
ones could be activated by the squaramide moiety through
double hydrogen-bonding interactions in a manner similar
to that of chalcone (Figure 1). Witnessing the rapid growth
of chiral squaramide-promoted asymmetric catalytic reac-
tions,[6] we embarked on the evaluation of the chiral squara-
mide-catalyzed sulfa-Michael addition of both alkane- and
arenethiols to α,β-unsaturated N-acylated oxazolidinones.
Introduction
Enantiomerically pure β-sulfurated carboxylic acid deriv-
atives are important building blocks in organic synthesis.[1]
As substructures, they exist in pharmaceuticals and various
biologically active compounds.[2] Among the existing enan-
tioselective methods for the construction of β-sulfurated
acids,[3] the Michael-type addition of thiols to α,β-unsatu-
rated acid derivatives was regarded as the most direct and
efficient strategy. Since the pioneering work of Kanema-
sa,[4a] much attention has been paid over the past decade to
developing enantioselective catalytic variants of such pro-
cesses. Asymmetric sulfa-Michael additions involving α,β-
unsaturated acid derivatives have been reported using chiral
metal complexes[4] and organocatalysts.[5] Recently, Deng
and co-workers developed a 6Ј-thiourea-substituted cin-
chona alkaloid catalyst for the reaction between α,β-unsat-
urated N-acylated oxazolidinones and simple alkanethiols
to provide β-sulfurated carboxylic acid derivatives in up to
96%ee.[5b] However, such high enantioselectivity relied on
cryogenic reaction conditions, and the scope of the reaction
was limited to certain nucleophiles. To the best of our
knowledge, there are only a few examples that afford excel-
Figure 1. Hydrogen-bonding interaction with squaramide moiety.
Results and Discussion
To evaluate the catalysts, initial experiments were per-
lent enantioselectivity with a broad scope of reaction part- formed for the reaction between phenylmethanethiol (8a)
ners. Therefore, the development of an efficient catalytic and N-cinnamoyloxazolidin-2-one (7a). Squaramide cata-
system suitable for use with both arene- and alkanethiols lysts 5a–c and 6 incorporating a cinchona alkaloid or di-
continues to be a major challenge.
aminocyclohexane scaffold, which have been previously re-
Our laboratory has recently identified a family of chiral ported by us and other chemists, were screened (Figure 2).
squaramide catalysts, which exhibit outstanding catalytic As shown in Table 1, all catalysts smoothly promoted the
activity in the sulfa-Michael addition to trans-chalcones.[5d] reaction at room temperature (Table 1, Entries 1–4). Cin-
chona alkaloid based squaramide 5c was identified as the
best catalyst to yield the desired Michael adduct 9a in 99%
yield and 98%ee. Subsequently, various solvents were then
tested. As expected, nonpolar solvents (e.g., toluene, dichlo-
romethane, and chloroform) without Lewis basic sites were
optimal when used in conjunction with these types of hy-
drogen-bonding catalysts (Table 1, Entries 4–8). With suc-
cessful results for the catalytic efficiency in the initial
[a] Fudan-DSM Joint Laboratory for Synthetic Methods and
Chiral Technology, Department of Chemistry, Fudan
University,
220 Handane Road, Shanghai 200433, People’s Republic of
China
Fax: +86-21-65643811
E-mail: rfchen@fudan.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100403.
Eur. J. Org. Chem. 2011, 5071–5076
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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L. Dai, H. Yang, F. Chen
FULL PAPER
screening, we conducted the reaction on a 5 mmol scale and Table 2. Asymmetric conjugate addition of 8 to 7 with catalyst 5c.[a]
decreased the catalyst loading to 1 mol-%. To our delight,
the enantioselectivity and the yield were maintained at
equally excellent levels (Table 1, Entry 9).
Entry
R
RЈ
Product Time Yield
ee
[h] [%][b] [%][c]
1
2
3
4
5
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
Me (7b)
C6H5 (7a)
C6H5 (7a)
C6H5 (7a)
C6H5 (7a)
C6H5 (7a)
Bn (8a)
4-ClBn (8b)
4-MeOBn (8c)
furfuryl (8d)
cyclopentyl (8e)
cyclopentyl (8e)
iPr (8f)
C6H5 (8g)
C6H5 (8g)
4-MeC6H4 (8h)
4-BrC6H4 (8i)
2-BrC6H4 (8j)
Bn (8a)
9b
9c
9d
9e
9f
48
24
48
48
120
48
60
24
24
24
24
24
48
48
24
24
48
36
36
24
24
24
84
93
83
99
53
88
99
96
94
89
91
90
88
94
87
95
85
96
92
83
90
93
97[d]
97
97
96
97
98
97
84
86[d]
90
73
82
98
98
99
99
95
97
99
95
94
95
6[e]
7[e]
8
9f
9g
9h
9h
9i
Figure 2. Structures of chiral squaramides 5 and 6.
9[f]
10[f]
11[f]
12[f]
13[f]
14[g]
15
16
17[e]
18
19
20
21
22
9j
Table 1. Asymmetric conjugate addition of phenylmethanethiol
(8a) to 3-cinnamoyloxazolidin-2-one (7a) with squaramide cata-
lysts.[a]
9k
9a
9a
9l
9m
9n
9o
9p
9q
9r
9s
Bn (8a)
4-MeOBn (8c)
furfuryl (8d)
cyclopentyl (8e)
2-ClC6H4 (7c) 4-MeOBn (8c)
4-ClC6H4 (7d) 4-MeOBn (8c)
2-furyl (7e)
1-naphthyl (7f) 4-MeOBn (8c)
1-naphthyl (7f) 4-ClBn (8b)
4-MeOBn (8c)
Entry
Solvent
Catalyst
Yield [%][b]
ee [%][c]
[a] Unless noted, reactions were carried out in toluene with 5c
(2 mol-%) at room temperature. [b] Yield of isolated product.
[c] Determined by HPLC analysis using a Chiralcel AD-H or OD-
H column. [d] Absolute configuration was determined by compari-
son of the optical rotation with literature data.[4a,4d,5b] [e] Reactions
were carried out in CHCl3 with 5 mol-% catalyst loading. [f] Molec-
ular sieves (4 Å, 40 mg) were added. [g] Water (1 equiv.) was added.
1
2
3
4
5
6
7
toluene
toluene
toluene
toluene
CH2Cl2
CHCl3
EtO2
5a
5b
5c
6
5c
5c
5c
5c
5c
91
90
99
90
93
97
83
81
93
81
85
98
–63[d]
96
98
87
81
99
8
THF
toluene
9[e]
Under the optimized conditions, the reaction with thio-
phenol gave the desired products with acceptable enantio-
selectivity (84%ee), but the result was not reproducible
(Table 2, Entry 8). The X-ray crystal structure analysis of
squaramide catalyst 5c[7] (Figure 3) reveals that the inter-
molecular hydrogen bonds are mediated by one molecule of
water. A trace amount of water mixed with the catalyst may
[a] Unless noted, reactions were carried out with 7a (0.25 mmol)
and 8a (0.5 mmol) in solvent (1.0 mL) at room temperature for 12–
24 h. [b] Isolated yields. [c] Determined by HPLC analysis using a
Chiralcel OD-H column. [d] Reversed enantioselectivity was ob-
tained. [e] The reaction was conducted on a 5 mmol scale with
1 mol-% catalyst loading.
Under the optimized reaction conditions, the scope of affect the enantioselectivity of the reactions involving arene-
the nucleophiles was examined by using various thiols. As thiols as nucleophiles. After a simple screening, it was dis-
shown in Table 2, several para-substituted phenyl- and fur- covered that the addition of powdered molecular sieves
ylmethanethiols were combined with N-crotonyloxazolidin- (4 Å) improved the reproducibility of the process and
2-one (7b) in reactions catalyzed by 5c (2 mol-%), providing slightly increased the enantioselectivity (86%ee, Table 2,
the corresponding adducts in high yields and excellent Entry 9). Under the same conditions using molecular sieves
enantioselectivities (Ն 96%ee, Table 2, Entries 1–4). Reac- (4 Å) as an additive, we conducted the reactions with aro-
tions using aliphatic thiols became very slow under the matic thiols bearing different substituents (Table 2, En-
same conditions. Although excellent enantioselectivity tries 10–12). With p-toluenethiol, the resulting adduct was
(97%ee) was obtained in the case of cyclopentanethiol, the obtained in good enantiomeric purity. However, electron-
reaction required a prolonged reaction time (120 h) and af- withdrawing substituents on the aromatic ring led to a de-
forded the corresponding adduct in 53% yield (Table 2, En- crease in the enantiomeric excess. In contrast, the reactions
try 5). Further developments revealed that increasing the with alkanethiols were not sensitive to the presence of
catalyst loading (5 mol-%) and changing the reaction sol- water. To clarify the effects of water on the catalytic pro-
vent from toluene to chloroform significantly improved the cesses, we carried out the model reaction of 7a and 8a with
yields (Table 2, Entries 6 and 7).
the addition of the molecular sieves (4 Å). The reaction
5072
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Eur. J. Org. Chem. 2011, 5071–5076

Chiral Squaramide-Catalyzed Enantioselective Sulfa-Michael Addition
gave adduct 9a with a consistent enantioselectivity, but in a methylmagnesium bromide in methanol at 0 °C afforded the
somewhat lower yield (Table 2, Entry 13). On the other corresponding ester 10 in excellent yield. A subsequent oxi-
hand, the addition of water (1 equiv.) in the same reaction dation of 10 with 30% H2O2 in the presence of Na2WO4 as
led to no significant change in terms of yield and enantio- a catalyst gave the desired sulfone 11 without any loss of
selectivity (Table 2, Entry 14). These results indicate that enantiomeric excess (Scheme 1).
the catalytic process involving alkanethiols as the nucleo-
phile well tolerated water.
Conclusions
We have demonstrated that squaramide catalyst 5c pro-
motes the sulfa-Michael addition to α,β-unsaturated N-
acylated oxazolidinones with good yields and high enantio-
selectivities. On the basis of these studies, we developed a
facile access to β-sulfurated carboxylic acid derivatives.
Mild conditions and a broad scope of substrates make this
approach very competitive in the synthesis of enantiomer-
ically pure β-sulfurated carboxylic acid derivatives.
Experimental Section
General Information: All the solvents were purified according to
standard methods. The racemic sulfa-Michael adducts were pre-
Figure 3. Packing of 5c in the crystal, intermolecular hydrogen
pared from the corresponding thiols and α,β-unsaturated N-acyl-
ated oxazolidinones in the presence of triethylamine. All other
chemicals used in this study were obtained from commercial
bonding between 5c and H2O.
Next, a variety of Michael acceptors were investigated.
It was found that the sulfa-Michael addition process cata-
lyzed by 5c was also applicable to various α,β-unsaturated
N-acylated oxazolidinones. It did not matter whether aro-
matic, heterocyclic groups, or fused-ring systems in the β-
position of the electrophiles were used, the reactions gave
adducts with high enantioselectivities. These results demon-
strate that steric as well as electronic variations in the β-
substituents of the Michael acceptors have a limited effect
on the stereoselection of the conjugate addition (Table 2,
Entries 15–22).
1
sources and used without further purification. H (400 MHz) and
13C NMR (100 MHz) spectroscopic data were recorded with a
Bruker Avance 400 spectrometer in CDCl3 by using tetramethylsil-
ane (TMS) as standard. Optical rotations were recorded with a
Jasco P1020 digital polarimeter. HPLC analysis was performed by
using
(0.46 cmϫ25 cm),
(0.46 cmϫ25 cm) or AS-H (0.46 cmϫ25 cm) column.
a
Shimadzu LC-10A with
a
Daicel Chiralcel OJ-H
OD-H (0.46 cmϫ25 cm),
AD-H
Typical Procedure for the Asymmetric Addition of Thiols to α,β-
Unsaturated N-Acylated Oxazolidinones: To a solution of α,β-un-
saturated N-acylated oxazolidinone 7 (0.25 mmol) and catalyst 5c
in solvent (1.0 mL) was added thiol 8 (0.50 mmol). The reaction
mixture was stirred at room temperature for 8–60 h. The solvent
was then evaporated under reduced pressure, and the residue was
The synthetic utility of the adducts in the synthesis of β-
mercapto acid derivatives was clear.[5b] Another application
was demonstrated by the derivatization of 9i to methyl β-
tosylbutanoate (11), which is potentially useful as a chiral purified by flash chromatography [ethyl acetate/petroleum ether,
auxiliary[8] or an important intermediate[2d,2e] in the synthe-
from 1:5 to 1:3 (v/v)] to afford the conjugate addition product 9.
sis of biologically active compounds. Treatment of 9i with
(R)-3-[3-(Benzylthio)-3-phenylpropanoyl]oxazolidin-2-one (9a): The
crude product was purified by flash chromatography [SiO2, petro-
leum ether/ethyl acetate, 4:1 (v/v)] to give compound 9a in 99%
yield and 98%ee [determined by HPLC, chiral AD-H, hexane/2-
propanol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column tempera-
ture 30 °C, tmajor = 21.0 min, tminor = 19.5 min]. [α]2D5 = 201 (c =
1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 3.43–3.60 (m, 4 H),
3.82–3.97 (m, 2 H), 4.25–4.38 (m, 3 H), 7.20–7.38 (m, Ar) ppm.
13C NMR (100 MHz, CDCl3): δ = 170.25, 153.32, 141.32, 137.88,
128.95, 128.54, 128.42, 128.09, 127.44, 126.99, 62.05, 44.31, 42.44,
41.60, 35.72 ppm.
(S)-3-[3-(Benzylthio)butanoyl]oxazolidin-2-one (9b): The crude
product was purified by flash chromatography [SiO2, petroleum
ether/ethyl acetate, 4:1 (v/v)] to give compound 9b in 84% yield
and 97%ee [determined by HPLC, chiral OD-H, hexane/2-prop-
anol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column temperature
30 °C, tmajor = 28.9 min, tminor = 25.5 min]. [α]2D5 = –15.7 (c = 1.0,
CHCl3) {ref.[5b] [α]2D5 = –15.0 (c = 0.25, CHCl3), 94%ee; ref.[4a]
[α]2D5 = –17.27 (c = 2.90, CHCl3), 87%ee}. 1H NMR (400 MHz,
Scheme 1. Transformation of 9i to 11.
Eur. J. Org. Chem. 2011, 5071–5076
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L. Dai, H. Yang, F. Chen
FULL PAPER
CDCl3): δ = 1.32 (d, J = 6.6 Hz, 3 H), 3.07 (m, 1 H), 3.26 (m, 2 anol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column temperature
H), 3.79 (dd, J1 = 13.2 Hz, J2 = 16.6 Hz, 2 H), 3.92–4.06 (m, 2 H), 30 °C, tmajor = 12.3 min, tminor = 14.4 min]. [α]2D5 = –11.5 (c = 1.0,
1
4.38 (dd, J1 = 7.4 Hz, J2 = 8.3 Hz, 2 H), 7.20–7.34 (m, Ar) ppm.
13C NMR (100 MHz, CDCl3): δ = 171.02, 153.38, 138.45, 128.88,
128.47, 126.94, 62.05, 42.45, 35.65, 35.33, 21.67, 21.61 ppm.
CHCl3). H NMR (400 MHz, CDCl3): δ = 1.24 (d, J = 7.0 Hz, 3
H), 1.26 (d, J = 7.2 Hz, 3 H), 1.33 (d, J = 6.6 Hz, 3 H), 3.02 (m, 2
H), 3.32 (m, 2 H), 4.02 (t, J = 8 Hz, 2 H), 4.40 (t, J = 8 Hz, 2 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 171.25, 153.43, 62.08,
42.89, 42.51, 34.46, 34.35, 23.85, 23.64, 22.22 ppm.
(S)-3-[3-(4-Chlorobenzylthio)butanoyl]oxazolidin-2-one (9c): The
crude product was purified by flash chromatography [SiO2, petro-
leum ether/ethyl acetate, 10:3 (v/v)] to give compound 9c in 93%
yield and 97%ee [determined by HPLC, chiral AD-H, hexane/2-
propanol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column tempera-
ture 30 °C, tmajor = 22.5 min, tminor = 20.9 min]. [α]2D5 = –16.5 (c =
1.0, CHCl3) {ref.[5b] [α]2D5 = –13.2 (c = 0.5, CHCl3), 93%ee}. 1H
NMR (400 MHz, CDCl3): δ = 1.32 (d, J = 6.6 Hz, 3 H), 3.04 (dd,
(S)-3-[3-(Phenylthio)butanoyl]oxazolidin-2-one (9h): The crude
product was purified by flash chromatography [SiO2, petroleum
ether/ethyl acetate, 10:3 (v/v)] to give compound 9h in 94% yield
and 86%ee [determined by HPLC, chiral OD-H, hexane/2-prop-
anol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column temperature
30 °C, tmajor = 14.80 min, tminor = 16.08 min]. [α]2D5 = –11.5 (c = 1.0,
J1 = 6.6 Hz, J2 = 15.9 Hz, 1 H), 3.16–3.30 (m, 2 H), 3.74 (dd, J1 = CHCl3) {ref.[4a] [α]2D5 = –11.05 (c = 1.23, CHCl3), 52%ee; ref.[4d]
13.5 Hz, J2 = 18.2 Hz, 2 H), 3.96 (dt, J1 = 3.3 Hz, J2 = 8.1 Hz, 2
[α]2D4 = –12.7 (c = 1.26, CHCl3), 90%ee}. 1H NMR (400 MHz,
H), 4.38 (t, J = 8.2 Hz, 2 H), 7.26 (s, Ar) ppm. 13C NMR CDCl3): δ = 1.35 (d, J = 6.8 Hz, 3 H), 3.14 (dd, J1 = 7.3 Hz, J2 =
(100 MHz, CDCl3): δ = 170.90, 153.39, 137.05, 132.70, 130.23,
128.60, 62.07, 42.48, 42.44, 35.66, 34.64, 21.65, 21.59 ppm.
17 Hz, 1 H), 3.23 (dd, J1 = 6.5 Hz, J2 = 17 Hz, 1 H), 3.76 (qt, J1
= 6.8 Hz, J2 = 7.3 Hz, 1 H), 3.96 (td, J1 = 8.0 Hz, J2 = 3.3 Hz, 2
H), 4.36 (t, J = 8.0 Hz, 2 H), 7.22–7.46 (m, Ar) ppm. 13C NMR
(100 MHz, CDCl3): δ = 194.65, 172.57, 148.48, 146.90, 142.01,
140.08, 58.51, 33.94, 33.81, 29.64, 7.52 ppm.
(S)-3-[3-(4-Methoxybenzylthio)butanoyl]oxazolidin-2-one (9d): The
crude product was purified by flash chromatography [SiO2, petro-
leum ether/ethyl acetate, 10:3 (v/v)] to give compound 9d in 83%
yield and 97%ee [determined by HPLC, chiral OD-H, hexane/2-
propanol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column tempera-
ture 30 °C, tmajor = 36.4 min, tminor = 32.6 min]. [α]2D5 = –14.7 (c =
1.0, CHCl3) {ref.[5b] [α]2D5 = –16.6 (c = 0.5, CHCl3), 96%ee}. 1H
(S)-3-[3-(p-Tolylthio)butanoyl]oxazolidin-2-one (9i): The crude
product was purified by flash chromatography [SiO2, petroleum
ether/ethyl acetate, 10:3 (v/v)] to give compound 9h in 89% yield
and 90%ee [determined by HPLC, chiral OD-H, hexane/2-prop-
NMR (400 MHz, CDCl3): δ = 1.32 (d, J = 6.8 Hz, 3 H), 3.03–3.08 anol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column temperature
(m, 1 H), 3.20–3.24 (m, 2 H), 3.75 (d, J = 3.3 Hz, 2 H), 3.79 (s, 3
H), 3.97 (td, J1 = 7.6 Hz, J2 = 4.4 Hz, 2 H), 4.38 (t, J = 8.0 Hz, 2
30 °C, tmajor = 23.4 min, tminor = 20.1 min]. [α]2D5 = –20.1 (c = 1.0,
1
CHCl3). H NMR (400 MHz, CDCl3): δ = 1.33 (d, J = 6.8 Hz, 3
H), 6.84 (d, J = 8.2 Hz, 2 H), 7.25 (m, J = 8.2 Hz, 2 H) ppm. 13C H), 2.32 (s, 3 H), 3.11 (dd, J1 = 7.4 Hz, J2 = 17.0 Hz, 1 H), 3.23
NMR (100 MHz, CDCl3): δ = 171.05, 158.59, 153.38, 130.38, (dd, J1 = 6.6 Hz, J2 = 17.0 Hz, 1 H), 3.64 (qt, J1 = 6.8 Hz, J2
=
129.95, 113.89, 62.04, 55.24, 42.46, 35.52, 34.69, 21.69, 21.63 ppm.
7.0 Hz, 1 H), 3.95 (t, J = 8.6 Hz, 2 H), 4.37 (t, J = 8.6 Hz, 2 H),
7.12 (d, J = 7.9 Hz, 2 H), 7.37 (d, J = 8.0 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 194.77, 172.58, 152.99, 147.93, 143.47,
142.96, 58.50, 33.97, 33.78, 30.05, 7.45, 7.32 ppm.
(S)-3-[3-(Furan-2-ylmethylthio)butanoyl]oxazolidin-2-one (9e): The
crude product was purified by flash chromatography [SiO2, petro-
leum ether/ethyl acetate, 4:1 (v/v)] to give compound 9e in 99%
yield and 96%ee [determined by HPLC, chiral OD-H, hexane/2-
propanol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column tempera-
ture 30 °C, tmajor = 24.8 min, tminor = 26.6 min]. [α]2D5 = –26.4 (c =
1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 1.33 (d, J = 6.6 Hz,
(S)-3-[3-(p-Bromophenylthio)butanoyl]oxazolidin-2-one (9j): The
crude product was purified by flash chromatography [SiO2, petro-
leum ether/ethyl acetate, 10:3 (v/v)] to give compound 9j in 91%
yield and 73%ee [determined by HPLC, chiral OD-H, hexane/2-
3 H), 3.06 (dd, J1 = 9.3 Hz, J2 = 18.6 Hz, 1 H), 3.26–3.66 (m, 2 propanol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column tempera-
H), 3.79 (dd, J1 = 14.8 Hz, J2 = 20.3 Hz, 2 H), 3.99 (dt, J1 = 2 Hz, ture 30 °C, tmajor = 25.3 min, tminor = 23.3 min]. [α]2D5 = –3.2 (c =
J2 = 8 Hz, 2 H), 4.39 (t, J = 8 Hz, 2 H), 6.19 (dd, J1 = 0.5 Hz, J2 1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 1.35 (d, J = 6.8 Hz,
= 3.2 Hz, 1 H), 6.28 (dd, J1 = 1.8 Hz, J2 = 3.2 Hz, 1 H), 7.33 (dd,
3 H), 3.12 (dd, J1 = 7.3 Hz, J2 = 17.1 Hz, 1 H), 3.22 (dd, J1 =
J1 = 0.7 Hz, J2 = 1.8 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): 6.6 Hz, J2 = 17.1 Hz, 1 H), 3.75 (qt, J1 = 6.7 Hz, J2 = 7.0 Hz, 1
δ = 170.98, 153.42, 151.81, 142.15, 110.45, 107.37, 62.10, 42.43, H), 3.96 (t, J = 8.6 Hz, 2 H), 4.39 (t, J = 8.6 Hz, 2 H), 7.32 (d, J
35.81, 27.50, 21.51, 21.41 ppm.
= 8.4 Hz, 2 H), 7.41 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 194.48, 172.59, 148.84, 147.51, 145.90,
132.89, 58.59, 34.00, 33.70, 29.87, 7.46 ppm.
(S)-3-[3-(Cyclopentylthio)butanoyl]oxazolidin-2-one (9f): The crude
product was purified by flash chromatography [SiO2, petroleum
ether/ethyl acetate, 4:1 (v/v)] to give compound 9f in 88% yield and
98%ee [determined by HPLC, chiral AD-H, hexane/2-propanol,
70:30 (v/v), 0.5 mL/min, λ = 220 nm, column temperature 30 °C,
tmajor = 13.8 min, tminor = 14.5 min]. [α]2D5 = –10.2 (c = 1.0, CHCl3)
{ref.[5b] [α]2D5 = –7.4 (c = 0.5, CHCl3), 94%ee}. 1H NMR (400 MHz,
CDCl3): δ = 1.36 (d, J = 6.7 Hz, 3 H), 1.45–1.60 (m, 5 H), 1.72 (m,
(S)-3-[3-(o-Bromophenylthio)butanoyl]oxazolidin-2-one (9k): The
crude product was purified by flash chromatography [SiO2, petro-
leum ether/ethyl acetate, 10:3 (v/v)] to give compound 9k in 90%
yield and 82%ee [determined by HPLC, chiral OD-H, hexanes/2-
propanol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column tempera-
ture 30 °C, tmajor = 36.4 min, tminor = 29.0 min]. [α]2D5 = –21.6 (c =
2 H), 2.01 (m, 2 H), 3.03 (dd, J1 = 9.4 Hz, J2 = 18.4 Hz, 1 H), 3.17 1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 1.42 (d, J = 6.8 Hz,
(tt, J = 7.1 Hz, 1 H), 3.30–3.37 (m, 2 H), 4.02 (t, J = 8 Hz, 2 H),
3 H), 3.24 (m, 2 H), 3.90 (qt, J1 = 6.8 Hz, J2 = 6.3 Hz, 1 H), 3.98
4.40 (t, J = 8 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = (t, J = 8.0 Hz, 2 H), 4.39 (t, J = 8.0 Hz, 2 H), 7.06–7.59 (m, Ar)
171.29, 153.43, 62.07, 42.85, 42.52, 35.65, 34.37, 34.20, 24.82, ppm. 13C NMR (100 MHz, CDCl3): δ = 194.34, 172.57, 150.87,
22.11 ppm.
145.85, 140.85, 140.61, 138.89, 58.59, 33.98, 33.33, 7.01 ppm.
(S)-3-[3-(Isopropylthio)butanoyl]oxazolidin-2-one (9g): The crude
product was purified by flash chromatography [SiO2, petroleum
(R)-3-[3-(p-Methoxybenzylthio)-3-phenylpropanoyl]oxazolidin-2-one
(9l): The crude product was purified by flash chromatography
ether/ethyl acetate, 4:1 (v/v)] to give compound 9g in 99% yield [SiO2, petroleum ether/ethyl acetate, 4:1 (v/v)] to give compound 9l
and 97%ee [determined by HPLC, chiral AD-H, hexane/2-prop- in 87% yield and 99%ee [determined by HPLC, chiral AS-H, hex-
5074
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5071–5076

Chiral Squaramide-Catalyzed Enantioselective Sulfa-Michael Addition
ane/2-propanol, 70:30 (v/v), 0.5 mL/min, λ = 220 nm, column tem-
perature 30 °C, tmajor = 47.8 min, tminor = 44.4 min]. [α]2D5 = 199 (c
= 1.0, CHCl3). H NMR (400 MHz, CDCl3): δ = 3.42–3.59 (m, 4
raphy [SiO2, petroleum ether/ethyl acetate, 4:1 (v/v)] to give com-
pound 9q in 83% yield and 95%ee [determined by HPLC, chiral
AD-H, hexane/2-propanol, 95:5 (v/v), 0.5 mL/min, λ = 220 nm,
1
H), 3.78 (s, 3 H), 3.81–3.96 (m, 2 H), 4.25–4.38 (m, 3 H), 6.79 (d, column temperature 30 °C, tmajor = 74.9 min, tminor = 71.9 min].
J = 8.6 Hz, 2 H), 7.14 (d, J = 8.6 Hz, 2 H), 7.22–7.37 (m, Ar) ppm. [α]2D5 = 131 (c = 1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ =
13C NMR (100 MHz, CDCl3): δ = 170.28, 158.62, 153.32, 141.44,
3.47–3.69 (m, 4 H), 3.78 (s, 3 H), 3.91–3.98 (m, 2 H), 4.34–4.43 (m,
130.04, 129.81, 128.51, 128.10, 127.40, 113.84, 62.04, 55.25, 44.26, 3 H), 6.20 (d, J = 8.6 Hz, 1 H), 6.30 (br. s, 1 H), 6.83 (d, J = 8.6 Hz,
42.45, 41.62, 35.11 ppm.
2 H), 7.20 (d, J = 8.6 Hz, 2 H), 7.36 (br. s, 1 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 169.97, 158.67, 153.75, 153.33, 130.54,
129.73, 114.27, 113.54, 110.28, 107.01, 62.13, 42.46, 39.18, 37.87,
37.27, 35.00 ppm.
(R)-3-[3-(Furan-2-ylmethylthio)-3-phenylpropanoyl]oxazolidin-2-one
(9m): The crude product was purified by flash chromatography
[SiO2, petroleum ether/ethyl acetate, 4:1 (v/v)] to give compound
9m in 95% yield and 99%ee [determined by HPLC, chiral AD-H,
hexane/2-propanol, 90:10 (v/v), 0.5 mL/min, λ = 220 nm, column
temperature 30 °C, tmajor = 31.7 min, tminor = 30.3 min]. [α]2D5 = 214
(R)-3-[3-(4-Methoxybenzylthio)-3-(naphthalen-1-yl)propanoyl]-
oxazolidin-2-one (9r): The crude product was purified by flash
chromatography [SiO2, petroleum ether/ethyl acetate, 4:1 (v/v)] to
give compound 9r in 90% yield and 94%ee [determined by HPLC,
chiral OD-H, hexane/2-propanol, 90:10 (v/v), 0.5 mL/min, λ =
1
(c = 1.0, CHCl3). H NMR (400 MHz, CDCl3): δ = 3.44–3.62 (m,
4 H), 3.83–3.98 (m, 2 H), 4.27–4.43 (m, 3 H), 3.79 (dd, J1
=
14.8 Hz, J2 = 20.3 Hz, 2 H), 3.99 (dt, J1 = 2 Hz, J2 = 8 Hz, 2 H),
4.39 (t, J = 8 Hz, 2 H), 6.11 (d, J = 3.2 Hz, 1 H), 6.28 (dd, J1 =
2 Hz, J2 = 3.2 Hz, 1 H), 7.22–7.39 (m, Ar, furan-H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 170.18, 153.37, 151.39, 141.96, 141.01,
128.68, 128.21, 127.63, 110.41, 107.61, 62.10, 44.32, 42.45, 41.45,
27.79 ppm.
220 nm, column temperature 30 °C, tmajor = 48.6 min, tminor
=
61.2 min]. [α]2D5 = 48.4 (c = 1.0, CHCl3). 1H NMR (400 MHz,
CDCl3): δ = 3.52 (d, J = 13.2 Hz, 1 H), 3.61 (d, J = 13.2 Hz, 1 H),
3.70 (dd, J1 = 7.0 Hz, J2 = 16.9 Hz, 1 H), 3.75–3.95 (m, 3 H), 3.78
(s, 3 H), 4.24–4.34 (m, 2 H), 5.18 (br. s, 1 H), 6.78 (d, J = 8.6 Hz,
2 H), 7.10 (d, J = 8.6 Hz, 2 H), 7.43–8.02 (m, Ar) ppm. 13C NMR
(100 MHz, CDCl3): δ = 188.28, 173.33, 166.87, 146.01, 142.52,
138.81, 137.76, 137.65, 137.23, 136.20, 135.21, 132.80, 132.24,
131.77, 129.10, 117.36, 52.72, 44.30, 28.22, 26.98, 19.50, 12.28 ppm.
(R)-3-[3-(Cyclopentylthio)-3-phenylpropanoyl]oxazolidin-2-one (9n):
The crude product was purified by flash chromatography [SiO2,
petroleum ether/ethyl acetate, 4:1 (v/v)] to give compound 7a in
85% yield and 95%ee [determined by HPLC, chiral AD-H, hexane/
2-propanol, 70:30 (v/v), 1.0 mL/min, λ = 220 nm, column tempera-
ture 30 °C, tmajor = 6.85 min, tminor = 8.35 min]. [α]2D5 = 147 (c =
1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ = 1.25–1.98 (m, 8 H),
2.81 (tt, J = 7.1 Hz, 1 H), 3.54 (dd, J1 = 2 Hz, J2 = 7.6 Hz, 2 H),
3.86–4.00 (m, 2 H), 4.28–4.40 (m, 2 H), 4.42 (t, J = 7.4 Hz, 1 H),
7.20–7.40 (m, Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 170.51,
153.38, 142.21, 128.37, 127.93, 127.34, 62.07, 44.84, 43.24, 42.48,
41.90, 34.07, 33.31, 24.95, 24.76 ppm.
(R)-3-[3-(4-Chlorobenzylthio)-3-(naphthalen-1-yl)propanoyl]ox-
azolidin-2-one (9s): The crude product was purified by flash
chromatography [SiO2, petroleum ether/ethyl acetate, 4:1 (v/v)] to
give compound 9s in 93% yield and 95%ee [determined by HPLC,
chiral OD-H, hexane/2-propanol, 90:10 (v/v), 0.5 mL/min, λ =
220 nm, column temperature 30 °C, tmajor = 27.7 min, tminor
=
30.0 min]. [α]2D5 = 51.6 (c = 1.0, CHCl3). 1H NMR (400 MHz,
CDCl3): δ = 3.50 (d, J = 13.4 Hz, 1 H), 3.63 (d, J = 13.6 Hz, 1 H),
3.66 (dd, J1 = 6.8 Hz, J2 = 17.0 Hz, 1 H), 3.77–3.96 (m, 3 H), 4.27–
4.38 (m, 2 H), 5.18 (br. s, 1 H), 7.07 (d, J = 8.4 Hz, 2 H), 7.16 (d,
J = 8.4 Hz, 2 H), 7.42–7.98 (m, Ar) ppm. 13C NMR (100 MHz,
CDCl3): δ = 170.47, 153.42, 136.37, 133.94, 132.72, 130.95, 130.31,
128.95, 128.47, 128.24, 126.24, 125.77, 125.36, 62.11, 42.50, 41.51,
35.37, 29.70 ppm.
(R)-3-[3-(2-Chlorophenyl)-3-(4-methoxybenzylthio)propanoyl]ox-
azolidin-2-one (9o): The crude product was purified by flash
chromatography [SiO2, petroleum ether/ethyl acetate, 10:3 (v/v)] to
give compound 9o in 96% yield and 97%ee [determined by HPLC,
chiral AD-H, hexane/2-propanol, 70:30 (v/v), 0.5 mL/min, λ =
220 nm, column temperature 30 °C, tmajor = 29.2 min, tminor
=
27.2 min]. [α]2D5 = 83.2 (c = 1.0, CHCl3). 1H NMR (400 MHz,
CDCl3): δ = 3.39 (dd, J1 = 7.4 Hz, J2 = 17 Hz, 1 H), 3.60–3.67 (m,
3 H), 3.76 (s, 3 H), 3.91 (m, 2 H), 4.34 (m, 2 H), 4.92 (t, J = 7.4 Hz,
1 H), 6.79 (d, J = 8.6 Hz, 2 H), 7.13 (d, J = 8.6 Hz, 2 H), 7.17–
7.57 (m, Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 169.94,
158.66, 153.42, 138.98, 133.53, 129.92, 129.72, 129.54, 129.10,
128.34, 127.18, 113.86, 62.15, 55.34, 42.48, 41.17, 40.93, 35.75 ppm.
The Asymmetric Synthesis of Methyl β-Tosylbutanoate: To a solu-
tion of 9i (56 mg, 0.02 mmol) in CH3OH (2 mL) at 0 °C was added
CH3MgBr (3 m in ether, 10 μL) with a syringe. After stirring at the
same temperature for 30 min, the reaction was quenched by adding
hydrochloric acid (1 n solution, 2 mL). The mixture was extracted
with dichloromethane (3ϫ5 mL), and then the combined organic
layers were washed with brine, dried with Na2SO4, and concen-
trated under reduced pressure. The residue was purified by silica
gel column chromatography [dichloromethane/petroleum ether, 1:3
(v/v)] to afford product 10 as a colorless oil (43 mg, 96% yield). 1H
NMR (400 MHz, CDCl3): δ = 1.52 (d, J = 6.8 Hz, 3 H), 2.54 (s, 3
H), 2.65 (dd, J1 = 8.5 Hz, J2 = 15.6 Hz, 1 H), 2.81 (dd, J1 = 6.0 Hz,
J2 = 15.6 Hz, 1 H), 3.73 (qt, J1 = 7.6 Hz, J2 = 6.7 Hz, 1 H), 3.87
(s, 3 H), 7.34 (d, J = 7.8 Hz, 2 H), 7.55 (d, J = 7.8 Hz, 2 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 172.12, 138.00, 133.88, 130.01,
129.92, 51.87, 41.85, 40.01, 21.32, 21.05 ppm. Product 10 (45 mg,
0.20 mmol) was dissolved in toluene (5 mL) and ethyl acetate
(5 mL). After the solution was cooled to 0 °C, a solution of
Na2WO4·2H2O (7.5 mg, 0.020 mmol) in water (0.5 mL ) was added,
and then H2O2 (30% solution, 100 μL, 0.98 mmol) was added
dropwise. The resulting mixture was stirred at room temperature
overnight and then diluted with water (5 mL). The mixture was
extracted with ethyl acetate (3ϫ3 mL), and the combined organic
(R)-3-[3-(4-Chlorophenyl)-3-(4-methoxybenzylthio)propanoyl]ox-
azolidin-2-one (9p): The crude product was purified by flash
chromatography [SiO2, petroleum ether/ethyl acetate, 10:3 (v/v)] to
give compound 9p in 92% yield and 99%ee [determined by HPLC,
chiral AD-H, hexane/2-propanol, 70:30 (v/v), 0.5 mL/min, λ =
220 nm, column temperature 30 °C, tmajor = 35.4 min, tminor
=
31.4 min]. [α]2D5 = 211 (c = 1.0, CHCl3). 1H NMR (400 MHz,
CDCl3): δ = 3.43 (m, 2 H), 3.51 (m, 2 H), 3.78 (s, 3 H), 3.81–3.93
(m, 2 H), 4.24 (dd, J1 = 7.2 Hz, J2 = 7.7 Hz, 1 H), 4.28–4.37 (m, 2
H), 6.81 (d, J = 8.6 Hz, 2 H), 7.12 (d, J = 8.6 Hz, 2 H), 7.25–7.37
(m, Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 169.99, 158.70,
153.33, 140.11, 132.99, 129.90, 129.50, 128.65, 113.89, 62.10, 55.31,
43.39, 42.41, 41.59, 35.16 ppm.
(R)-3-[3-(Furan-2-yl)-3-(4-methoxybenzylthio)propanoyl]oxazol-
idin-2-one (9q): The crude product was purified by flash chromatog-
Eur. J. Org. Chem. 2011, 5071–5076
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5075

L. Dai, H. Yang, F. Chen
FULL PAPER
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layers were washed with brine, dried with Na2SO4, and concen-
trated under reduced pressure. The residue was purified by silica
gel column chromatography [dichloromethane/petroleum ether, 1:1
(v/v)] to afford the product 11 as a white solid (43 mg, 85% yield);
90%ee [determined by HPLC, chiral OD-H, hexane/2-propanol,
90:10 (v/v), 0.5 mL/min, λ = 220 nm, column temperature 30 °C,
tmajor = 28.0 min, tminor = 19.8 min]. MS (EI+): m/z = 256 [M]+.
1H NMR (400 MHz, CDCl3): δ = 1.28 (d, J = 7.2 Hz, 3 H), 2.34
(dd, J1 = 10.0 Hz, J2 = 16.4 Hz, 1 H), 2.42 (s, 3 H), 2.95 (dd, J1 =
4.0 Hz, J2 = 16.4 Hz, 1 H), 3.53 (m, 1 H), 3.63 (s, 3 H), 7.34 (d, J
= 8.0 Hz, 2 H), 7.74 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 170.62, 134.70, 130.94, 129.84, 128.30,
56.55, 52.20, 34.43, 21.63, 13.90 ppm.
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Supporting Information (see footnote on the first page of this arti-
cle): Copies of the NMR and HPLC spectra for all products.
Acknowledgments
Thanks are expressed to Dr. Zhenxia Chen for performing the X-
ray analysis.
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Received: March 23, 2011
Published Online: July 21, 2011
5076
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 5071–5076