Diastereo- and enantioselective conjugate addition of 3-chlorooxindoles to nitroalkenes catalyzed by binaphthyl-modified organocatalyst

Full text of DOI:10.1002/bkcs.10264

Note
DOI: 10.1002/bkcs.10264
BULLETIN OF THE
H. J. Jeong et al.
KOREAN CHEMICAL SOCIETY
Diastereo- and Enantioselective Conjugate Addition of 3-Chlorooxindoles
to Nitroalkenes Catalyzed by Binaphthyl-modified Organocatalyst
*
Hyun Jung Jeong, Su Jin Kwon, and Dae Young Kim
Department of Chemistry, Soonchunhyang University, Chungnam 336-745, Korea.
*E-mail: dyoung@sch.ac.kr
Received December 24, 2014, Accepted January 9, 2015, Published online April 24, 2015
Keywords: Conjugate addition, 3-Chlorooxindoles, Asymmetric catalysis, Bifunctional organocatalysts
Oxindole derivatives have attracted considerable attention in
organic synthesis and medicinal chemistry because of their
prevalence in a number of natural and biologically active
molecules.1 Notably, 3,3-disubstituted oxindoles bearing a
quaternary stereogenic center at position 3 are considered as
crucial fragments of a number of natural products and medic-
inally important agents.2 Therefore, the stereocontrolled syn-
thesis of 3,3-disubstituted oxindole derivatives has become
the subject of enormous interest over the past decades. Among
the established strategies for the synthesis of chiral 3,3-
disubstituted oxindoles, transition metal-catalyzed asymmet-
ric reactions have been intensively studied.3 Recently, a num-
ber of successful examples using various 3-monosubstituted
oxindoles as nucleophiles reacting with diverse electrophiles
to afford 3,3-disubstituted oxindoles have been reported.4
However, there are a few reports for the synthesis of chiral
3-chloro-3-substituted oxindoles by the catalytic enantiose-
lective C C bond formation from 3-chlorooxindoles.5
Although this method has been satisfied some extent as effi-
cient process, new organocatalytic conjugate addition of
3-chlorooxindoles to nitroalkenes is highly desired.
As part of a research program related to the development of
synthetic methods for the enantioselective construction of
stereogenic carbon centers,6 we recently reported enantiose-
lective conjugate addition of active methylenes and methines
using chiral organocatalysts.7 Herein, we describe the enantio-
selective conjugate addition reaction of 3-chlorooxindoles to
nitroalkenes catalyzed by binaphthyl-modified bifunctional
organocatalysts bearing both central and axial chiral elements
(Figure 1).
the yields and enantiomeric excesses. The effective catalyst
loading could be reduced to 5 mol% without compromising
the yield or the enantioselectivity (entries 14–15). The
N
N
HN
HN
HN
HN
S
O
CF3
CF3
F3C
F3C
I
II
N
HN
N
HN
O
O
HN
HN
O
O
F3C
F3C
CF3
CF3
IV
III
Ph
Ph
N
N
Ph
Ph
HN
HN
HN
HN
S
O
CF3
CF3
F3C
F3C
In an attempt to validate the feasibility of the organocataly-
tic enantioselective Michael addition of 3-chlorooxindoles,
we investigated a reaction system with 3-chloroindolin-2-
one (1a) with β-nitrostyrene (2a) in the presence of
10 mol% of catalyst in dichloromethane at room temperature.
We first surveyed the effect of the structure of catalysts I–VIII
on enantioselectivity (Table 1, entries 1–8). High yields and
excellent enantioselectivities were observed for binaphthyl-
derived squaramide catalyst VIII (93% ee, entry 8).
A survey of the reaction media indicated that this reaction
was highly solvent-dependent (entries 9–13). Among the sol-
vents probed, the halogenated solvents gave the best results in
VI
V
Ph
Ph
Ph
N
HN
N
Ph
HN
O
O
HN
HN
O
O
F3C
F3C
CF3
CF3
VIII
VII
Figure 1. Structures of organocatalysts.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1516–1519
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KOREAN CHEMICAL SOCIETY
Table 1. Optimization of the reaction conditions.a
Table 2. Substrate scope.a
Ar
Ph
Cl
Cl
NO2
Cl
NO2
Cl
cat. (10 mol %)
NO2
cat. VIII (5 mol %)
NO2
R
O
R
O
Ar
Ph
O
O
CH2Cl2, rt, 24 h
N
N
H
solvent, rt, 24 h
N
H
N
H
H
3
1
2
1a
2a
3a
Yieldb (%)
drc
eed (%)
Entry
1, R
2, Ar
Yieldb (%)
drc
eed (%)
Entry
Cat.
Solvent
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
H
Ph
4-Me-Ph
3a, 83
3b, 85
3c, 71
3d, 84
3e, 79
3f, 77
3g, 91
3h, 64
3i, 90
3j, 86
3k, 80
3l, 71
13:1
10:1
8:1
10:1
11:1
8:1
6:1
12:1
8:1
93
90
89
90
95
94
95
97
91
89
89
98
1
2
3
4
5
6
7
8
I
II
III
IV
V
VI
VII
VIII
VIII
VIII
VIII
VIII
VIII
VIII
VIII
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CHCl3
95
73
70
52
54
68
73
85
73
70
56
trace
trace
83
2:1
5:1
1.2:1
3:1
3:1
3:1
20:1
14:1
10:1
19:1
1.5:1
—
87
87
90
91
78
82
92
93
92
91
68
—
—
93
93
4-OMe-Ph
4-F-Ph
3-F-Ph
2-F-Ph
2-NO2-Ph
3-NO2-Ph
2-furyl
2-thienyl
Ph
9
9
10
11
12
H
4-Cl
6-Cl
8:1
15:1
19:1
10
11
12
13
14e
15f
ClCH2CH2Cl
Et2O
Ph
THF
PhMe
CH2Cl2
CH2Cl2
a Reaction conditions: 3-chlorooxindoles (1, 0.3 mmol), nitroalkene (2,
0.45 mmol), catalyst IV (0.015 mmol), solvent (3.0 mL) at room
temperature.
—
13:1
13:1
20
b Isolated yield.
a Reaction conditions: 3-chlorooxindole (1a, 0.3 mmol), β-nitrostyrene
c Determined by 1H NMR analysis.
(2a, 0.45 mmol), catalyst (0.03 mmol), solvent (3.0 mL) at room
temperature.
d Enantiopurity was determined by HPLC analysis using Chiralcel OD-H
(3a), OF (3h), Chiralpak IB (3b, 3d, 3g , 3i, and 3l), IB-3 (3e and 3f), IC
(3j and 3k), and ID (3c) columns.
b Isolated yield.
c Determined by 1H NMR analysis.
d Enantiopurity was determined by HPLC analysis using Chiralcel OD-H
column.
method provides a practical entry to biologically useful chiral
3-chloro-3-substituted oxindoles.
e 5 mol% catalyst loading.
f 2.5 mol% catalyst loading.
Experimental
absolute configuration of 3 was established by comparison of
the optical rotation and chiral HPLC analysis with previously
reported values.5
General. All commercial reagents and solvents were used
without purification. TLC analyses were carried out on pre-
coated silica gel plates with F254 indicator. Visualization
was accomplished by UV light (254 nm), I2, p-anisaldehyde,
ninhydrin, andphosphomolybdic acid solutionasanindicator.
Purification of reaction products was carried out by flash
chromatography using Merck silica gel 60 (Darmstadt,
With the optimized conditions in hand, we proceeded to
investigate the scope of the enantioselective conjugate addi-
tion of 3-chlorooxindoles with various nitroalkenes 2 in the
presence of 5 mol% of binaphthyl-modified squaramide-
tertiary amine catalyst IV in dichloromethane at room temper-
ature (Table 2, entries 1–10). The corresponding Michael
products 3a–3j were formed in high yields (71–91%), high
diastereoselectivities (6–19:1), and excellent enantioselectiv-
ities (89–95%). The substituents of the aromatic nitroalkenes
had limited effects on the reaction efficiency. A chlorine atom
substitution on the aryl ring of the 3-chlorooxindoles 1k–1l
providedcorrespondingproductsinhighyieldsandhighenan-
tioselectivities (89–98%, entries 11–12).
In summary, we have developed highly efficient catalytic
enantioselective Michael addition reactions of 3-
chlorooxindoles to nitroalkenes using bifunctional organoca-
talyst. The desired Michael products were obtained in high
yields and diasteroselectivities. Also, the excellent enantios-
electivities were observed (89–95% ee). We believe that this
1
Germany, 230–400 mesh). H NMR and 13C NMR spectra
were recorded on a Jeol ECS400 MHz NMR (Tokyo, Japan,
400 MHz for 1H and 100 MHz for 13C). Chemical shift values
(δ) are reported in ppm relative to Me4Si (δ 0.0 ppm). Optical
rotations were measured on a JASCO-DIP-1000 digital polar-
imeter (Tokyo, Japan) with a sodium lamp. The enantiomeric
excesses (ee) were determined by HPLC. HPLC analysis
was performed on Younglin M9100 Series (Seoul, Korea),
measured at 230 nm using the indicated chiral column.
Typical Procedure for the Michael Addition of 3-
Chlorooxindole(1a) with β-Nitrostyrene(2a). Toasolution
of 3-chloroxindole (1a, 0.3 mmol, 50.3 mg) and catalyst VIII
(0.015 mmol, 12.2 mg) in CH2Cl2 (3.0 mL) was added
β-nitrostyrene (2a, 0.45 mmol, 67.1 mg). Reaction mixture
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KOREAN CHEMICAL SOCIETY
was stirred for 1 day at room temperature, concentrated, and
purified by flash column chromatography (CH2Cl2:EtOAc
= 20:1) to afford the Michael adduct (3a, 83 mg, 83%).
(R)-3-chloro-3-((S)-2-nitro-1-phenylethyl)indolin-2-one
MHz, Chloroform-d) δ 8.08 (s, 1H), 6.98–6.92 (m, 2H), 6.88
(d, J = 8 Hz, 1H), 6.54 (d, J = 7.6 Hz, 1H), 7.36–7.29 (m, 3H),
7.12 (td, J = 15.4, 1 Hz, 1H), 5.75 (dd, J = 14, 4 Hz, 1H), 5.16
(dd, J = 13.8, 11 Hz, 1H), 4.64 (dd, J = 11, 3.8 Hz, 1H); the ee
value was 94%, tR (major) = 27.4 min, tR (minor) = 20.2 min
(Chiralcel IB-3, λ = 230 nm, Hex/i-PrOH 95/5, flow rate =
1.0 mL/min).
27
1
(3a). ½αꢀD = −172.16 (c = 1, CH2Cl2); H NMR (400 MHz,
Chloroform-d) δ 7.79 (s, 1H), 7.31 (td, J = 15.6, 1.4 Hz,
1H), 7.28–7.24 (m, 1H), 7.19–7.15 (m, 2H), 7.05 (td, J =
14.8, 1.4 Hz, 1H), 6.99–6.97 (m, 2H), 6.9 (d, J = 8 Hz, 1H),
6.79 (d, J = 8Hz, 1H), 5.67 (dd, J = 13.4, 3.8 Hz, 1H), 5.15
(dd, J = 13.2, 11.2 Hz, 1H), 4.29 (dd, J = 11, 3.4 Hz, 1H);
13C NMR (101 MHz, CDCl3) δ 173.86, 139.92, 132.64,
131.16, 129.50, 129.17, 128.97, 128.67, 127.25, 126.06,
123.47, 110.81, 75.62, 66.13, 50.72; the ee value was 93%,
tR (major) = 29.4 min, tR (minor) = 21.9 min (Chiralcel OD-
H, λ = 230 nm, Hex/i-PrOH 95/5, flow rate = 1.0 mL/min).
(R)-3-chloro-3-((S)-2-nitro-1-(p-tolyl)ethyl)indolin-2-one
(R)-3-chloro-3-((S)-2-nitro-1-(2-nitrophenyl)ethyl)indo-
23
lin-2-one (3g). ½αꢀD = −91.16 (c = 1, CH2Cl2); 1H NMR (400
MHz, Chloroform-d) δ 8.49 (s, 1H), 7.88 (dd, J = 8.2, 1.4 Hz,
1H), 7.80–7.78 (m, 1H), 7.68 (td, J = 15.6, 1.4 Hz, 1H), 7.57
(td, J = 15.6, 1.2 Hz, 1H), 7.29 (dd, J = 8, 1.2 Hz, 1H), 6.96 (d,
J = 4 Hz, 1H), 6.86 (td, J = 15.2, 0.8 Hz, 1H), 6.26 (d, J = 7.6
Hz, 1H), 5.82 (dd, J = 14, 3.6 Hz, 1H), 5.28 (dd, J = 10.6, 3.4
Hz, 1H), 5.17 (dd, J = 13.8, 10.6 Hz, 1H); the ee value was
95%, tR (major) = 68.0 min, tR (minor) = 55.0 min (Chiralcel
IB, λ = 230 nm, Hex/i-PrOH 95/5, flow rate = 1.0 mL/min).
(R)-3-chloro-3-((S)-2-nitro-1-(3-nitrophenyl)ethyl)indo-
22
1
(3b). ½αꢀD = −88.08 (c = 1, CH2Cl2); H NMR (400 MHz,
Chloroform-d) δ 7.82 (s, 1H), 7.30 (td, J = 15.6, 1.2 Hz,
1H), 7.06 (td, J = 15.6, 1 Hz, 1H), 6.98–6.93 (m, 3H), 6.85
(d, J = 8 Hz, 2H), 6.79 (d, J = 8, 1H), 5.64 (dd, J = 13.2, 3.6
Hz, 1H), 5.12 (dd, J = 13.2, 11.6 Hz, 1H), 4.26 (dd, J =
11.4, 3.8 Hz, 1H), 2.26 (s, 3H); the ee value was 90%, tR
(major) = 17.8 min, tR (minor) = 13.8 min (Chiralcel IB, λ =
230 nm, Hex/i-PrOH 95/5, flow rate = 1.0 mL/min).
23
1
lin-2-one (3h). ½αꢀD = −102.40 (c = 1, CH2Cl2); H NMR
(400 MHz, Chloroform-d) δ 7.68 (s, 1H), 7.31 (td, J = 15.4,
1 Hz, 1H), 7.10–7.05 (m, 2H), 6.97 (d, J = 7.6 Hz, 1H),
6.80–6.77 (m, 2H), 6.57 (d, J = 7.2 Hz, 1H), 6.48–6.47 (m,
1H), 5.65 (dd, J = 13.2, 3.6 Hz, 1H), 5.12 (dd, J = 13.2,
11.6 Hz, 1H), 4.28 (dd, J = 11.6, 3.6 Hz, 1H); the ee value
was 97%, tR (major) = 78.0 min, tR (minor) = 107.3 min
(Chiralcel OF, λ = 230 nm, Hex/i-PrOH 95/5, flow rate =
1.0 mL/min).
(R)-3-chloro-3-((S)-1-(4-methoxyphenyl)-2-nitroethyl)
indolin-2-one (3c). ½αꢀ2D2 = −93.76 (c = 0.5, CH2Cl2); 1H
NMR (400 MHz, Chloroform-d) δ 7.03 (td, J = 15.4, 1.2 Hz,
1H), 7.17 (s, 1H), 7.07 (td, J = 15.2, 1.2 Hz, 1H), 7.00–6.96
(m, 1H), 6.87 (d, J = 8.8 Hz, 2H), 6.75 (d, J = 8 Hz, 1H),
6.68 (d, J = 8.8 Hz, 2H), 5.62 (dd, J = 9.4, 3.4 Hz, 1H), 5.09
(dd, J = 13, 11.8 Hz, 1H), 4.27 (dd, J = 11.6, 3.6 Hz, 1H),
3.74 (s, 3H). The ee value was 89%, tR (major) = 35.1 min,
tR (minor) = 32.9 min (Chiralcel ID, λ = 230 nm, Hex/i-PrOH
95/5, flow rate = 1.0 mL/min).
(R)-3-chloro-3-((R)-1-(furan-2-yl)-2-nitroethyl)indolin-
23
1
2-one (3i). ½αꢀD = −73.12 (c = 1, CH2Cl2); H NMR (400
MHz, Chloroform-d) δ 8.15 (s, 1H), 7.30 (td, J = 15.6, 1.0
Hz, 1H), 7.25–7.24 (m, 1H), 7.04 (td, J = 15, 1 Hz, 1H),
6.87 (d, J = 8 Hz, 1H), 6.80 (d, J = 8 Hz, 1H), 6.29–6.23 (m,
2H), 5.64 (dd, J = 13.6, 3.6 Hz, 1H), 5.16 (dd, J = 13.8, 11
Hz, 1H), 4.44 (dd, J = 11.2, 3.6 Hz, 1H); the ee value was
91%, tR (major) = 19.9 min, tR (minor) = 17.4 min (Chiralcel
IB, λ = 230 nm, Hex/i-PrOH 95/5, flow rate = 1.0 mL/min).
(R)-3-chloro-3-((R)-2-nitro-1-(thiophen-2-yl)ethyl)indo-
(R)-3-chloro-3-((S)-1-(4-fluorophenyl)-2-nitroethyl)indo-
23
lin-2-one (3d): ½αꢀD = −90.92 (c = 1, CH2Cl2); 1H NMR (400
MHz, Chloroform-d) δ 7.97 (s, 1H), 7.33 (td, J = 15.4, 1.4 Hz,
1H), 7.08 (td, J = 15.6, 1 Hz, 1H), 6.98–6.94 (m, 3H),
6.89–6.81 (m, 3H), 5.65 (dd, J = 13.2, 3.6 Hz, 1H), 5.09
(dd, J = 13.2, 11.2 Hz, 1H), 4.30 (dd, J = 11.4, 3.4 Hz, 1H);
the ee value was 90%, tR (major) = 22.4 min, tR (minor) =
16.8 min (Chiralcel IB, λ = 230 nm, Hex/i-PrOH 95/5, flow
rate = 1.0 mL/min).
22
lin-2-one (3j). ½αꢀD = −82.92 (c = 1, CH2Cl2); 1H NMR (400
MHz, Chloroform-d) δ 8.10 (s, 1H), 7.35 (td, J = 15.6, 1.4 Hz,
1H), 7.19–7.17 (m, 1H), 7.08 (td, J = 15.4, 1.2 Hz, 1H), 6.95
(d, J = 7.2 Hz, 1H), 6.87–6.80 (m, 3H), 5.70 (dd, J = 13, 3.4
Hz, 1H), 5.02 (dd, J = 13.2, 11.2 Hz, 1H), 4.63 (dd, J =
11.2, 3.2 Hz, 1H); the ee value was 89%, tR (major) = 20.8
min, tR (minor) = 19.2 min (Chiralcel IC, λ = 230 nm, Hex/i-
PrOH 95/5, flow rate = 1.0 mL/min).
(R)-3-chloro-3-((S)-1-(3-fluorophenyl)-2-nitroethyl)indo-
28
lin-2-one(3e).½αꢀD = −113.92 (c = 1, CH2Cl2); 1H NMR (400
(R)-3,4-dichloro-3-((S)-2-nitro-1-phenylethyl)indolin-2-
MHz, Chloroform-d) δ 7.92 (s, 1H), 7.33 (td, J = 15.6, 1 Hz,
1H), 7.19–7.14 (m, 1H), 7.07 (td, J = 15, 1 Hz, 1H),
7.00–6.95 (m, 1H), 6.91 (d, J = 8 Hz, 1H), 6.84–6.79 (m,
2H), 5.67 (dd, J = 13.4, 3.4 Hz, 1H), 5.10 (dd, J = 13.4,
11.4 Hz, 1H), 4.29 (dd, J = 11.6, 3.6 Hz, 1H); the ee value
was 95%, tR (major) = 122.1 min, tR (minor) = 102.7 min
(Chiralcel IB-3, λ = 230 nm, Hex/i-PrOH 99/1, flow rate =
1.0 mL/min).
28
one (3k). ½αꢀD = −86.72 (c = 1, CH2Cl2); 1H NMR (400 MHz,
Chloroform-d) δ 7.98 (s, 1H), 7.24–7.10 (m, 5H), 6.97–6.95
(m, 2H), 6.63 (dd, J = 7.4, 1.2 Hz, 1H), 5.51 (dd, J = 13.6,
3.2 Hz, 1H), 5.38 (dd, J = 13.4, 11.8 Hz, 1H), 4.56 (dd, J =
11.6, 3.2 Hz, 1H); the ee value was 89%, tR (major) = 12.8
min, tR (minor) = 15.3 min (Chiralcel IC, λ = 230 nm, Hex/i-
PrOH 95/5, flow rate = 1.0 mL/min).
(R)-3-chloro-3-((S)-1-(2-fluorophenyl)-2-nitroethyl)indo-
(R)-3,6-dichloro-3-((S)-2-nitro-1-phenylethyl)indolin-2-
23
24
1
lin-2-one (3f ). ½αꢀD = −70.92 (c = 1, CH2Cl2); 1H NMR (400
one (3l). ½αꢀD = −280.64 (c = 0.25, CH2Cl2); H NMR (400
Bull. Korean Chem. Soc. 2015, Vol. 36, 1516–1519
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MHz, Chloroform-d) δ 7.34 (s, 1H), 7.32–7.21 (m, 3H),
7.04–7.02 (m, 2H), 7.00 (dd, J = 8.2, 1.8 Hz, 1H), 6.80 (d, J
= 2 Hz, 1H), 6.69 (d, J = 8 Hz, 1H), 5.67 (dd, J = 13.2, 3.6
Hz, 1H), 5.12 (dd, J = 13.6, 11.2 Hz, 1H), 4.24 (dd, J =
10.8, 3.6 Hz, 1H); the ee value was 98%, tR (major) = 125.6
min, tR (minor) = 115.4 min (Chiralcel IB, λ = 230 nm, Hex/
i-PrOH 99/1, flow rate = 1.0 mL/min).
Acknowledgment. This research was supported by Soon-
chunhyang University Research Fund.
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K. Yamatsugu, M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2009,
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4. (a) T. Bui, S. Syed, C. F. Barbas III. , J. Am. Chem. Soc. 2009, 131,
8758; (b) N. Bravo, I. Mon, X. Companyo, A.-N. Alba, A.
Moyano, R. Rios, Tetrahedron Lett. 2009, 50, 6624; (c) X. Li,
B. Zhang, Z.-G. Xi, S. Luo, J.-P. Cheng, Adv. Synth. Catal.
2010, 352, 416; (d) X. Li, Z.-G. Xi, S. Luo, J.-P. Cheng, Org. Bio-
mol. Chem. 2010, 8, 77; (e) H. J. Lee, S. H. Kang, D. Y. Kim,
Synlett 2011, 22, 1559; (f ) H. J. Lee, D. Y. Kim, Bull. Korean
Chem. Soc. 2012, 33, 3171; (g) H. J. Lee, S. B. Woo, D. Y.
Kim, Molecules 2012, 17, 7523.
5. (a) A. Noole, I. Jarving, F. Werner, M. Lopp, A. Malkov, T. Kan-
ger, Org. Lett. 2012, 14, 4922; (b) X. Dou, W. Yao, B. Zhou,
Y. Lu, Chem. Commun. 2013, 49, 9224; (c) R. C. da Silva, I. Chat-
terjee, E. Escudero-Adan, M. Q. Paixao, P. Melchiorre, Asian J.
Org. Chem. 2014, 3, 466.
6. For selected our recent works for the formation of C C bonds,
see: (a) Y. K. Kang, D. Y. Kim, J. Org. Chem. 2009, 74, 5734;
(b) S. H. Kang, Y. K. Kang, D. Y. Kim, Tetrahedron 2009, 65,
5676; (c) J. H. Lee, D. Y. Kim, Adv. Synth. Catal. 2009, 351,
1779; (d) Y. Y. Oh, S. M. Kim, D. Y. Kim, Tetrahedron Lett.
2009, 50, 4674; (e) H. W. Moon, M. J. Cho, D. Y. Kim, Tetrahe-
dron Lett. 2009, 50, 4896; (f ) B. K. Kwon, S. M. Kim, D. Y. Kim,
7. For our selected works using organocatalysts, see: (a) D. Y. Kim,
S. C. Huh, Tetrahedron 2001, 57, 8933; (b) D. Y. Kim, S. C. Huh,
S. M. Kim, Tetrahedron Lett. 2001, 42, 6299; (c) D. Y. Kim,
E. J. Park, Org. Lett. 2002, 4, 545; (d) D. Y. Kim, S. M. Kim,
K. O. Koh, J. Y. Mang, K. Lee, Bull. Korean Chem. Soc. 2003,
24, 1425; (e) E. J. Park, M. H. Kim, D. Y. Kim, J. Org. Chem.
2004, 69, 6897; (f ) S. H. Jung, D. Y. Kim, Tetrahedron Lett.
2008, 49, 5527; (g) S. M. Kim, J. H. Lee, D. Y. Kim, Synlett
2008, 19, 2659; (h) J. H. Lee, D. Y. Kim, Adv. Synth. Catal.
2009, 351, 1779; (i) B. K. Kwon, D. Y. Kim, Bull. Korean Chem.
Soc. 2009, 30, 1441; (j) H. W. Moon, D. Y. Kim, Bull. Korean
Chem. Soc. 2011, 32, 291; (k) H. J. Lee, J. H. Kim, D. Y. Kim,
Bull. Korean Chem. Soc. 2011, 32, 785; (l) H. J. Lee, S. H. Kang,
D. Y. Kim, Bull. KoreanChem. Soc. 2011, 32, 1125;(m)J. H. Lee,
D. Y. Kim, Bull. Korean Chem. Soc. 2012, 33, 3537; (n) J. H. Lee,
S. B. Woo, D. Y. Kim, Tetrahedron Lett. 2012, 53, 3374;
(o) Y. J. Lim, D. Y. Kim, Bull. Korean Chem. Soc. 2012, 33,
1825; (p) H. W. Moon, D. Y. Kim, Bull. Korean Chem. Soc.
2012, 33, 2845; (q) Y. J. Lim, D. Y. Kim, Bull. Korean Chem.
Soc. 2013, 34, 1955; (r) J. Y. Lee, D. Y. Kim, Bull. Korean
Chem. Soc. 2013, 34, 2569;(s)Y. K. Kang, H. J. Lee, H. W. Moon,
D. Y. Kim, RSC Adv. 2013, 3, 1332; (t) Y. K. Kang, D. Y. Kim,
Adv. Synth. Catal. 2013, 355, 3131; (u) C. W. Suh, D. Y. Kim,
Org. Lett. 2014, 16, 5374; (v) C. W. Suh, D. Y. Kim, Bull. Korean
Chem. Soc. 2014, 35, 98.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1516–1519
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1519