Thiourea-catalyzed intramolecular allylic amination: Synthesis of dihydroquinoline derivatives

Full text of DOI:10.1002/bkcs.10014

Note
DOI: 10.1002/bkcs.10014
BULLETIN OF THE
H. J. Lee et al.
KOREAN CHEMICAL SOCIETY
Thiourea-catalyzed Intramolecular Allylic Amination: Synthesis
of Dihydroquinoline Derivatives
*
Hyun Joo Lee, Da Eun Lee, and Dae Young Kim
Department of Chemistry, SoonchunhyangUniversity, Chungnam336-745, Korea. *E-mail:dyoung@sch.ac.kr
Received August 6, 2014, Accepted September 12, 2014, Published online January 5, 2015
The dihydroquinoline structure exists in a large number of nat-
ural products and biologically active molecules. Particularly,
the reactivity with catalyst III in the presence of various addi-
tives, such as benzoic acid, trifluoroacetic acid (TFA), trifluor-
omethanesulfonic acid (TfOH), 2,4-dinitrobenzensulfonic acid
(DNBS), HCl,andHBr(Table 1,entries3–9). Amongtheaddi-
tives probed, the best result (85% yield) was achieved when the
reaction was conducted in HBr (Table 1, entry 9). A survey of
thereactionmediaindicatedthatseveralcommonsolvents,such
as dichloromethane, chloroform, methyl tert-butyl ether
(MTBE), tetrahydrofuran (THF), and toluene were well toler-
ated in this allylic amination (Table 1, entries 9–14). Among
the solvents probed, the best result was achieved when the reac-
tion was conducted in toluene (Table 1, entry 9). The combina-
tion of catalyst III and HBr showed the highest activity for this
ally lamination. With the use of catalyst III or HBr alone, the
reaction gave 2 in low yields (Table 1, entries 15 and 16).
With the optimal reaction conditions in hand, the scope of
the reaction was explored, as seen in Table 2. Organocatalyst
III-catalyzed intramolecular allylic amination reaction of N-
protected 2-aminophenyl-substituted allyl alcohol proved to
be a general approach for the synthesis of versatile 1,2-
dihydroquinolines 2. The thiourea-catalyzed synthesis of sub-
stituted dihydroquinolines could tolerate a methoxy-, chloro-,
or naphthyl group at the terminal position of the allylic alcohol
moiety, giving 2b–2e with 85–98% yields (entries 1–4). Mod-
erate yield was obtained when styryl-substituted allylic alco-
hol 1f was used as the substrate (entry 5).
1
many of these naturally occurring 1,2-dihydroquinolines and
their synthetic analogs are important precursors for the synthe-
2
sis of natural products and pharmaceuticals. Therefore, the
developmentofnew and efficient syntheticroutes for theprep-
aration of dihydroquinoline analogs is of importance to both
3
–12
organic synthetic and medicinal chemistry.
Recently, effi-
cient synthetic methodologies for the preparation for dihydro-
quinolines have focused on catalytic systems. Some notable
examples include the cascade reaction of anilines with alkynes3
catalyzed 4by transition metals such as palladium,
,5
6
7
ruthenium, silver, and gold ; the condensation reaction
8
of anilines with ketones catalyzed by scandium triflate, sili-
cotungstic acid, and zeolite ; the allylation of quinolines
mediated by indium ; and metal-catalyzed allylic amina-
tion. The organocatalyst-mediated carbon–carbon and car-
bon–heteroatom bond formations have gained considerable
attention because organocatalysis is one of the most powerful
and environmentally benign processes.
9
10
1
1
12
As a part of the research program related to the development
13
ofsyntheticmethods fortheformationofcarbon–carbon and
1
4
carbon–heteroatom bonds, we recently reported the organo-
catalytic α-alkylation of cyclic ketones by S 1-type reaction
N
15
of alcohols. We then turned our attention to an intramolec-
1
6
ular version of S 1-type reaction of alcohols. To the best of
N
our knowledge, there are no examples for organocatalytic syn-
thesis of dihydroquinolines from 2-aminophenyl-1-en-3-ol
derivatives using intramolecular allylic amination reaction.
Here, we report an efficient synthetic method to 1,2-
We next attempted to extend our strategy to develop
theasymmetricversionofthisorganocatalyzedintramolecular
allylic amination reaction. In the presence of the chiral catalyst
IV, the intramocular allylic amination reaction of (E)-4-
phenyl-2-(2-(tosylamino)phenyl)but-3-en-2-ol (1a) pro-
ceeded to afford the chiral product 2aà with moderate enan-
tioselectivity (40% ee, Scheme 1).
dihydroquinoline derivatives involving intramolecular S 1-
N
type amination of N-protected 2-aminoaryl-1-en-3-ols cata-
lyzed by an organocatalyst at room temperature.
To determine suitable reaction conditions for the intramo-
lecular allylic amination reaction of N-protected 2-aminophe-
nyl-substituted allyl alcohol, we chose (E)-4-phenyl-2-(2-
Although the reason for the observed reactivity of this cat-
alyst system is still unclear, we suppose that it is nucleophilic
addition of the sulfonamide unit to the allylic cation moiety, as
shown in Scheme 2. The halophilic thiourea catalyst might
effectively induce ionization of allylic alcohol 1 in the pres-
ence of HBr to generate the allylic carbocation intermediates
3, in which the thiourea is associated with the bromide anion.
In conclusion, we have developed an efficient thiourea-
catalyzed intramolecular allylic amination reaction of N-
protected 2-aminophenyl-substituted allyl alcohol, which
proved to be a general approach for the synthesis of versatile
(tosylamino)phenyl)but-3-en-2-ol (1a) to optimize the reac-
tion conditions by varying the catalyst, additives, and solvent.
The results are summarized in Table 1.
Both palladium complex I and phosphoric acid II gave the
dihydroquinoline product in moderate yields (Figure 1). The
catalyst system comprising thiourea III with trimethylsilyl
chloride (TMSCl) as additive afforded the dihydroquinoline
2a with high yield (Table 1, entries 1–3). We then examined
Bull. Korean Chem. Soc. 2015, Vol. 36, 370–373
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a
a
Table 1. Optimization of the reaction conditions
Table 2. Thiourea-catalyzed intramolecular allylic amination
OH
OH
cat. (10 mol%)
HX (20 mol%)
cat. III (10 mol%)
HBr (20 mol%)
Ar
solvent, rt
NH
Ts
N
PhMe, rt
NH
Ts
N
Ar
Ts
Ts
1a
2a
1
2
Yield
(%)
Entry
Cat.
HX
Solvent
Time (h)
Yield (%)
Entry
1
Alcohol, 1
Product 2
1
2
3
4
5
6
7
8
9
I
II
—
—
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
CH Cl
1
2
0.5
1
1
1
1
0.5
1
0.5
1
1
61
57
70
10
43
50
51
73
89
35
40
57
45
70
35
trace
OH
N
III
III
III
III
III
III
III
III
III
III
III
III
—
III
Me SiCl
3
Ts
98
PhCO
TFA
TfOH
2
H
NH
Ts
2
b
1b
DNBS
HCl
HBr
HBr
HBr
HBr
HBr
HBr
HBr
—
OH
1
1
1
1
1
1
1
a
0
1
2
3
4
5
6
2
2
N
CHCl
3
2
3
Ts
96
94
NH
Ts
OMe
OMe
Et O
2
2c
MTBE
THF
PhMe
PhMe
1
0.5
1
1
c
5
OH
Reactions were carried out with 1a (0.3 mmol), catalyst (0.03 mmol),
N
and HX (0.06 mmol) in solvent (1.0 mL).
Ts
NH
Ts
Cl
Cl
2d
2
+
1d
O O
P
O
PPh2
Pd
OH2
-
2X
OH
NCMe
OH
PHPh2
N
4
Ts
85
65
X = OTf
NH
Ts
II
2e
I
1e
F3C
S
S
CF3
CF3
S
NH HN
OH
N
N
NH
HN
H
H
Ph
N
Ph
F3C
5
III
IV
Ts
NH
Ts
2f
Figure 1. Structure of the catalysts.
1f
1,2-dihydroquinolines 2. The desired 1,2-dihydroquinolines 2
were obtained in moderate to high yields (65–98%) in 1 h at
room temperature. Further details and application of this
a
Reactions were carried out with 1 (0.3 mmol), catalyst III (0.03 mmol),
and HBr (0.06 mmol) in toluene (1.0 mL) for 1 h.
asymmetricversion ofintramolecular S 1-typeaminationwill
N
be presented in due course.
(TLC) analyses were carried out on precoated silica gel plates
Experimental
with the F254 indicator. Visualization was accomplished by
UV light (254 nm), with I , p-anisaldehyde, ninhydrin, and
2
General. All reagents and solvents were commercial grade
and used without purification. Thin-layer chromatography
phosphomolybdic acid solution as indicators. Purification of
reaction products was carried out by flash chromatography
Bull. Korean Chem. Soc. 2015, Vol. 36, 370–373
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371

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OH
Hz, 1H), 6.27 (d, J = 9.6 Hz, 1H), 6.02 (d, J = 6.0 Hz, 1H),
13
5
.87 (dd, J = 9.6, 6.0 Hz, 1H), 2.34 (s, 3H); C NMR (100
Ph
cat. IV (20 mol%)
MHz, CDCl ) δ 143.4, 138.4, 136.1, 132.9, 129.1, 128.6,
3
TMSCl (40 mol%)
MTBE, 0°C, 24h
1
1
28.4, 128.2, 127.9, 127.6, 127.4, 127.2, 126.5, 126.3,
25.5, 57.0, 21.5.
NH
Ts
N
*
Ph
Ts
2
-(4-Methoxyphenyl)-1-tosyl-1,2-dihydroquinoline (2c).
1
a
2a*, 88%yield
0%ee
1
H NMR (400 MHz, CDCl ) δ 7.63 (d, J = 7.6 Hz, 1H),
7
3
3
4
.33 (d, J = 8.0 Hz, 2H), 7.23–7.18 (m, 3H), 7.14–7.08 (m,
H), 7.04 (d, J = 8.0 Hz, 2H), 6.95 (d, J = 7.6 Hz, 1H), 6.26
Scheme 1. Asymmetric version of thiourea-catalyzed intramolecular
allylic amination.
(d, J = 9.6 Hz, 1H), 5.98 (d, J = 6.0 Hz, 1H), 5.87 (dd, J =
13
9
.6, 6.0 Hz, 1H), 3.81 (s, 3H); 2.35(s, 3H); C NMR (100
MHz, CDCl ) δ 143.3, 137.7, 136.2, 135.3, 132.9, 129.2,
3
S
1
29.1, 128.7, 128.2, 127.7, 127.4, 127.3, 126.7, 126.4,
OH
N
H
N
H
126.2, 126.2, 125.4, 56.8, 21.6, 21.1.
2-(4-Chlorophenyl)-1-tosyl-1,2-dihydroquinoline (2d). H
1
cat. III
Ar
X
HX
NMR (400 MHz, CDCl ) δ 7.63 (d, J = 8.0 Hz, 1H), 7.32 (d, J
3
NH
Ts
N
Ar
=
8.0 Hz, 2H), 7.27 (d, J = 8.0 Hz, 2H), 7.24–7.10 (m, 6H),
Ar
Ts
6
.96 (d, J = 8.0 Hz, 1H), 6.28 (d, J = 9.6 Hz, 1H), 5.98 (d, J
1
2
NH
Ts
13
=
6.0, 1H), 5.85 (dd, J = 9.6, 6.0 Hz, 1H), 2.35 (s, 3H);
C
NMR (100 MHz, CDCl ) δ 143.6; 136.9, 136.0, 133.8,
3
3
1
1
1
32.7, 129.2, 128.9, 128.6, 128.5, 127.6, 127.2, 126.6,
26.4, 126.0, 125.9, 56.2, 21.6.
-(Naphthalen-1-yl)-1-tosyl-1,2-dihydroquinoline (2e). H
Scheme 2. Proposed reaction mechanism.
1
1
NMR (CDCl , 400 MHz) δ 7.76–7.58 (6H, m), 7.40–7.33
using Merck (Germany) silica gel 60 (230–400 mesh). H and
C NMR spectra were recorded on a Jeol ECS 400 (400 MHz
for H; 100 MHz for C) instrument (Tokyo, Japan). Chem-
ical shift values (δ) are reported in ppm relative to Me Si (0.0
ppm). The enantiomeric excesses were determined by HPLC,
which was performed on Younglin M930 and M9100 Series
instrument (Young Lin, Seoul, Korea), and measured at
3
1
3
(4H, m), 7.07–7.19 (4H, m), 6.96 (1H, d, J = 1.62, 7.33 Hz),
1
13
6
.33 (1H, d, J = 9.60 Hz), 6.16 (1H, d, J = 5.86 Hz), 5.93
13
(1H, dd, J = 5.88, 9.58 Hz), 2.34 (3H, s); C NMR (CDCl3,
4
1
1
1
00 MHz) δ 143.4, 136.1, 135.6, 133.0, 132.8, 128.7,
28.4, 128.3, 128.0, 127.7, 127.5, 126.5, 126.3, 126.1,
26.0, 125.9, 125.7, 57.0, 21.5.
1
2
54 nm using Chiralpak IC column (Daicel, Tokyo, Japan).
(E)-2-Styryl-1-tosyl-1,2-dihydroquinoline (2f ). H NMR
(
E)-4-Phenyl-2-(2-(tosylamino)phenyl)but-3-en-2-ol (1a)
(400 MHz, CDCl ) δ 7.77–7.71 (m, 1H), 7.35–7.31 (m,
3
and (E)-3-aryl-1-(2-(tosylamino)phenyl)prop-2-en-1-ol deri-
vatives 1b–1e were prepared in accordance with literature
methods.
2H), 7.28–7.26 (m, 1H), 7.26–7.10 (m, 6H), 7.09–7.06
(m, 2H), 6.98–6.93 (m, 1H), 6.55–6.50 (m, 1H), 6.19–6.15
(m, 1H), 6.05–6.03 (m, 1H), 5.75–5.69 (m, 1H), 5.59–5.56
12
13
(
m, 1H), 2.34 (s, 3H); C NMR (125 MHz, CDCl ) δ
3
General Procedure for the Thiourea-catalyzed Intramo-
lecular Allylic Amination. To a stirred solution of 2-amino-
phenyl-1-en-3-ols1(0.3 mmol)intoluene(0.8 mL)wasadded
the catalyst III (0.03 mmol) and hydrobromic acid (0.06
mmol) at room temperature. The reaction mixture was stirred
for 1 h at room temperature. After completion of the reaction,
the resultant solution was concentrated in-vacuo and the
obtained residue was purified by flash chromatography
1
1
5
43.5, 136.4, 136.0, 133.0, 132.1, 129.1, 128.4, 128.2,
27.8, 127.5, 127.2, 126.6, 126.5, 126.0, 125.4, 125.3,
6.2, 21.7.
Asymmetric Version for the Thiourea-catalyzed Intramo-
lecular Allylic Amination of 1a. To a stirred solution of (E)-
4
-phenyl-2-(2-(tosylamino)phenyl)but-3-en-2-ol (1a, 0.2
mmol) in MTBE (0.8 mL) was added catalyst IV (0.04 mmol)
ꢀ
and Me SiCl (0.08 mmol) at 0 C. The reaction mixture was
(
EtOAc/hexane, 1:5) to afford product 2.
-Methyl-2-phenyl-1-tosyl-1,2-dihydroquinoline (2a).
NMR (400 MHz, CDCl ) δ 7.63 (d, J = 7.8 Hz, 1H),
3
ꢀ
1
stirred for 1 day at 0 C. After completion of the reaction,
4
H
the resultant solution was concentrated in-vacuo and the
obtained residue was purified by flash chromatography
3
7
6
=
.41–7.32 (m, 4H), 7.24–7.18 (m, 4H), 7.14–7.08 (m, 3H),
(
EtOAc/hexane, 1:5) to afford product 2aÃ.
.97 (d, J = 7.8 Hz, 1H), 5.91 (d, J = 4.2 Hz, 1H), 5.63 (d, J
1
3
4-Methyl-2-phenyl-1-tosyl-1,2-dihydroquinoline (2aÃ).
4.2 Hz, 1H), 2.35 (s, 3H), 1.72 (s, 3H); C NMR (100
23
½
αꢁ = +27.9 (c = 1.00, CHCl ); HPLC (85:15, n-hexane:i-
MHz, CDCl ) δ 143.5, 138.5, 136.1, 132.9, 129.1, 128.6,
D
3
3
PrOH, 254 nm, 1.0 mL/min) Chiralpak IC column, t =
1
1
28.4, 128.2, 127.9, 127.6, 127.4, 127.2, 126.5, 126.3,
R
2
5.4 min (major), t = 30.2 min (minor), 40% ee.
R
25.5, 57.0, 21.7, 21.5.
1
2
-Phenyl-1-tosyl-1,2-dihydroquinoline (2b).
H NMR
(
4
400 MHz, CDCl ) δ 7.64 (d, J =7.9 Hz, 1H), 7.38–7.30 (m,
Acknowledgment. This research was supported by the Soon-
chunhyang University Research Fund.
3
H), 7.26–7.18 (m, 4H), 7.14–7.06 (m, 3H), 6.95 (d, J = 7.9
Bull. Korean Chem. Soc. 2015, Vol. 36, 370–373
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References
2356; l) S. J. Yoon, Y. K. Kang, D. Y. Kim, Synlett 2011, 22,
4
1
2
20; m) H. J. Lee, S. H. Kang, D. Y. Kim, Synlett 2011, 22,
559; n) H. J. Lee, S. M. Kim, D. Y. Kim, Tetrahedron Lett.
012, 53, 3437; o) H. J. Lee, S. B. Woo, D. Y. Kim, Tetrahedron
1
. a)R. D. Dillard, D. E. Pavey, D. N. Benslay, J. Med. Chem. 1973,
6, 251; b) J. V. Johnson, B. S. Rauckman, D. P. Baccanari,
B. Roth, J. Med. Chem. 1989, 32, 1942; c) A. Balayer, T. Seve-
net, H. Schaller, A. H. A. Hadi, A. Chiaroni, C. Riche, M. Païs,
Nat. Prod. Lett. 1993, 2, 61.
1
Lett. 2012, 53, 3374; p) H. J. Lee, D. Y. Kim, Synlett 2012,
2
5
3, 1629; q) H. W. Moon, D. Y. Kim, Tetrahedron Lett. 2012,
3, 6569; r) H. J. Lee, D. Y. Kim, Bull. Korean Chem.
Soc. 2012, 33, 3171; s) J. H. Lee, D. Y. Kim, Bull. Korean Chem.
Soc. 2013, 34, 1619; t) C. W. Suh, T. H. Han, D. Y. Kim,
Bull. Korean Chem. Soc. 2013, 34, 1623; u) C. W. Suh, C. W.
Chang, K. W. Choi, Y. J. Lim, D. Y. Kim, Tetrahedron Lett.
2
. a) F. Abe, T. Yamauchi, H. Shibuya, I. Kitagawa, M. Yamashita,
Chem. Pharm. Bull. 1998, 46, 1235; b) B. Pedram, A. van Oeve-
ren, D. E. Mais, K. B. Marschke, P. M. Verbost, M. B. Groen,
L. Zhi, J. Med. Chem. 2008, 51, 3696; c) J. Fotie, M. Kaiser,
D. A. Delfin, J. Manley, C. S. Reid, J.-M. Paris, T. Wenzler,
L. Maes, K. V. Mahasenan, C. Li, K. A. Werbovetz, J. Med.
Chem. 2010, 53, 966.
2
013, 54, 3651; v)Kang, Y. K.; Lee, H. J.; Moon, H. W.;
Kim, D. Y. RSC Adv. 2013, 3, 1332; w) D. Y. Kim, Bull.
Korean Chem. Soc. 2013, 34, 3463; x) M. H. Kim, D. Y. Kim,
Bull. Korean Chem. Soc. 2013, 34, 3891; y) Y. K. Kang, D.
Y. Kim, Adv. Synth. Catal. 2013, 355, 3131; z) Y. K. Kang,
D. Y. Kim, Chem. Commun. 2014, 50, 222; aa) C. W. Suh,
S. B. Woo, D. Y. Kim, Asian J. Org. Chem. 2014, 3, 399;
ab) C. W. Suh, D. Y. Kim, Bull. Korean Chem. Soc. 2014,
3
. G. Lu, J. L. Portscheller, H. C. Malinakova, Organometallics
2
005, 24, 945.
. C. S. Yi, S. Y. Yun, I. A. Guzei, J. Am. Chem. Soc. 2005,
27, 5782.
4
1
5
6
7
. C. S. Yi, S. Y. Yun, J. Am. Chem. Soc. 2005, 127, 17000.
. Y. Luo, Z. Li, C.-J. Li, Org. Lett. 2005, 7, 2675.
. X.-Y. Liu, P. Ding, J.-S. Huang, C.-M. Che, Org. Lett. 2007,
3
5, 98.
1
4. For selected work by us on synthetic methodology for the forma-
tion of carbon-heteroatom bonds, see: a) E. J. Park, H. R. Kim,
C. W. Joung, D. Y. Kim, Bull. Korean Chem. Soc. 2004, 25,
9
, 2645.
. M.-E. Theoclitou, L. A. Robinson, Tetrahedron Lett. 2002,
3, 3907.
. R. Kamakshi, B. S. R. Reddy, Catal. Commun. 2007, 8, 825.
8
1451; b) H. R. Kim, D. Y. Kim, Tetrahedron Lett. 2005, 46,
3115; c) S. M. Kim, H. R. Kim, D. Y. Kim, Org. Lett.
2005, 7, 2309; d) S. M. Kim, Y. K. Kang, K. Lee, J. Y. Mang,
4
9
1
1
1
0. A. Hegedus, Z. Hell, T. Vargadi, A. Potor, I. Gresits, Catal. Lett.
007, 117, 99.
1. S. H. Lee, Y. S. Park, M. H. Nam, C. M. Yoon, Org. Biomol.
Chem. 2004, 2, 2170.
D. Y. Kim, Bull. Korean Chem. Soc. 2006, 27, 423; e) S. M.
Kim, Y. K. Kang, M. J. Cho, D. Y. Kim, Bull. Korean Chem.
Soc. 2007, 28, 2435; f ) Y. K. Kang, M. J. Cho, S. M. Kim, D.
Y. Kim, Synlett 2007, 18, 1135; g) J. Y. Mang, D. Y. Kim, Bull.
Korean Chem. Soc. 2008, 29, 2091; h) J. Y. Mang, D. G. Kwon,
D. Y. Kim, Bull. KoreanChem. Soc. 2009, 30, 249;i) S. H. Kang,
Y. K. Kang, D. Y. Kim, Tetrahedron 2009, 65, 5676; j) N. R.
Lee, S. M. Kim, D. Y. Kim, Bull. Korean Chem. Soc.
2
2. a) P. Kothandaraman, S. J. Foo, P. W. H. Chan, J. Org. Chem.
2
009, 74, 5947; b) Z. Wang, S. Li, B. Yu, H. Wu, Y. Wang,
X. Sun, J. Org. Chem. 2012, 77, 8615.
1
3. For selected work by us on synthetic methodology for the forma-
tion of C-C bonds, see: a) Y. K. Kang, D. Y. Kim, J. Org. Chem.
2
2
2
009, 30, 829; k) Y.,. K. Kang, D. Y. Kim, Curr. Org. Chem.
010, 14, 917; l) S. H. Kang, D. Y. Kim, Adv. Synth. Catal.
010, 352, 2783; m) H. J. Lee, D. Y. Kim, Tetrahedron
2
3
009, 74, 5734; b) J. H. Lee, D. Y. Kim, Adv. Synth. Catal. 2009,
51, 1779; c) H. W. Moon, M. J. Cho, D. Y. Kim, Tetrahedron
Lett. 2009, 50, 4896; d) Y. Y. Oh, S. M. Kim, D. Y. Kim,
Tetrahedron Lett. 2009, 50, 4674; e) B. K. Kwon, S. M. Kim,
D. Y. Kim, J. Fluorine Chem. 2009, 130, 759; f ) J. H. Lee,
D. Y. Kim, Synthesis 2010, 42, 1860; g) Y. K. Kang, S. M.
Kim, D. Y. Kim, J. Am. Chem. Soc. 2010, 132, 11847; h) H.
W. Moon, D. Y. Kim, Tetrahedron Lett. 2010, 51, 2906; i) S.
H. Kang, B. K. Kwon, D. Y. Kim, Tetrahedron Lett. 2011, 52,
Lett. 2012, 53, 6984; n) Y. K. Kang, H. H. Kim, K. H. Koh,
D. Y. Kim, Tetrahedron Lett. 2012, 53, 3811; o) Y. J. Lim,
D. Y. Kim, Bull. Korean Chem. Soc. 2013, 34, 1955; p) S. B.
Woo, C. W. Suh, K. O. Koh, D. Y. Kim, Tetrahedron Lett.
2
013, 54, 3359.
5. H. J. Lee, S. H. Kang, D. Y. Kim, Bull. Korean Chem. Soc. 2011,
2, 1125.
6. A. Baeza, C. Najera, Synthesis 2014, 46, 25.
1
1
3
3
1
247; j) Y. K. Kang, K. H. Suh, D. Y. Kim, Synlett 2011, 22,
125; k) Y. K. Kang, D. Y. Kim, Tetrahedron Lett. 2011, 52,
Bull. Korean Chem. Soc. 2015, Vol. 36, 370–373
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
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