Development of madelung-type indole synthesis using copper-catalyzed amidation/condensation strategy

Article abstract of DOI:10.3987/COM-16-13440

A new method for Madelung-type indole synthesis was investigated, and it was found that the amidation of 2-iodophenylacetonitrile with various alkanamides proceeds smoothly in the presence of CuI and a diamine ligand. The subsequent cyclization of the C-N

Full text of DOI:10.3987/COM-16-13440

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HETEROCYCLES, Vol. 92, No. 5, 2016
HETEROCYCLES, Vol. 92, No. 5, 2016, pp. 900 - 909. © 2016 The Japan Institute of Heterocyclic Chemistry
Received, 16th February, 2016, Accepted, 4th March, 2016, Published online, 10th March, 2016
DOI: 10.3987/COM-16-13440
DEVELOPMENT OF MADELUNG-TYPE INDOLE SYNTHESIS USING
COPPER-CATALYZED AMIDATION/CONDENSATION STRATEGY
Masahiro Abe, Charline Denneval, Kanako Nozawa-Kumada, and Yoshinori
Kondo*
Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki
Aza Aoba, Aobaku, Sendai 980-8578, Japan; E-mail:ykondo@m.tohoku.ac.jp
Abstract – A new method for Madelung-type indole synthesis was investigated,
and it was found that the amidation of 2-iodophenylacetonitrile with various
alkanamides proceeds smoothly in the presence of CuI and a diamine ligand. The
subsequent cyclization of the C-N coupling products takes place under the
coupling reaction conditions.
INTRODUCTION
Indoles are one of the most ubiquitous heterocycles in biologically active natural products, and the indole
moiety appears as a substructure of numerous pharmaceuticals, agrochemicals and functional materials.1
The substituted indoles have been referred to as privileged structures for drug discovery2 and the study of
indole syntheses has been an important research area for synthetic chemists.3 The Madelung indole
synthesis is one of the most versatile methods for the synthesis of 2,3-substituted indoles, which involves
intramolecular cyclization of an N-(2-alkylphenyl)alkanamide with a strong base at elevated
temperatures.4 The most common conditions employed include potassium alkoxide at temperatures of
o
200-300 C and also use reactive bases like LDA or n-BuLi. Relevant intramolecular condensation
reactions have been investigated for indole ring construction that provide various 2,3-substituted indole
derivatives.5 A modified Madelung-type cyclization for the preparation of indole-3-carboxylate
derivatives has also been investigated using the phenylalkanamide substrates with a cyanomethyl or an
alkoxylcarbonylmethyl group.6 Although this cyclization method is considered to be useful, the drawback
lies on the limited construction of the anilide substrate for the cyclization. On the other hand,
transition-metal-catalyzed amidation of aryl halides has been widely investigated and the Cu-catalyzed
Goldberg amidation reaction has also been well employed with the important finding of considerable
acceleration by organic ligands.7 In order to develop a new Madelung-type indole synthesis, we have
designed
a
new
tandem
one-pot
Cu-catalyzed amidation/cyclization process
from

HETEROCYCLES, Vol. 92, No. 5, 2016
901
2-halophenylacetonitrile or 2-halophenylacetates for 3-substituted indoles as shown in Scheme 1.
Recently, ortho-selective iodination of phenylacetic acid derivatives in the presence of palladium catalyst
was reported by Yu et al.8 and the methodology is considered to be advantageous for the access to the
substrates for this Cu-catalyzed amidation/intramolecular condensation strategy. The strong bases have
been employed for the Madelung cyclization, but we anticipated that the one–pot amidation/condensation
procedure would be able to be achieved by an appropriate choice of substrates and reaction conditions.
EWG
EWG
O
EWG
R3
N
R2
intramolecular
condensation
O
Cu-amidation
R1
R1
R1
HN
R2
R3
N
R2
R3
X
X = I, Br
Scheme 1. Synthetic strategy of sequential amidation/condensation
RESULTS AND DISCUSSION
We started with the reaction of 2-iodophenylacetonitrile and 2-pyrrolidone. The reaction was carried out
o
in the presence of CuI, ligand A, K3PO4 in toluene 110 C for 24 h and the amidated product 4aa was
obtained with the cyclized cyanoindole 3aa. In order to convert amidated product 4aa to cyclized
cyanoindole 3aa, we initially focused our study on the solvent effect of this reaction. We anticipated that
intramolecular cyclization reaction would proceed smoothly in more soluble solvents for K3PO4. Dioxane
gave a lower yield (29%) while DMF gave a good yield (75%) and no amidated product 4aa was detected
(Table 1, entries 2, 3).
Table 1. Optimization of conditions for amidation/condensation
O
CN
I
CN
x eq.
HN
CN
2a
O
H2N
NH2
CuI (5 mol%)
ligand (20 mol%)
K3PO4 (2 eq.)
N
N
ligand A
1a
3aa
4aa
solvent, 110 °C, 24 h
solvent
toluene
dioxane
DMF
toluene
toluene
toluene
toluene
ligand
entry
1a
2a
3a
4
5
6
7
x
4aa (%)
3aa (%)
45
29b
75b
78
91
29b
28b
1.2
1.2
1.2
2.0
3.0
3.0
3.0
A
A
A
A
A
B
C
46
55b
ndb,c
7b
0
0
MeHN
NHMe
ligand B
MeHN
NHMe
0
ligand C
isolated yield. a with 10 mol% ligand. b NMR yield. c not detected.

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HETEROCYCLES, Vol. 92, No. 5, 2016
By increasing an amount of 2-pyrrolidone in toluene, amidated product 4aa was successfully altered in
the cyclized cyanoindole 3aa (entries 4, 5). We observed that with 3 equiv of 2-pyrrolidone in toluene,
this reaction afforded only the desired product 3aa in the highest yield (entry 5).
The role of the excess amide in the cyclization is not clear, but one plausible explanation is that the amide
proton works to activate carbonyl of the amidated product to render it more electrophilic or to activate the
nitrile to make the methylene proton more acidic. Among the ligands which were reported to be effective
for the amidation by Buchwald’s group, ligand B and ligand C were ineffective for this reaction (entries 6,
7). With these optimized conditions in hand, the substrate scope of this method was explored (Scheme 2).
At first, the scope was investigated by coupling a range of alkanamides to 2-iodophenylacetonitrile. It was
found that the reactions including 6 and 7 member ring amides proceed with lower yields when the more
hindered cyclic amides were used (3ab, 3ac). This method was also effective for formamide (3ad). Other
aryl iodide substrates with EWG (electron-withdrawing group) functionalized methylene were examined
for the amidation/condensation. For instance, tert-butoxycarbonyl (3ba, 3bd), ethoxycarbonyl (3cd), and
phenylsulfonyl (3dd) were suitable as EWGs. In case of 3ba, higher temperature was needed to complete
the cyclization reaction. As expected, the halogen group on the aromatic ring can be selectively amidated
with a preference for the iodo substituted position (3ed).
O
EWG
EWG
R2
N
R1
R1
(3.0 eq.)
N
R2
H
CuI (5 mol%), ligand (20 mol%)
I
K3PO4 (2 eq.), toluene, 110 °C, 24 h
t
t
CO2 Bu
CN
CN
CN
CN
CO2 Bu
H
H
N
N
N
N
N
N
Me
3bd
71%
Me
3ad
52%
3ba
40%a
3aa
91%
3ab
61%
3ac
39%
Cl
t
t
CO2Et
H
SO2Ph
H
CO2 Bu
CO2 Bu
MeO
MeO
H
H
N
N
N
N
Me
3cd
51%
Me
3dd
59%
Me
Me
3ed
61%
3fd
66%
isolated yield. a at 150 °C
Scheme 2. Synthesis of diversely functionalized indole derivatives

HETEROCYCLES, Vol. 92, No. 5, 2016
903
The substrate bearing two electron-donating groups on the aromatic ring whose electronic effects are
considered to be unfavorable for both Cu-catalyzed amidation and subsequent condensation, was tolerated
for this reaction (3fd). When N-methylacetamide was used for the reaction with 1a, the amidation did not
proceed and the dehalogenation of the substrate was observed.
The plausible reaction pathway for this indole formation via amidation/condensation is described in
Scheme 3. The amides are also considered to play an important role for enhancing cyclization other than
acting as a nucleophile as suggested in Table 1, entries 1, 4, 5.
O
O
base
-
N
R1
R2
HN
R1
R2
Ligand exchange
CuI
N
N
N
N
Cu
N
-
+
I
Cu
O
R1
N
N
I
R2
ligand
EWG
EWG
O
Cyclization
EWG
R2
N
R1
Amidation
base
N
R1
R2
I
H2O
Scheme 3. Plausible mechanism for indole formation
Our next interest was to focus on the synthesis of azaindole using the methodology. Azaindoles have
attracted much attention due to their physicochemical and pharmacological properties, and can be
considered as a bioisostere of an indole or purine moiety.9 We investigated the 7-azaindole synthesis
using 2-(2-bromopyridin-3-yl)acetonitrile as a substrate in the presence of 5 mol% CuI, 20 mol% ligand
A, 3 equiv. 2-pyrrolidone and the reaction mixture was heated in toluene at 110 °C for 24 h. The reaction
gave the desired 7-azaindole derivative 3ha in 29% yield. By using ligand B in place of ligand A, the
coupling reaction proceeded smoothly in higher yield and the product was obtained in 64% (Scheme 4).
O
CN
HN
2a
CN
(3.0 eq.)
CuI (5 mol%), ligand B (20 mol%)
N
N
Br
N
K3PO4 (2 eq.), toluene, 110 °C, 24 h
1h
3ha
64%
Scheme 4. Synthesis of azaindolecarbonitrile

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HETEROCYCLES, Vol. 92, No. 5, 2016
CONCLUSION
It was found that the amidation of 2-iodophenylacetonitrile with various alkanamides proceeds smoothly
in the presence of CuI and a diamine ligand. The subsequent cyclization of the C-N coupling products
takes place under the coupling reaction conditions. The use of copper catalyzed process is considered to
be attractive from the viewpoint of potential economic advantages.10 A new Cu-catalyzed straightforward
synthesis of 3-functionalized indoles is demonstrated.11 Further studies on the scope of the substrate and
the application of the methodology are underway.
EXPERIMENTAL
General: Unless otherwise noted, reactions were carried out under an argon atmosphere using dry
solvents. Melting points (mp) were determined with a Yazawa micro melting point apparatus and
uncorrected. Infrared (IR) data were recorded on Shimadzu software. The spectra were acquired in 32
scans per spectrum at a resolution of four, and absorbance frequencies are reported in reciprocal
centimeters (cm-1). NMR data were recorded on either a JEOL AL400 spectrometer (395.75 MHz for 1H,
1
99.50 MHz for 13C) or a JEOL ECA600 spectrometer (600.172 MHz for H, 150.907 MHz for 13C).
Chemical shifts are expressed in G (parts per million, ppm) values, and coupling constants (J) are
1
expressed in hertz (Hz). H NMR spectra were referenced to a tetramethylsilane (TMS) as an internal
13
standard or to a solvent signal (CDCl3: 7.26 ppm). C NMR spectra were referenced to a solvent signal
(CDCl3: 77.16 ppm). The following abbreviations are used: s = singlet, d = doublet, t = triplet, q = quartet,
quint = quintet, dd = double doublet, m = multiplet, br.s = broad singlet. Low and high resolution mass
spectra (LRMS and HRMS) were obtained from Mass Spectrometry Resource, Graduate School of
Pharmaceutical Sciences, Tohoku University, on a JEOL JMS-DX303 and JMS-700 spectrometer
respectively.
General procedure for indole synthesis by Cu-catalyzed amidation reaction. A dried re-sealable vial
with a Teflon stir bar was charged with amide (3.0 equiv, 1.5 mmol), CuI (5 mol%, 0.025 mmol), K3PO4
(2.0 equiv, 1.0 mmol). The vial was sealed with a rubber septum and evacuated and refilled with argon
three times through
a
syringe needle. Under an argon atmosphere, toluene (0.5 mL),
trans-1,2-diaminocyclohexane (20 mol%, 0.1 mmol) and aryl halide (0.50 mmol) were each added via
syringe. The rubber septum was then removed and quickly replaced with a Teflon screw cap and the
reaction mixture was stirred at 110 °C for 24 h. The resulting suspension was allowed to reach room
temperature and filtered through a pad of silica gel eluting with AcOEt (10 mL). The filtrate was
concentrated and the residue was purified by flash chromatography to afford a pure product.
2,3-Dihydro-1H-pyrrolo[1,2-a]indole-9-carbonitrile (3aa). Obtained as colorless prisms (83 mg, 91%)
1
(Recrystallized from AcOEt/hexane, mp 128–130 °C). H NMR (400 MHz, CDCl3/TMS) G (ppm): 2.70

HETEROCYCLES, Vol. 92, No. 5, 2016
905
(quintet, J = 7.3 Hz, 2H), 3.18 (t, 2H, J = 7.3 Hz), 4.14 (t, J = 7.3 Hz, 2H), 7.22–7.28 (m, 3H), 7.65–7.67
13
(m, 1H). C{1H} NMR (100 MHz, CDCl3) G (ppm): 24.7, 26.8, 44.9, 77.7, 110.6, 116.5, 119.4, 121.8,
122.7, 132.0, 132.2, 152.9. LRMS (EI) m/z: 182 (M+). HRMS: Calcd. for C12H10N2: 182.0844. Found:
182.0828. IR (neat, cm-1): 2924, 2852, 2211, 1544, 1452, 1423, 1302, 1242, 1119, 1026, 1011 cm-1.
6,7,8,9-Tetrahydropyrido[1,2-a]indole-10-carbonitrile (3ab). Obtained as yellow prisms (60 mg, 61%)
(Recrystallized from AcOEt/hexane, mp 104–105 °C). 1H NMR (400 MHz, CDCl3/TMS) G (ppm): 1.92–
1.98 (m, 2H), 2.08–2.14 (m, 2H), 3.08 (t, J = 6.8 Hz, 2H), 4.04 (t, J = 6.3 Hz, 2H), 7.22–7.31 (m, 3H),
7.62–7.66 (m, 1H). 13C{1H} NMR (100 MHz, CDCl3) G (ppm): 19.8, 22.6, 23.3, 42.6, 109.7, 116.5, 118.9,
122.3, 122.7, 127.4, 135.5, 146.3. LRMS (EI) m/z: 196 (M+), 168 (M+–28). HRMS: Calcd. for C13H12N2:
196.1000. Found: 196.0977. IR (neat, cm-1): 2956, 2936, 2925, 2854, 2202, 1532, 1490, 1477, 1456, 1445,
1422, 1361, 1351, 1318, 1270, 1258, 1246, 1195, 1163, 1093, 1046, 1016, 934, 902, 824, 757, 748 cm-1.
7,8,9,10-Tetrahydro-6H-azepino[1,2-a]indole-11-carbonitrile (3ac). Obtained as yellow prisms (41 mg,
39%) (Recrystallized from AcOEt/hexane, mp 133–134 °C). 1H NMR (400 MHz, CDCl3/TMS) G (ppm):
1.76–1.83 (m, 4H), 1.89–1.95 (m, 2H), 3.08 (t, J = 5.8 Hz, 2H), 4.20 (t, J = 4.9 Hz, 2H), 7.20–7.33 (m,
3H), 7.6 (d, J = 7.3 Hz, 1H). 13C{1H} NMR (100 MHz, CDCl3) G (ppm): 26.8, 27.5, 28.6, 30.8, 45.5, 84.3,
109.7, 116.8, 119.4, 121.8, 123.0, 127.2, 136.1, 151.7. LRMS (EI) m/z: 210 (M+). HRMS: Calcd. for
C14H14N2: 210.1157. Found: 210.1146. IR (neat, cm-1): cm-1.2928., 2854, 2207, 1529, 1475, 1462, 1427,
1359, 1331, 1249, 1206, 1184, 1086, 985, 747, 739 cm-1.
1-Methyl-indole-3-carbonitrile (3ad). Obtained as colorless prisms (41 mg, 52%) (Recrystallized from
1
AcOEt/hexane, mp 61–63 °C). H NMR (400 MHz, CDCl3/TMS) G (ppm): 3.84 (s, 3H), 7.25–7.40 (m,
3H), 7.54 (s, 1H), 7.75 (d, J = 8.3 Hz, 1H). 13C{1H} NMR (100 MHz, CDCl3) G (ppm): 33.7, 85.6, 110.4,
116.0, 119.9, 122.2, 124.0, 127.9, 135.6, 136.1. LRMS (EI) m/z: 358 (M+), 91 (M+–267). HRMS: Calcd.
for C10H8N2: 357.9967. Found: 357.9950. IR (neat, cm-1): 3113, 3057, 3041, 2211, 1530, 1458, 1420,
1378, 1358, 1334, 1250, 1204, 1158, 1126, 1066, 1009, 936, 848, 767, 750 cm-1.
tert-Butyl 2,3-dihydro-1H-pyrrolo[1,2-a]indole-9-carboxylate (3ba). Obtained as colorless prisms (51
1
mg, 40%) (Recrystallized from AcOEt/hexane, mp 161–162 °C). H NMR (400 MHz, CDCl3/TMS) G
(ppm): 1.63 (s, 9H), 2.59 (quintet, J = 7.3 Hz, 2H), 3.23 (t, J = 7.3 Hz, 2H), 4.03 (t, J = 7.3 Hz, 2H),
7.14–7.22 (m, 3H), 8.07–8.09 (m, 1H). 13C{1H} NMR (100 MHz, CDCl3) G (ppm): 21.8, 22.3, 24.4, 40.0,
75.0, 96.4, 105.4, 117.1, 117.2, 126.6, 128.3, 148.2, 160.8. LRMS (EI) m/z: 257 (M+), -201 (M+–56), 156
(M+–101). HRMS: Calcd. for C16H19NO2 257.1416. Found: 257.1404. IR (neat, cm-1): 2978, 2932, 2891,
2681, 1673, 1540, 1507, 1473, 1452, 1424, 1391, 1368, 1335, 1301, 1288, 1247, 1206, 1165, 1154, 1126,
1110, 1018, 1008, 935, 885, 784,750 cm-1.
1
tert-Butyl 1-methyl-1H-indole-3-carboxylate (3bd). Obtained as yellow oil. (82 mg, 71%) H NMR

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HETEROCYCLES, Vol. 92, No. 5, 2016
(400 MHz, CDCl3/TMS) G (ppm): 1.63 (s, 9H), 3.73 (s, 3H), 7.26 (br.s, 3H), 7.67 (s, 1H), 8.14 (br.s, 1H).
13C{1H} NMR (100 MHz, CDCl3) G (ppm): 28.7, 33.3, 79.8, 108.8, 109.7, 121.66, 121.69, 122.6, 126.7,
135.1, 137.3, 164.7. LRMS (EI) m/z: 231 (M+), 175 (M+–56), 158 (M+–73). HRMS: Calcd. for
C14H17NO2 231.12593. Found: 231.12502. IR (neat, cm-1): 3112, 3053, 3004, 2975, 2931, 2881, 1685,
1616, 1533, 1466, 1424, 1390, 1379, 1366, 1337, 1277, 1266, 1231, 1167, 1149, 1099, 1059, 1004, 933,
855, 831, 774, 747, 714 cm-1.
Ethyl 1-methyl-1H-indole-3-carboxylate (3cd). Obtained as colorless prisms (52 mg, 51%)
(Recrystallized from hexane, mp 73–74 °C). 1H NMR (400 MHz, CDCl3/TMS) G (ppm): 1.39-1.42 (t, J =
7.3 Hz, 3H), 3.76 (s, 1H), 4.34-4.40 (q, J = 7.3 Hz, 2H), 7.23-7.32 (m, 3H), 7.73 (s, 1H), 8.15–8.20 (m,
1H). 13C{1H} NMR (100 MHz, CDCl3) G (ppm): 14.7, 33.4, 59.7, 107.3, 109.8, 121.7, 121.9, 122.8,
126.7, 135.2, 137.3, 165.2. LRMS (EI) m/z: 203 (M+), 158 (M+-56). HRMS: Calcd. for C12H13NO2
203.0946. Found: 203.0934. IR (neat, cm-1): 3117, 3053, 2991, 2938, 2901, 1679, 1533, 1521, 1479, 1429,
1390, 1371, 1336, 1272, 1233, 1163, 1153, 1128, 1104, 1032, 1014, 929, 879, 851, 829, 777, 771, 751,
739 cm-1.
1-Methyl-3-(phenylsulfonyl)-1H-indole (3dd). Obtained as colorless needless (80 mg, 59%)
(Recrystallized from AcOEt/hexane, mp 167–168 °C). 1H NMR (400 MHz, CDCl3/TMS) G (ppm): 3.76 (s,
1H), 7.23–7.30 (m, 3H), 7.39–7.45 (m, 3H), 7.74 (s, 1H), 7.91–7.94 (m, 1H), 7.99–8.02 (m, 2H). 13C{1H}
NMR (100 MHz, CDCl3) G (ppm): 33.7, 110.5, 115.0, 119.8, 122.5, 123.7, 124.3, 126.7, 129.1, 132.5,
133.8, 137.4, 143.6. LRMS (EI) m/z: 271 (M+). HRMS: Calcd. for C15H13NO2S 271.06670. Found:
271.06591. IR (neat, cm-1): 3116, 1515, 1457, 1443, 1382, 1329, 1299, 1289, 1250, 1173, 1143, 1129,
1118, 1080, 1025, 1015, 999, 982, 847, 756, 745, 719 cm-1.
tert-Butyl 4-chloro-1-methyl-1H-indole-3-carboxylate (3ed). Obtained as colorless prisms (81 mg,
61%) (Recrystallized from hexane, mp 120 °C). 1H NMR (400 MHz, CDCl3/TMS) G (ppm): 1.61 (s, 9H),
3.78 (s, 3H), 7.16–7.23 (m, 3H), 7.69 (s, 1H). 13C{1H} NMR (100 MHz, CDCl3) G (ppm): 28.6, 33.6, 80.5,
108.5, 109.8, 123.2, 123.5, 123.7, 127.1, 136.5, 139.0, 163.5. LRMS (EI) m/z: 265 (M+), 209 (M+–56),
192 (M+–73). HRMS: Calcd. for C14H16ClNO2 265.08696. Found: 265.08587. IR (neat, cm-1): 3117, 2977,
2932, 2918, 1708, 1559, 1527, 1472, 1448, 1421, 1389, 1363, 1335, 1231, 1200, 1181, 1160, 1147, 1113,
1065, 1041, 1005, 948, 874, 858, 848, 829, 781, 767, 743, 725 cm-1.
tert-Butyl 5,6-dimethoxy-1-methyl-1H-indole-3-carboxylate (3fd). Obtained as colorless prisms (96
1
mg, 66%) (Recrystallized from AcOEt/hexane, mp 187–189 °C). H NMR (400 MHz, CDCl3/TMS) G
(ppm): 1.63 (s, 9H), 3.73 (s, 3H), 3.93 (s, 3H), 3.96 (s, 3H), 6.74 (s, 1H), 7.54 (s, 1H), 7.64 (s, 1H).
13C{1H} NMR (100 MHz, CDCl3) G (ppm): 28.6, 33.5, 56.1, 56.3, 79.57, 93.0, 103.0, 108.3, 119.8, 131.4,
133.0, 146.5, 147.3, 164.8. LRMS (EI) m/z: 291 (M+), 235 (M+–56). HRMS: Calcd. for C16H21NO4

HETEROCYCLES, Vol. 92, No. 5, 2016
907
291.14706. Found: 291.14675. IR (neat, cm-1): 3007, 2968, 2940, 2908, 2833, 1686, 1533, 1506, 1486,
1456, 1448, 1368, 1359, 1311, 1272, 1261, 1240, 1210, 1171, 1139, 1095, 1058, 1037, 1025, 941, 864,
851, 831, 804, 771 cm-1.
7,8-Dihydro-6H-pyrido[3,2-b]pyrrolizine-5-carbonitrile (3ha). Obtained as colorless prisms (59 mg,
64%) (Recrystallized from AcOEt/hexane, mp 167–169 °C). 1H NMR (400 MHz, CDCl3/TMS) G (ppm):
3.74 (quint, J = 4.9 Hz, 2H), 3.25 (t, J = 4.9 Hz, 2H), 4.31 (t, J = 4.9 Hz, 2H), 7.19 (dd, J = 5.5 Hz, J =
13
3.0 Hz, 1H), 7.94–7.96 (m, 1H), 8.33 (d, J = 2.4 Hz, 1H). C{1H} NMR (100 MHz, CDCl3) G (ppm):
25.2, 26.9, 44.5, 76.89, 115.5, 117.9, 125.0, 127.9, 143.9, 144.0, 153.8. LRMS (EI) m/z: 183 (M+), 156
(M+–27). HRMS: Calcd. for C11H9N3 183.0796. Found: 183.0790. IR (neat, cm-1): 3051, 2966, 2938,
2906, 2217, 1595, 1566, 1540, 1482, 1448, 1426, 1416, 1381, 1372, 1347, 1317, 1297, 1282, 1230, 1211,
1163, 1128, 1033, 982, 938, 861, 802, 797, 774 cm-1.
ACKNOWLEDGEMENT
This work was partly supported by a Grant-in-Aid for Scientific Research (B) (No. 23390002), a
Grant-in-Aid for Challenging Exploratory Research (No. 25670002) from Japan Society for the
promotion of Science, a Grant-in-Aid for Scientific Research on Innovative Areas “Advanced Molecular
Transformations by Organocatalysis” (No. 23105009) and the project “Platform for Drug Discovery,
Informatics, and Structural Life Science” from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
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