Cu-Catalyzed Cyanation of Indoles with Acetonitrile as a Cyano Source

Article abstract of DOI:10.1021/acs.joc.5b01419

Cu-catalyzed cyanation of indoles with acetonitrile for the synthesis of 3-cyanoindoles has been developed. The Cu/TEMPO/(Me₃Si)₂ system has been identified to promote highly efficient and selective C-H cyanation of indoles by use of unactivated acetonitrile as a cyano source via a sequential iodination/cyanation process in one pot. This reaction furnishes 3-cyanoindoles in moderate to good yields and tolerates a series of functional groups. Moreover, low-cost copper catalysts and hazardless acetonitrile as a cyano source feature the practicability of this reaction.

Full text of DOI:10.1021/acs.joc.5b01419

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Note
Cu-catalyzed Cyanation of Indoles with Acetonitrile as A Cyano Source
Mengdi Zhao, Wei Zhang, and Zengming Shen
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b01419 • Publication Date (Web): 14 Aug 2015
Downloaded from http://pubs.acs.org on August 15, 2015
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Cuꢀcatalyzed Cyanation of Indoles with Acetonitrile as A Cyano
Source
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Mengdi Zhao, Wei Zhang and Zengming Shen*
School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800
Dongchuan Road, Shanghai, 200240, China
Eꢀmail: shenzengming@sjtu.edu.cn
Abstract
Cuꢀcatalyzed cyanation of indoles with acetonitrile for the synthesis of 3ꢀcyanaindoles
has been developed. Cu/TEMPO/(Me Si) system has been identified to promote
3
2
highly efficient and selective C-H cyanation of indoles by use of unactivated
acetonitrile as a cyano source via sequential iodination/cyanation process in one pot.
This reaction furnishes 3ꢀcyanaindoles in moderate to good yields and tolerates a
series of functional groups. Moreover, lowꢀcost copper catalyst and hazardless
acetonitrile as a cyano source feature the practicability of this reaction.
Indole nitriles display widely biological activities and exist in many dyes,
herbicides, agrochemicals, pharmaceuticals and natural products as a backbone of
1
their structural frameworks. Notably, 3ꢀcyanoindole is a key building block in
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pharmaceutical syntheses, material science and fine chemistry. Beyond these
functions, the versatile cyano group can be easily transferred into a broad range of
functional groups, for example, aldehydes, amines, amidines, tetrazoles, amides and
3
their carboxyl derivatives.
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The significant progresses have been made in the development of the synthesis of
4
3
ꢀcyanoindoles. The classical methods include: 1) Sandmeyer and Rosenmundꢀvon
5
ꢀ6
Braun reactions, in which stoichiometric and toxic CuCN is used as a cyanating
7
reagent, 2) transition metalꢀcatalyzed cyanation of aryl (pseudo)halides and 3)
8
multiꢀstep organic transformation. Despite these advances, the simple and
straightforward access to 3ꢀcyanoindoles remains desirable.
Scheme 1. The synthesis of 3ꢀcyanoindoles via C-H cyanation
Due to the attraction of direct C−H functionalization protocol avoiding the need of
prefunctionalization of substrates, the development of transition metalꢀcatalyzed C−H
9
activation has witnessed stupendous growing in the past decades. Indole C−H
1
0
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cyanation is a direct pathway to form 3ꢀcyanoindole promoted by Cu, Pd and other
1
2
Lewis acids (Scheme 1). In these procedures, the employment of cyano sources can
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be classified as metal cyanides (NaCN, CuCN, TMSCN, K [Fe(CN) ]), BnCN,
+
tꢀBuNC, electrophilic CN reagents (NCTs, BrCN), and the combined cyano sources
(
NH
4
I/DMF, DMF, NH
4
HCO
3
/DMSO, TMEDA/(NH
4
)
2
CO
3
)
(Scheme 1).
Nevertheless, almost all of these methods suffer from limitations. Metal cyanides are
frequently used as cyanide sources. A significant problem is the high affinity of the
cyanide ion for the transition metal, which often results in rapid deactivation of
catalyst. Moreover, most of the cyano sources, in particular KCN, CuCN, and
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TMSCN, have notorious toxicity. Although K [Fe(CN) ] is exceptionally nontoxic, its
slow solubility in organic solvent limited its applicability. Recently, the investigation
of combined cyano sources as an alternative strategy has attracted considerable
10aꢀc,11a,13
attention and a significant progress has been made in this field.
cat. Cu/Si
R1
CN
(1)
(2)
N
H
2
R = directing group
R2
our group previous work15a
R1
H
+
CH3
CN
N
R2
CN
NIS, base
R1
cat. Cu/Si/TEMPO
N
2
R2
R = Me
This work
Scheme 2. The cyanation of indoles with acetonitrile.
Acetonitrile is a common solvent which features readily available, inexpensive,
1
4
abundant and hazardless properties. In connection with our ongoing project on the
cleavage of acetonitrile, we have recently developed that unactivated acetonitrile
could serve as an attractive cyano source via copperꢀcatalyzed C-CN bond cleavage
15
under Cu/Si or Cu/Si/TEMPO system. Li and Zhu groups discovered that Cu/Ag
16
system is also suitable for acetonitrile C-CN bond cleavage. Notably, we found that
Cu/Si system for the C-H cyanation of indoles was exclusively occurred at 2ꢀposition
of indoles with acetonitrile to yield the corresponding 2ꢀcyanoindoles, in which the
directing group such as pyridine or pyrimidine on the nitrogen atom of indole controls
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15a
regioselectivity (Scheme 2, eq 1). We sought to develop a complementary method
for the preparation of 3ꢀcyanoindoles with common solvent, acetonitrile, as the cyano
source. Herein, we report catalytic tandem cyanation of indoles with acetonitrile as a
cyano source under Cu/Si/TEMPO system via an iodination process to exclusively
furnish 3ꢀcyanoindoles (Scheme 2, eq 2).
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Initially, we chose Nꢀmethylindole 1a as a model substrate. The direct cyanation
of indole with CH
3 2
CN was first studied in the presence of Cu(OAc) /1,10ꢀphen,
(
Me Si) and TEMPO. However, no reaction was observed under this system (Table 1,
3
2
entry 1). We reasoned that electronꢀrich indoles facilitate electrophilic substitution
reactions. On the contrary, Cuꢀcatalyzed acetonitrile C-CN cleavage gives out the
ꢀ
+
15
CN anion not CN cation.
Therefore, we envisioned the sequential
iodination/cyanation process for the cyanation of indoles. A series of parameters such
as ligand, base, additive, and temperature were screened. To our delight, the
iodination of Nꢀmethylindole 1a was smoothly performed in the presence of NIS and
KOH at room temperature for 2 hours; the generated indole iodide is able to undergo
2
the catalytic cyanation with acetonitrile promoted by Cu(OAc) /1,10ꢀphen (20 mol%)
o
at 150 C in one pot, giving the desired 3ꢀcyanoindoles 2a in 48% yield (Table 1,
entry 2). In order to increase the solubility of KOH in acetonitrile, a trace amount of
water (2.5 v%) was added into the reaction (entries 3ꢀ13). Under these conditions,
various ligands were screened for the cyanation of indoles. It is found that these
ligands L1ꢀL3 and L5 have the similar effect on the transformation of indoles to
provide 2a in moderate yields (entries 2ꢀ4 and 6). With L1 as a promising ligand in
hand, a series of bases were next examined (entries 7ꢀ13). The observation revealed
that tꢀBuOLi is slightly better than KOH, other bases such as t-BuONa, tꢀBuOK,
KOAc, K CO , Na CO , and Cs CO are inferior to KOH. Pleasingly, when all of the
2
3
2
3
2
3
o
reagents were added in one time and then directly heated upon to 150 C, the
achievement of the oneꢀpot tandem iodination/cyanation was observed, smoothly
providing 3ꢀcyanoindole in 81% yield (entry 13).
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a
Table 1．Optimization for the synthesis of 3ꢀcyanoindoles with acetonitrile
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a
2
Conditions: 1a (0.2 mmol), NIS (1.05 equiv), base (1.1 equiv), Cu(OAc) (20 mol%), ligand (20
o
mol%), (Me
3
Si)
2
(1 equiv), TEMPO (2 equiv), CH
3
CN (1.2 mL), O
2
, 150 C, 2 days. Reaction was
o
b
c
2
run at room temperature for 2 hours, and then it was heated at 150 C. Isolated yield. H O (2.5
d
o
v%, 30 uL). Reaction was directly heated upon to 150 C without adding water.
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a,b
Table 2. Cuꢀcatalyzed cyanation of indoles with acetonitrile
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a
Conditions: 1 (0.3 mmol), NIS (1.1 equiv), KOH (1.05 equiv), Cu(OAc)2 (20 mol%),
1
,10ꢀphenanthroline (L1, 20 mol%), (Me
3
Si)
2 3
(1 equiv), TEMPO (2 equiv), CH CN (1.2 mL), 150
o
o
b
C, O
2
. All of reactions were directly heated upon to 150 C. Isolated yield.
With the optimal conditions in hand, the scope and limitation for the cyanation of
indoles has been explored. As illustrated in Table 2, we found that both electronꢀrich
and ꢀdeficient substituents on indole rings could be tolerated well under this system,
furnishing cyanated products exclusively at the 3ꢀposition of indole. It is observed
that electronꢀrich group substituted substrates reacted more efficiently than
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electronꢀdeficient group substituted substrates, which is consistent with the rule of
electrophilic iodination of indole. For example, substrates bearing MeO (1b) and Me
(1c) groups gave the desired 3ꢀcyanoindoles 2bꢀc in 70ꢀ67% yields, respectively. The
reactions of substrates 1dꢀe containing halogen atoms with acetonitrile smoothly
performed to yield the expected 3ꢀcyanoindoles 2dꢀe in high yields (for F, 88% yield;
for Cl, 79% yield) which could be handled for further application.
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Electronꢀwithdrawing substituents such as COOMe (1f), CN (1g), NO
2
(1h) and CHO
(1i) were compatible under the standard conditions to give 3ꢀcyanoindoles with
moderate yields. When the 2ꢀposition of indole is occupied by a phenyl group, this
substrate 1k slowly undertaken cyanation within 5 days to form the corresponding
3
ꢀcyanoindole 2k in 78% yield. By changing substitutents on nitrogen atom, we found
that 1Hꢀindole with free NH did not undergo this reaction, whereas substrates with
phenyl 1l and benzyl group 1mꢀn on nitrogen atom led to the cyanation process.
Interestingly, this Cuꢀcatalyzed TEMPO system was also suitable for
Nꢀmethylꢀ1Hꢀpyrrolo[2,3ꢀb]pyridine heteroaromatic ring (1o), providing the desired
cyanated product 2o in 80% yield. However, other heteroarenes such as benzofuran,
benzothiophene, and Nꢀmethylpyrrole did not work under standard conditions.
Scheme 3. Proposed reaction pathway.
Based on our mechanistic studies regarding the cyanation of simple arenes and
15
boronic acids reported by our group, a proposed reaction pathway was displayed in
3 2
Scheme 3. Acetonitrile first reacts with TEMPO under the [Cu]/(Me Si) system to
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release the cyanide anion by the C-CN cleavage. The cyanide anion then takes part in
the cyanation of 3ꢀiodoꢀindole 3 starting from the iodination of indole 1 with NIS to
yield the desired 3ꢀcyanoꢀindole 2.
In conclusion, Cuꢀcatalyzed cyanation of indoles with acetonitrile has been
discovered. This C-H functionlization of indoles involved sequential
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3 2
iodination/cyanation in one pot. Cu/TEMPO/(Me Si) system displays efficient
activity for the cyanation of indoles and acetonitrile C-CN cleavage, gives the
corresponding 3ꢀcyanaindole in moderate to good yields, and tolerates a series of
2
functional groups, including OMe, Me, F, Cl, CHO, NO and so on. Moreover,
inexpensive copper catalyst and abound and hazardless acetonitrile as a cyano source
make this system applicable.
■
EXPERIMENTAL SECTION
General Considerations. All solvents were dried and distilled before use
1
according to the standard methods. H NMR spectra were recorded on a 400 MHz
spectrometer. Chemical shifts were quoted in parts per million (ppm) referenced to
13
the appropriate solvent peak or 0.0 ppm for tetramethylsilane. C NMR spectra were
recorded on a 100 MHz spectrometer. Chemical shifts were reported in ppm
referenced to the center line of a triplet at 77.0 ppm of chloroformꢀd. Infrared (IR)
spectra were recorded with a thin film on the KBr plate. High resolution mass spectra
were obtained with a QꢀTOF MS Spectrometer.
General procedure for copperꢀcatalyzed cyanation of indoles with
acetonitrile as the cyano source. An ovenꢀdried Schlenk tube, which was equipped
2
with a magnetic stir bar and charged with Cu(OAc) (20 mol%, 11 mg), was
evacuated and backfilled with oxygen three times. Under oxygen, 1,10ꢀphenanthroline
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(
20 mol%, 11 mg), TEMPO (0.6 mmol, 94 mg), KOH (0.31 mmol, 17 mg),
acetonitrile (1.2 mL), corresponding indole substrate (0.3 mmol), (Me
3 2
Si) (0.3 mmol,
4
4 mg) and NIS (0.33 mmol, 74 mg) were added into the tube. The reaction was
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o
stirred at 150 C for the indicated time. Then, the mixture was cooled to room
temperature, poured into saturated Na S solution (15 mL), and extracted with ethyl
acetate (3×20 mL). The combined organic layers were dried over Na SO , filtered,
2
2
4
and concentrated in vacuo. The residue was purified by column chromatography using
petroleum ether/ethyl acetate as the eluent to give the corresponding cyanated
product.
1
1
-Methyl-1H-indole-3-carbonitrile (2a): brown oil (38 mg, 81% yield); H NMR
(400 MHz, CDCl
3
) δ 7.74 (d, J = 7.6 Hz, 1H), 7.52 (s, 1H), 7.39ꢀ7.27 (m, 3H), 3.82 (s,
ꢀ1
3
H). IR (KBr) ν 3119, 2217, 1533, 1469, 1250, 1199, 1159, 1130, 744 cm . MS (EI)
+
10a
m/z: 156 (M ), 155, 141, 128, 114, 101, 88, 78, 28, 18.
5
-Methoxy-1-methyl-1H-indole-3-carbonitrile (2b): yellow solid (39 mg, 70%
o
1
yield); m.p. 105ꢀ106 C. H NMR (400 MHz, CDCl
3
) δ 7.48 (s, 1H), 7.26 (d, J = 8.8
Hz, 1H), 7.14 (d, J = 2.4 Hz, 1H), 6.97 (dd, J = 8.8, 2.4 Hz, 1H), 3.87 (s, 3H), 3.80 (s,
ꢀ1
3H). IR (KBr) ν 3113, 2926, 2208, 1623, 1534, 1493, 1230, 1138, 825, 806 cm . MS
+
10a
(
EI) m/z: 186 (M ), 171, 143, 128, 116, 101, 89, 18.
1,5-Dimethyl-1H-indole-3-carbonitrile (2c): brown oil (34 mg, 67% yield); H
NMR (400 MHz, CDCl ) δ 7.51 (s, 1H), 7.45 (s, 1H), 7.25 (d, J = 8.4 Hz, 1H), 7.15 (d,
J = 8.4 Hz, 1H), 3.78 (s, 3H), 2.47 (s, 3H). IR (KBr) ν 3121, 2923, 2218, 1695, 1534,
1
3
ꢀ1
+
1
487, 1381, 1123, 806 cm . MS (EI) m/z: 170 (M ), 169, 155, 140, 127, 115, 101, 85,
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0a
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8.
5
-Fluoro-1-methyl-1H-indole-3-carbonitrile (2d): pale yellow solid (46 mg, 88%
o
1
yield); m.p. 70ꢀ71 C. H NMR (400 MHz, CDCl
3
) δ 7.57 (s, 1H), 7.36 (d, J = 8.8,
0
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3
1
H), 7.32 (dd, J = 9.2, 4.4 Hz, 1H), 7.08 (t, J = 9.2 Hz, 1H), 3.85 (s, 3H). IR (KBr) ν
ꢀ1
+
125, 2214, 1629, 1533, 1490, 1190, 905, 858, 788 cm . MS (EI) m/z: 174 (M ), 159,
10a
47, 132, 120, 87, 57, 18.
-Chloro-1-methyl-1H-indole-3-carbonitrile (2e): yellow solid (45 mg, 79%
5
o
1
3
yield); m.p. 96ꢀ97 C. H NMR (400 MHz, CDCl ) δ 7.73 (t, J = 1.2 Hz, 1H), 7.58 (s,
13
1
1
H), 7.31 (d, J = 1.2 Hz, 2H), 3.85 (s, 3H). C NMR (100 MHz, CDCl ) δ 136.5,
3
34.4, 128.6, 128.3, 124.4, 119.2, 115.1, 111.4, 85.2, 33.8. IR (KBr) ν 3115, 2212,
ꢀ1
1728, 1704, 1620, 1534, 1319, 1246, 1146, 1098, 763 cm . HRMS (ESI) Calcd for
+
(C
10
H
7
ClN
2
+ Na ): 213.0195, found: 213.0191.
Methyl 3-cyano-1-methyl-1H-indole-5-carboxylate (2f): yellow solid (24 mg, 37%
o
1
yield); m.p. 164ꢀ165 C. H NMR (400 MHz, CDCl ) δ 8.52 (d, J = 1.6 Hz, 1H), 8.07
3
(dd, J = 8.8, 1.6 Hz, 1H), 7.65 (s, 1H), 7.43 (d, J = 8.8 Hz, 1H), 3.96 (s, 3H), 3.90 (s,
ꢀ1
3
H). IR (KBr) ν 3115, 2212, 1728, 1534, 1319, 1245, 1146, 743, cm . MS (EI) m/z:
10a
214 (M+), 183, 155, 128, 101, 91, 77, 28, 18.
1
-Methyl-1H-indole-3,5-dicarbonitrile (2g): pale yellow solid (21 mg, 38%
o
1
yield); m.p. 173ꢀ172 C. H NMR (400 MHz, CDCl ) δ 8.08 (s, 1H), 7.72 (s, 1H),
3
7
.58 (d, J = 8.6 Hz, 1H), 7.49 (d, J = 8.6 Hz, 1H), 3.92 (s, 3H). IR (KBr) ν 3113, 2224,
ꢀ1
+
1702, 1535, 1138, 1122, 1062, 813 638 cm . MS (EI) m/z: 181 (M ), 180, 153, 139,
10a
9
1, 28, 18.
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-Methyl-5-nitro-1H-indole-3-carbonitrile (2h): pale yellow solid (22 mg, 37%
o
1
yield); m.p. 160ꢀ161 C. H NMR (400 MHz, CDCl
3
) δ 8.73 (d, J = 2.2 Hz, 1H), 8.27
(
dd, J = 9.0, 2.2 Hz, 1H), 7.75 (s, 1H), 7.49 (d, J = 9.0 Hz, 1H), 3.95 (s, 3H). IR (KBr)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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36
37
38
39
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41
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49
50
51
52
53
54
55
56
57
58
59
60
ꢀ
1
+
ν 3118, 2229, 1710, 1536, 1340, 1096, 1062, 815, 735 cm . MS (EI) m/z: 201 (M ),
10a
1
71, 155, 143, 128, 101, 28, 18.
5
-Formyl-1-methyl-1H-indole-3-carbonitrile (2i): pale yellow solid (21 mg, 37%
o
1
yield); m.p. 202ꢀ203 C. H NMR (400 MHz, CDCl
3
) δ 10.11 (s, 1H), 8.29 (d, J = 0.8
Hz, 1H), 7.94 (dd, J = 8.8, 1.6 Hz, 1H), 7.69 (s, 1H), 7.52 (d, J = 8.8 Hz, 1H), 3.93 (s,
1
3
3
H). C NMR (100 MHz, CDCl ) δ 191.9, 139.3, 137.5, 131.6, 127.8, 125.0 123.9,
3
1
14.9 111.4, 88.1, 34.2. IR (KBr) ν 3124, 2219, 1685, 1611, 1534, 1458, 1186, 1121,
ꢀ1
+
1060, 809 621 cm . HRMS (ESI) Calcd for (C11
07.0525.
1,6-Dimethyl-1H-indole-3-carbonitrile (2j): deep yellow solid (31 mg, 61%
8 2
H N O + Na ): 207.0534, found:
2
o
1
yield); m.p. 102ꢀ103 C. H NMR (400 MHz, CDCl ) δ 7.61 (d, J = 8.2 Hz, 1H), 7.45
3
(s, 1H), 7.17 (d, J = 0.6 Hz, 1H), 7.11 (dd, J = 8.2, 0.6 Hz, 1H), 3.79 (s, 3H), 2.51 (s,
ꢀ1
3
H). IR (KBr) ν 3115, 2210, 1625, 1533, 1467, 1386, 801 cm . MS (EI) m/z: 170
+
10a
(M ), 155, 140, 128, 115, 101, 85, 77, 51, 39.
1
-Methyl-2-phenyl-1H-indole-3-carbonitrile (2k): deep yellow solid (51 mg, 73%
o
1
yield); m.p. 104ꢀ105 C. H NMR (400 MHz, CDCl ) δ 7.80ꢀ7.77 (m, 1H), 7.59ꢀ7.52
3
(
m, 5H), 7.44ꢀ7.33 (m, 3H), 3.76 (s, 3H). IR (KBr) ν 3055, 2214, 1659, 1533, 1467,
ꢀ1
+
1398, 1252, 811, 748, 700 cm . MS (EI) m/z: 232 (M ), 204, 190, 116, 102, 88, 77,
10a
5
1.
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2
2
2
2
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3
3
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1
0a
1
-phenyl-1H-indole-3-carbonitrile (2l) : white solid (46 mg, 71% yield); m.p.
o
1
1
15ꢀ116 C. H NMR (400 MHz, CDCl
3
) δ 7.85ꢀ7.83 (m, 1H), 7.81 (s, 1H), 7.60ꢀ7.56
(
m, 2H), 7.53ꢀ7.48 (m, 4H), 7.36ꢀ7.34 (m, 2H). IR (KBr) ν 3123, 2924, 2224, 1599,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ꢀ1
+
1
540, 1481, 1459, 1225, 736 cm . MS (EI) m/z: 218 (M ), 203, 190, 115, 109, 96, 77,
5
1.
1
-Benzyl-1H-indole-3-carbonitrile (2m): yellow solid (59 mg, 85% yield); m.p.
o
1
6
3
6ꢀ67 C. H NMR (400 MHz, CDCl ) δ 7.80ꢀ7.77 (m, 1H), 7.61 (s, 1H), 7.38ꢀ7.29
(
m, 6H), 7.16ꢀ7.13 (m, 2H), 5.35 (s, 2H). IR (KBr) ν 3115, 3030, 2215, 1530, 1464,
ꢀ1
+
10a
1
173, 1013 cm . MS (EI) m/z: 232 (M ), 216, 204, 191, 176, 102, 91, 65, 39.
1
-Benzyl-5-fluoro-1H-indole-3-carbonitrile (2n): deep yellow oil (42 mg, 56%
1
yield); H NMR (400 MHz, CDCl
3
) δ 7.64 (s, 1H), 7.43 (dd, J = 8.4, 2.4 Hz, 1H),
7
.39ꢀ7.34 (m, 3H), 7.29ꢀ7.27 (m, 1H), 7.15ꢀ7.13 (m, 2H), 7.04 (td, J = 12, 2.4 Hz, 1H),
13
5.33 (s, 2H). C NMR (100 MHz, CDCl
32.4, 129.4, 128.9 (d, JCꢀF = 7.4 Hz), 127.3, 115.6, 113.0 (d, JCꢀF = 26.3 Hz), 112.3,
112.2, 105.4 (d, JCꢀF = 24.7 Hz), 86.5 (d, JCꢀF = 4 Hz), 51.5. IR (KBr) ν 2215, 1528,
3
) δ 159.5 (d, JCꢀF = 238.3 Hz), 136.5, 135.1,
1
ꢀ1
+
1
540, 1485, 1392, 1183, 900, 703 cm . HRMS (ESI) Calcd for (C16
273.0804, found: 273.0810.
-Methyl-1H-pyrrolo[2,3-b]pyridine-3-carbonitrile (2o): pale yellow solid (38
11 2
H N F + Na ):
1
o
1
mg, 80% yield); m.p. 87ꢀ88 C. H NMR (400 MHz, CDCl ) δ 8.47 (dd, J = 4.8, 1.6
3
Hz, 1H), 8.08 (dd, J = 7.6, 1.2 Hz, 1H), 7.74 (s, 1H), 7.28ꢀ7.25 (m, 1H), 3.96 (s, 3H).
ꢀ1
IR (KBr) ν 3117, 2221, 1685, 1602, 1533, 1451, 1412, 1304, 1150, 772 cm . MS (EI)
+
10a
m/z: 157 (M ), 156, 129, 102, 88, 79, 64, 51, 28, 13.
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Acknowledgments
This work was supported by the National Natural Sciences Foundation of China
21272001), Shanghai Education Committee (13ZZ014) and Shanghai Jiao Tong
(
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University. We are grateful for Instrumental Analysis Center of SJTU for compound
analysis.
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Supporting Information Available. Copies of H NMR and C NMR spectra for all
new products. This material is available free of charge via the Internet at
http://pubs.acs.org.
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